WO2025259515A2

WO2025259515A2 - Combination treatment

Info

Publication number: WO2025259515A2
Application number: PCT/US2025/032393
Authority: WO
Inventors: Sungeun Kim; Bram D. ESTES; Priya Ganesan; Ian Nevin FOLTZ; Yan Zheng; Darren L. BATES; Christine S. Vissinga; Dora TOLEDO WARSHAVIAK; Khaled M.K.Z. Ali; Hongyu Wang; Nithya Srinivasan; Mark KROENKE; Jackson EGEN
Original assignee: Amgen Inc
Current assignee: Amgen Inc
Priority date: 2024-06-11
Filing date: 2025-06-05
Publication date: 2025-12-18
Anticipated expiration: 2026-12-11
Also published as: WO2025259515A3

Abstract

The present invention relates treating cancer, such as treating a solid tumor, by combining a bispecific molecule that simultaneously targets PD-L1 and 4-1BB, and a multispecific T cell engager molecule that targets CD3 and a Tumor Antigen.

Description

COMBINATION TREATMENT CROSS-REFERENCE TO RELATED APPLICATIONS [1] This application claims the benefit of U.S. Provisional Patent Application No.63/658,725, filed June 11, 2024. SEQUENCE LISTING [2] The instant application contains a Sequence Listing which has been submitted electronically in “xml” format and is identified by the file name 10965-WO01-SEC_ST26_SequenceListing.xml, created May 27, 2025, which is 501,863 bytes in size. The subject matter contained in the electronic format of this sequence listing is incorporated herein by reference in its entirety. FIELD OF THE INVENTION [3] The present invention relates combination therapy for treatment of cancer. BACKGROUND OF THE INVENTION [4] The PD-1/PD-L1 axis is involved in the suppression of T cell immune responses in cancer. Antagonists of this pathway have been clinically validated across a number of solid tumor indications. The U.S. Food and Drug Administration (FDA) has approved a number of PD-1 and PD-L1 inhibitors for treatment of cancer, including pembrolizumab, nivolumab, cemiplimab, dostarlimab, retifanlimab, toripalimab, atezolizumab, avelumab, and durvalumab. These PD-1/PD-L1 inhibitors are used to treat solid tumors such as melanoma, metastatic non-small cell lung cancer, head and neck squamous cell carcinoma, as well as Hodgkins’s lymphoma. [5] 4-1BB, which is also known as CD137 or TNFRSF9, is a member of the TNF receptor superfamily. 4-1BB was first identified as a molecule whose expression is induced by T-cell activation (Kwon Y.H. and Weissman S.M. (1989), Proc. Natl. Acad. Sci. USA 86, 1963-1967). Subsequent studies demonstrated expression of 4-1BB in T- and B-lymphocytes, NK-cells, NKT-cells, monocytes, neutrophils, and dendritic cells as well as cells of non- hematopoietic origin such as endothelial and smooth muscle cells. Expression of 4-1BB in different cell types is mostly inducible and driven by various stimulatory signals, such as T-cell receptor (TCR) or B-cell receptor triggering, as well as signaling induced through co- stimulatory molecules or receptors of pro-inflammatory cytokines. [6] It has been reported that systemic administration of 4-1BB-specific agonistic antibodies induces expansion of CD8+ T-cells associated with liver toxicity (Dubrot J. et al. (2010), Cancer Immunol. Immunother.59, 1223-1233). In human clinical trials (ClinicalTrials.gov, NCT00309023), 4-1BB agonistic antibodies (BMS-663513) administered once every three weeks for 12 weeks induced stabilization of the disease in patients with melanoma, ovarian or renal cell carcinoma. However, the same antibody given in another trial (NCT00612664) caused grade 4 hepatitis leading to termination of the trial (Simeone E. and Ascierto P.A. (2012), J. Immunotoxicology 9, 241-247). Therefore, there is a need for new generation agonists that effectively engage 4-1BB while avoiding undesired side effects. [7] T cell engagers (TCEs) are molecules engineered to redirect the immune system’s T cells to recognize and kill cancer cells. They are designed to bind to a target antigen expressed on a cancer cell and to a co-stimulatory molecule on T cells, such as CD3. These therapeutic molecules then engage T cells that are present in tumors but not capable of recognizing cancer cells, redirecting their activity toward the tumor. One example class of TCEs are BiTE^® (Bi-specific T cell Engager) molecules. [8] BiTE^® molecules are recombinant protein constructs made from two linked binding domains. One binding domain of the BiTE^® molecule is specific for a selected tumor surface antigen on target cells; the second binding domain is specific for CD3, a subunit of the T cell receptor complex on T cells. By their particular design, BiTE^® molecules are uniquely suited to transiently connect T cells with target cells and, at the same time, potently activate the inherent cytolytic potential of T cells against target cells. For example, Blinatumomab (brand name Blincyto®) has been approved for treatment for Philadelphia chromosome-negative relapsed or refractory acute lymphoblastic leukemia. [9] Despite the success of anti-PD-1/PD-L1 therapy and BiTE therapy, there is still a need for compositions capable of vigorously directing the body’s immune system to attack cancer cells or pathogen-infected cells. SUMMARY OF THE INVENTION [10] Based on the disclosure provided herein, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following embodiments (E). E1. A method for treating cancer, comprising administering to a subject in need thereof a therapeutic effective amount of: (a) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB; and (b) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA). E2. The method of E1, wherein said PD-L1 is human PD-L1, and/or said 4-1BB is human 4-1BB. E3. The method of E1 or E2, wherein said CD3 is human CD3, and/or said TA is human TA. E4. The method of any one of E1-E3, wherein said multispecific T cell engager molecule is a bispecific T cell engager molecule comprising a CD3-binding domain and a TA-binding domain. E5. The method of any one of E1-E4, wherein said multispecific T cell engager molecule is a BiTE® molecule, wherein said CD3-binding domain is a single-chain Fv (scFv) that binds to CD3, and wherein said TA-binding is a single-chain Fv (scFv) that binds to said TA. E6. The method of any one of E1-E5, wherein said subject is human. E7. The method of any one of E1-E6, wherein cancer is solid tumor. E8. The method of any one of E1-E7, wherein the cancer is brain cancer, bladder cancer, breast cancer, clear cell kidney cancer, cervical cancer, colon cancer, rectal cancer, endometrial cancer, gastric cancer, head/neck squamous cell carcinoma, lip cancer, oral cancer, liver cancer, lung squamous cell carcinoma, melanoma, mesothelioma, non-small-cell lung cancer (NSCLC), non-melanoma skin cancer, ovarian cancer, pancreatic cancer, prostate cancer, renal cell carcinoma, sarcoma, small-cell lung cancer (SCLC), Squamous Cell Carcinoma of the Head and Neck (SCCHN), triple negative breast cancer, renal cell carcinoma, or thyroid cancer. E9. The method of any one of E1-E7, wherein the cancer is adrenocortical tumor, alveolar soft part sarcoma, carcinoma, chondrosarcoma, desmoid tumors, desmoplastic small round cell tumor, endocrine tumors, endodermal sinus tumor, epithelioid hemangioendothelioma, Ewing sarcoma, germ cell tumor, hepatoblastoma, hepatocellular carcinoma, melanoma, nephroma, neuroblastoma, non- rhabdomyosarcoma soft tissue sarcoma (NRSTS), osteosarcoma, paraspinal sarcoma, retinoblastoma, rhabdomyosarcoma, synovial sarcoma, or Wilms tumor. E10 The method of any one of E1-E7, wherein the cancer is acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), or chronic myeloid leukemia (CML). E11. The method of any one of E1-E7, wherein the cancer is diffuse large B-cell lymphoma (DLBCL), follicular lymphoma, Hodgkin's lymphoma (HL), mantle cell lymphoma (MCL), multiple myeloma (MM), myelodysplastic syndrome (MDS), non-Hodgkin's lymphoma (NHL), or small lymphocytic lymphoma (SLL). E12. The method of any one of E1-E11, wherein said CD3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:154, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:153. E13. The method of any one of E1-E11, wherein said CD3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:163, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:162. E14. The method of any one of E1-E11, wherein said CD3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:172, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:171. E15. The method of any one of E1-E11, wherein said CD3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:415, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:414. E16. The method of any one of E1-E11, wherein said CD3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:436, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:435. E17. The method of any one of E1-E12, wherein said CD3-binding domain comprises: (a) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:147, 148, and 149, respectively; and (b) a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:150, 151, and 152, respectively. E18. The method of any one of E1-E11 and E13, wherein said CD3-binding domain comprises: (a) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:156, 157, and 158, respectively; and (b) a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:159, 160, and 161, respectively. E19. The method of any one of E1-E11 and E14, wherein said CD3-binding domain comprises: (a) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:165, 166, and 167, respectively; and (b) a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:168, 169, and 170, respectively. E20. The method of any one of E1-E11 and E15, wherein said CD3-binding domain comprises: (a) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:411, 412, and 413, respectively; and (b) a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:408, 409, and 410, respectively. E21. The method of any one of E1-E11 and E16, wherein said CD3-binding domain comprises: (a) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:432, 433, 434, respectively; and (b) a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:429, 430, 431, respectively. E22. The method of any one of E1-E21, wherein said CD3-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:153, 162, 171, 414, or 435; and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:154, 163, 172, 415, or 436. E23. The method of any one of E12-E22, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E24. The method of E23, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID Nos.454-471. E25. The method of E23 or E24, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E26. The method of any one of E1-E25, wherein said CD3-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 155, 164, 175, 176, 416, or 437. E27. The method of any one of E1-E26, wherein said Tumor Antigen is CD33, preferably human CD33; optionally, the cancer is acute myeloid leukemia (AML). E28. The method of E27, wherein said CD33-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:185 or 186, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:183 or 184. E29. The method of E27 or E28, wherein said CD33-binding domain comprises: (a) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:177, 178, and 179, respectively; and (b) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:180, 181, and 182, respectively. E30. The method of any one of E27-E29, wherein said CD33-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:183 or 184, and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:185 or 186. E31. The method of any one of E28-E30, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E32. The method of E31, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E33. The method of E31 or E32, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E34. The method of any one of E27-E33, wherein CD33-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 187 or 188. E35. The method of any one of E27-E34, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:189, 190, or 191. E36. The method of any one of E1-E26, wherein said Tumor Antigen is EGFRvIII, preferably human EGFRvIII; optionally, the cancer is glioblastoma or malignant glioma. E37. The method of E36, wherein said EGFRvIII-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:199, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:198. E38. The method of E36 or E37, wherein said EGFRvIII-binding domain comprises: (a) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 192, 193, and 194, respectively; and (b) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:195, 196, and 197, respectively. E39. The method of any one of E36-E38, wherein said EGFRvIII-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:198; and (ii) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:199. E40. The method of any one of E37-E39, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E41. The method of E40, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E42. The method of E40 or E41, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E43. The method of any one of E36-E42, wherein said EGFRvIII-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:200. E44. The method of any one of E36-E43, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 201 or 202. E45. The method of any one of E1-E26, wherein said Tumor Antigen is MSLN, preferably human MSLN; optionally, the cancer is ovarian cancer, pancreatic cancer, or mesothelioma. E46. The method of E45, wherein said MSLN-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:210, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:209. E47. The method of E45 or E46, wherein said MSLN-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 203, 204, and 205, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:206, 207, and 208, respectively. E48. The method of any one of E45-E47, wherein said MSLN-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:209; and (ii) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:210. E49. The method of any one of E46-E48, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E50. The method of E49, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E51. The method of E49 or E50, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E52. The method of any one E45-E51, wherein said MSLN-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:211. E53. The method of any one of E45-E52, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:212, 213, or 214. E54. The method of any one of E1-E26, wherein said Tumor Antigen is CDH19, preferably human CDH19; optionally, the cancer is melanoma. E55. The method of E54, wherein said CDH19-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:223 or 224, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:221 or 222. E56. The method of E54 or E55, wherein said CDH19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:215, 216, and 217, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:218, 219, and 220, respectively. E57. The method of any one of E54-E56, wherein said CDH19-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:221 or 222; and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:223 or 224. E58. The method of any one of E55-E57, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E59. The method of E58, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E60. The method of E58 or E59, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E61. The method of any one E54-E60, wherein said CDH19-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:225 or 226. E62. The method of any one of E54-E61, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of the sequences selected from SEQ ID NOs:227-232. E63. The method of any one of E1-E26, wherein said Tumor Antigen is FLT3, preferably human FLT3; optionally, the cancer is AML. E64. The method of E63, wherein said FLT3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:240, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:239. E65. The method of E63 or E64, wherein said FLT3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 233, 234, and 235, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:236, 237, and 238, respectively. E66. The method of any one of E63-E65, wherein said FLT3-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:239; and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:240. E67. The method of any one of E64-E66, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E68. The method of E67, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E69. The method of E67 or E68, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E70. The method of any one E63-E69, wherein said FLT3-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:241. E71. The method of any one of E63-E70, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:242 or 243. E72. The method of any one of E1-E26, wherein said Tumor Antigen is DLL3, preferably human DLL3; and optionally, the cancer is small cell lung cancer (SCLC). E73. The method of E72, wherein said DLL3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:251, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:252. E74. The method of E72 or E73, wherein said DLL3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 244, 245, and 246, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:247, 248, and 249, respectively. E75. The method of any one of E72-E74, wherein said DLL3-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:250; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:251. E76. The method of any one of E73-E75, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E77. The method of E76, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E78. The method of E76 or E77, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E79. The method of any one E72-E78, wherein said DLL3-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:252. E80. The method of any one of E72-E79, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:253 or 254. E81. The method of E72, wherein said DLL3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:262, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:261. E82. The method of E72 or E81, wherein said DLL3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 255, 256, and 257, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:258, 259, and 260, respectively. E83. The method of any one of E72 and E81-E82, wherein said DLL3-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:261; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:262. E84. The method of any one E72 and E81-E83, wherein said DLL3-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:265 or 266. E85. The method of any one of E72 and E81-E84, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:265, and an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:266. E86. The method of any one of E1-E26, wherein said Tumor Antigen is CD19, preferably human CD19; optionally, the cancer is Acute Lymphoblastic Leukemia (ALL), or Non-Hodgkin's Lymphoma (NHL). E87. The method of E86, wherein said CD19-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:274, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:273. E88. The method of E86 or E87, wherein said CD19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 267, 268, and 269, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 270, 271, and 272, respectively. E89. The method of any one of E86-E88, wherein said CD19-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:273; and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:274. E90. The method of any one of E87-E89, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E91. The method of E90, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E92. The method of E90 or E91, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E93. The method of any one E86-E92, wherein said CD19-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:275. E94. The method of any one of E86-E93, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of the sequences selected from SEQ ID NO:276. E95. The method of E86, wherein said CD19-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:405, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:406. E96. The method of E86 or E95, wherein said CD19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 402, 403, and 404, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 399, 400, and 401, respectively. E97. The method of any one of E86 and E95-E96, wherein said CD19-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:406; and (b) a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:405. E98. The method of any one of E95-E97, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E99. The method of E98, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E100. The method of E98 or E99, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E101. The method of any one E86 and E95-E100, wherein said CD19-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:407. E102. The method of any one of E86 and E95-E101, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of the sequences selected from SEQ ID NO:417. E103. The method of any one of E1-E26, wherein said Tumor Antigen is BCMA, preferably human BCMA; optionally, the cancer is multiple myeloma. E104. The method of E103, wherein said BCMA-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:284, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:283. E105. The method of E103 or E104, wherein said BCMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 277, 278, and 279, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:280, 281, and 282, respectively. E106. The method of any one of E103-E105, wherein said BCMA-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:283; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:284. E107. The method of any one of E104-E106, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E108. The method of E107, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E109. The method of E107 or E108, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E110. The method of any one E103-E109, wherein said BCMA-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:285. E111. The method of any one of E103-E110, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:286 or 287. E112. The method of any one of E1-E26, wherein said Tumor Antigen is PSMA, preferably human PSMA; and optionally, the cancer is prostate cancer. E113. The method of E112, wherein said PSMA-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:295, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:294. E114. The method of E112 or E113, wherein said PSMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 288, 289, and 290, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 219, 292, and 293, respectively. E115. The method of any one of E112-E114, wherein said PSMA-binding domain comprises: (i) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:294; (ii) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:295. E116. The method of any one of E113-E115, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E117. The method of E116, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E118. The method of E116 or E117, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E119. The method of any one E112-E118, wherein said PSMA-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:296. E120. The method of any one of E112-E119, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of the sequences selected from SEQ ID NOs:297-302. E121. The method of E112, wherein said PSMA-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:311 or 312, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:309 or 310. E122. The method of E120 or E121, wherein said PSMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 303, 304, and 305, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 306, 307, and 308, respectively. E123. The method of any one of E112 and E121-E122, wherein said PSMA-binding domain comprises: (i) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:309 or 310; (ii) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:311 or 312. E124. The method of any one of E121-E123, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E125. The method of E124, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E126. The method of E124 or E125, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E127. The method of any one E112 and E121-E126, wherein said PSMA-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:313 or 314. E128. The method of any one of E112 and E121-E127, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of the sequences selected from SEQ ID NOs:315-325. E129. The method of any one of E1-E26, wherein said Tumor Antigen is CD70, preferably human CD70; optionally, the cancer is AML or RCC. E130. The method of E129, wherein said CD70-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:333, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:332. E131. The method of E129 or E130, wherein said CD70-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 326, 327, and 328, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 329, 330, and 331, respectively. E132. The method of any one of E129-E131, wherein said CD70-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:332; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:333. E133. The method of any one of E130-E132, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E134. The method of E133, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E135. The method of E133 or E134, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E136. The method of any one E129-E135, wherein said CD70-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:334. E137. The method of any one of E129-E136, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:335. E138. The method of any one of E1-E26, wherein said Tumor Antigen is CLDN18.2, preferably human CLDN18.2; optionally, the cancer is gastric cancer. E139. The method of E138, wherein said CLDN18.2-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:343 or 348, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:342 or 347. E140. The method of E138 or E139, wherein said CLDN18.2-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 336, 337, and 338, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 339, 340, and 341, respectively. E141. The method of any one of E138-E140, wherein said CLDN18.2-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:342 or 347; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:343 or 348. E142. The method of any one of E139-E141, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E143. The method of E142, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E144. The method of E142 or E143, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E145. The method of any one E138-E144, wherein said CLDN18.2-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:344 or 349. E146. The method of any one of E138-E145, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NO:345, 346, 350, and 351. E147. The method of any one of E1-E26, wherein said Tumor Antigen is MUC17, preferably human MUC17; optionally, the cancer is gastric cancer. E148. The method of E147, wherein said MUC17-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:359, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:358. E149. The method of E147 or E148, wherein said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 352, 353, and 354, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 355, 356, and 357, respectively. E150. The method of any one of E147-E149, wherein said MUC17-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 358; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:359. E158. The method of any one of E148-E150, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E159. The method of E158, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E160. The method of E158 or E159, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E161. The method of any one E147-E160, wherein said MUC17-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to residues 1-242 of SEQ ID NO:360. E162. The method of any one of E147-E161, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:360. E163. The method of E147, wherein said MUC17-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:368, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:367. E164. The method of E147 or E163, wherein said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 361, 362, and 363, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 364, 365, and 366, respectively. E165. The method of any one of E147 and E163-E164, wherein said MUC17-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 367; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:368. E166. The method of any one of E163-E165, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E167. The method of E166, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E168. The method of E166 or E167, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E169. The method of any one E147 and E163-E168, wherein said MUC17-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to residues 1-242 of SEQ ID NO:369. E170. The method of any one of E147and E163-E169, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:369. E171. The method of E147, wherein said MUC17-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:377, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:376. E172. The method of E147 or E171, wherein said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 370, 371, and 372, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 373, 374, and 375, respectively. E173. The method of any one of E147 and E171-E172, wherein said MUC17-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 376; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:377. E174. The method of any one of E171-E173, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E175. The method of E174, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E176. The method of E174 or E175, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E177. The method of any one E147 and 171-E176, wherein said MUC17-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to residues 1-241 of SEQ ID NO:378. E162. The method of any one of E147 and E171-E177, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:378. E163. The method of E147, wherein said MUC17-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:386, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:385. E164. The method of E147 or E163, wherein said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 379, 380, and 381, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 382, 383, and 384, respectively. E165. The method of any one of E147 and E163-E164, wherein said MUC17-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 385; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:386. E166. The method of any one of E163-E165, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E167. The method of E166, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E168. The method of E166 or E167, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E169. The method of any one E147 and E163-E168, wherein said MUC17-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to residues 1-241 of SEQ ID NO:387. E170. The method of any one of E147 and E163-E169, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:387. E171. The method of any one of E1-E26, wherein said Tumor Antigen is CDH3, preferably human CDH3; optionally, the cancer is breast cancer, lung cancer, or colon cancer. E172. The method of E171, wherein said CDH3-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:395, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:394. E173. The method of E171 or E172, wherein said CDH3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 388, 389, and 390, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 391, 392, and 393, respectively. E174. The method of any one of E171-E173, wherein said CDH3-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:394; and (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:395. E175. The method of any one of E172-E174, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E176. The method of E175, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E177. The method of E175 or E176, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E178. The method of any one E171-E177, wherein said CDH3-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:396. E179. The method of any one of E171-E178, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NO:397 or 398. E180. The method of any one of E1-E26, wherein said Tumor Antigen is CLDN6, preferably human CLDN6; optionally, the cancer is NSCLC or ovarian cancer. E181. The method of E180, wherein said CLDN6-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:425, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:424. E182. The method of E180 or E181, wherein said CLDN6-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 418, 419, and 420, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 421, 422, and 423, respectively. E183. The method of any one of E180-E182, wherein said CLDN6-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:424; (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:425. E184. The method of any one of E180-E183, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E185. The method of E184, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E186. The method of E184 or E185, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E187. The method of any one E180-E186, wherein said CLDN6-binding domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:426. E188. The method of any one of E103-E110, wherein said multispecific T cell engager comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:427 or 428. E189. The method of any one of E1-E26, wherein said Tumor Antigen is STEAP1, preferably human STEAP1; optionally, the cancer is prostate cancer. E190. The method of E189, wherein said STEAP1-binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:445, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:444. E192. The method of E190 or E191, wherein said STEAP1-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 438, 439, and 440, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 441, 442, and 443, respectively. E183. The method of any one of E180-E182, wherein said STEAP1-binding domain comprises: (a) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:444 or 449; (b) and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:445. E184. The method of any one of E180-E183, wherein said STEAP1-binding domain comprises a Fab moiety, and wherein said Fab comprises: (a) a heavy chain that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:446 or 450; (b) and a light chain that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:447. E185. The method of any one of E180-E184, wherein said multispecific T cell engager comprises: (a) a heavy chain that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:448, 451, 452, or 453; (b) and a light chain that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:447. E186. The method of any one of E1-E185, wherein said multispecific T cell engager further comprises a single-chain Fc (scFc). E187. The method of E186, wherein said scFc comprises SEQ ID NO: 473 or 474. E188. The method of E186 or E187, wherein said scFc is connected to the TA-binding domain or the CD3-binding domain via a linker. E189. The method of E188, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E190. The method of E188 or E189, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E191. The method of any one of E1-E190, wherein said multispecific T cell engager further comprises a histidine tag (SEQ ID NO:472). E192. The method of any one of E1-E191, wherein said CD3-binding domain and said TA-binding domain are connected by a linker. E193. The method of E192, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E194. The method of any one of E1-E193, wherein said PD-L1 binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:47, 49, or 50, and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:46, 48, or 51. E195. The method of any one of E1-E194, wherein said PD-L1 binding domain comprises: (1) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 34, 35, and 36, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:37, 38, and 39, respectively; or (2) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 40, 41, and 42, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:43, 44, and 45, respectively. E196. The method of any one of E1-E195, wherein said PD-L1 binding domain comprises: (1) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:46; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:47; (2) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:48; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:49; (3) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:46; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:50; or (3) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:51; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:50. E197. The method of any one of E194-E196, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E198. The method of E197, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E199. The method of E197 or E198, wherein said linker comprises (Gly4Ser)n (SEQ ID NO: 467) or (Gly3Ser)n (SEQ ID NO: 466), where n is an integer of 1, 2, 3, 4, 5, or 6. E200. The method of any one of E1-E199, wherein said 4-1BB binding domain comprises: (a) a light chain variable region (VL) that comprises the CDR-L1, CDR-L2, and CDR-L3 of SEQ ID NO:53, 55, 57, 59, 61, or 63; and (b) a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR- H3 of SEQ ID NO:52, 54, 56, 58, 60, or 62. E201. The method of any one of E1-E200, wherein said 4-1BB binding domain comprises: (1) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 4, 5, and 6, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:1, 2, and 3, respectively; (2) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 10, 11, and 12, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:7, 8, and 9, respectively; (3) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 13, 14, and 15, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:16, 17, and 18, respectively; or (4) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 19, 20, and 21, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:22, 23, and 24, respectively. E202. The method of any one of E1-E201, wherein said 4-1BB binding domain comprises: (1) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:52; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:53; (2) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:54; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:55; (3) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:56; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:57; (4) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:58; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:59; (5) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:60; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:61; or (6) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:62; and a VL that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:63. E203. The method of any one of E200-E202, wherein said VH and VL are joined by a linker to form a single chain Fv (scFv). E204. The method of E203, wherein said linker is a peptide linker comprising a sequence selected from any one of SEQ ID NOs.454-471. E205. The method of any one of E1-E199, wherein said 4-1BB binding domain comprises a heavy chain variable region (VH) that comprises the CDR-H1, CDR-H2, and CDR-H3 of SEQ ID NO:64, 65, or 475. E206. The method of any one of E1-E199 and E205, wherein said 4-1BB binding domain comprises: (1) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 25, 26, and 27, respectively (2) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:28, 29, and 30 respectively; or (3) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 31, 32, and 33, respectively. E207. The method of any one of E1-E199 and E205-E206, wherein said 4-1BB binding domain comprises: (1) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:64; (2) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:65; or (3) a VH that comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:475. E209. The method of any one of E205-E207, and wherein said 4-1BB binding domain does not comprise a light chain variable region (VL). E210. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH1, VH2, VH3, VH4, or VH5 framework sequence. E211. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH1 framework sequence. E212. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH2 framework sequence. E213. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH3 framework sequence. E214. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH4 framework sequence. E215. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, and E181-E209, wherein said VH comprises a VH framework derived from a human germline VH5 framework sequence. E216. The method of any one of E210-E115, wherein said VH comprises a VH framework sequence that is at least 90% identical to the human VH germline framework sequence from which it is derived. E217. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, E181-E204, and E210-E216, wherein said VL comprises a VL framework derived from a human germline Vκ framework sequence. E218. The method of any one of E12-E26, E28-E35, E37-E44, E46-E53, E55-E62, E64-E71, E73-E85, E87-E102, E104-E111, E113-E128, E130-E137, E139-E146, E148-E170, E172-E179, E181-E204, and E210-E216, wherein said VL comprises a VL framework derived from a human germline Vλ framework sequence. E219. The method of E217 and E218, wherein said VL comprises a VL framework sequence that is at least 90% identical to the human VL germline framework sequence from which it is derived. E220. The method of any one of E210-E219, wherein said VL comprises a VL framework sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to the human VL germline framework sequence from which it is derived, and/or said VH comprises a VH framework sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to the human VH germline framework sequence from which it is derived. E221. The method of any one of E1-E193, wherein said PD-L1 binding domain comprises a VH comprising the amino acid sequence of SEQ ID NO:46 and a VL comprising the amino acid sequence of SEQ ID NO:47. E222. The method of any one of E221, wherein said 4-1BB binding domain comprises a VH comprising the amino acid sequence of SEQ ID NO:65. E223. The method of any one of E1-E193, wherein said PD-L1 binding domain comprises a VH comprising the amino acid sequence of SEQ ID NO:51 and a VL comprising the amino acid sequence of SEQ ID NO:50. E224. The method of any one of E1-E223, wherein said 4-1BB binding domain comprises a VH comprising the amino acid sequence of SEQ ID NO:60 and a VL comprising the amino acid sequence of SEQ ID NO:61. E225. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) a first heavy chain that comprises, from N-terminus to C-terminus: VH_A – CH1 – monomeric CH2 – monomeric CH3; (ii) a second heavy chain that comprises, from N-terminus to C-terminus: VHB – first linker – monomeric CH2’ – monomeric CH3’; and (iii) a light chain that comprises, from N-terminus to C-terminus: VL_A – CL; wherein said VHA-CH1 and said VLA-CL form a Fab that binds to PD-L1, said VHB binds to 4-1BB, and said monomeric CH2 – monomeric CH3 from (i) and monomeric CH2’ – monomeric CH3’ from (ii) form a Fc region. (FIG.17E) E226. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VHA – CH1 – first linker – VHB – second linker – monomeric CH2 – monomeric CH3; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VL_A – CL; wherein said VH_A-CH1 and said VL_A-CL form a Fab that binds to PD-L1, said VH_B binds to 4-1BB, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17D) E227. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VH_A – CH1 – first linker – scFv – third linker – monomeric CH2 – monomeric CH3, wherein said scFv comprises a VHB and a VLB, and wherein said VHB and VLB are connected via a second linker; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VLA – CL; wherein said VHA-CH1 and said VLA-CL form a Fab that binds to PD-L1, said scFv binds to 4-1BB, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17B) E228. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VHA – CH1 – first linker – scFv – third linker – monomeric CH2 – monomeric CH3, wherein said scFv comprises a VH_B and a VL_B, and wherein said VH_B and VL_B are connected via a second linker; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VL_A – CL; wherein said VHA-CH1 and said VLA-CL form a Fab that binds to 4-1BB, said scFv binds to PD-L1, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17B) E229. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) a first heavy chain that comprises, from N-terminus to C-terminus: VH_A – CH1 – monomeric CH2 – monomeric CH3; (ii) a second heavy chain that comprises, from N-terminus to C-terminus: VHB – CH1’ – monomeric CH2’ – monomeric CH3’; (iii) a first light chain that comprises, from N-terminus to C-terminus: VL_A – CL; and (iv) a second light chain that comprises, from N-terminus to C-terminus: VLB – CL’; wherein said VHA-CH1 and said VLA-CL form a first Fab that binds to 4-1BB, wherein said VHB-CH1’ and said VL_B-CL’ form a second Fab that to PD-L1, and wherein said monomeric CH2 – monomeric CH3 from (i) and monomeric CH2’ – monomeric CH3’ from (ii) form a Fc region. (FIG.17F) E230. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VHA – CH1 – monomeric CH2 – monomeric CH3 – first linker - VH_B; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VL_A – CL; wherein said VHA-CH1 and said VLA-CL form a Fab that binds to PD-L1, said VHB binds to 4-1BB, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17C) E231. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VH_A – CH1 – monomeric CH2 – monomeric CH3 – first linker - scFv, wherein said scFv comprises a VHB and a VLB, and wherein said VHB and VLB are connected via a second linker; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VL_A – CL; wherein said VH_A-CH1 and said VL_A-CL form a Fab that binds to PD-L1, said scFv binds to 4-1BB, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17A) E232. The method of any one of E1-E224, wherein said bispecific molecule comprises: (i) two copies of a heavy chain that comprises, from N-terminus to C-terminus: VHA – CH1 – monomeric CH2 – monomeric CH3 – first linker - scFv, wherein said scFv comprises a VH_B and a VL_B, and wherein said VH_B and VL_B are connected via a second linker; and (ii) two copies of a light chain that comprises, from N-terminus to C-terminus: VLA – CL; wherein said VHA-CH1 and said VLA-CL form a Fab that binds to 4-1BB, said scFv binds to PD-L1, and said two copies of monomeric CH2 – monomeric CH3 form a Fc region. (FIG.17A) E233. The method of any one of E225-E232, wherein said first linker, second linker, and third linker each independently is a peptide linker comprising a sequence selected from any one of SEQ ID NOs. 454-471. E234. The method of any one of E225-E233, wherein said CH1 and/or CH1’ domain is the CH1 domain of an IgG (for example IgG1, lgG2, lgG3, or lgG4). E235. The method of any one of E225-E234, wherein said CH1 and/or CH1’ domain is the CH1 domain of a human IgG (for example, human IgG1, human IgG2, human IgG3, or human IgG4). E236. The method of any one of E225-E235, wherein said CH1 and/or CH1’ domain is the CH1 domain of a human IgG1. E237. The method of any one of E225-E236, wherein said CH1 and/or CH1’ domain comprises a sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 90%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 76, 79, 90, 107, 109, 113, or 117. E238. The method of any one of E225-E237, wherein the Fc region is the Fc region of an IgA (for example IgA1 or lgA2), IgD, IgE, IgM, or IgG (for example IgG1, lgG2, lgG3, or lgG4). E239. The method of any one of E225-E238, wherein the Fc region is the Fc region of an IgG. E240. The method of any one of E225-E239, wherein the IgG is selected from the group consisting of IgG1, lgG2, lgG3, and lgG4. E241. The method of any one of E225-E240, wherein said Fc region is derived from an IgG1 Fc, and further comprises one or more mutations selection from the group consisting of: L234A, L235A, L235E, G237A, and combination thereof (numbering according to the EU index). E242. The method of E241, comprising L234A and L235A mutations. E243. The method of any one of E225-E242, wherein said Fc region is derived from an IgG1 Fc, and further comprises one or more mutations selection from the group consisting of: V259C, A287C, R292C, V302C, L306C, V323C, I332C, and a combination thereof (numbering according to the EU index). E244. The method of any one of E225-E243, wherein said Fc region is derived from an IgG1 Fc, and further comprises one or more mutations selection from the group consisting of: L242C, A287C, R292C, N297G, V302C, L306C, K334C, and a combination thereof (numbering according to the EU index). E245. The method of E244, comprising a N297G mutation. E246. The method of E244, comprising A287C, N297G, and L306C mutations. E247. The method of E244, comprising R292C, N297G, and V302C mutations. E248. The method of any one of E225-E247, wherein said Fc region is derived from an IgG1 Fc, and further comprises one or more mutations selection from the group consisting of: M252Y, S254T, T256E, and a combination thereof. E249. The method of E248, comprising M252Y, S254T, T256E mutations. E250. The method of any one of E225-E249, wherein the lysine residue (K) at the C-terminus of the Fc region is deleted. E251. The method of any one of E225-E249, wherein the lysine residue (K) at the C-terminus of the Fc region is present. E252. The method of any one of E225-E249, wherein the glycine and lysine residues (GK) at the C- terminus of the Fc region are present. E253. The method of any one of E225-E249, wherein the glycine and lysine residues (GK) at the C- terminus of the Fc region are deleted. E254. The method of any one of E225-E253, wherein said Fc region comprises a sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 90%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NO: 77, 80, 81, 91, 98-103, 111, 115, and 119. E255. The method of any one of E225-E254, wherein said CL and/or CL’ domain is the CL domain of a kappa light chain or lambda light chain. E256. The method of any one of E225-E254, wherein said CL and/or CL’ domain is the CL domain of a human kappa light chain or human lambda light chain. E257. The method of any one of E225-E256, wherein said CL and/or CL’ domain comprises an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NO: 67, 69, 72, 74, 75, 78, 82, and 84-89. E258. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 121, (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 122, and (iii) a third polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 123. E259. The method of any one of E1-E258, wherein said bispecific molecule comprises: (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123. E260. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 124, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 125. E261. The method of any one of E1-E257 and E260, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125. E262. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 126, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 127. E263. The method of any one of E1-E257 and E262, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127. E264. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 129, (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 130, (iii) a third polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 131; and (iv) a fourth polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 132. E265. The method of any one of E1-E258 and E264, wherein said bispecific molecule comprises: (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and (iv) a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132. E266. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 133, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 134. E267. The method of any one of E1-E257 and E266, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134. E268. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 135, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 136. E269. The method of any one of E1-E257 and E268, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136. E270. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 138, (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 139, and (iii) a third polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 140. E271. The method of any one of E1-E257 and E270, wherein said bispecific molecule comprises: (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140. E272. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 141, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 142. E273. The method of any one of E1-E257 and E272, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142. E274. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 143, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 144. E275. The method of any one of E1-E257 and E274, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144. E276. The method of any one of E1-E257, wherein said bispecific molecule comprises: (i) a first polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 145, and (ii) a second polypeptide comprising an amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical SEQ ID NO: 146. E277. The method of any one of E1-E257 and E276, wherein said bispecific molecule comprises: (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146. E278. A kit comprising (a) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB; and (b) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA), and (c) instructions for use. E279. The kit of E278, comprising a multispecific T cell engager molecule of any one of E5 and E12- E193. E280. The kit of E278 or E279, comprising a bispecific molecule of any one of E194-E277. E281. A pharmaceutical composition comprising (a) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB; and (b) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA); and (iii) a pharmaceutically acceptable carrier, excipient, or diluent. E282. The pharmaceutical composition of E281, comprising a multispecific T cell engager molecule of any one of E5 and E12-E193. E283. The pharmaceutical composition of E193 or E194, comprising a bispecific molecule of any one of E194-E277. E284. A bispecific molecule comprising a first binding domain that binds to PD-L1 and a second binding domain that binds to 4-1BB; and a multispecific T cell engager molecule comprising a third binding domain that binds to CD3 and a fourth binding domain that binds to a Tumor Antigen (TA), for use as a medicament. E285. A bispecific molecule comprising a first binding domain that binds to PD-L1 and a second binding domain that binds to 4-1BB; and a multispecific T cell engager molecule comprising a third binding domain that binds to CD3 and a fourth binding domain that binds to a Tumor Antigen (TA), for use in treating cancer in a subject. E286. Use of a bispecific molecule comprising a first binding domain that binds to PD-L1 and a second binding domain that binds to 4-1BB; and a multispecific T cell engager molecule comprising a third binding domain that binds to CD3 and a fourth binding domain that binds to a Tumor Antigen (TA), in the manufacture of a medicament for treating cancer in a subject. E287. Use of a bispecific molecule comprising a first binding domain that binds to PD-L1 and a second binding domain that binds to 4-1BB; and a multispecific T cell engager molecule comprising a third binding domain that binds to CD3 and a fourth binding domain that binds to a Tumor Antigen (TA), for treating cancer in a subject. [11] The use of section headings herein is merely for the convenience of reading, and not intended to be limiting per se. The entire document is intended to be viewed as a unified disclosure, and it should be understood that all combinations of features described herein are contemplated. BRIEF DESCRIPTION OF THE FIGURES [12] FIGs.1A-1C show functional comparison of different PDL1x41BB bispecific format. FIG.1A: serially diluted bispecific molecules or monoclonal antibodies (mAbs) were added to Jurkat NFAT- luc2/human PD-1 reporter cell line co-cultured with the CHO human PD-L1 stable cell line, and luminescence was measured 6 hours later. FIG.1B: serially diluted bispecific molecules or mAbs were added to4-1BB/NFkB-luc reporter cell line co-cultured with CHO cells stably expressed PDL1 and CD32a, and luminescence was measured 6 hours later. FIG.1C: serially diluted bispecific antibodies were added to the T cells co-cultured with aAPCs expressing both PD-L1 and CD32a, and IL-2 secretion in the culture supernatant were collected and measured 48 hours later. [13] FIGs.2A-2B show average tumor volumes (Fig.2A) and cumulative survival curves (Fig.2B) of MC38 tumor bearing mice following treatment as indicated. Mice received the indicated treatments (Table 1) once the tumors were randomized. Tumor were measured with a digital caliper twice every week until the end of study. Survival curves were analyzed for statistical significance using the Kaplan-Meier estimator with Mantel-Cox log rank test to compare curves. [14] FIGs.3A-3B show Individual tumor growth curves (FIG.3A) and cumulative survival curves (FIG. 3B) of B16F10-huEpCAM tumor bearing mice following treatment as indicated. Mice received the indicated treatments (Table 2) once the tumors were randomized. Tumor were measured with a digital caliper twice every week until the end of study. Survival curves were analyzed for statistical significance using the Kaplan-Meier estimator with Mantel-Cox log rank test to compare curves. [15] FIG.4 shows specific detection of PDL1 at the surface of PDL1-expressing target cell lines with monoclonal antibody clone 29E.2A3. Parental C4-2B-Luc, SHP77-Luc and NUGC4-Luc cancer cell lines were transduced with a viral construct encoding the human CD274 gene (PDL1). Parental cells and PDL1-transduced cells were incubated with a PE-conjugated isotype control antibody or the PE- conjugated anti-PDL1 mouse monoclonal antibody (clone 29E.2A3) at a concentration of 2 ug/mL for 1 h at 4°C. Cell-bound anti-PDL1 mAb was detected by flow cytometry. PE fluorescence values for each line was plotted as histograms, demonstrating a specific PDL1 signal in the transduced lines (grey histograms), compared to isotype control signal (white histograms). [16] FIGs.5A-5E show dose-dependent target cell lysis of human tumor cell lines mediated by T cell engagers (TCE) alone or in combination with molecules 21B2 or 26597. FIGs.5A&5E: C4-2B-PDL1-Luc prostate cancer cells expressing PDL1, STEAP1, and PSMA. FIG.5B: SHP77-PDL1-Luc small cell lung cancer cells expressing PDL1 and DLL3. FIGs.5C-5D: NUGC4-PDL1-Luc gastric cancer cells expressing PDL1, MUC17 and CLDN18.2. These engineered cancer cells were co-cultivated for 96 hours with human pan-T cells at an E:T cell ratio of 1 to 1 and increasing concentrations of the following T cell engagers (TCEs): (A) an anti-PSMA BiTE® molecule, (B) an anti-DLL3 BiTE® molecule, (C) an anti- MUC17 BiTE® molecule, (D) an anti-CLDN18.2 BiTE® molecule, and (E) an anti-STEAP1 T-cell engager. Assays were supplemented, as indicated, with the anti-PDL1 monoclonal antibody 21B2 or the PDL1x4- 1BB bispecific antibody 26597 at a concentration of 3 nM. Target cell lysis was monitored by luciferase activity measurement and the specific cytotoxicity was plotted at each concentration in comparison to the no TCE control condition. The effective concentration inducing 50 percent of cell lysis (EC50) for each condition tested is indicated in the tables below the graphs. Each datapoint represents the mean of triplicate values (combination conditions) or duplicate values (TCE alone condition). [17] FIGs.6A-6F show decrease in the target cell lysis EC50 value of TCE molecules in combination with molecules 21B2 or 26597. EC50 values from the redirected lysis of cancer cell line (6A & 6E) C4-2B- PDL1-Luc prostate cancer cells expressing PDL1, PSMA, and STEAP1 (6B) SHP77-PDL1-Luc small cell lung cancer cells expressing PDL1 and DLL3, and (6C-6D) NUGC4-PDL1-Luc gastric cancer cells expressing PDL1, MUC17 and CLDN18.2 co-cultivated for 96 hours with human pan-T cells at an E:T cell ratio of 1 to 1, and increasing concentrations of the following T cell engager molecule (TCE): (6A) anti- PSMA BiTE^® molecule, (6B) anti-DLL3 BiTE^® molecule, (6C) anti-MUC17 BiTE^® molecule, (6D) anti- CLDN18.2 BiTE^® molecule, and (6E) anti-STEAP1 T-cell engager alone or in the presence of the anti- PDL1 monoclonal antibody 21B2 or the PDL1x4-1BB bispecific antibody 26597 at a concentration of 3 nM. Experimental T cell-mediated cell lysis EC50 values with three independent T cell donors are plotted in each graph (from values in Table 3). FIG.6F is a plot combining the mean cell lysis EC50 value from all three T cell donors (Means column in Table 3) for each TCE and combination groups. The statistical significance of the difference between treatment conditions was analyzed with a two-way ANOVA Tukey multiple comparison test in GraphPad Prism 7.05, for individual TCE molecules (A-D), or for all the TCE molecules combined (6F), resulting in p values annotated as follow: * < 0.05; ** < 0.005; *** <0.001; **** < 0.0001; n.s = non significant. [18] FIGs.7A-7B show greater shift in target cell lysis EC50 for TCEs in combination with molecule 26597 compared to combinations with molecule 21B2. The mean cell lysis EC50 fold shift of all T cell engagers tested (anti-PMSA, anti-DLL3, anti-MUC17, anti-CLDN18.2) in combination with molecules 21B2 or 26597 were plotted from Table 4 as (7A) individual box plots for each T cell donor or (7B) box plots for all T cell donors combined. The mean fold shift from Table 2 is indicated above each box. The statistical significance of the differences between the TCE EC50 fold shift in the 21B2 and 26597 combination groups was analyzed with a paired T-test comparing treatment groups for (A) individual T cell donors, or (B) all three T cell donors combined, using Microsoft Excel 2016 and resulting in p values annotated as follow: ** < 0.005; *** < 0.001; **** < 0.0001. [19] FIGs.8A-8D show the cytotoxicity mediated by combinations of anti-DLL3 BiTE molecule and 4- 1BBxPD-L1 bispecific molecules. Human PBMC were co-cultured with SHP-77-luc-PD-L1 cells, stably transduced to overexpress luciferase and PD-L1, at an E:T cell ratio of 1:1. Serial dilutions of 4-1BBxPD- L1 bispecific molecule combined with the indicated anti-DLL3 BiTE molecule concentrations were added for 48 or 120 hours. Redirected target cell lysis was determined by analysis of Viability Dye⁺ dead target cells by flow cytometry. Each data point represents the mean of duplicates. Error bars represent SD. FIGs.8A and 8C are from one donor, and FIGs.8B and 8D are from a second donor. [20] FIGs.9A-9D show T-cell activation, induced by combinations of anti-DLL3 BiTE molecules and the 4-1BBxPD-L1 bispecific molecule. Human PBMC were co-cultured with SHP-77-luc-PD-L1 cells at an E:T cell ratio of 1:1. Serial dilutions of 4-1BBxPD-L1 bispecific molecule combined with the indicated anti- DLL3 BiTE molecule concentrations were added for 48 hours. Expression of T-cell activation marker CD25 (FIGs.9A-9B) or 4-1BB (FIGs.9C-9D) on CD4⁺ or CD8⁺ T cells was determined by flow cytometry. FIGs.9A and 9C are from one donor, and FIGs.9B and 9D are from a second donor. [21] FIGs.10A-10D show T-cell proliferation, induced by combinations of anti-DLL3 BiTE molecule and 4-1BBxPD-L1 bispecific molecule. Human PBMC were co-cultured with SHP-77-luc-PD-L1 cells. Increasing concentrations 4-1BBxPD-L1 bispecific molecule combined with the indicated anti-DLL3 BiTE molecule concentrations were added for 48 or 120 hours. Anti-DLL3 BiTE molecule and 4-1BBxPD-L1 bispecific molecule-induced expression of the proliferation marker Ki67 was determined by intracellular staining and flow cytometry after 48 hours (A, B). The number of CD4⁺ or CD8⁺ T cells per well was determined by flow cytometry after 120 hours (C, D). FIGs.10A and 10C are from one donor, and FIGs. 10B and 10D are from a second donor. [22] FIGs.11A-11D show expression of granzyme b and perforin in CD8⁺ or CD4⁺ T cells, induced by the combination of anti-DLL3 BiTE and 4-1BBxPD-L1 bispecific molecules. Human PBMC were co- cultured with SHP-77-luc-PD-L1 cells and serial dilutions of 4-1BBxPD-L1 bispecific molecule combined with the indicated anti-DLL3 BiTE molecule concentrations were added for 72 hours. Anti-DLL3 BiTE molecule- and 4-1BBxPD-L1 bispecific molecule-induced expression of intracellular granzyme B (A, B) or perforin (C, D) was determined in permeabilized CD8⁺ or CD4⁺ T cells by staining with specific antibodies and flow cytometry. [23] FIGs.12A-12D show cytokine release, induced by combinations of anti-DLL3 BiTE molecule and 4- 1bbxpd-l1 bispecific molecule. Human PBMC were co-cultured with SHP-77-luc-PD-L1 cells at an E:T cell ratio of 1:1. Serial dilutions of 4-1BBxPD-L1 bispecific molecule combined with the indicated anti-DLL3 BiTE molecule concentrations were added for 48 hours. Cytokine concentrations in the cell culture supernatants were measured by flow cytometry using the human BD CBA Th1/Th2 Kit II. [24] FIGs.13A-13C show BiTE molecule-mediated redirected lysis in presence of 4-1BBxPD-L1 bispecific molecule. Human T cells were co-cultured with cancer cell lines NUGC-4-luc-PD-L1 (A), GSU-luc-PD-L1 (B), or C4-2B-luc-PD-L1 (C) stably transduced to overexpress luciferase and PD-L1. Serial dilutions of anti- MSLN BiTE molecule, anti-CLDN18.2 BiTE molecule, or anti-PSMA BiTE molecule, respectively, in combination with 3 nM 4-1BBxPD-L1 bispecific molecule were added for 96 hours. BiTE molecule-mediated specific lysis was determined by measuring luciferase activity of viable target cells. [25] FIGs.14A-14F show cytokine release of T cells induced by anti-MSLN-BiTE or anti-CLDN18.2- BiTE molecules and their combination with 4-1BBxPD-L1 bispecific molecule. Human T cells were co-culture with NUGC-4-luc-PD-L1 (A, B, C) or GSU-luc-PD-L1 (D, E, F) stably transduced to overexpress luciferase and PD- L1. Increasing BiTE concentrations and 4-1BBxPD-L1 bispecific molecule (3 nM) were added for 96 hours. Cytokine concentrations in the cell culture supernatants were measured by flow cytometry. [26] FIGs.15A-15D show the impact of PD-L1 expression level on BiTE molecule-mediated cytotoxicity. Human PBMC were co-cultured with SHP-77-luc or SHP-77-luc-PD-L1 at an E:T cell ratio of 1:1. Serial dilutions of DLL3-BiTE were added for 72 hours. The DLL3-BiTE-mediated redirected tumor cell lysis was determined by analysis of PI⁺ lysed tumor cells by flow cytometry (A). Expression of PD-L1 on target cells (B) as well as expression of 4-1BB and PD-1 on T cells (C, D) was determined by extracellular staining by flow cytometry. [27] FIGs.16A-16D show specific lysis and cytokine release mediated by 4-1BBxPD-L1 bispecific molecule and anti-DLL3-BiTE molecule, when using endogenous PD-L1 expressing SHP-77-luc versus SHP-77-luc-PD-L1. Human PBMC were co-cultured with cancer cell lines SHP-77-luc or SHP-77-luc-PD-L1 stably overexpressing PD-L1. Combinations of 4-1BBxPD-L1 bispecific molecule and anti-DLL3 BiTE molecule were added for 96 hours. Specific lysis of SHP-77-luc (A) or SHP-77-luc-PD-L1 (C) was determined by luminescence assay measuring luciferase activity of viable target cells. Concentrations of IFNγ (B, D) in the cell culture supernatants were measured by flow cytometry. [28] FIGs.17A-17F provides domain information of certain bispecific formats, including IgG-scFv, Fab- scFv-Fc, IgG-VH, Fab-VH-Fc, [Fab*VH] hetero-Fc, and hetero-Ig. Letters “a” and “b” are used to indicate the first antigen (“a”) or the second antigen (“b”) that the bispecific molecule binds to. The VH and VL domains are designated as VHA, VHB, VLA, and VLB, accordingly. DETAILED DESCRIPTION OF THE INVENTION 1. OVERVIEW [29] 4-1BB (also referred to as “41BB”) is an immune co-stimulatory protein expressed on activated T cells. Agonizing 4-1BB by crosslinking antibody enhances T cell proliferation, survival and cytokine production upon TCR engagement. However, clinical development of 4-1BB agonistic antibodies has been hampered by dose-limiting hepatotoxicity. For example, phase I and II data from Urelumab (BMS- 663513) revealed a liver toxicity that appeared to be on target and dose dependent, halting initial clinical development of Urelumab. The anti-hu4-1BB huIgG2 utomilumab (PF-05082566) displays a better safety profile but lower agonistic potency. [30] To overcome this challenge, bispecific molecules disclosed herein aim to promote target-mediated clustering of 4-1BB. It is understood that 4-1BB undergoes trimerization upon binding to its ligand (4- 1BBL); and 4-1BB multimerization and clustering (“crosslinking”) is a prerequisite for its signaling pathway. Therefore, the 4-1BB binding domains disclosed herein are “crosslinking dependent,” meaning that the agonistic activity of the molecule is dependent upon the crosslinking of 4-1BB. Without 4-1BB crosslinking, the binding of the bispecific molecules to 4-1BB leads to minimal agonist activity, thereby avoiding toxicities exhibited by Urelumab. The bispecific molecules take advantage of this “crosslinking dependent” effect, and the activation of 4-1BB is controlled through a PD-L1 binding moiety. [31] PD-L1 (also referred to as “PDL1”), which is also known as B7-H1 or CD274, is expressed in multiple types of cancers (e.g., breast cancer, lung cancer, melanoma). In the tumor microenvironment, PD-L1, expressed on tumor cells, binds to the inhibitory checkpoint receptor, PD-1, on activated tumor infiltrating lymphocytes. The interaction between PD-L1 and PD-1 delivers an inhibitory signal to T cells and ultimately dampen T-cell receptor signaling cascades. In the bispecific molecules disclosed herein, the anti-PD-L1 arm serves two functions: (i) it blocks PD-1/PD-L1 signaling pathway, and (ii) it serves as an “anchoring” moiety, bringing the 4-1BB-binding arm in close proximity to each other. Specifically, in tumor microenvironment, the PD-L1-binding arm brings 4-1BB-binding moiety in close proximity to each other, thereby triggering the crosslinking and activation of 4-1BB. [32] Further, as exemplified herein, when the 4-1BBxPD-L1 bispecific molecules are combined with a multispecific T cell engager, synergistic anti-tumor effects are observed. For example, when an exemplary 4-1BBxPD-L1 bispecific molecule and a bispecific T cell engager targeting tumor antigen CLDN18.2 were co-administered, the reduction in tumor volume was much more significant when compared with 4- 1BBxPD-L1 bispecific alone, or CLDN18.2 T cell engager alone. [33] One particular surprising discovery (Example 2) is that the exemplary 4-1BBxPD-L1 bispecific molecule disclosed herein showed efficacy in PD-L1^low tumor models. Specifically, it was discovered that the 4-1BBxPD-L1 bispecific molecule was just as effective as a 4-1BB agonist antibody (crosslinking via Fc gamma receptor in vivo) plus a PDL1 blocking antibody, when combined with a CLDN18.2 T cell engager. This provides a significant advantage in cancer treatment. Patients would not need to be screened for PD-L1 expression, and even those patients with tumors that do not normally express high level of PD-L1 (e.g., prostate cancer) can be treated using the exemplary 4-1BBxPD-L1 bispecific molecules and the T cell engagers disclosed herein. [34] Example 4 and further evidence showing the superior enhancement of various T cell engagers’ potency with a PDL1-41BB bispecific molecule, as compared to a PDL1 antibody alone. Finally, data from Example 5 suggests that combining an anti-DLL3 BiTE molecule and a 4-1BBxPD-L1 bispecific molecule induced expression of 4-1BB, which is believed to act as a positive feedback loop for 4-1BBxPD-L1 bispecific molecule. The observed dose-dependent synergy is believed to enhance the activities of both 4-1BBxPD-L1 bispecific molecule and the T cell engager. 2. DEFINITIONS [35] Collectively, antibodies form a family of plasma proteins known as immunoglobulins and comprise of immunoglobulin domains. (Janeway et al., Immunobiology: The Immune System in Health and Disease, 4^th ed., Elsevier Science Ltd./Garland Publishing, 1999). As used herein, the term “antibody” refers to a protein having a conventional immunoglobulin format, comprising heavy and light chains, and comprising variable and constant regions. For example, an antibody may be an IgG which is a “Y-shaped” structure of two identical pairs of polypeptide chains, each pair having one “light” (typically having a molecular weight of about 25 kDa) and one “heavy” chain (typically having a molecular weight of about 50-70 kDa). An antibody has a variable region and a constant region. In IgG formats, the variable region is generally about 100-110 or more amino acids, comprises three complementarity determining regions (CDRs), is primarily responsible for antigen recognition, and substantially varies among other antibodies that bind to different antigens. The constant region allows the antibody to recruit cells and molecules of the immune system. The variable region is made of the N-terminal regions of each light chain and heavy chain, while the constant region is made of the C-terminal portions of each of the heavy and light chains. (Janeway et al., “Structure of the Antibody Molecule and the Immunoglobulin Genes”, Immunobiology: The Immune System in Health and Disease, 4^th ed. Elsevier Science Ltd./Garland Publishing, (1999)). [36] Antibodies can comprise any constant region known in the art. Human light chains are classified as kappa and lambda light chains. Heavy chains are classified as mu, delta, gamma, alpha, or epsilon, and define the antibody's isotype as IgM, IgD, IgG, IgA, and IgE, respectively. IgG has several subclasses, including, but not limited to IgG1, IgG2, IgG3, and IgG4. IgM has subclasses, including, but not limited to, IgM1 and IgM2. Embodiments of the present disclosure include all such classes or isotypes of antibodies. The light chain constant region can be, for example, a kappa- or lambda-type light chain constant region, e.g., a human kappa- or lambda-type light chain constant region. The heavy chain constant region can be, for example, an alpha-, delta-, epsilon-, gamma-, or mu-type heavy chain constant regions, e.g., a human alpha-, delta-, epsilon-, gamma-, or mu-type heavy chain constant region. Accordingly, in exemplary embodiments, the antibody is an antibody of isotype IgA, IgD, IgE, IgG, or IgM, including any one of IgG1, IgG2, IgG3 or IgG4. [37] An antibody can be cleaved into fragments by enzymes, such as, e.g., papain and pepsin. Papain cleaves an antibody to produce two Fab fragments and a single Fc fragment. Pepsin cleaves an antibody to produce a F(ab’)2 fragment and a pFc’ fragment. In exemplary aspects of the present disclosure, the antigen binding protein of the present disclosure comprises an antigen binding fragment of an antibody. [38] A “variable domain” refers to the variable region of the antibody light chain (VL) or the variable region of the antibody heavy chain (VH), either alone or in combination. As known in the art, the variable domains of the heavy and light chains each consist of four framework regions (FR) connected by three complementarity determining regions (CDRs), and contribute to the formation of the antigen-binding site of antibodies. In general, a VH or VL domain framework comprises four framework sub-regions, FR1, FR2, FR3 and FR4, interspersed with CDRs, shown as the following structure: FR1 - CDR1 - FR2 - CDR2 - FR3 - CDR3 - FR4. A “framework sequence” refers to the sequence of FR1, FR2, FR3, and FR4, in essence the sequence of a variable domain minus the three CDR sequences. [39] As used herein, “Complementarity Determining Regions” (CDRs) can be identified according to the definitions of the Kabat, Chothia, the accumulation of both Kabat and Chothia, AbM, contact, North, and/or conformational definitions or any method of CDR determination well known in the art. See, e.g., Kabat et al., 1991, Sequences of Proteins of Immunological Interest, 5th ed. (hypervariable regions); Chothia & Lesk, 1987, J Mol Biol., 196:901-917 (structural loop structures). The identity of the amino acid residues in a particular antibody that make up a CDR can be determined using methods well known in the art. AbM definition of CDRs is a compromise between Kabat and Chothia and uses Oxford Molecular’s AbM antibody modeling software (Accelrys®). The “contact” definition of CDRs is based on observed antigen contacts, set forth in MacCallum et al., 1996, J. Mol. Biol., 262:732-745. The “conformational” definition of CDRs is based on residues that make enthalpic contributions to antigen binding (see, e.g., Makabe et al., 2008, J. Biol. Chem., 283:1156-1166). North has identified canonical CDR conformations using a different preferred set of CDR definitions (North et al., 2011, J. Mol. Biol.406: 228-256). In another approach, referred to herein as the “conformational definition” of CDRs, the positions of the CDRs may be identified as the residues that make enthalpic contributions to antigen binding (Makabe et al., 2008, J Biol. Chem.283:1156-1166). Martin definition (also called enhanced Chothia definition) combines the Kabat and Chothia definitions and differs from them only in the heavy chain, where CDR- H1 includes all residues of Kabat and Chothia while CDR-H2 is seven residues shorter than that defined by Kabat (Martin, Bioinformatics tools for antibody engineering. Handbook of Therapeutic Antibodies. Weinheim: Wiley-VCH Verlag GmbH; (2008). p.95–117; see also the database maintained by the Institute of Structural and Molecular Biology at the University College London, http://www.bioinf.org.uk/abs/#cdrid). Still other CDR boundary definitions may not strictly follow one of the above approaches, but will nonetheless overlap with at least a portion of the Kabat CDRs, although they may be shortened or lengthened in light of prediction or experimental findings that particular residues or groups of residues or even entire CDRs do not significantly impact antigen binding. For example, “combined” CDRs may also be used. Therefore, a CDR may refer to CDRs defined by any approach known in the art, including combinations of approaches. For any given embodiment containing more than one CDR, the CDRs (or other residue of the antibody) may be defined in accordance with any of Kabat, Chothia, North, AbM, Contact, IMGT, Martin, combined Kabat and Chothia, and/or conformational definitions. [40] For example, Table N1 shows several commonly used definitions of CDRs: Table N1. Definitions of CDRs. Loop Kabat AbM Chothia¹ Contact² IMGT L1 L24-L34 L24-L34 L26-L32 L30-L36 L27-L32 7; CDR-H1:H26-32; CDR-H2:H52-56; CDR-H3:H95-102. Table N1 is a consensus of Chothia definition based upon Chothia & Lesk (1987) (e.g., CDR-H3) and Chothia et al., 1989, Nature 342:877-883 (e.g., CDR-H2). 2. Any of the numbering schemes can be used for these CDR definitions, except the contact definition uses the Chothia or Martin (Enhanced Chothia) definition. 3. The end of the Chothia CDR-H1 loop when numbered using the Kabat numbering convention varies between H32 and H34 depending on the length of the loop. (This is because the Kabat numbering scheme places the insertions at H35A and H35B.) [41] The CDR sequences provided in the Sequence Tables are based on the Kabat definition. However, other definitions for CDRs may also be used. [42] Human germline VH and VL sequences are divided into subfamilies. VH subfamilies include VH1, VH2, VH3, VH4, and VH5 subfamilies. VL subfamilies include Vκ and Vλ subfamilies, with Vκ often being further divided into Vκ1, Vκ2, Vκ3, Vκ4, Vκ5, and Vκ6, and Vλ often being further divided into Vλ1, Vλ2, Vλ3, Vλ4, Vλ5, Vλ6, Vλ7, Vλ8, Vλ9, Vλ10, and Vλ11. In particular, human germline framework designation (such as VH1, VH2, VH3) is not to be confused with the VH_A, VH_B, VL_A, and VL_A designation of used herein. The 4-1BB x PD-L1 bispecific molecules disclosed herein in general have two sets of VHs and VLs, one set of VH-VL form a V-domain that binds 4-1BB and the other set of VH-VL form another V- domain that binds PD-L1. To provide clarity, one set of VH and VL are designated as VH_A and VL_A, and the other set of VH and VL are designated as VH_B and VL_B. [43] The architecture of antibodies has been exploited to create a growing range of alternative formats that span a molecular-weight range of at least about 12–150 kDa and has a valency (n) range from monomeric (n = 1), to dimeric (n = 2), to trimeric (n = 3), to tetrameric (n = 4), and potentially higher. [44] The building block that is most frequently used to create novel antibody-based formats is the single-chain variable (V)-domain antibody fragment (scFv). Although the two domains of the Fv fragment, VL and VH, are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VL and VH regions pair to form monovalent molecules (see e.g., Bird et al. Science 242:423- 426 (1988) and Huston et al., 1988, Proc. Natl. Acad. Sci. USA 85:5879-5883). [45] Also disclosed herein are “heavy chain only” molecules. This type of antigen-binding proteins lack the light chain of a conventional antibody. Examples of such “heavy chain only” molecules include, for example, single domain molecules such as UniDabs® (VH only); and homodimeric molecules comprising the VH antigen-binding domain and the CH2 and CH3 constant domains, in the absence of the CH1 domain (e.g., UniAb®). Non-limiting examples of “heavy chain only” antigen binding proteins are described, for example, in WO2018/039180. Such heavy chain only molecules can be produced by UniRat®, which is a triple knockout rat wherein the expressions of the native variable coding sequences and the heavy and light chain constant regions have been inactivated. The UniRat has been genetically modified to exclusively express the full human VDJ repertoire (all VH families), with transgenes of human heavy chain variable domains linked to a conserved rat Fc. Immunization of the UniRat elicits a normal antibody response that results in the expression of UniAbs, human heavy-chain-only antibodies of approximately 80 kDa, contrasting with the standard ~150 kDa human IgG. In particular, VH domains from the UniRat, called UniDab, approximately 12.5 kDa (~100 amino acids), can be assembled as modular domains of multispecific antigen binding proteins. [46] Bispecific formats can generally be divided into five major classes: BsIgG, appended IgG, BsAb fragments, bispecific fusion proteins and BsAb conjugates. See, e.g., Spiess et al., Molecular Immunology 67(2) Part A: 97-106 (2015). [47] Many of the antibody-derived molecules disclosed herein comprise two different chains, one derived from the heavy chain of an antibody, and one derived from the light chain of an antibody. Although the heavy/light chain has been modified and is no longer the classical immunoglobulin heavy/light chain, for convenience, it is still generally called “heavy chain” or “HC” if it is based on heavy chain backbone, and “light chain” or “LC” if it is based on light chain backbone. For example, for tetravalent bispecific molecule IgG-scFv, the “HC” comprises an IgG heavy chain fused to an scFv. It would be apparent to a skilled artisan whether HC is a traditional immunoglobulin heavy chain or a modified version based on immunoglobulin heavy chain backbone. [48] The term “binding domain” or “binding moiety” in general refers to a domain or a moiety which specifically binds to / interacts with / recognizes a given target epitope or a given target side on the target molecules (antigens), e.g., 4-1BB, PD-L1, CD3. Within the context of this invention, the binding domain or binding moiety is based on the structure and/or function of an antibody, e.g. of a full-length immunoglobulin, or an antigen-binding fragment thereof, such as Fv, scFv, or Fab, as described above. For example, an antigen-binding domain "binds" to an antigen if it binds with greater affinity, avidity, more readily, and/or with greater duration than it binds to other substances. For example, a 4-1BB binding domain that binds to the 4-1BB is a domain that binds 4-1BB with greater affinity, avidity, more readily, and/or with greater duration than it binds to other proteins that are not 4-1BB. It is also understood by reading this definition that, for example, a binding domain which specifically or preferentially binds to a first target may or may not specifically bind to a second target. If numerical examples are of interest, an antigen-binding domain that binds to an antigen may bind with a K_D value that is numerically less than 1x10^-6 M, 1x10^-7 M, 1x10^-8 M, or 1x10^-9 M. 3. MULTISPECIFIC T CELL ENGAGERS [49] Multispecific T cell engagers disclosed herein generally comprises a binding domain that binds to CD3, and a binding domain that binds to a Tumor Antigen (TA). [50] Tumor Antigens (TAs) refer to antigens that are targeted by immuno-oncology therapies. In general, there are two major classes of tumor antigens that are targeted by immune-oncology therapies: tumor antigens with low tumor specificity (also called “tumor-associated antigens” or “TAAs”), and tumor antigens with high tumor specificity. [51] Exemplary antigens with low tumor specificity (TAAs) include tumor associated “differentiation antigens” and tumor associated “overexpressed antigens.” Differentiated antigens and overexpressed antigens are normal host proteins that demonstrate distinct expression profiles between host and tumor cells. Differentiation antigens are proteins that are shared between the tumor and the normal tissue of origin but distinct from other tissues, and overexpressed antigens are proteins aberrantly expressed normal proteins that provide a growth and/or survival advantage to the tumors. In general, the dysregulation of gene pathways as a result of mutations within the tumor cells results in the atypical expression of unmutated proteins that would otherwise be expressed at relatively lower levels, or not at all, in normal cells of that tissue type in its current developmental state. [52] Tumor Associated Differentiation Antigens. Differentiation Antigens are associated with proteins displaying a cell lineage-specific pattern of expression, or present during specific developmental stages. Much of the interest in differentiation antigens as potential targets of the immune system and therapeutic approaches stems from studies on melanoma, where researchers have documented spontaneous T cell responses against peptides derived from GP100, Melan-A/MART-1, and tyrosinase. The potential to treat a wide range of patients continues to drive new research focused on specifically targeting cancerous cells that aberrantly express differentiation antigens. For example, CD19 is such differentiation antigen, in this case found on normal and malignant B cells, that can be targeted in patients with acute lymphoblastic leukemia (ALL) and other B cell tumors. Recently, adoptive transfer of anti-CD19 chimeric antigen receptor (CAR) T cells in patients with relapsed and refractory ALL has shown high rates (up to 90%) of complete remission in part due to the strength and anti-tumor activity of this immunotherapy. Other well- characterized differentiation antigens include, e.g., TRP2 and CEA. [53] Tumor Associated Overexpressed antigens. Overexpressed antigens are another class of TAs that have been shown to play a role in driving the malignant phenotype of many tumors. Overexpressed antigens are normal cellular proteins expressed in greater abundance in cancerous cells. In leukemic cells, Wilms tumor 1 (WT1) is commonly overexpressed and helps drive the oncogenic process. In several epithelial tumors, such as breast and ovarian cancer, overexpression of ERBB2 (HER2/NEU) is typically associated with poor prognoses, but this protein may also serve as a potential immunotherapy target because of its increased expression on the surface of cancerous cells that exhibit heightened proliferation. Other well-characterized overexpressed antigens include, e.g., PRAME, RAGE-1, and mesothelin. [54] Antigens with high tumor specificity include cancer/testis antigens (CTAs) and Tumor-specific antigens (TSAs). [55] Cancer/testis (germline) antigens. Exemplary CTAs include, e.g., Melanoma Antigen Gene (MAGE) family, BAGE, GAGE, and NY-ESO-1. CTAs are expressed in testes, fetal ovaries, or trophoblasts, but are otherwise absent in healthy somatic cells. For example, many MAGE proteins are restricted in expression to reproductive tissues, but are aberrantly expressed in a wide-variety of cancer types. The attractiveness in targeting CTAs can, in part, be attributed to: 1) their disrupted gene regulation in various tumor types, 2) their limited expression in normal tissues, 3) their lack of presentation in germline and trophoblastic cells, which do not display MHC class I molecules on their surface, and 4) their immunogenic potential. [56] Tumor-specific antigens. Tumor-specific antigens (TSAs) generally arise from tumor-specific mutations, which result in the exclusive expression of neoantigens in tumors and, by definition, their absence in normal cells. Another source of TSAs that have been shown to elicit tumor recognition by T cells are the viral proteins expressed by cells infected with oncoviruses such as HPV and EBV. Gene mutations can result in the expression of new peptides, via point mutations, altering the phase of a gene's reading frame, or chromosomal translocations, and exemplary mutated antigens include, e.g., CDK4, EGFRvIII, KRAS, BRCA1/2, p53, and TGF-βRII. Oncogenic viral antigens are abnormal proteins expressed by cells infected with oncoviruses that can be at the origin of several types of cancers. Exemplary oncogenic viral antigens include, e.g., HPV E6/E7, EBV EBNA1/LMP1/LMP2. [57] Non-limiting examples of tumor antigens as disclosed herein include CD19, CD33, EGFRvIII, MSLN, CDH19, FLT3, DLL3, CDH3, BCMA, CD70, CLDN18.2, CLDN6, MUC17, STEAP1, and PSMA. [58] Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults, and CD33 is a useful target for the treatment of patients with AML, as it is expressed on the cell surface of more than 80% of leukemia isolates from patients with AML. Accordingly, multispecific T cell engagers that target CD33 are particularly suitable for treatment of AML. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [59] Epidermal growth factor receptor variant III (EGFRvIII) is a truncated variant of EGFR. EGFRvIII does not contain a ligand-binding domain of wild type EGFR, and is constitutively active. EGFRvIII expression has been found only in tumors and not in normal tissue. In particular, expression of EGFRvIII has been associated with glioblastoma and malignant glioma. Accordingly, multispecific T cell engagers that target EGFRvIII are particularly suitable for treatment of glioblastoma and malignant glioma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [60] Mesothelin (MSLN) is highly expressed in >80% of ovarian and pancreatic tumors and mesothelioma. Expression of MSLN in normal tissues appears restricted to mesothelial cell surfaces such as the pleural, pericardial, and peritoneal layer. Accordingly, multispecific T cell engagers that target NSLN are particularly suitable for treatment of mesothelioma, ovarian, and pancreatic cancer. In addition. NSCLC and gastric cancers are also suitable candidates for MSLN-targeting T cell engagers. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [61] CDH19 is a Type II Cadherin that mediates cell adhesion. CDH19 is expressed in about 50% melanoma patients. Accordingly, multispecific T cell engagers that target CDH19 are particularly suitable for treatment of melanoma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [62] FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is expressed almost exclusively in the hematopoietic compartment. Mutations in FLT3 are among the most commonly occurring and clinically relevant mutations in patients with AML. Accordingly, multispecific T cell engagers that target FLT3 are particularly suitable for treatment of AML. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [63] Delta-like ligand 3 (DLL3) is an inhibitory Notch pathway ligand that is highly upregulated and aberrantly expressed on the cell surface in small cell lung cancer (SCLC) and other high-grade neuroendocrine tumors. DLL3 surface expression has been found to correlate with time to tumor progression in 10 SCLC and 1 large cell neuroendocrine carcinoma (LCNEC) patient-derived xenograft models. Accordingly, multispecific T cell engagers that target DLL3 are particularly suitable for treatment of SCLC and neuroendocrine carcinoma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [64] CDH3 (P-Cadherin) is a cadherin involved in calcium-dependent cell adhesion. It is expressed in breast, lung and colon cancer, and its expression is also detected in basal epithelial cell layer of some normal tissues including skin, esophagus and trachea. Further, upregulation of CDH3 in cancer is associated with increased cell invasion and metastasis and poor survival. Accordingly, multispecific T cell engagers that target CDH3 are particularly suitable for treatment of breast, lung and colon cancers. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [65] B-cell maturation antigen (BCMA) is an attractive target for multiple myeloma because BCMA expression is restricted to plasma cells and it is highly expressed on multiple myeloma cells. BCMA functions to promote plasma cell survival. Accordingly, multispecific T cell engagers that target BCMA are particularly suitable for treatment of multiple myeloma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [66] CD70 is a member of the tumor necrosis factor super family 7 (TNFSF7) and is a type II transmembrane surface antigen highly expressed on a small subset of activated memory T and B cells or non-lymphoid cells, such as stromal cells of the thymic medulla, and mature dendritic cells. CD70 is aberrantly expressed in hematologic malignancies and a number of solid tumors, including brain tumors, RCC, thymic carcinoma, nasopharyngeal carcinoma, ovarian, lung, colon and pancreatic cancer and melanoma, in particular AML and RCC. Accordingly, multispecific T cell engagers that target CD70 are particularly suitable for treatment of AML and RCC, as well as brain tumors, thymic carcinoma, nasopharyngeal carcinoma, ovarian, lung, colon and pancreatic cancers and melanoma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [67] CLDN18.2 is an isoform of Claudin 18. Claudin proteins are a family of 24 tetraspan transmembrane proteins that are major components of cellular tight junctions. Claudin 18 has two isoforms, Claudin 18.1 forms part of tight junctions in normal lung, and Claudin 18.2 is localized primarily to normal stomach, with low expression in intestine and pancreas. In cancer cells, CLDN18.2 is delocalized and is no longer restricted to tight junctions. CLDN 18.2 is an attractive target in gastric cancer due to its high expression in cancer and relatively restricted normal tissue expression. Accordingly, multispecific T cell engagers that target CLDN18.2 are particularly suitable for treatment of gastric cancer. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [68] Claudin 6 (CLDN6) is tetraspan protein that localizes to cellular tight junctions and regulates ion transport. It is expressed during embryonic lung development but silenced in most adult tissues. It is overexpressed in 17% of Non-small cell lung cancer (NSCLC) and 37% of high-grade serous ovarian cancer (HGSOC). Accordingly, multispecific T cell engagers that target CLDN6 are particularly suitable for treatment of NSCLC and ovarian cancer. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [69] Mucin-17 (MUC17) is a membrane-bound mucin that is involved in cell-cell contacts. Overexpression and/or deregulation of MUC17 expression in cancer is associated with loss of polarity and changes in cell adhesion or migration. Aberrant activities of MUC17 are believed to be associated with gastric cancer, as well as esophageal, pancreatic, and colorectal cancers. Accordingly, multispecific T cell engagers that target MUC17 are particularly suitable for treatment of gastric cancer, esophageal cancer, pancreatic cancer, and colorectal cancer. Such treatment may be combined with the 4-1BB x PD- L1 bispecific molecules disclosed herein. [70] Prostate-specific membrane antigen (PSMA) is a transmembrane protein expressed in all types of prostatic tissue. Studies have consistently shown elevated expression of PSMA in prostate cancer. Accordingly, multispecific T cell engagers that target PSMA are particularly suitable for treatment of prostate cancer. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [71] Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is a cell surface antigen for therapeutic targeting in prostate cancer. Studies using prostate adenocarcinoma cell lines have identified STEAP1 as the most highly enriched cell surface antigen. STEAP1 is strongly expressed in >80% of mCRPC with bone or lymph node involvement, 62% of Ewing sarcoma, and multiple other cancer types. STEAP1 belongs to the STEAP family of metalloreductases that can form homotrimers or heterotrimers with other STEAP proteins. STEAP1 has an established functional role in promoting cancer cell proliferation, invasion, and epithelial-to-mesenchymal transition. Furthermore, STEAP1 demonstrates limited expression in normal tissue27 which makes it a highly compelling target for cancer therapy. [72] CD19 is a transmembrane receptor involved in signal transduction in B lymphocytes. It is present on normal B cells early in ontogeny and throughout all developmental stages except on plasma cells. CD19 is an attractive target as it is expressed on virtually all B-lineage malignancies. For example, Blincyto® (Blinatumomab), a T cell engager that targets CD19, has been approved for treatment of Acute Lymphoblastic Leukemia (ALL), a rare blood cancer characterized by an overproduction of lymphoblasts. CD19-targeting T cell engagers may also be useful to treat patients with Non-Hodgkin's Lymphoma (NHL), in particular B-cell NHLs. NHLs are a heterogeneous group of malignancies, classified broadly according to lineage (i.e., T or B cell), and with further categorization by morphologic or immunophenotypic features. Diffuse large B cell lymphoma (DLBCL) is a highly aggressive type of NHL. In the adult population, DLBCL is the most frequent subtype representing 30% to 40% of all NHLs. Accordingly, multispecific T cell engagers that target CD19 are particularly suitable for treatment of NHL (e.g., DLBCL), mantle cell lymphoma, and follicular lymphoma. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [73] Other possible use of CD19-targeting T cell engagers includes, e.g., Acute bi-phenotypic leukemia, Acute leukemia, Acute lymphocytic leukemia, Acute myeloid leukemia, B-cell lymphoma, B-cell prolymphocytic leukemia, myelogenous leukemia, Burkitt’s leukemia, Burkitt’s lymphoma, Cerebellar ataxia, Chronic lymphocytic leukemia, Chronic myeloid leukemia, Leukemia, Lymphocytic leukemia, Malignant melanoma, Plasma cell myeloma, and Stem cell transplant. Such treatment may be combined with the 4-1BB x PD-L1 bispecific molecules disclosed herein. [74] In certain embodiments, the multispecific T cell engagers are Bispecific T cell engager (BiTE®) molecules. BiTE molecules are recombinant protein constructs made from two flexibly linked binding domains, each domain derived from an antigen-binding fragment of an antibody. One binding domain of BiTE® molecule is specific for a tumor antigen (such as PSMA, CLDN18.2, EGFRvIII); the second binding domain is specific for CD3, a subunit of the T cell receptor complex on T cells. Once bound to the target antigen expressed on the surface of the respective target cells, binding of CD3 leads to activation and clonal expansion of cytotoxic T cells. Linking T-cells and target cells leads to the formation of an immunological synapse. By their design, BiTE® molecules are uniquely suited to transiently connect T cells with target cells and, at the same time, potently activate the inherent cytolytic potential of T cells against target cells. See e.g., WO 99/54440, WO 2005/040220, and WO 2008/119567. [75] In addition, the T cell engagers may have an immunoglobulin-based multispecific format, including those depicted in FIGs 17A-17F. For example, the STEAP1 x CD3 bispecific molecule disclosed herein comprises four polypeptides, two light chains (VL-CL), one standard immunoglobulin heavy chain (VH- CH1-CH2-CH3), and one modified heavy chain wherein a CD3-binding scFv is inserted at the hinge region (VH-CH1-linker-scFv-linker-CH2-CH3). Additionally, full length heavy and light chains disclosed herein may be used to make hetero-Ig where one arm binds to CD3 and one arm binds to TA. For example, full length CD3-binding domain (such as SEQ ID NOs.175 and 176) may be used to pair with full length DLL3-binding domain (such as SEQ ID NOs: 265 and 266) to form a hetero-Ig. [76] Accordingly, in certain embodiments, the T cell engagers comprise two binding domains, each binding domain comprising a VH and a VL. Table N2 below summarizes the SEQ ID assignment of exemplary CD3 and TA binding domains, and the sequences of exemplary binding domains and T cell engagers are provided in Sequence Table D. CDRs are defined according to Kabat; however, any other CDR definitions may be used. Table N2 Target VH CDRs VL CDRs VH VL scFv TA x CD3 Bispecific D 1 1 2 14714 1 1 4 1 , 2 , , , 2 3 4 7 , , 2 , , , , , 6 1 8 8 7 7 452+447 453+447 CD3 429-431 432-434 435 436 437 448+447 7 7 7 [77] The exemplary CDR sequences disclosed herein may be combined with any suitable framework sequence, such as a human germline VH or VL framework sequence. [78] Preferred human germline light chain frameworks are frameworks derived from Vκ or Vλ germlines. It will be understood that if a sequence is “derived from” one or more germlines, what is referred to is a structural relationship, in which the features of a sequence correspond to the noted germline sequences, but may comprise somatic mutations or other amino acid differences relative to the noted germline sequence. For a sequence to be “derived from” a germline, an actual process of deriving that sequence from a germline sequence (either via molecular biology or computational analysis) is not necessarily required. For example, VL frameworks may be derived from one of the framework of the following germlines: DPK9 (IMGT name: IGKV1-39), DPK12 (IMGT name: IGKV2D-29), DPK18 (IMGT name: IGKV2-30), DPK24 (IMGT name: IGKV4-1), HK102_V1 (IMGT name: IGKV1-5), DPK1 (IMGT name: IGKV1-33), DPK8 (IMGT name: IGKV1-9), DPK3 (IMGT name: IGKV1-6), DPK21 (IMGT name: IGKV3- 15), Vg_38K (IMGT name: IGKV3-11 ), DPK22 (IMGT name: IGKV3-20), DPK15 (IMGT name: IGKV2- 28), DPL16 (IMGT name: IGLV3-19), DPL8 (IMGT name: IGLV1-40), V1-22 (IMGT name: IGLV6-57). Alternatively or in addition, the framework sequence may be derived from a human germline consensus framework sequence, such as the framework of human Vλ1 consensus sequence, Vλ3 consensus sequence, Vκ1 consensus sequence, Vκ2 consensus sequence, Vκ3 consensus sequence. Sequences of human germline frameworks are available from various public databases, such as V-base, IMGT, NCBI, or Abysis. [79] The CD3 and TA binding domains described herein may comprise a VL framework, wherein the framework may comprise one or more amino acid substitutions, additions, or deletions, while still retaining functional and structural similarity with the germline from which it was derived. In some aspects, the VL framework comprises a sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to a human germline VL framework sequence. In some aspects, the CD3 or TA binding domain comprises a VL framework comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 amino acid substitutions, additions or deletions relative to the human germline VL framework sequence. In certain embodiments, the substitution(s) do not change binding affinity (KD) value by more than 1000-fold, more than 100-fold, or 10-fold. [80] The VH framework sequence can be derived from a human VH1 germline, a VH2 germline, a VH3 germline, a human VH4 germline, or a VH5 germline. For example, VH frameworks may be derived from the framework of one of the following germlines: DP54 or IGHV3-7, DP47 or IGHV3-23, DP71 or IGHV4- 59, DP75 or IGHV1-2_02, DP10 or IGHV1-69, DP7 or IGHV1-46, DP49 or IGHV3-30, DP51 or IGHV3-48, DP38 or IGHV3-15, DP79 or IGHV4-39, DP78 or IGHV4-30-4, DP73 or IGHV5-51, DP50 or IGHV3-33, DP46 or IGHV3-30-3, DP31 or IGHV3-9. Alternatively, or in addition, the framework sequence may be derived from the framework of a consensus sequence, such as: VH1 germline consensus sequence, VH2 germline consensus sequence, VH3 germline consensus sequence, VH4 germline consensus sequence, or VH5 germline consensus sequence. [81] The CD3 and TA binding domains described herein may comprise a VH framework, wherein the framework may comprise one or more amino acid substitutions, additions, or deletions, while still retaining functional and structural similarity with the germline from which it was derived. In some aspects, the VH framework comprises a sequence that is at least 90%, at least 91 %, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to a human germline VH framework sequence. In some aspects, the CD3 or TA binding domain comprises a VH framework comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 amino acid substitutions, additions or deletions relative to the human germline VH framework sequence. In certain embodiments, the substitution(s) do not change binding affinity (KD) value by more than 1000-fold, more than 100-fold, or 10-fold. [82] In exemplary aspects, the VH or VL of the CD3 or TA binding domain comprises an amino acid sequence that is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to one of the amino acid sequences references in the Sequence Table. [83] For T cell engagers that comprise a scFv, the VH and VL of a CD3 or TA binding domain are generally connected by a linker to form a scFv. A “linker” is a molecule or group of molecules that connect two separate entities (e.g., the VH chain and the VL chain of the CD3-binding domain) to one another and can provide spacing and flexibility between the two entities such that they are able to achieve a conformation in which they, e.g., bind to their respective targets (e.g., CD3). Protein linkers are particularly preferred, and they may be expressed as a component of the recombinant protein using standard recombinant DNA techniques well-known in the art. In addition, another linker can be used to connect the CD3 binding domain and the TA binding domain. For recombinant proteins described herein comprising two or more linkers (for example, multispecific T cell engagers comprising two scFv domains, BiTE molecules comprising two scFv domains, BiTE molecules comprising two scFv domains and an HLE, and 4-1BB x PD-L1 bispecific molecules), the linkers may all be the same, or some or all of the linkers may be different from each other. [84] In some embodiments, the linker is a peptidyl linker. In some embodiments, the peptidyl linker comprises about 1 to 30 amino acid residues. Exemplary linkers include, e.g., a glycine rich peptide; or a peptide comprising glycine and serine. A glycine rich peptide linker comprises a peptide linker, wherein at least 25% of the residues are glycine. Glycine rich peptide linkers are well known in the art (e.g., Chichili et al. Protein Sci.2013 February; 22(2): 153-167). The peptidyl linker may also be a proline-threonine rich peptide linker. Exemplary linker sequences are provided as SEQ ID NOs.454-471. [85] Mutations may be introduced to scFv to further improve stability. For example, it has been reported that insufficient interface stability between the heavy and light chains of scFv fragments could be the main cause of irreversible scFv inactivation. Fv fragments have been reported to dissociate into heavy-chain variable domains (VH) and light-chain variable domains (VL) with K_D values ranging from 10⁻⁹ to 10⁻⁶ M. An interdomain disulfide bond have been used to further improve scFv stability. For example, mutation to Cys at the site of H44 (Kabat numbering), and mutation to Cys at L100 (Kabat numbering) would not significantly affect the domain folding. The two cysteines can then form an intramolecular disulfide bond to further stabilize the scFv. Specific examples are shown as anti-CD33 scFv (SEQ ID NOs.187 and 188), where a mutation at H44 (G to C) and at L100 (Q to C) are used to create disulfide bonds. Such mutation is sometimes referred to as “cysteine clamp.” [86] The use (or non-use) of cysteine clamp may require evaluation of stability and biologically activities of the scFv. In general, it is believed that the removal of the constant domain (CH1 and Cλ or Cκ) lowers the stability of the Fv domain. This may require the addition of a linker fusion between the VH and VL domains to avoid molecule dissociation. With the decreased interface between the HC and LC, some Fv domains may have an increased probability of being in a dissociated state, exposing their hydrophobic VH and VL interfaces. This could cause increased aggregation, and require additional stability using a disulfide bond or cysteine clamp to covalently link the VH to the VL. On the other hand, although cysteine clamp tends to create a stabilized product post purification, it could also lead to other issues. A poorly positioned cys-clamp can alter the orientation of the VH and VL domains such that it exposes new interfaces or cause a loss in antigen binding due to a new paratope interface. If possible, a scFv domain fusion lacking a cys-clamp with good biophysical properties would be preferential. [87] In addition to CD3 binding domain and TA binding domain, additional moieties may be included, such as histidine tag (6-His) (SEQ ID NO: 472) and a half-life extending (HLE) moiety. Examples of HLE moieties include, e.g., serum albumin and Fc. In particular, single-chain Fc (scFc), where two chains of monomeric CH2-CH3 are connected via a linker (CH2-CH3-linker-CH2-CH3), has been described in US 2014/0302037, US 2014/0308285, WO 2014/144722, WO 2014/151910 and WO 2015/048272. Examples of scFc moieties are shown as SEQ ID NOs: 473 and 474 in Sequence Table D. 4. 4-1BB X PD-L1 BISPECIFIC MOLECULES [88] In various aspects, the invention provides bispecific molecule binds to both 4-1BB and PD-L1 (sometimes referred to as “4-1BB x PD-L1” bispecific). [89] Sequences of exemplary PD-L1 binding domains are provided in Sequence Tables A2 and A3, and sequences of exemplary 4-1BB binding domains are provided in Sequence Table A1 and A4. As explained in detail above, the exemplary CDR sequences disclosed herein may be combined with any suitable framework sequence, such as a human germline VH or VL framework sequence. Preferred human germline light chain frameworks are frameworks derived from Vκ or Vλ germlines, as disclosed in detail above. The VH framework sequence can be derived from a human VH1 germline, a VH2 germline, a VH3 germline, a human VH4 germline, or a VH5 germline. [90] The 4-1BB and PD-L1 binding domains described herein may also comprise a VL framework, wherein the framework may comprise one or more amino acid substitutions, additions, or deletions, while still retaining functional and structural similarity with the germline from which it was derived. In some aspects, the VL framework comprises a sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to a human germline VL framework sequence. In some aspects, the 4-1BB or PD-L1 binding domain comprises a VL framework comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 amino acid substitutions, additions or deletions relative to the human germline VL framework sequence. In certain embodiments, the substitution(s) do not change binding affinity (KD) value by more than 1000-fold, more than 100-fold, or 10-fold. [91] The 4-1BB and PD-L1 binding domains described herein may also comprise a VH framework, wherein the framework may comprise one or more amino acid substitutions, additions, or deletions, while still retaining functional and structural similarity with the germline from which it was derived. In some aspects, the VH framework comprises a sequence that is at least 90%, at least 91 %, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to a human germline VH framework sequence. In some aspects, the 4-1BB or PD-L1 binding domain comprises a VH framework comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 amino acid substitutions, additions or deletions relative to the human germline VH framework sequence. In certain embodiments, the substitution(s) do not change binding affinity (KD) value by more than 1000-fold, more than 100-fold, or 10-fold. [92] In exemplary aspects, the VH or VL of the 4-1BB or PD-L1 binding domain comprises an amino acid sequence that is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to one of the amino acid sequences referenced in Sequence Tables A3-A4. [93] In exemplary aspects, the 4-1BB or PD-L1 binding domain is an scFv. The scFv may comprise an amino acid sequence that is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to one of the scFv amino acid sequences referenced in Sequence Table C, such as SEQ ID NO:128 or 137. Additional mutations, such as cysteine clamp, may be introduced to enhance stability. The use (or non-use) of cysteine clamp may require evaluation of stability and biologically activities of the scFv. [94] The 4-1BB x PD-L1 bispecific molecules described herein also comprise heavy and light chain constant regions. Exemplary sequences of the constant regions are shown in Sequence Table B. In general, amino acid residues in the IgG heavy constant domain of an antibody are numbered according the EU index of Edelman et al., 1969, Proc. Natl. Acad. Sci. USA 63(1):78-85 as described in Kabat et al., 1991, referred to herein as the “EU index numbering.” Typically, the constant domain comprises from residue 118 to 447, and the Fc domain comprises from residue 236 to 447 of the human lgG1 constant domain. Comparison between EU numbering and other numbering systems can be found, e.g., at IGMT database. One example of the amino acid sequence of human IgG constant region is provided herein as SEQ ID NO:94. CH1 domain comprises residues 1-98, hinge region comprises residues 99-110, CH2 domain comprises residues 111-223, and CH3 domain comprises residues 224-330. [95] For example, a Fab comprises a CH1 domain and a CL domain, in addition to the above-described VH domain and VL domains. The CH1 domain can be derived from the CH1 domain of an IgA (e.g., IgA1 or lgA2), IgG, IgE, or IgG (e.g., IgG1, lgG2, lgG3, or lgG4). In some embodiments, the CH1 domain comprises wild type sequence of a CH1 domain. In some embodiments, the CH1 domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 76, 79, 90, 107, 109, 113, or 117. [96] The CL domain can be derived from kappa or lambda CL sequences. Specifically, the amino acid sequences of example human kappa and lambda constant regions are provided (SEQ ID NOs:84-87). Note that the first residue (“R” in SEQ ID NO:85 and “G” in SEQ ID NO:87) is considered an optional junction residue. This residue sometimes is shown as the first residue in the CL domain, and sometimes as the last residue in the VL domain; both are accepted in the art. In exemplary embodiments, the CL domain comprises an amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NOs: 67, 69, 72, 74, 75, 78, 82, and 84-89. [97] The bispecific molecules disclosed herein further comprises an Fc region. Fc region is the tail region of an immunoglobulin that interacts with Fc receptors and some proteins of the complement system. In IgG, IgA and IgD antibody isotypes, the Fc region comprises two copies of monomeric CH2- CH3; IgM and IgE Fc regions comprises two copies of monomeric CH2-CH3-CH4. Exemplary IgG Fc region (CH2-CH3) sequences are shown in Table E. In addition to the exemplary constant domains provided in Table E, the Fc region can be derived from the Fc region of an IgA (e.g., IgA1 or lgA2), IgG, IgE, or IgG (e.g., IgG1, lgG2, lgG3, or lgG4). In some embodiments, the Fc region comprises wild type sequence of an Fc region. In some embodiments, the Fc region comprises one or more mutations resulting in altered biological activity, such as to improve half-life/stability or to render the antibody more suitable for expression and/or manufacturability. For example, mutations may be introduced into the Fc region to reduce the effector activity (e.g., WO 2005/063815), and/or to increase the homogeneity during the production of the recombinant protein. [98] In some embodiments, the Fc region is the Fc region of human lgG1 and comprises one or more of the following effector-null mutations: L234A, L235A, and G237A (numbering according to the EU index). It has been reported that a single mutation of L235E was sufficient for knocking out binding to Fc receptors on U937 cells. Furthermore, the 100-fold reduction in binding to FcγR also resulted in lower T cell activation and proliferation in the presence of the L235E Fc mutant IgG1. Building upon this initial mutation it was found that the combination of L234A and L235A (commonly called LALA mutations) eliminated FcγRIIa binding. These two mutations were later shown to eliminate detectable binding to FcγRI, IIa, and IIIa for both IgG1 and IgG4. Other sites have been reported to knockout Fc receptor binding, such as Gly237Ala, Glu318Ala, Asp265Ala and Glu233Pro mutations. [99] Accordingly, in certain embodiments, the Fc region is derived from an IgG Fc, and further comprises one or more mutations selection from the group consisting of: L234A, L235A, L235E, G237A, and combination thereof (numbering according to the EU index). In exemplary embodiments, the Fc region comprises L234A and L235A mutations. [100] In exemplary embodiments, the Fc region comprises a Stable Effector Functionless (SEFL) mutation to reduce the ability to interact with Fcγ receptors. SEFL mutations are known in the art. See, e.g., Liu et al., J Biol Chem 292: 1876-1883 (2016); and Jacobsen et al., J. Biol. Chem.292: 1865-1875 (2017). Further, US US9546203 discloses a Fc region comprising a N297G mutation, and one or more substitutions at position V259, A287, R292, V302, L306, V323, or I332, using EU numbering scheme, with a cysteine amino acid residue. In exemplary aspects, the SEFL mutation comprises one or more of the following mutations, numbered according to the EU system: L242C, A287C, R292C, N297G, V302C, L306C, and/or K334C. In exemplary aspects, the SEFL mutation comprises N297G. In exemplary aspects, the SEFL mutation comprises A287C, N297G, and L306C. In other exemplary aspects, the SEFL mutation comprises R292C, N297G, and V302C (i.e., SEFL2-2). [101] Accordingly, in certain embodiments, the Fc region is derived from an IgG Fc, and further comprises one or more mutations selection from the group consisting of: V259C, A287C, R292C, V302C, L306C, V323C, I332C, and a combination thereof. In exemplary embodiments, the Fc region is derived from an IgG Fc, and further comprises one or more mutations selection from the group consisting of: L242C, A287C, R292C, N297G, V302C, L306C, K334C, and a combination thereof. In another exemplary embodiment, the Fc region comprises a N297G mutation. In another exemplary embodiment, the Fc region comprises A287C, N297G, and L306C mutations. In another exemplary embodiment, the Fc region comprises R292C, N297G, and V302C mutations. [102] Additional mutations may be introduced to the constant domains. For example, the C-terminal Lys residue of CH3 domain may be clipped, or the C-terminal Gly-Lys dipeptide may be clipped (e.g., compare SEQ ID NO: 92 vs.93 vs.94). [103] In exemplary aspects, the CH1 domain, the Fc (CH2-CH3) domain, and the CL domain comprises an amino acid sequence that is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to one of the amino acid sequences referenced in Sequence Table B. For example, the Fc region may comprise a sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 90%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to any one of SEQ ID NO: 77, 80, 81, 91, 98-103, 111, 115, and 119 [104] Many different formats of bispecific molecules have been exemplified, some of which are depicted in FIGs.17A-17F. [105] In these exemplary configurations, different VH chains and VL chains are generally referred to as VH_A, VH_B, VL_A, or VL_B, indicating that they bind to two different antigens, a or b. Sometimes, the constant domain may also need to be engineered to ensure correct heavy chain and light chain pairing. Since the engineering in constant domains generally involve limited number of mutations, different versions of constant domains are generally distinguished by CH1 versus CH1’, CH2 vs CH2’, CH3 vs CH3’, or CL vs CL’. [106] In one particular example, the bispecific molecule comprises an IgG moiety and a scFv moiety. As shown in FIG.17A, there are two Fab moieties that bind to one antigen (e.g., PD-L1 or 4-1BB). Each Fab moiety comprises two chains: a heavy chain comprising a heavy chain variable domain A (VHA) and a CH1 domain, and a light chain comprising a light chain variable domain A (VL_A) and a CL domain. Each Fab is connected to one chain of Fc (monomeric CH2- monomeric CH3) to form an antibody (IgG). Because this part of the structure is essentially an IgG, there is no new linker between Fab and Fc (Fab and Fc are connected through “hinge” sequence just like a wildtype IgG). In addition, there are two scFv moieties that bind to the other antigen (e.g., 4-1BB or PD-L1). A first linker then connects the C-terminus of one CH3 domain to the N-terminus of one scFv. Each scFv comprises a heavy chain variable domain B (VH_B) and a light chain variable domain B (VL_B); and the VH_B and VL_B are connected via a second linker. This structure is sometimes referred to as “IgG-scFv” format (one or more scFv moieties attached to an IgG molecule). Because each target (PD-L1, 4-1BB) has two binding domains, the bispecific molecules exemplified in FIG.17A is often referred herein to as “bivalent” bispecific molecules; nonetheless, it should be noted that it is also acceptable in the art to refer to such kind of molecule as “tetravalent,” as altogether there are four binding domains. This configuration is sometimes referred to as IgG-scFv. [107] In another particular example, the bispecific molecule comprises a scFv moiety that is inserted between the Fab and Fc (hinge) region of an immunoglobulin (sometimes referred to as “Fab-scFv-Fc”). For example, as shown in FIG.17B, the bispecific molecule may comprises: (i) two Fab moieties that bind to one antigen (e.g., 4-1BB or PD-L1), wherein each Fab moiety comprises two chains: a heavy chain comprising a heavy chain variable domain A (VHA) and a CH1 domain, and a light chain comprising a light chain variable domain A (VLA) and a CL domain; (ii) two scFv moieties that bind to another antigen (e.g., PD-L1 or 4-1BB), wherein each scFv comprises a heavy chain variable domain B (VH_B) and a light chain variable domain B (VL_B); and (iii) one Fc region that comprises two chains, each chain comprising a monomeric CH2 domain and a monomeric CH3 domain. A first linker connects the C-terminus of one CH1 domain to the N-terminus of one scFv, a second linker links the VHB and VLB of the scFv moiety, and a third linker connects the C-terminus of one scFv to the N-terminus of one chain of the Fc region. Similar to the IgG-scFv structure, the molecule exemplified in FIG.17B is essentially a tetravalent molecule, with two binding moieties for PD-L1 and two binding moieties for 4-1BB, but often called bivalent bispecific molecules. This configuration is sometimes referred to as Fab-scFv-Fc. [108] In another exemplary configuration, the bispecific molecule comprises two VH-only binding domains inserted between the Fab and Fc (hinge) region of an immunoglobulin (FIG.17D). A first linker links the C-terminus of the Fab with the N-terminus of the VH, and a second linker linkers the C-terminus of the VH with the N-terminus of the Fc. This configuration is sometimes referred to as Fab-VH-Fc. [109] In another exemplary configuration, the bispecific molecule comprises two VH-only binding domains, each linked to one C-terminus of an IgG heavy chain (FIG.17C). This configuration is sometimes referred to as IgG-VH. [110] In another exemplary configuration, the bispecific molecule is a hetero-IG, comprising one scFv linked to one CH2-CH3 chain, and one Fab linked to the other CH2-CH3 chain. This configuration involves monovalent binding of one antigen through one Fab, and monovalent binding of the second antigen through one scFv. The two heavy chains are asymmetric and there is only one light chain. The configuration is also referred to as [Fab*scFv] hetero-Fc. [111] In another exemplary configuration, the bispecific molecule comprises one VH-only binding domain linked to one CH2-CH3 chain, and one Fab linked to the other CH2-CH3 chain (FIG.17E). This configuration involves monovalent binding of one antigen through one Fab, and monovalent binding of the second antigen through one VH-only binding domain. The two heavy chains are asymmetric and there is only one light chain. The configuration is also referred to as [Fab*VH] hetero-Fc. [112] FIG.17F illustrates another configuration, essentially a hetero-IgG molecule. In this configuration, one heavy chain and one light chain form a Fab that binds to one antigen, and a second heavy chain and a second light chain form a second Fab that binds to a second antigen. The molecule is an asymmetric molecule with one 4-1BB binding domain and one PD-L1 binding domain. To ensure that the heavy chain and light chain are paired correctly (i.e., CH1 pairs with CL, and CH1’ pairs with CL’), charge pairs may need to be created in CH1, CH1’, CL, and CL’. For example, (i) CH1 may comprises a mutation to a positively charged residue and CL may comprise a mutation to a negatively charged residue, such that said CH1 and CL form a first charge pair (left arm of FIG.17F), and (ii) CH1’ may comprise a mutation to a negatively charged residue and CL’ may comprise a mutation to a positively charged residue, such that said CH1’ and CL’ form a second charge pair (right arm of Fig.17F). Because the CL comprises a negatively charged residue, and the CH1’ also comprises a negatively charged residue, the likelihood of CL and CH1’ mis-pairing is unlikely. That way, mixed pairing of 4-1BB light and PD-L1 heavy chain, or vice versa, can be reduced or inhibited. [113] Similarly, charge pairs can be introduced to CH2 and CH3 domains, such that one heavy chain from the PD-L1 binding arm, and one heavy chain from the 4-1BB binding arm, are paired to form a hetero-Fc. Molecules with asymmetric heavy chains (such as those shown in FIG.17E and FIG.17F) need charge pairs in the Fc region to ensure that the two different heavy chains are paired correctly. [114] The positively charged residues and negatively charged residues can be introduced at multiple positions in CH1, CH2, CH3, and CL domains, as long as the residue is present on the surface of the constant domain (such that it can interact with the corresponding residue to form a charge pair), and that the mutation does not generally disrupt the conformation of the constant domain. [115] Positively charged residues include lysine, arginine and histidine. In an exemplary embodiment, lysine (K) is used. In an exemplary embodiment, arginine (R) is used. Negatively charged residues include aspartic acid and glutamic acid. In an exemplary embodiment, glutamic acid (E) is used. Exemplary charge-pairs are provided as part of the constant region sequences in the Sequence Table. [116] Linkers are often needed to link different binding domains. In addition, scFv also requires a linker to link the VH and VL chains. Protein linkers are particularly preferred, and they may be expressed as a component of the recombinant protein using standard recombinant DNA techniques well-known in the art. For recombinant proteins described herein comprising two or more linkers (for example IgG-scFv and Fab-scFv-Fc formats), the linkers may all be the same, or some or all of the linkers may be different from each other, as described in detail above. [117] Sequences of Exemplary bispecific molecules are provided in Sequence Table C. In exemplary aspects, the PD-L1 x 4-1BB bispecific molecule comprises an amino acid sequence that is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to one of the amino acid sequences referenced in Sequence Table C. 5. METHODS OF TREATMENT [118] In another aspect, the invention provides a method for treating cancer, comprising administering to a subject in need thereof a therapeutic effective amount of: (a) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB; and (b) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA). The combination therapy of the present disclosure is useful for enhancing T cell activity by activating a co-stimulatory immune checkpoint molecule (4-1BB), and a T-cell co-receptor (CD3). It can also reduce T cell exhaustion by inhibiting PD-L1 signaling pathway. [119] Accordingly, provided herein are methods of enhancing T cell activity in a subject, enhancing T cell survival and effector function, restricting terminal differentiation and loss of replicative potential, promoting T cell longevity, and enhancing cytotoxicity against target (e.g., cancer) cells. In exemplary embodiments, the methods comprise administering to a subject the 4-1BB x PD-L1 bispecific molecules disclosed herein and the multispecific T cell engagers disclosed herein in an effective amount. In exemplary aspects, the T cell activity or immune response is directed against a cancer cell or cancer tissue. In exemplary aspects, the immune response is a humoral immune response. In exemplary aspects, the immune response is an innate immune response. In exemplary aspects, the immune response which is enhanced is a T-cell mediated immune response. [120] As used herein, the term “enhance” and words stemming therefrom may not be a 100% or complete enhancement or increase. Rather, there are varying degrees of enhancement of which one of ordinary skill in the art recognizes as having a potential benefit or therapeutic effect. In this respect, the pharmaceutical compositions of the present disclosure may enhance, e.g., T cell activity or enhance an immune response, to any amount or level. In exemplary embodiments, the enhancement provided by the methods of the present disclosure is at least or about a 10% enhancement (e.g., at least or about a 20% enhancement, at least or about a 30% enhancement, at least or about a 40% enhancement, at least or about a 50% enhancement, at least or about a 60% enhancement, at least or about a 70% enhancement, at least or about a 80% enhancement, at least or about a 90% enhancement, at least or about a 95% enhancement, at least or about a 98% enhancement). [121] Methods of measuring T cell activity and immune responses are known in the art. T cell activity can be measured by, for example, a cytotoxicity assay, such as those described in Fu et al., PLoS ONE 5(7): e11867 (2010). Other T cell activity assays are described in Bercovici et al., Clin Diagn Lab Immunol. 7(6): 859–864 (2000). Methods of measuring immune responses are described in e.g., Macatangay et al., Clin Vaccine Immunol 17(9): 1452-1459 (2010), and Clay et al., Clin Cancer Res.7(5):1127-35 (2001). [122] Additionally provided herein are methods of treating a subject with cancer and methods of treating a subject with a solid tumor. In exemplary embodiments, the method comprises administering to the subject the 4-1BB x PD-L1 bispecific molecules disclosed herein and the multispecific T cell engagers disclosed herein, in an amount effective for treating the cancer or the solid tumor in the subject. The cancer treatable by the methods disclosed herein can be any cancer, e.g., any malignant growth or tumor caused by abnormal and uncontrolled cell division that may spread to other parts of the body through the lymphatic system or the blood stream. The cancer in some aspects is one selected from the group consisting of acute lymphocytic cancer, acute myeloid leukemia, alveolar rhabdomyosarcoma, bone cancer, brain cancer, breast cancer, cancer of the anus, anal canal, or anorectum, cancer of the eye, cancer of the intrahepatic bile duct, cancer of the joints, cancer of the neck, gallbladder, or pleura, cancer of the nose, nasal cavity, or middle ear, cancer of the oral cavity, cancer of the vulva, chronic lymphocytic leukemia, chronic myeloid cancer, colon cancer, esophageal cancer, cervical cancer, gastrointestinal carcinoid tumor, Hodgkin lymphoma, hypopharynx cancer, kidney cancer, larynx cancer, liver cancer, lung cancer, malignant mesothelioma, melanoma, multiple myeloma, nasopharynx cancer, non-Hodgkin lymphoma, ovarian cancer, pancreatic cancer, peritoneum, omentum, and mesentery cancer, pharynx cancer, prostate cancer, rectal cancer, renal cancer (e.g., renal cell carcinoma (RCC)), small intestine cancer, soft tissue cancer, stomach cancer, testicular cancer, thyroid cancer, ureter cancer, and urinary bladder cancer. In particular aspects, the cancer is selected from the group consisting of: head and neck, ovarian, cervical, bladder and oesophageal cancers, pancreatic, gastrointestinal cancer, gastric, breast, endometrial and colorectal cancers, hepatocellular carcinoma, glioblastoma, bladder, lung cancer, e.g., non-small cell lung cancer (NSCLC), bronchioloalveolar carcinoma. In particular embodiments, the tumor is non-small cell lung cancer (NSCLC), head and neck cancer, renal cancer, triple negative breast cancer, and gastric cancer. In exemplary aspects, the subject has a tumor (e.g., a solid tumor, a hematological malignancy, or a lymphoid malignancy) and the pharmaceutical composition is administered to the subject in an amount effective to treat the tumor in the subject. In other exemplary aspects, the tumor is non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), head and neck cancer, renal cancer, breast cancer, melanoma, ovarian cancer, liver cancer, pancreatic cancer, colon cancer, prostate cancer, gastric cancer, lymphoma or leukemia, and the pharmaceutical composition is administered to the subject in an amount effective to treat the tumor in the subject. [123] As used herein, the term “treat,” as well as words related thereto, do not necessarily imply 100% or complete treatment. Rather, there are varying degrees of treatment of which one of ordinary skill in the art recognizes as having a potential benefit or therapeutic effect. In this respect, the methods of treating cancer of the present disclosure can provide any amount or any level of treatment. Furthermore, the treatment provided by the method of the present disclosure can include treatment of one or more conditions or symptoms or signs of the cancer being treated. Also, the treatment provided by the methods of the present disclosure can encompass slowing the progression of the cancer. For example, the methods can treat cancer by virtue of enhancing the T cell activity or an immune response against the cancer, reducing tumor or cancer growth, reducing metastasis of tumor cells, increasing cell death of tumor or cancer cells, and the like. In exemplary aspects, the methods treat by way of delaying the onset or recurrence of the cancer by 1 day, 2 days, 4 days, 6 days, 8 days, 10 days, 15 days, 30 days, two months, 4 months, 6 months, 1 year, 2 years, 4 years, or more. In exemplary aspects, the methods treat by way increasing the survival of the subject. [124] In some embodiments of the present disclosure, the subject is a mammal, including, but not limited to, mammals of the order Rodentia, such as mice and hamsters, and mammals of the order Logomorpha, such as rabbits, mammals from the order Carnivora, including Felines (cats) and Canines (dogs), mammals from the order Artiodactyla, including Bovines (cows) and Swines (pigs) or of the order Perssodactyla, including Equines (horses). In some aspects, the mammals are of the order Primates, Ceboids, or Simoids (monkeys) or of the order Anthropoids (humans and apes). In some aspects, the mammal is a human. [125] The 4-1BB x PD-L1 bispecific molecule, and the multispecific T cell engager may be administered concurrently or sequentially. [126] The 4-1BB x PD-L1 bispecific molecule may be selected from any one of molecules listed in Sequence Table C. The multispecific T cell engager (TCE) may be selected from any one of the molecules selected from Sequence Table D. In particular, the following combinations are contemplated: (1) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (2) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (3) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (4) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (5) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (6) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (7) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (8) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (9) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (10) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (11) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (12) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (13) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (14) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (15) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (16) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (17) PD-L1 x 4-1BB bispecific molecule (56761), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (18) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (19) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (20) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (21) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (22) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (23) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (24) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (25) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (26) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (27) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (28) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (29) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (30) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (31) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (32) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (33) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (34) PD-L1 x 4-1BB bispecific molecule (56132), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (35) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (36) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (37) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (38) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (39) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (40) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (41) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (42) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (43) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (44) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (45) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (46) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (47) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (48) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (49) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (50) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (51) PD-L1 x 4-1BB bispecific molecule (56039), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (52) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (53) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (54) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (55) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (56) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (57) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (58) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (59) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (60) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (61) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (62) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (63) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (64) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (65) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (66) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (67) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (68) PD-L1 x 4-1BB bispecific molecule (56042), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (69) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (70) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (71) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (72) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (73) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (74) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (75) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (76) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (77) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (78) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (79) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (80) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (81) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (82) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (83) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (84) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (85) PD-L1 x 4-1BB bispecific molecule (56762), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (86) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (87) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (88) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (89) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (90) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (91) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (92) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (93) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (94) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (95) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (96) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (97) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (98) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (99) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (100) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (101) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (102) PD-L1 x 4-1BB bispecific molecule (44988), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (103) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (104) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (105) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (106) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (107) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (108) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (109) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (110) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (111) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (112) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (113) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (114) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (115) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (116) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (117) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (118) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (119) PD-L1 x 4-1BB bispecific molecule (56639), comprising a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (120) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (121) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (122) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (123) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (124) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (125) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (126) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (127) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (128) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (129) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (130) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (131) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (132) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (133) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (134) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (135) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (136) PD-L1 x 4-1BB bispecific molecule (56040), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (137) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (138) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (139) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (140) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (141) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (142) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (143) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (144) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (145) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (146) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (147) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (148) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (149) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (150) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (151) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (152) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; (153) PD-L1 x 4-1BB bispecific molecule (56041), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447; (154) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CD33 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 189, 190, or 191; (155) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with an EGFRvIII x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 201 or 202; (156) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a MSLN x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 212, 213, or 214; (157) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CDH19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 227, 228, 229, 230, 231, or 232; (158) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a FLT3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 242 or 243; (159) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a DLL3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 253 or 254; (160) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a DLL3 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 265, and a second polypeptide comprising SEQ ID NO:266; (161) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 276; (162) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a BCMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 286 or 287; (163) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a PSMA x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 297, 298, 299, 300, 301, 302, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, or 325; (164) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CD70 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 335; (165) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CLDN18.2 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 345, 346, 350, or 351; (166) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a MUC17 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 360, 369, 378, or 387; (167) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CDH3 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 397 or 398; (168) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CD19 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 417; (169) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a CLDN6 x CD3 TCE, as exemplified by a polypeptide comprising SEQ ID NO: 427 or 428; or (170) PD-L1 x 4-1BB bispecific molecule (26597), comprising two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146; in combination with a STEAP1 x CD3 TCE, as exemplified by a molecule comprising a first polypeptide comprising SEQ ID NO: 448, 451, 452, or 453, and a second polypeptide comprising SEQ ID NO: 447. [127] Also provided herein are combination therapy, wherein a therapeutically effective amount of PD-1 or PD-L1 pathway inhibitor is also administered. [128] PD-1/PD-L1 pathway inhibitors disclosed herein include an antibody, or antigen binding fragment of an antibody, which binds to PD-1 or PD-L1, in particular human PD-1 or human PD-L1. The antibody may be a human antibody, a humanized antibody, or a chimeric antibody. In some embodiments, the constant region of the antibody comprises the constant region from human IgG1, IgG2, IgG3, or IgG4, as disclosed in detail above. The antigen binding fragment maybe, for example, Fab, Fab’-SH, F(ab’)2, scFv and Fv fragments, as disclosed in detail above. [129] In certain embodiments, the antibody, or antigen-binding portion thereof, binds to PD-1, such as human PD-1. Examples of antibodies that bind to human PD-1, are described, e.g, in US7488802, US7521051, US8008449, US8354509, US8168757, WO2004/004771, WO2004/072286, WO2004/056875, and US2011/0271358. Specific anti-human PD-1 antibodies useful for the invention described herein include, for example: K-3945 (Pembrolizumab, Keytruda^®; U.S. Patent No.8,952,136); M-3475, a humanized IgG4 mAb with the structure described in WHO Drug Information, Vol.27, No.2, pages 161-162 (2013); nivoiumab (BMS-936558), a human IgG4 mAb with the structure described in WHO Drug Information, Vol.27, No.1, pages 68-69 (2013); the humanized antibodies h409A11, h409A16 and h409A17, which are described in WO2008/156712; AMP-514, which is being developed by Medlmmune; humanized antibody CT-011 (Pidilizumab) a monoclonal antibody being developed by Medivation, and anti-PD-1 antibodies disclosed in WO2015/119923 (the heavy and light chains comprise SEQ ID NO: 21 and SEQ ID NO: 22, respectively). Additional PD-1 inhibitors include Cemiplimab (Libtayo, approved for the treatment of cutaneous squamous cell carcinoma (CSCC) or locally advanced CSCC who are not candidates for curative surgery or curative radiation); and Dostarlimab (Jemperli, approved for the treatment of mismatch repair deficient (dMMR) recurrent or advanced endometrial cancer and mismatch repair deficient (dMMR) recurrent or advanced solid tumors). [130] In certain embodiments, the antibody, or antigen-binding portion thereof, binds to PD-L1, such as human PD-L1. Examples of mAbs that bind to human PD-L1 are described, e.g., in WO2013/019906, W02010/077634 and US8383796. Specific anti-human PD-L1 antibodies useful for the invention described herein include, for example, MPDL3280A (Atezolizumab), MEDI4736 (Durvalumab), SB0010718C (Avelumab), BMS-936559, and an antibody which comprises the heavy chain and light chain variable regions of SEQ ID NO: 24 and SEQ ID NO: 21, respectively, of WO2013/019906. [131] In certain embodiments, the PD-1/PD-L1 antibody, or antigen-binding portion thereof described herein inhibits the signal transduction resulting from the interaction of PD-1 with one or more of its binding partners, such as PD-L1, or PD-L2. In certain embodiments, the antibody, or antigen-binding fragment thereof, inhibits at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the binding interactions between PD-1 and PD-L1 or PD-L2. [132] Accordingly, provided herein is a for treating cancer, comprising administering to a subject in need thereof a therapeutic effective amount of: (i) a bispecific molecule described herein, comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB, (ii) a multispecific T cell engager molecule described herein, comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA); and (iii) an antibody that binds to human PD-1, such as Pembrolizumab, Nivolumab, Cemiplimab, Dostarlimab, Retifanlimab, and Toripalimab. Preferred PD-1 antibodies are Pembrolizumab and Nivolumab. [133] Also provided herein is a method for treating cancer, comprising administering to a subject in need thereof a therapeutic effective amount of: (i) a bispecific molecule described herein, comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB, (ii) a multispecific T cell engager molecule described herein, comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA); and (iii) an antibody that binds to human PD- L1, such as Atezolizumab, Avelumab, and Durvalumab. Preferred PD-L1 antibodies are Atezolizumab and Durvalumab. 6. Kits [134] The present disclosure additionally provides kits comprising (a) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB; and (b) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA), and (c) instructions for use, in a container. In exemplary aspects, the 4-1BB x PD-L1 bispecific molecule, and the multispecific T cell engager, are provided in the kit as a unit dose. For purposes herein “unit dose" refers to a discrete amount dispersed in a suitable carrier. In exemplary aspects, the unit dose is the amount sufficient to provide a subject with a desired effect, e.g., treatment of cancer. In exemplary aspects, the kit comprises several unit doses, e.g., a week or month supply of unit doses, optionally, each of which is individually packaged or otherwise separated from other unit doses. In some embodiments, the components of the kit/unit dose are packaged with instructions for administration to a patient. In some embodiments, the kit comprises one or more devices for administration to a patient, e.g., a needle and syringe, and the like. In some aspects, the 4-1BB x PD-L1 bispecific molecule and the multispecific T cell engager are pre-packaged in a ready to use form, e.g., a syringe, an intravenous bag, etc. In exemplary aspects, the ready to use form is for a single use. In exemplary aspects, the kit comprises multiple single use, ready to use forms of the 4-1BB x PD-L1 bispecific molecule, and the multispecific T cell engager. In some aspects, the kit further comprises other therapeutic or diagnostic agents or pharmaceutically acceptable carriers (e.g., solvents, buffers, diluents, etc.), including any of those described herein. [135] In various aspects, the kit comprises a combination comprising a 4-1BB x PD-L1 bispecific molecule as exemplified in Sequence Table C, and a T cell Engager as exemplified in Sequence Table D. [136] The following examples are given merely to illustrate the present invention and not in any way to limit its scope. EXAMPLES Example 1. Two different formats of PD-L1x4-1BB bispecific molecules show similar potency in functional assays [137] PD1 reporter assay. GloResponse Jurkat NFAT-luc2/human PD-1 stable effector cells (Promega, #CS187102) and the CHO human PD-L1 stable cell line (Promega, #CS178103) were co-cultured at a ratio of 1.25:1 in the presence of serially diluted antibodies in triplicate for 6 hours at 370C. Luminescence was measured using Bio-Glo Luciferase Assay System (Promega, #G7940). [138] 41BB reporter assay. CHO cells stably expressing human 4-1BB and NFkB-luc were co-cultured with CHO-K1 cells that stably express PD-L1 and CD32 at a ratio of 1:1. Serially diluted antibodies were added to the co-culture in triplicate and incubated for 6 hours at 370C. Luminescence was measured using Bio-Glo Luciferase Assay System (Promega, #G7940). [139] Generation of artificial antigen presenting cells (aAPC). CHOK1 expressing αCD3scFv clones under Hygromycin B selection were generated using transient transfection of αCD3scFv in pcDNA3.1- HygroB. CHO/αCD3scFv cells were also sequentially transfected with pcDNA3-1-Zeo_HuPD-L1 and under Hygromycin B and zeocin selection, sorted for high PD-L1 expression and then transduced with gfp retroviral expression vector containing Hu CD32a/FcgRII. Final aAPCs were sorted for Low αCD3scFv, high human PD-L1 and CD32a expression. [140] aAPC and human primary T cell coculture assay. Chinese Hamster Ovary (CHO) cells expressing anti-humanCD3scFv, human PD-L1 and human Cd32a were used as aAPCs in co-culture assay with human Pan T Cells to test PDL1x41BB bispecific antibodies with different formats. Bispecific antibodies were serially diluted from 25nM (final in assay) and added in triplicate to co-culture assay with aAPCs and Pan T-cells (isolated from human PBMC using Miltenyi Pan T cell isolation Kit # 130-096-535) at 1:2 ratio (50,000 aAPCs + 100,000 Pan T cells) per well in 96-well tissue culture plate. At 48 hours supernatants from co-culture wells were collected and frozen/stored at -80^oC. IL-2 released in supernatants were quantitated in MesoScale Discovery IL-2 V-Plex assay (#K151QQD). IL-2 concentrations were analyzed using GraphPad Prism 4 parameter curve fit. [141] When both IgG-scFv and Fab-scFv-Fc formats of PDL1x41BB bispecific molecule were tested for their potency in various in vitro assays, we found both formats of molecule showing similar EC50 potency value shown in FIGs 1A-1C. FIG.1A shows a PD1 reporter assay to test the potency of PDL1 blocking by both format of bispecific molecule, where they showed similar potency as each other and as the PD-L1 mAb that was used as parental clone to engineer these bispecific molecules. Meanwhile, a 4-1BB mAb or isotype control human IgG1 were also included as negative control, and they were indeed inactive in this assay. FIG.1B shows a 4-1BB reporter assay to the test the potency of 4-1BB stimulation by both formats of bispecific molecules, where they also showed similar potency as each other, and were more potent than 4-1BB mAb, primarily due to the fact that 4-1BB signaling requires multimeric crosslinking, and PDL1-binding based crosslinking (used by bispecific molecules) was demonstrated previously to be more robust than Fc gamma receptor (CD32) mediated crosslinking (used by 4-1BB mAb). Both isotype control and PDL1 mAbs in this assay were also inactive, serving as negative controls. FIG.1C shows an in vitro coculture assay to evaluate the combination effect of PDL1 blocking and 4-1BB stimulation on T cells response, where both formats of bispecific molecules also show similar potency. These functional data clearly demonstrated the functional equivalency of both IgG-scFv and Fab-scFv-Fc formats of PDL1x41BB bispecific molecules. Example 2. Efficacy of CLDN18.2 BiTE Molecule Alone and in Combination with Anti-4-1BB and/or Anti-PD-L1 or Bispecific Anti-4-1BB/Anti-PD-L1 against Syngeneic KPCM5 Pancreatic Cancer in HuCD3KI Mice [142] Mice. Female huCD3KI mice were ten weeks old with a body weight (BW) range of 18.2 to 23.3 grams on Day 0 of the study. The animals were fed ad libitum water (reverse osmosis, 1 ppm Cl), and NIH 31 Modified and Irradiated Lab Diet® consisting of 18.0% crude protein, 5.0% crude fat, and 5.0% crude fiber. The mice were housed on irradiated Enrich-o’cobs™ Laboratory Animal Bedding in static microisolators on a 12- hour light cycle at 20–22°C (68–72°F) and 40–60% humidity. [143] Tumor Cell Culture. KPCM5 (KPC M5T1) mouse pancreatic cancer cells were maintained in Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% FBS, 2 mM glutamine, 1 mM sodium pyruvate, 1X non-essential amino acids (NEAA), 100 units/mL penicillin, 100 μg/mL streptomycin sulfate and 25 μg/mL gentamicin. The tumor cells were cultured in tissue culture flasks in a humidified incubator at 37 °C, in an atmosphere of 5% CO2 and 95% air. Cell viability was recorded as 97.0% before implant. [144] In Vivo Tumor Implantation and Growth. On the day of implant, KPCM5 cells were harvested during log phase growth and resuspended in phosphate buffered saline (PBS). Each test mouse was shaved on the right flank and then subcutaneously (s.c.) implanted there with 2 x 10⁵ cells (in a 0.1 mL tumor cell suspension). Tumor growth was monitored as the average size approached the target range of 50 to 100 mm³. Tumors were measured in two dimensions using digital calipers, and tumor volume in mm³ was calculated. Twelve days after implant, tumor-bearing mice were sorted into eight groups (n = 10 per group) according to tumor volume, with individual tumor volumes ranging from 62.50 to 126.00 mm³ and group mean tumor volumes between 80.0 and 84.1 mm³. Tumors were measured with a digital caliper to two decimal places three times per week for the duration of the study. [145] Therapeutic Agents. On each day of dosing control BiTE molecule and CLDN18.2 BiTE molecule, stock solutions were diluted in PBS to obtain 0.03 mg/mL dosing solutions, which delivered 150 µg/kg when administered in a dosed in a volume of 5 mL/kg (0.1 mL/20 g mouse), adjusted to individual BW. On each day of dosing anti-4-1BB, anti-PD-L1, mIgG1 and mIgG2a isotype control antibodies were diluted in PBS to obtain 0.75 mg/mL dosing solutions, which delivered 150 µg/animal when administered in a fixed volume of 0.2 mL. On each day of dosing the 4-1BBxPD-L1 bispecific molecule, the molecule was diluted in PBS to obtain a 1 mg/mL dosing solutions, which delivered 200 µg/animal when administered in a fixed volume of 0.2 mL. [146] Treatment. On Day 0 tumor-bearing mice with individual tumor volumes between 62.50 and 126.00 mm³ were sorted into eight groups (n = 10 per group) and dosing was initiated on the next day according to the treatment plan. Control and CLDN18.2 BiTE molecules were administered intravenously (i.v.) once a week for two weeks at 150 µg/kg in a volume of 5 mL/kg (0.1 mL per 20 g mouse), adjusted to the BW of each animal. Antibodies were administered intraperitoneally (i.p.) once every three days for four total doses (q3d x 4) in a fixed volume of 0.2 mL/animal; all monoclonal antibodies were dosed at 150 µg/animal. The 4-1BBxPD-L1 bispecific molecule was dosed at 200 µg/animal. [147] Treatment scheme is shown below (Table 1). “41BBxPD-L1 Bispecific”: in this example, bispecific IgG-scFv format was used; “control”: a control BiTE® molecule that does not bind CLDN18.2 was used; “CLDN18.2”: a BiTE® molecule that specific bind CLDN18.2 was used. Table 1 Group N Tx 1 (41BB arm) Tx 2 (PD-L1 arm) Tx 3 (BiTE arm) IP; Q3Dx4; 150ug for mAb IP; Q3Dx4; 150ug 150ug/kg RO; 1x/wk x 2 7 10 41BBxPD-L1 Bispecific Isotype control Control BiTE molecule 8 10 41BBxPD-L1 Bispecific Isotype control CLDN18.2 BiTE molecule [148] We evauated t e e cacy o CLDN18.2 BTE moecue aone and n combnaton wt ant-PDL1 and/or anti-41BB or 41BBxPDL1 bispecific molecule against established syngeneic KPCM5 pancreatic cancer model in human CD3 KI mice. Under the conditions described in Table 1, treatment of tumor- bearing mice with CLDN18.2 BiTE molecule combined with the 41BBxPDL1 bispecific molecule (Group 8) or CLDN18.2 BiTE molecule combined with anti-41BB mAb alone (Group 4) or together with anti-PDL1 mAb (Group 6) displayed similar efficacies measured by tumor growth inhibition (49-52% in FIG.2A) and overall survival (FIG.2B). CLDN18.2 BiTE molecule alone (Group 2), or with anti-PDL1, were less efficacious in this in vivo model. [149] In KPCM5 model, the expression of PD-L1 on tumor is generally very low. Initially, there was significant concern as to whether 41BBxPDL1 bispecific molecule could show efficacy in this model. The concern was that without sufficient expression of PD-L1, the 4-1BB targeting moiety would not be able to crosslink the target, thereby activating the 4-1BB signaling pathway. Surprisingly, the data show that the 41BBxPDL1 bispecific molecule was just as effective as a 4-1BB agonist antibody (crosslinking via Fc gamma receptor in vivo) plus a PDL1 blocking antibody in combination with CLDN18.2 BiTE molecule (Group 8 vs. Group 6), where it showed synergistic effect when co-administered with CLDN18.2 BiTE molecule. Without wishing to be bound by a particular theory, it is believed that in tumor tissue, there are often tumor-infiltrating immune cells present (such as tumor infiltrating myeloid cells). These immune cells express PD-L1. Therefore, the expression of PD-L1 by these tumor infiltrating cells is sufficient to allow the 41BBxPDL1 bispecific molecule to be recruited to the tumor tissue and to crosslink. This provides a significant advantage in cancer treatment. Patients would not need to be screened for PD-L1 expression, and even those patients with tumors that do not normally express high level of PD-L1 (e.g., prostate cancer) can be treated using this molecule. Example 3. Efficacy of EpCAM BiTE Molecule Alone and in Combination with Anti-4-1BB and/or Anti-PD-L1 or Bispecific Anti-4-1BB/Anti-PD-L1 against Syngeneic B16F10-huEpCAM tumor in HuCD3KI Mice [150] Tumor Cell Culture and implantation. B16F10-huEpCAM cells were cultured in 10% FBS, 1% Pen/Strep, Glutamax in DMEM. The cells were collected ~75% confluency, counted, and resuspended in DMEM @ 2e6/mL. Cells had viability of 96.5%, resuspended in 51.6mL of DMEM, kept on ice until implantation. huCD3KI mice were inoculated with 2E5 B16.F10-huEpCAM cells subcutaneously on the right flank of shaved and tagged mice. Mice were monitored biweekly, recording body weights, tumor volume and health observations of mice until study end date. [151] Treatment. Tumor-bearing mice were sorted into eight groups (n = 10 per group) and dosing was initiated on the next day according to the treatment plan. Control and huEpCAM BiTE molecules were administered intravenously (i.v.) once a week for two weeks at 50 µg/kg. Antibodies were administered intraperitoneally (i.p.) once every three days for four total doses (q3d x 4) in a fixed volume of 0.2 mL/animal; all monoclonal antibodies were dosed at 150 µg/animal; the 41BBxPD-L1 bispecific molecule was dosed at 200 µg/animal. [152] Treatment scheme is shown below (Table 2). “41BBxPD-L1 Bispecific”: in this example, bispecific IgG-scFv format was used. Table 2 Group N Tx 1 (41BB arm) Tx 2 (PD-L1 arm) Tx 3 (BiTE arm) IP; Q3Dx4; 150ug for mAb IP; Q3Dx4; 150ug 50ug/kg RO; 1x/wk x 2 f i ifi [153] We evaluated the efficacy of EpCAM BiTE molecule alone and in combination with anti-PDL1 and/or anti-41BB or 41BBxPDL1 bispecific molecule against established syngeneic B16F10-huEpCAM melanoma model in human CD3 KI mice. In contrast to KPCM5 mouse model described in example 2, B16F10-huEpCAM tumor cell line expresses high level of PDL1, and therefore were considered to be able to provide robust crosslinking support for the bispecific molecule beyond tumor infiltrating myeloid cells. Indeed, under the conditions described in Table 2, treatment of tumor-bearing mice with EpCAM BiTE molecule combined with the 41BBxPDL1 bispecific molecule (Group 8) or EpCAM BiTE molecule combined with anti-41BB mAb and anti-PDL1 mAb (Group 6) displayed very robust but similar efficacies measured by tumor growth inhibition (9 out of 10 tumor free mice in group 8 vs.8 out 10 tumor free mice in group 6, Figure 3A) and overall survival (Figure 3B). CLDN18.2 BiTE molecule alone (Group 2) or with anti-PDL1 alone were less efficacious in this in vivo model. EpCAM BiTE molecule combined with a 4- 1BB mAb (Group 4) also show better efficacy than BiTE molecule alone with 2 out of 10 tumor free mice, but adding PDL1 blockade in this model definitely further improved efficacy as shown in Groups 6 and 8, presumably because of the high PDL1 expression and therefore move active PD1 suppression on T cells for this tumor model. Example 4.4-1BBxPD-L1 bispecific molecule achieves superior enhancement of in vitro T cell- mediated cell lysis potency of T cell engager molecules compared to a PD-L1 antibody. 4.1 Introduction [154] The recruitment of cytotoxic T cells by bispecific T cell engagers (TCEs) is a potent anti-tumor mechanism of action with promising application for the treatment of solid malignancies. Two classes of T cell engagers, referred to as BiTE^® and XmAb^®, both comprise a single chain Fv recognizing the CD3e membrane protein at the surface of T cells and a protein domain recognizing a tumor-associated antigen (TAA) at the surface of cancer cells. By simultaneously binding to the CD3-positive T cells and target antigen-positive tumor cells, BiTE^® and XmAb^® bispecific molecules efficiently induce clustering of the T cell receptor (TCR), independently of MHC-class I/peptide complex recognition, and redirect cytotoxic T cells to induce killing of target positive tumor cells. [155] PD-L1, the cognate ligand for the PD1 T cell receptor, acts as inhibitory receptor that disables effector T cells function and activation. Some cancer cells express PD-L1, which helps them evade the immune system.4-1BB is an immune co-stimulatory protein expressed on activated T cells that enhances T cell proliferation, survival and cytokine production upon TCR engagement. [156] We hypothesized that a PDL1-41BB bispecific molecule, in the presence of a PDL1-expressing cancer cell line and T cells, will induce the cross-linking of the 4-1BB co-stimulatory receptor on T cells and that this signal will enhance the ability of TCE molecules to kill cancer cells. We further hypothesize that enhancement of TCE-induced cell lysis will be more pronounced with a PDL1-41BB bispecific molecule compared to an anti-PDL1 antibody, since a PDL1-41BB bispecific would not only block PD1 signaling on T cells, but also induce 41BB crosslinking and enhance T cell co-stimulation. 4.2 Results [157] To test these hypotheses across a representative set TCE-mediated cell lysis assays, three PDL1- and luciferase-expressing cancer cell lines were produced using sequential retroviral delivery of the firefly luciferase and human CD274 (PDL1) genes (FIG.4), and were selected based on their TAA expression profile, suitable for testing specific TCE molecules: the prostate cancer cell line C4-2B-PDL1-Luc expresses the PSMA and STEAP1 TAAs, the small cell lung cancer cell line SHP77-PDL1-Luc expresses the DLL3 TAA and the gastric cancer NUGC4-PDL1-Luc cell line expresses the MUC17 and CLDN18.2 TAAs. The target cell lines were subsequently used in T cell redirected lysis assays in the presence of human T cells from three independent donors and increasing concentrations of individual TCEs: C4-2B- PDL1-Luc cells were tested in the presence an anti-PSMA BiTE^® molecule, SHP77-PDL1-Luc cells were tested in the presence of anti-DLL3 BiTE^® molecule, and NUGC4-PDL1-Luc cells were tested in the presence of an anti-MUC17 BiTE^® molecule or an anti-CLDN18.2 BiTE^® molecule. For each assay, TCE- mediated lysis activity was assessed in the presence or absence of an anti-PDL1 antibody (21B2) or a PDL1-41BB bispecific molecule (26597). A representative set of TCE-mediated lysis curves obtained in the presence of T cell donor 1 are presented, which indicate a lower effective concentration inducing 50% cell lysis (EC50) for TCE molecules in the presence of the PDL1 antibody 21B2 compared to TCE alone, and an even lower EC50 value for TCE molecules in the presence of the PDL1-41BB bispecific molecule 26597 (FIGs.5A-5E). The mean EC₅₀ values obtained for each TCE molecule, and for each T cell donor, alone or in combination with 21B2 or 26597 are summarized in Table 3. Table 3. Target Cell Lysis EC50 of TCEs Alone or in Combination with Molecules 21B2 or 26597 Target Cell Lysis EC₅₀ (pM) 1 4 4 3 [158] Plotting of the EC50 values for all three T cell donors for each TCE assay highlights the trend of a lower EC₅₀ value in the 21B2 combination group, and an even lower EC₅₀ value in the presence of 26597 (FIGs.6A-6E). In these individual datasets, due to the relatively high assay variability between T cell donors, the differences between the 21B2 combination groups and their corresponding 26597 combination groups are not statistically significant, but the difference between the TCE alone treatment group and the corresponding 26597 combination groups are all statistically significant. An analysis of the entire dataset for a difference in mean EC₅₀ values for all three T cell donors between treatment groups across all the TCEs reveals a statistically significant difference between all treatment groups, indicating that the mean EC50 values of TCE molecules in combination with 26597 is lower than those in the 21B2 combination (FIG.6F). To reduce the variation in absolute TCE-induced EC50 values, the dataset was normalized to focus on the relative shift in EC₅₀ values for each combination group compared to the TCE alone group (Table 4). This normalized data was then analyzed for a statistically significant difference in the potency increase between the two combination treatment groups for each T cell donor (FIG.7A) and for all T cell donor data combined (FIG.7B). This analysis indicates that TCEs in combination with molecule 26597 induced a statistically significant gain in mean potency of 3.3 to 4.7-fold (average 3.7- fold) compared to the combination with molecule 21B2, which induced a gain in mean potency of only 1.6 to 1.7-fold (average 1.7 fold), thus demonstrating the superior enhancement of TCE potency with a PDL1- 41BB bispecific molecule compared to a PDL1 antibody. Table 4. Normalized Change in Target Cell Lysis EC₅₀ (Fold Shift Between TCEs Alone and in Combination with Molecules 21B2 or 26597) Change in EC50 vs. TCE Alone (Fold Shift) T Cell _Treatment 4.3 Materials and Methods [159] Generation of PDL1-overexpressing target cell lines. GP2-293 cells were cultured in DMEM media supplemented with 10% fetal bovine serum, 1% Pen/Strep, 1% HEPES, and 1% GlutaMAX. Cells were plated at 75% confluency in 10 cm dishes and incubated at 37°C, 5% CO2 overnight. The next morning, cells were transfected. To tube A, 45 µL of Lipofectamine 3000 and 500 µL of OptiMEM media were added. To tube B, 15 µg of MSCV_GFP_PD-L1 plasmid, 1.8 µg of VSV-g plasmid, 30 µL P3000 reagent, and 500 µL of OptiMEM media were added. Tubes A and B were mixed and incubated at room temperature for 10 minutes, then the contents of tube B was added to tube A and incubated at room temperature for 20 minutes. The mixture was added dropwise to dishes of GP2-293 cells which were incubated at 37°C, 5% CO2 overnight. The next morning, the media was removed and replaced with 10 mL of fresh culture media. That afternoon, target cells were plated at 75% confluence in 6 well plates and incubated at 37°C, 5% CO₂ overnight. The following morning, viral supernatants were collected from GP2-293 cells and centrifuged (5 minutes, 1200 rpm). Supernatants were collected in a new tube, and polybrene was added at 1:1000. Media was removed from plates containing target cells and 2 mL of viral supernatant was added. Plates containing target cells and viral supernatants were centrifuged for 1.5 hours at 1200 x g at 32°C then incubated at 37°C, 5% CO₂. Culture media was added after 5 hours. Four days later, cells were analyzed for GFP and PD-L1 expression by flow cytometry with a FACSymphony. PD-L1 was detected using a PE-conjugated antibody, clone 29E.2A3. Cells < 70% positive for PD-L1 expression were sorted on a BD Melody sorter. [160] Assessing T cell -mediated target cell lysis by T cell engagers (TCE), alone or in combination with anti-PDL1 antibody 21B2 or PDL1-41BB bispecific molecule 26597. T cell dependent cellular cytotoxicity (TDCC) assay: TCE molecules were diluted in cell culture media (RPMI, 10% heat inactivated fetal bovine serum, 1X GlutaMAX, 1X Pen/Strep), serially diluted (1:3, 22 total) and transferred to black, clear bottom 384-well plates using a Bravo liquid handling robot triplicate for combination groups, duplicates for TCE alone conditions). Human pan T cells from three donors (2500 cells/20 µL) followed by target cells overexpressing PDL1 were plated in 384-well assay plates (2500 cells/20 µL; full plate) such that the final effector to target cell (E:T) ratio was 1:1. Molecules 21B2 or 26597 (15 nM in 10 µL) were added to each T cell donor to reach a final concentration of 3 nM. Plates were covered with MicroClime lids and incubated at 37°C, 5% CO2 for 96 hours. After 96 hours, 30 µL of Steady-Glo reagent (Promega) was added to each well and plates incubated for 10 minutes in the dark at room temperature. Luminescence was detected using a BioTek Neo plate reader. Specific cytotoxicity was calculated relative to target cells incubated with T cells without TCE. GraphPad Prism 7.05 software was used to plot cell cytotoxicity curves, calculate the effective concentration leading to 50% lysis (EC50) using four parameter variable slope curve fitting, plot mean EC50 curves and normalized fold-shift box-plots by treatment groups, and analyze the data for statistical significance using two-way ANOVA Tukey multiple comparison tests. Normalized data was analyzed using two-tailed parametric paired T-test comparing treatment groups using the Excel Microsoft Office 2016 software. Example 5. Assessment of the Combination of 4-1BBxPD-L1 Bispecific Molecule with Bispecific T- cell Engager Molecules 5.1. Methods [161] 5.1.1 Tumor Cell Lines and PBMC. Selected tumor cell lines were lentivirally transduced to overexpress firefly luciferase and/or retrovirally transduced to overexpress PD-L1. For the analysis of cell lysis in flow cytometry assays, the fluorescent membrane dyes Vybrant DiO or DiL were used to label target cells and distinguish them from effector cells. Human PBMC were prepared from buffy coats. Human CD3⁺ T cells were enriched from PBMC using the appropriate Miltenyi Biotec Pan T Cell Isolation Kit, according to the manufacturer’s instructions. [162] 5.1.2 Multiparametric Cytotoxicity Assay by Flow Cytometry. Bioactivity of the 4-1BBxPD-L1 bispecific molecule and TCE bioactivity (redirected lysis, T-cell activation, T-cell proliferation, cytokine release, granzyme B and perforin expression) was determined in multiparametric cytotoxicity assays and flow cytometry. In a typical assay, PBMC were co-cultured with DiO- or DiL-labeled target cells in 96-well at an E:T cell ratio of 1:1. Serial dilutions of the 4-1BBxPD-L1 bispecific molecule alone, or in combination with BiTE molecules were added to the cells to assess dose-dependent cell lysis. Plates were incubated for 48 to 120 hours as indicated at 37°C in a 5% CO2 humidified incubator. Thereafter, adherent cells were detached and pooled with non-adherent cells of the same wells and washed with FACS buffer. Human PBMC were stained with a fluorochrome-labeled CD14 antibody to define DiO⁺ or DiL⁺/CD14- target cells. In a typical multiparametric assay additional antibodies directed against CD4, CD8 or other T- cell markers (e.g CD25⁺, 4-1BB) T cells were added. After extracellular staining, cells were washed with PBS and subsequently resuspended in PBS containing 0.1% Fixable Viability Dye efluor 506 to further proceed with intracellular staining (e.g. granzyme B, perforin, or Ki67⁺) using a Cytofix/Cytoperm Kit and later distinguish live from dead cells by flow cytometry. In assays with extracellular staining only, cells were washed with FACS buffer and subsequently resuspended in FACS buffer containing propidium iodide (PI) to distinguish live from dead cells. [163] Cells were analyzed with an iQue3 flow cytometer and data evaluated using ForeCyt software. The DiO- or DiL-labeled target cells were gated for Viability Dye staining or PI uptake. Analysis of the cytotoxicity assays was performed with the four-parameter nonlinear fit model sigmoidal dose-response [variable slope] integrated into GraphPad Prism software. [164] 5.1.3. Determination of Redirected Target Cell Lysis by Steady-Glo Luciferase assay. The luciferase assay was performed similar to the flow cytometry-based assay. However, target cells previously transduced to overexpress luciferase, were not stained with DiO or DiL, but luciferase activity of viable target cells was measured in the assay supernatants. In a typical assay, PBMC were co-cultured with tumor cell lines at an E:T cell ratio of 5:1 or 1:1, as indicated. Various concentrations of the respective BiTE molecule and 4-1BBxPD-L1 bispecific molecule were added to the samples to assess dose-dependent cell specific lysis. After incubation as indicated, 100 μL/well of assay supernatant was removed for cytokine determination and Steady-Glo reagent was added to the cells. Luminescence was measured with a BioTek luminometer and the specific lysis was calculated based on the percentage of measured value of sample. [165] 5.1.4. Determination of Cytokine Release. Cytokine concentrations were determined in supernatants of cytotoxicity assays using the human BD CBA Th1/Th2 Kit II. Briefly, undiluted supernatant or cytokine standard, bead mixture, and detection reagent were mixed and incubated at room temperature for 3 hours. Samples were washed, and pellets resuspended in wash buffer. Analysis was performed using a flow cytometer and respective software. Cytokine standards were used to plot calibration curves and to calculate the amount of each analyte present in the test samples. 5.2 Results and Discussion 5.2.1 Impact of the 4-1BBxPD-L1 Bispecific Molecule on the Bioactivity of Anti-DLL3 BiTE Molecules [166] The pharmacodynamic effect of the combination of the 4-1BBxPD-L1 bispecific molecule and anti- DLL3 BiTE molecule was determined in multiparametric cytotoxicity assays. [167] Human PBMC were co-cultured with DLL3-positive human small cell lung carcinoma cell line SHP- 77-luc-PD-L1, stably transduced to express luciferase and PD-L1. Serial dilutions of 4-1BBxPD-L1 bispecific molecule and various concentrations of anti-DLL3 BiTE molecule were combined and added for 48 to 120 hours. [168] Cytotoxicity of 4-1BBxPD-L1 Bispecific Molecule, Anti-DLL3 BiTE Molecule and their Combination. Cytotoxicity of was determined by flow cytometry and analysis of Viability Dye⁺ SHP-77-luc-PD-L1 cells. Anti-DLL3 BiTE molecule-mediated lysis of the target cells SHP-77-luc-PD-L1 was increased in a dose- dependent and synergistic manner, when combined with 4-1BBxPD-L1 bispecific molecule (FIGs.8A-8D). 4-1BBxPD-L1 bispecific molecule alone or at low (≤ 30 pM) anti-DLL3 BiTE molecule concentrations had no effect on target cell viability after 48 hours [169] The calculated ECxx values derived from the dose-response curves varied (Table 5). In summary, EC₅₀ values for target cell lysis ranged from 17 to 932 pM 4-1BBxPD-L1 bispecific molecule when combined with 7.8 to 250 pM anti-DLL3 BiTE molecules. Different rows represent different PBMC donors. Table 5. ECxx Values of 4-1BBxPD-L1 Bispecific Molecule-mediated Cytotoxicity When Combined with Anti-DLL3 BiTE Molecule Incubation Anti-DLL3 BiTE Time _molecule ^{4-1BBxPD-L1 bispecific} ] [170] T-cell Activation Induced by 4-1BBxPD-L1 Bispecific Molecule, Anti-DLL3 BiTE Molecule and Their Combination. Expression of the T-cell activation marker CD25 and the target surface protein 4-1BB was determined by extracellular staining and flow cytometry after 48 hours. Anti-DLL3 BiTE molecule induced the expression of CD25 as well as 4-1BB on T cells. Expression was further augmented when combined with 4-1BBxPD-L1 bispecific molecule (FIGs.9A-9D). The 4-1BBxPD-L1 bispecific molecule alone showed no effect on the expression of CD25 or 4-1BB on T cells. [171] The anti-DLL3 BiTE molecule and 4-1BBxPD-L1 bispecific molecule-induced expression of 4-1BB is supposed to act as a positive feedback loop for 4-1BBxPD-L1 bispecific molecule and might enhance the activity of the combination of the two molecules. [172] Impact of Anti-DLL3 BiTE Molecule, 4-1BBxPD-L1 Bispecific Molecule and Their Combination on T-cell Proliferation. T-cell proliferation was assessed by immunofluorescence staining and flow cytometry in the combination assay using anti-DLL3 BiTE molecule and 4-1BBxPD-L1 bispecific molecule. Anti- DLL3 BiTE molecule induced the expression of the proliferation marker Ki67 in T cells, which was further increased by addition of 4-1BBxPD-L1 bispecific molecule in a dose-dependent manner. Accordingly, the number of T cells increased when anti-DLL3 BiTE molecule was combined with 4-1BBxPD-L1 bispecific molecule, while 4-1BBxPD-L1 bispecific molecule alone showed no effect on T-cell proliferation (FIGs. 10A-10D). [173] Induction of Granzyme B and Perforin Expression by Anti-DLL3 BiTE Molecule, 4-1BBxPD-L1 Bispecific Molecule and Their Combination. The induction of perforin and granzyme B expression in T cells by anti-DLL3 BiTE molecule, 4-1BBxPD-L1 bispecific molecule and their combination was evaluated in co-cultures of human PBMC and SHP-77-luc-PD-L1. After 72 hours anti-DLL3 BiTE molecule induced an accumulation of intracellular granzyme B and perforin in CD8⁺ and CD4⁺ T cells which was further increased in a dose-dependent and synergistic manner, when combined with 4- 1BBxPD-L1 bispecific molecule (FIGs.11A-11D).4-1BBxPD-L1 bispecific molecule alone did not induce expression of granzyme B or perforin in CD8⁺ and CD4⁺ T cells. [174] Cytokine Release Induced by Anti-DLL3 BiTE Molecule, 4-1BBxPD-L1 Bispecific Molecule and Their Combination. Cytokine release induced by anti-DLL3 BiTE molecule and 4-1BBxPD-L1 bispecific molecule was evaluated in co–cultures of SHP-77-luc-PD-L1 and human PBMC. Cell culture supernatants were collected after 48 hours and IL-2, IFNγ, TNF, and IL-6 concentrations were measured. Combinations of 4-1BBxPD-L1 bispecific molecule and anti-DLL3 BiTE molecule induced augmented cytokine levels in a dose dependent and synergistic manner (FIGs.12A-12D). 5.2.2 Combination of 4-1BBxPD-L1 Bispecific Molecule with BiTE Molecules Directed Against Diverse Targets [175] Combinations of BiTE molecules with 4-1BBxPD-L1 bispecific molecule were analyzed in cytotoxicity assays using anti-MSLN-BiTE molecule, anti-CLDN18.2-BiTE molecule, or anti-PSMA-BiTE molecule, respectively, and corresponding tumor cell lines stably transduced to overexpress PD-L1 and luciferase. To determine specific target cell lysis, human T cells were co-cultured with target cell lines and increasing concentrations of the respective target-specific BiTE molecules were added in combination with 3 nM 4-1BBxPD-L1 bispecific molecule. Specific lysis of the target cells was determined by luminescence assay measuring luciferase activity of viable tumor cells. [176] The results indicate that BiTE molecule-mediated redirected lysis increased when combined with 4- 1BBxPD-L1 bispecific molecule, with EC50 values being up to 10-fold lower for the combination compared to a BiTE molecule alone (FIGs.13A-13C, Table 6). Table 6. EC₅₀ values of BiTE molecule-mediated Cytotoxicity and in Combination with 4-1BBxPD-L1 Bispecific Molecule BiTE + BiTE/ T Cell 4-1BBxPD-L1 T r t C ll Lin D n r Bispecific BiTE Alone Difference [177] Cytokine release induced by anti-MSLN BiTE molecule or anti-CLDN18.2 BiTE molecules alone or in combination with 4-1BBxPD-L1 bispecific molecules [3nM] was assessed in cell culture supernatant. [178] Samples with BiTE molecules alone showed only low cytokine concentrations, whereas the combination of BiTE and 3 nM 4-1BBxPD-L1 bispecific molecules induced dose-dependent cytokine release (FIGs.14A-14F). 5.2.3. Impact of PD-L1 Expression Level on 4-1BBxPD-L1 Bispecific Molecule Activity [179] The impact of the PD-L1 expression level on bioactivity of the 4-1BBxPD-L1 bispecific molecule was assessed in multiparametric cytotoxicity assay using either SHP-77-luc cells, expressing endogenous levels of PD-L1 or SHP-77-luc-PD-L1 cells, stably overexpressing PD-L1. Tumor cells were co-cultured with PBMC and serial dilutions of a DLL3-directed BiTE molecule for 72 hours. A higher EC50 value and a lower maximal lysis was observed for PDL-1 overexpressing cells compared to SHP-77-luc cells. Furthermore, a DLL3 BiTE molecule dose-dependent increase of endogenous PD-L1 expression on SHP- 77-luc, as well as an increased expression of the 4-1BB and PD-1 on T cells was observed (FIGs.15A- 15D). [180] Efficacy of 4-1BBxPD-L1 bispecific molecule on tumor cells expressing endogenous PD-L1 or cells transduced to stably express PD-L1 was demonstrated in co-cultures of human PBMC and SHP-77-luc or SHP-77-luc-PD-L1 using combinations of DLL3-BiTE and 4-1BBxPD-L1 bispecific molecule. In absence of 4-1BBxPD-L1 bispecific molecule, dose dependent cytotoxic efficacy of DLL3-BiTE was shown on SHP-77-luc expressing endogenous PD-L1, whereas specific lysis was suppressed in settings with SHP- 77-luc-PD-L1. The presence of 4-1BBxPD-L1 bispecific molecule increased specific lysis of both tumor cell lines, as well as the release of IFNγ in a dose dependent manner.4-1BBxPD-L1 bispecific molecule- dependent release of IFNγ was higher when SHP-77-luc-PD-L1 expressing high levels of PD-L1 were used, compared to SHP-77-luc (FIGs.16A-16D). [181] The impact of PD-L1 expression on activity of 4-1BBxPD-L1 bispecific molecule in combination with a DLL3-targeting BiTE was assessed in co-cultures of human PBMC and SHP-77-luc or SHP-77-luc-PD- L1 cells In the absence of the 4-1BBxPD-L1 bispecific molecule, dose-dependent DLL3-BiTE mediated redirected lysis was observed for SHP-77-luc cells, whereas specific lysis was reduced for SHP-77-luc- PD-L1 cells. The presence of 4-1BBxPD-L1 bispecific molecules redirected specific lysis of both tumor cell lines, as well as the release of IFNγ increased in a dose-dependent manner. The 4-1BBxPD-L1 bispecific molecule-induced release of IFNγ was higher in SHP-77-luc-PD-L1 assay supernatants compared to SHP-77-luc cells (FIGs.16A-16D). SEQUENCES Table A1. 4-1BB binding domain CDR Sequences Seq Seq Seq Name CDR1 CDR2 CDR3 No. No. No. V V DP (386334 UniDab) 567614-1BB DY Seq Seq Seq Name No. CDR1 No. CDR2 No. CDR3 56639 44988 Seq No. Name Sequence V V G V V G G V V . Seq Name Sequence No. 2_{56039 VH} ^{EEQLSESGGGLVQPGGSLRLSCAASGFTFSHPAMSWVRQAPGKGLEWVSAISGSGGSTYYAD} S S^D S S^S S F^E ^F S S F S S F E S D Seq Name Sequence No. SS GG YG EE RW DS VD AK KS DS ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSS GLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGG 5^{6762 heavy} PSVFLFPPKPKDTLYITREPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPCEEQYG EE RW SS GG YG EE RW DS SS GG YG KE RW DS DS SS VD AK DS KQ SS VD AK DS VD AK DS DS SS GG YG EE RW Human LC RTVAAPSVFI FPPSDEQLKS GTASVVCLLN NFYPREAKVQ WKVDNALQSG (kappa) NSQESVTEQD SKDSTYSLSS TLTLSKADYE KHKVYACEVT HQGLSSPVTK with SFNRGEC KQ SK DS KQ SS WY SK VL SS GG YN DE RW SS GG YN DE RW SS GG YN DE RW SS GG YG EE MTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRW QQGNVFSCSVMHEALHNHYTQKSLSLSP Human IGG1 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLSS GG YG EE RW SS GG YG EE RW WY SK VL WY SK VL WY SK VL WY SK VL WY SK VL WY SK VL SS GG YG EE RW Human IGG1 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSS HC constant GLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAAGG domain with PSVFLFPPKPKDTLYITREPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPCEEYG EE RW SS GG YG EE RW SS SS GG YG EE RW SS TK YT SS SV TY TK SS PR TK YT ₁₇ ^{Human IgG2} ASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSS CH1 GLYSLSSVVTVPSSNFGTQTYTCNVDHKPSNTKVDKTV 1₈ ^{Human IgG2} ERKCCVECPPCP KP TL Seq No. Name Sequence VLVSGAEVKKPGASVKVSCKASGYTFTGYYIHWVRAPGGLEWMGWINPNRGVTSS AS GL PS ST MT QQ PS PP LT YY TL DP AP NY PS PP LT SS AS GL GG GR GG VD AK DS ER PP SL EEQLSESGGGLVQPGGSLRLSCAASGFTFSHPAMSWVRQAPGKGLEWVSAISGSGGSTYY ADSVKGRFTISRDKSKNTLYLQMNSLRAEDTAVYYCAKSGYVGELLYYYGMDVWGQGTTV TVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAV VQ QK GS YA GG YV KA LD GF GG LL IK SS AS GL PS ST MT QQ PS PP LT YY AS GL PS ST MT QQ PS PP LT PS PP LT SS AS GL PS ST MT QQ TA LQ PS PP SDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLT LSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC QVQLVQSGAEVKKPGASVKVSCKASGYTFTGYYIHWVRQAPGQGLEWMGWINPNRGVTSS AS GL PS ST MT QQ TV SS MT GS YN LV PG CG SS AS GL PS ST MT QQ PS PP LT YY VT EV IE KT ER PP SL YY TV AV VQ QK GS YA GG YV KA LD PS PP LT QVQLVQSGAEVKKPGASVKVSCKASGYTFTGYYIHWVRQAPGQGLEWMGWINPNRGVTSS AQKFQGRVTMTRDTSVSTAYMELSSLRSDDTAVYYCARDATAVGFDYWGQGTLVTVSSAS TKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGL GP TI GS FA GG YV KA LD SS AS GL GP TM GS FA GG WY SK VL PS PP LT SEQ Description Sequence ID Anti-CD3 CDR-H1 (I2E) KYAIN Anti-CD3 CDR-H2 (I2E) RIRSKYNNYATYYADAVKD Anti-CD3 CDR-H3 (I2E) AGNFGSSYISYWAY ANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSN NKYAAKSYLSLTPEQWKSHRSYSCQVTHEGSTVEKTVAPTECS CD33 GGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCGSSTGAVTSGNY PNWVQQKPGQAPRGLIGGTKFLAPGTPARFSGSLLGGKAALTL SGVQPEDEAEYYCVLWYSNRWVFGGGTKLTVLGGGGDKTHTCP EGFRvIII (with cyc- QVQLVESGGGVVQSGRSLRLSCAASGFTFRNYGMHWVRQAPGK clamp) x CD3 CLEWVAVIWYDGSDKYYADSVRGRFTISRDNSKNTLYLQMNSL RAEDTAVYYCARDGYDILTGNPRDFDYWGQGTLVTVSSGGGGS Anti-MSLN x CD3 (I2C) QVQLVESGGGLVKPGGSLRLSCAASGFTFSDYYMTWIRQAPGK bispecific molecule GLEWLSYISSSGSTIYYADSVKGRFTISRDNAKNSLFLQMNSL RAEDTAVYYCARDRNSHFDYWGQGTLVTVSSGGGGSGGGGSGG VKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLT VDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK CDH19 QQKPGQAPRGLIGGTKFLAPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCVLWYSNRWVFGGGTKLTVL CDH1965254.007 x I2C QVQLVESGGGVVQPGGSLRLSCAASGFTFSSYGMHWVRQAPGK TAVYYCVRHGNFGNSYISYWAYWGQGTLVTVSSGGGGSGGGGS GGGGSQTVVTQEPSLTVSPGGTVTLTCGSSTGAVTSGNYPNWV QQKPGQAPRGLIGGTKFLAPGTPARFSGSLLGGKAALTLSGVQ GWYQQKPGKAPKRLIYAASTLQSGVPSRFSGSGSGTEFTLTIS SLQPEDFATYYCLQHNSYPLTFGCGTKVEIK FLT3_7 A8xCD3 QVTLKESGPTLVKPTETLTLTCTLSGFSLNNARMGVSWIRQPP DLL3_1_CCxCD3 QVQLQESGPGLVKPSETLSLTCTVSGGSISSYYWSWIRQPPGK Bispecific molecule CLEWIGYVYYSGTTNYNPSLKSRVTISVDTSKNQFSLKLSSVT AADTAVYYCASIAVTGFYFDYWGQGTLVTVSSGGGGSGGGGSG Anti-DLL3 light chain RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKV constant DNALQSGNSQESVTEQDSKDSTYSLESTLTLSKADYEKHKVYA CEVTHQGLSSPVTKSFNRGEC WVQQKPGQAPRGLIGGTKFLAPGTPARFSGSLLGGKAALTLSG VQPEDEAEYYCVLWYSNRWVFGGGTKLTVLGGGGDKTHTCPPC PAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPE LTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLY SKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK Anti-BCMA IC20 QVQLVQSGAEVKKPGASVKVSCKASGYTFTNHIIHWVRQAPGQ PGQAPRGLIGGTKFLAPGTPARFSGSLLGGKAALTLSGVQPED EAEYYCVLWYSNRWVFGGGTKLTVLGGGGDKTHTCPPCPAPEL LGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNW YYCVRHGNFGNSYISYWAYCGQGTLVTVSSGGGGSGGGGSGGG GSQTVVTQEPSLTVSPGGTVTLTCGSSTGAVTSGNYPNWVQQK PGQCPRGLIGGTKFLAPGTPARFSGSLLGGKAALTLSGVQPED Anti-PSMA VL with cys- DIQMTQSPSSLSASVGDRVTITCKASQNVDTNVAWYQQKPGQA clamp PKSLIYSASYVYWDVPSRFSGSASGTDFTLTISSVQSEDFATY PM76-B10.11 YCQQYDQQLITFGCGTKLEIK GGSGGGGSGGGGSGGGGSGGGGSGGGGSDKTHTCPPCPAPELL GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWY VDGVEVHNAKTKPCEEQYGSTYRCVSVLTVLHQDWLNGKEYKC SLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFL YSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKGG GGSGGGGSGGGGSGGGGSGGGGSGGGGSDKTHTCPPCPAPELL PM 76-B10.11 CD3 with QVQLVESGGGLVKPGESLRLSCAASGFTFSDYYMYWVRQAPGK cys-clamp, scFc_delGK CLEWVAIISDGGYYTYYSDIIKGRFTISRDNAKNSLYLQMNSL bispecific KAEDTAVYYCARGFPLLRHGAMDYWGQGTLVTVSSGGGGSGGG EAEYYCVLWYSNRWVFGGGTKLTVLGGGGDKTHTCPPCPAPEL LGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNW YVDGVEVHNAKTKPCEEQYGSTYRCVSVLTVLHQDWLNGKEYK CL-1 and CL-2 VH CDR-H2 WINPNSGGTKYAQKFQG VH CDR-H3 DRITVAGTYYYYGMDV VH QVQMVQSGAEVKKHGASVKVSCKASGYTFTGYYMHWVRQAPGQ CLEWMGWINPNSGGTKYAQKFQGRVTMTRDTSISTAYMELSRL CL-2 RSDDTAVYYCARDRITVAGTYYYYGMDVWGQGTTVTVSS QVQLVESGGGVVQPGRSLRLSCAASGFTFSNHGMHWVRQAPGK VH MU-2-C2 CLEWVAGIWSEGSNKYYADAVKGRFTISRDNSKNTLYLQMNSL RAEDTAVYYCARATYTTGWSYFDYWGQGTLVTVSS SGGGGSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAMNWV RQAPGKGLEWVARIRSKYNNYATYYADSVKDRFTISRDDSKNT AYLQMNNLKTEDTAVYYCVRHGNFGNSYISYWAYWGQGTLVTV VDVSHEDPEVKFNWYVDGVEVHNAKTKPCEEQYGSTYRCVSVL TVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVY TLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYK VL CDR2 CDH3 G8A 6-B12 WASTRES VL CDR3 CDH3 G8A 6-B12 QQYYSYPYT VH CDH3 G8A 6-B12 EVQLLESGGGLVQPGGSLRLSCAASGFSFSSYPINWVRQAPGK CD19 VH CDR3 RETTTVGRYYYAMDY CD19 VL DIQLTQSPASLAVSLGQRATISCKASQSVDYDGDSYLNWYQQI PGQPPKLLIYDASNLVSGIPPRFSGSGSGTDFTLNIHPVEKVD DRFSGSGSGTDFTLTISRLEPEDFAVYYCQQYGSSPLTFGCGT KLEIK EIVLTQSPGTLSLSPGERATLSCRASQSVSSSYLAWYQQKPGQ QAVVTQEPSLTVSPGGTVTLTCGSSTGAVTTSNYANWVQQKPG CD3 scFv VL KSPRGLIGGTNKRAPGVPARFSGSLLGGKAALTISGAQPEDEA DYYCALWYSNHWVFGGGTKLTVL Pyro-glu VQLVQSGAEVKKPGASVKVSCKASGYTFSTYWIEWVRQAPGQR TEAP1 F l LEWMGEILPGSGQTDFNEKFQGRVTFTADTSSDTAYMELSSLR VEVHNAKTKPCEEQYGSTYRCVSVLTVLHQDWLNGKEYKCKVS NKALPAPIEKTISKAKGQPREPQVYTLPPSREQMTKNQVKLTC LVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKL [182] The specification is most thoroughly understood in light of the teachings of the references cited within the specification. The embodiments within the specification provide an illustration of embodiments of the invention and should not be construed to limit the scope of the invention. The skilled artisan readily recognizes that many other embodiments are encompassed by the invention. All publications, patents, and sequences cited in this disclosure are incorporated by reference in their entirety. To the extent the material incorporated by reference contradicts or is inconsistent with this specification, the specification will supersede any such material. The citation of any references herein is not an admission that such references are prior art to the present invention. [183] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following embodiments.

Claims

CLAIMS 1. A method for treating cancer, comprising administering to a subject in need thereof a therapeutic effective amount of: (i) a bispecific molecule comprising a first binding domain that binds to PD-L1, and a second binding domain that binds to 4-1BB, wherein said PD-L1-binding domain comprises: (1) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 34, 35, and 36, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:37, 38, and 39, respectively; or (2) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 40, 41, and 42, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:43, 44, and 45, respectively; wherein said 4-1BB-binding domain comprises: (1) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 4, 5, and 6, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:1, 2, and 3, respectively; (2) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 10, 11, and 12, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR- L3 comprising amino acid sequences as set forth in SEQ ID NOs:7, 8, and 9, respectively; (3) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 13, 14, and 15, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:16, 17, and 18, respectively; (4) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 19, 20, and 21, respectively; and a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:22, 23, and 24, respectively; (5) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 25, 26, and 27, respectively; (6) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 28, 29, and 30, respectively; or (7) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 31, 32, and 33, respectively; and (ii) a multispecific T cell engager molecule comprising a third binding domain that binds to CD3, and a fourth binding domain that binds to a Tumor Antigen (TA).

2. The method of claim 1, wherein: said CD3-binding domain comprises: (1) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:147, 148, and 149, respectively; and a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:150, 151, and 152, respectively; (2) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:156, 157, and 158, respectively; and a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:159, 160, and 161, respectively; (3) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:165, 166, and 167, respectively; and a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:168, 169, and 170, respectively; (4) a VL that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:411, 412, and 413, respectively; and a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs:408, 409, and 410, respectively; or (5) a VL that comprises a CDR-L1, CDR-L2, and CDR- L3 comprising amino acid sequences as set forth in SEQ ID NOs: :432, 433, 434, respectively; and a VH that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 429, 430, 431, respectively.

3. The method of claim 1 or 2, wherein said Tumor Antigen is CD33.

4. The method of claim 3, wherein said CD33-binding domain comprises: (a) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 177, 178, and 179, respectively; and (b) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 180, 181, and 182, respectively.

5. The method of claim 3 or 4, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO:189, 190, or 191.

6. The method of claim 1 or 2, wherein said Tumor Antigen is EGFRvIII.

7. The method of claim 6, wherein said EGFRvIII-binding domain comprises: (a) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 192, 193, and 194, respectively; and (b) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 195, 196, and 197, respectively.

8. The method of claim 6 or 7, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 201 or 202.

9. The method of claim 1 or 2, wherein said Tumor Antigen is MSLN.

10. The method of claim 9, wherein said MSLN-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 203, 204, and 205, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 206, 207, and 208, respectively.

11. The method of claim 9 or 10, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 212, 213, or 214.

12. The method of claim 1, wherein said Tumor Antigen is CDH19.

13. The method of claim 12, wherein said CDH19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 215, 216, and 217, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 218, 219, and 220, respectively.

14. The method of claim 12 or 13, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to any one of the sequences selected from SEQ ID NOs: 227-232.

15. The method of claim 1 or 2, wherein said Tumor Antigen is FLT3.

16. The method of claim 15, wherein said FLT3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 233, 234, and 235, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 236, 237, and 238, respectively.

17. The method of claim 15 or 16, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 242 or 243.

18. The method of claim 1 or 2, wherein said Tumor Antigen is DLL3.

19. The method of claim 18, wherein said DLL3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 244, 245, and 246, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 247, 248, and 249, respectively.

20. The method of claim 18, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 253 or 254.

21. The method of claim 1 or 2, wherein said Tumor Antigen is CD19.

22. The method of claim 21, wherein: said CD19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID NOs: 267, 268, and 269, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 270, 271, and 272, respectively; or said CD19-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 402, 403, or 404, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 399, 400, or 401, respectively.

23. The method of claim 21 or 22, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 276 or 417.

24. The method of claim 1 or 2, wherein said Tumor Antigen is BCMA.

25. The method of claim 24, wherein said BCMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 277, 278, and 279, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 280, 281, and 282, respectively.

26. The method of claim 24 or 25, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 286 or 287.

27. The method of claim 1 or 2, wherein said Tumor Antigen is PSMA.

28. The method of claim 27, wherein: said PSMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 288, 289, and 290, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 219, 292, and 293, respectively; or said PSMA-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 303, 304, and 305, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs:306, 307, and 308, respectively.

29. The method of claim 27 or 28, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to any one of the sequences selected from SEQ ID NOs: 297-302 and 315-325.

30. The method of claim 1 or 2, wherein said Tumor Antigen is CD70.

31. The method of claim 30, wherein said CD70-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 326, 327, and 328, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 329, 330, and 331, respectively.

32. The method of claim 30 or 31, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO:335.

33. The method of claim 1 or 2, wherein said Tumor Antigen is CLDN18.2.

34. The method of claim 33, wherein said CLDN18.2-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 336, 337, and 338, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 339, 340, and 341, respectively.

35. The method of claim 33 or 34, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to any one of SEQ ID NO: 345, 346, 350, and 351.

36. The method of claim 1 or 2, wherein said Tumor Antigen is MUC17.

37. The method of claim 36, wherein: said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 352, 353, and 354, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 355, 356, and 357, respectively; said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 361, 362, and 363, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 364, 365, and 366, respectively; said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 370, 371, and 372, respectively; and (b) a light chain variable region (VL) that comprises a CDR- L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 373, 374, and 375, respectively; or wherein said MUC17-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 379, 380, and 381, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 382, 383, and 384, respectively.

38. The method of claim 36 or 37, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to any one of SEQ ID NO:360, 369, 378 and 387.

39. The method of claim 1 or 2, wherein said Tumor Antigen is CDH3.

40. The method of claim 39, wherein said CDH3-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 388, 389, and 390, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 391, 392, and 393, respectively.

41. The method of claim 39 or 40, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO:397 or 398.

42. The method of claim 1 or 2, wherein said Tumor Antigen is CLDN6.

43. The method of claim 42, wherein said CLDN6-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 418, 419, and 420, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 421, 422, and 423, respectively.

44. The method of claim 42 or 43, wherein said multispecific T cell engager comprises an amino acid sequence at least 90% identical to SEQ ID NO: 427 or 428.

45. The method of claim 1 or 2, wherein said Tumor Antigen is STEAP1.

46. The method of claim 45, wherein said STEAP1-binding domain comprises: (a) a heavy chain variable region (VH) that comprises a CDR-H1, CDR-H2, and CDR-H3 comprising amino acid sequences as set forth in SEQ ID Nos: 438, 439, and 440, respectively; and (b) a light chain variable region (VL) that comprises a CDR-L1, CDR-L2, and CDR-L3 comprising amino acid sequences as set forth in SEQ ID NOs: 441, 442, and 443, respectively.

47. The method of claim 45 or 46, wherein said multispecific T cell engager comprises a heavy chain that comprises an amino acid sequence at least 90% identical to SEQ ID NO:448, 451, 452, or 453; and a light chain that comprises an amino acid sequence at least 90% identical to SEQ ID NO:447.

48. The method of any one of claims 1-47, wherein said bispecific molecule comprises (1) (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO: 121, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO: 122, and (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO: 123; (2) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 124, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:125; (3) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 126, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:127; (4) (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO:129, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO:130, (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO:131; and (iv) a fourth polypeptide comprising the amino acid sequence of SEQ ID NO:132; (5) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 133, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:134; (6) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 135, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:136; (7) (i) a first polypeptide comprising the amino acid sequence of SEQ ID NO: 138, (ii) a second polypeptide comprising the amino acid sequence of SEQ ID NO: 139, and (iii) a third polypeptide comprising the amino acid sequence of SEQ ID NO: 140; (8) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 141, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:142; (9) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 143, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:144; or (10) (i) two copies of a first polypeptide comprising the amino acid sequence of SEQ ID NO: 145, and (ii) two copies of a second polypeptide comprising the amino acid sequence of SEQ ID NO:146.

49. The method of any one of claims 1-48, wherein said cancer is a solid tumor. .