CA2046016C - Hiv monoclonal antibody - Google Patents

Abstract

A monoclonal antibody is described capable of binding to a glycoprotein antigen having a molecular weight of about 12 x 10 4 daltons (gp120) present in the envelope of human immunodeficiency virus (HIV) and capable of substantially neutralizing the HIV, or fragments thereof. It has the characteristics of immunoglobulin class IgG, k, being capable of binding to glycoprotein antigen having a molecular weight of 12 x 10 4 daltons (gp120) of HTLV-III MN, being capable of recognizing at least one epitope which is present in the region of the amino acid sequence 303 to 325 of gp120 of HTLV-III MN, being capable of binding to the surface of HTLV-III MN viral particles and thereby inhibiting the infection of the viral particles to CD4-positive cells, and being capable of binding to the surface of cells infected with HTLV-III MN and thereby inhibiting the syncytium formation induced by interaction between the infected cells and uninfected cells. The monoclonal antibody is useful for the prophylaxis, treatment and diagnosis of AIDS.

Description

HIV MONOCLONAL ANTIBODY
This invention relates to an immunological technology for providing a novel substance for prophylaxis, and the treatment and diagnosis of viral infectious diseases. More particularly, it relates to a monoclonal antibody being capable of substantially neutralizing human immunodeficiency virus (abbreviated as HIV), which is the etiologic agent of acquired immunodeficiency syndrome (abbreviated as AIDS), and to a hybridoma being capable of secreting the monoclonal antibody.
Technical Background and Prior Art HIV is a retrovirus which is known to cause diseases such as AIDS and AIDS-related complex (abbreviated as ARC). It is well known that prototype HIV includes human T-lymphotropic virus type III (abbreviated as HTLV-III) and lymphadenopathy associated virus (abbreviated as LAV). The above diseases are prevalent worldwide, and it has been desired to develop a vaccine or a therapeutic method for the treatment thereof. However, successful therapies have not been developed to date. The most characteristic hematological anomaly in AIDS is the functional and quantitative loss of helper/inducer T-lymphocytes expressing CD4 antigen on the surface thereof. The immunodeficiency caused by HIV induces various disorders in the bio-phylactic mechanisms of the infected host.
Subsequently, opportunistic infections frequently occur such as Pneumocystis carinii pneumonia and rare malignant tumors such as Kaposi's sarcoma. The immunodeficiency caused by HIV is a progressive and irreversible disease with a high rate of mortality, and it is considered that the rate of mortality will reach 100 o within several years.
Upon initial infection of T-cells with HIV, the virus particles will first bind to the receptor CD4 antigen. The infection of HIV can also spread via cell-to-cell infection, when infected cells are fused with non-infected cells, particularly in organs such as the brain, lymphonodus, etc., syncytium (macropolycyte) is formed.
The syncytium formation is also observed in experiments in vitro. It is usually considered that the T-cells infected with HIV are easily susceptible to the cytopathic effect of HIV, and this will cause the loss of CD4-positive cells.
It is also known that HIV infects not only the helper/inducer T-lymphocytes but also infects monocyte and macrophages. Furthermore, most monocytes/macrophages and some T-lymphocytes have resistance to the cytopathic effect of HIV, and hence these cells retain the virus for a long period of time and continuously produce the virus.
Moreover, it is known that human blood serum infected by HIV contains an antibody to HIV, but the antibody has only a low neutralizing activity (cf. Weiss et al., Nature, 316, p. 69-72, 1985).
It is well known that the core antigen (gag) and the envelope antigen of HIV are present as the structural protein antigen of HIV. The HIV viral envelope protein is expressed as a precursor glycoprotein having a molecular weight of 160 kilodaltons (gp160) that is proteolytically cleaved to generate an external envelope glycoprotein having a molecular weight of 120 kilodaltons (gp120) and a trans-membrane envelope glycoprotein having a molecular weight of 41 kilodaltons (gp41). Among these, gp120 is the most important by the following reasons.
(1) When a test animal is infected with the gp120 or with a certain fragment derived from the gp120, a polyclonal neutralizing antibody is produced. This means that the gp120 is at least one of the target molecules of an antibody capable of neutralizing the virus (cf. Lasky et al., Science, 233, p. 209-212, 1986).
(2) At the first step of infection of HIV, gp120 binds to CD4 molecule of virus receptor. This means that the gp120 is the most important molecule as to the HIV
infection (McDougal et al., Science, 231, p. 382-385, 1986) .
(3) The synoytium formation by HIV, that is cell-to-cell infection of HIV, is induced by the direct interaction between the gp120 and the CD4 molecule of non-infected cells (cf. Lifson et al., Nature, 323, p. 725-728, 1985) .
Various monoclonal antibodies to constructive proteins of HTLV-III or LAV have been known. Examples include, an antibody against p24 which is one of core antigens present within virus (Veronese, F.D., Proc. Natl.

Acad. Sci., U.S.A., 82, p. 5199-5202, 1985); an antibody to a pol gene product encoding a reverse transcriptase of the virus (Veronese, F.D., Science, 231, p. 1289-1291, 1986);
and an antibody to gp41 which is another structural protein in the viral envelope (Veronese, F.D., Science, 229, p. 1402-1405, 1985). However, none of these known monoclonal antibodies is known to react with the gp120 antigen which is an important factor for the prophylaxis and treatment of AIDS. In contrast, it is reported that any monoclonal antibody being capable of effectively neutralizing the gp120 antigen could not be obtained even by immunizing animals with a purified LAV (Chassange, J. et al., J. Immunol., 136, p. 1442-1445, 1985).
There have hitherto been studied various methods for obtaining a monoclonal antibody being capable of effectively neutralizing an AIDS related virus and hence being useful for the prophylaxis, treatment and diagnosis of AIDS.
It has been reported that a monoclonal antibody to the gp120 antigen has been obtained by using a synthetic peptide as an immunogen and that an epitope recognized by the antibody is within the region of the amino acid sequence 503-532 of the HIV envelope (Chanh, T.C. et al., Eur. J. Immunol., 16, p. 1455-1468, 1986). However, the antibody had very weak binding activity as indicated both in Western blotting and immunofluorescent data. In this report, no evidence has shown the presence of the neutralizing activity of the monoclonal antibody disclosed.

The present inventors have also previously obtained a monoclonal antibody (0.5~) being capable of effectively neutralizing the virus by binding to the gp120 of HTLV-IIIB strain (Matsushita et al., J. Virology, 62, p.
2107-2114, 1988). However, the 0.5~ antibody can neutralize the HTLV-IIIB strain, but not the HTLV-IIIMN
strain which is more popular in the immunological field.
To date, no monoclonal antibody has been developed that can bind to gp120 of the HTLV-IIIMN, which can substantially neutralize the virus.
Brief Description of the Invention The present inventors have found a monoclonal antibody which can bind to the envelope antigen of HTLV-IIIMN: gp120 and can substantially neutralize the virus.
Thus, the present invention in its broadest aspect relates to a monoclonal antibody being capable of specifically binding to a glycoprotein antigen having a molecular weight of about 12 x 109 daltons (gp120) present in the envelope of human T-lymphotropic virus IIIMN
(HTLV-IIIMN) and capable of substantially neutralizing the HTLV-IIIMN or fragments thereof.
Brief Description of the Drawings Fig. 1 shows the reactivity of the monoclonal antibodies of the invention (u39.1 and u5.5) to the synthetic peptides of gp120 (amino acid sequence 303-325 or 308-329) derived from the various HIV mutants. An initial concentration of each antibody is 500 ug/ml.

Fig. 2 shows a reactivity of the monoclonal antibodies of the invention (u39.1 and u5.5) to the external envelope glycoprotein gp120 derived from the HTLV-IIIMN-infected cells.
Detailed Description of the Invention The term "neutralization" in this disclosure means inhibition of cell free infection of HIV and also cell-to-cell infection such as syncytium formation which occurs between HIV-infected cells and non-infected cells by interaction between the gp120 and CD4.
This invention provides a monoclonal antibody which can bind to a glycoprotein antigen having a molecular weight of about 12 x 104 daltons present in the envelope of HIV and can substantially neutralize the virus, and also fragments thereof.
The monoclonal antibody of this invention can recognize the envelope glycoprotein of HTLV-IIIMN strain:
gp120 and can neutralize the virus. The monoclonal antibody can be prepared by the following method.
A mammal (e. g. mouse, guinea pig, rabbit, etc.) is immunized with virus particles obtained from an appropriate HTLV-IIIMN-producing cell or purified envelope glycoprotein gp120; a recombinant peptide prepared by a recombinant DNA technology, preferably a recombinant peptide corresponding to the amino acid sequence 247-370 of gp120; or a synthetic peptide prepared based on the amino acid sequence of the virus protein, preferably a synthetic peptide corresponding to the amino acid sequence 303-325 of gp120. The spleen cells taken out from the thus immunized mammal are cell-fused with, for example, mouse myeloma cells to give a hybridoma, from which a purified envelope glycoprotein gp120 or cells responding to the above recombinant peptide or synthetic peptide are selected, and then the cells are cultivated to give the desired monoclonal antibody.
The above preparation of hybridoma can be carried out by the method of Kohler and Milstein (Nature, 256, p. 495, 1975). The virus particles or envelope glycoprotein gp120 used as the antigen include HTLV-IIIMN-producing cells prepared by sucrose density-gradient centrifugation method, e.g. derived from H9/HTLV-IIIMN; a recombinant peptide prepared by recombinant DNA technology;
or a synthetic peptide prepared based on the amino acid sequence of the virus protein; and further any other immunogen prepared by a conventional method. The mouse to be immunized may include a BALB/c mouse, F1 mouse of BALB/c mouse and other mouse, and the like. Immunization is carried out by using an antigen of 20 to 200 ~g per mouse (4 to 8 week age, weighing 20 to 30 g), wherein the antigen is administered 3 to 6 times for every 2 to 3 weeks. The feeding of mouse and the collection of spleen cells from the immunized mouse are carried out in a conventional manner.
Myeloma cells include MOPC-21NS/1 (Nature, 256, p. 495, 1975), SP2/0-Agl4 (Nature, 276, p. 269, 1979), p3X63Ag8-Ul (Eur. J. Immunol., 6, p. 511, 1976), p3X63Ag8 g (Nature, 256, p. 495, 1975), p3X63Ag8.653 (J. Immunol., 123, p. 1548, 1979), and the like.
The spleen cells and myeloma cells are mixed in a ratio of 1 . 1 to 10 . 1 by volume, and the cell-fusion is carried out in a phosphate buffer (pH 7.2 - 7.4) containing NaCl (about 0.85 wt.o), dimethylsulfoxide (10 - 20 v/v%) and polyethylene glycol having a molecular weight of 1,000 to 6,000, by incubating the mixture at 35 to 37°C for 1 to 5 minutes. The fused cells (hybridoma) can be collected from the base medium containing hypoxanthine (1.3 - 1.4 mg/dl), aminopterin (18 - 20 ug/dl), thymidine (375 - 4,000 ul/dl), streptomycin (50 - 100 ug/ml), penicillin (50 - 100 U/ml), glutamine (3.5 - 4.0 g/1) and fetal bovine serum (10 - 20 wt.o), wherein the fused cells grow. The base medium includes any medium which is usually used for cultivation of animal cells, such as RPMI1640 medium, Eagle's MEM medium, and the like. Cloning of the fused cells is repeated at least three times by limiting dilution method.
The hybridoma is cultivated in the same manner as usually used in cultivation of animal cells, whereby the desired monoclonal antibody of this invention is produced in the medium. For example, when the hybridoma (2 x 106 - 5 x 106 cells) is cultivated in RPMI1640 medium (10 - 20 ml) containing streptomycin (50 - 100 ~g/ml), penicillin (50 - 100 U/ml), glutamine (3.5 - 4.0 g/1) and fetal bovine serum (10 - 20 wt.o) in the presence of 5 0 C02 in a flask at 35 - 37°C for 3 to 7 days, whereby the antibody is secreted and accumulated in the medium. The hybridoma may also be grown by injecting intraperitoneally into a nude mouse or BALB/c mouse treated with PristaneTM, whereby the antibody is accumulated within the ascites.
That is, Pristane (0.5 - 1 ml) is intraperitoneally inoculated into the mouse, and two to three weeks after the inoculation, the hybridoma (5 x 106 - 1 x 10~ cells) is intraperitoneally transplanted thereto. After 7 to 10 days, accumulated ascites are collected. The monoclonal antibody contained in the culture medium or the ascites can be isolated by affinity chromatography with Affigel°
Protein A MAPS-IITM kit (BIO-RAD) or by any other conventional method.
The monoclonal antibody thus obtained can recognize an epitope on gp120 derived from HTLV-IIIMN
strain and can effectively neutralize the virus. The monoclonal antibody has the following characteristics:
(a) immunoglobulin class; IgG, x, (b) being capable of binding to glycoprotein antigen having a molecular weight of 12 x 10q daltons (gp120) of HTLV-IIIMN.
(c) being capable of recognizing at least one epitope which is present in the range of the amino acid sequence 303 to 325 (Tyr Asn Lys Arg Lys Arg Ile His Ile Gly Pro Gly Arg Ala Phe Tyr Thr Thr Lys Asn Ile Ile Gly) of gp120 of HTLV-IIIMN.
(d) being capable of binding to the surface of HTLV-IIIMN viral particles and thereby inhibiting the infection of the virus particles to CD4-positive cells, and (e) being capable of binding to the surface of cells infected with HTLV-IIIMN and thereby inhibiting the syncytium formation induced by interaction between the infected cells and uninfected cells.
Thus, the monoclonal antibody of this invention can clearly inhibit the cell-to-cell infection such as syncytium formation and/or cell-free virus infection such as infection with HTLV-IIIMN. Accordingly, the monoclonal antibody can be used for the prophylaxis and treatment of AIDS. Moreover, the monoclonal antibody of this invention is also useful for the inhibition of growth of AIDS-related viruses in a human host. Since the monoclonal antibody of this invention has a strong neutralizing activity against HTLV-IIIM~, it is also effective for the prevention of infection of the virus to uninfected T-cells.
A representative example of the hybridoma being capable of producing the monoclonal antibody of this invention has been deposited to Fermentation Research Institute, Agency of Industrial Science and Technology, Tsukuba, Japan under the Budapest Treaty as Accession No.
FERM BP-3402, deposited on February 10, 1990.
This invention is illustrated by the following Examples but should not be construed to be limited thereto.
Example 1 Preparation of monoclonal antibody:
Preparation of antigen (1) A synthetic peptide:
A synthetic peptide corresponding to the amino acid sequence 303 to 325 of the envelope glycoprotein gp120 of HTLV-IIIMN (Tyr Asn Lys Arg Lys Arg Ile His Ile Gly Pro Gly Arg Ala Phe Tyr Thr Thr Lys Asn Ile Ile Gly) is used as an immunogen and an antigen for assay.
The above peptide is prepared with ABI430A
Peptide Synthesizer (Applied Biosystem). The crude peptide thus prepared is removed from the substrate resin by TFMSA
method (Yanaihara, C., Experimental Medicine, 6, No. 10, p. 141-148, 1988) and purified by reverse phase high performance liquid chromatography (HPLC). The purification by reverse phase HPLC is repeated three times and the fractions containing the product are collected, and the product is subjected to amino acid analysis, by which it is confirmed that the amino acid sequence of the product corresponds well to that of HTLV-IIIMN strain, and thereby it is concluded that the product is a synthetic peptide of gp120 of HTLV-IIIMN strain.
The thus-obtained synthetic peptide (designated "SP-1") is lyophilized, and then is bound to an immunization carrier, KLH (Keyhole Limpet Hemocyanin) to give a peptide-KLH conjugate in the following manner.
The above peptide SP-1 (10 mg) is dissolved in 10 mM phosphate buffered saline (PBS, pH 7.0, 2 ml), thereto is added a solution of MBS crosslinking agent in dimethylformamide (40 mg/100 u1), and the mixture is stirred at room temperature for 30 minutes. The reaction mixture is washed with dichloromethane (2 ml) three times, and the aqueous layer (designated Absolution A") is separated.
Separately, KLH (20 mg) is dissolved in 0.2 M Tris-HCl buffer (pH 8.6, 8 M urea, 5 ml) thereto is added dithiothreitol (DTT), and the mixture is stirred at room temperature for one hour. To the reaction mixture is added 10 o trichloroacetic acid (3 ml), the resulting precipitate is separated by filtration with suction, washed with distilled water (2 ml) and then dissolved in 20 mM
sodium phosphate buffer (NaPB, pH 7.0, 0.6 M urea, 5 ml) to give a solution (Solution B).
The above Solution A and Solution B are mixed and stirred at room temperature for 3 hours, and the reaction product is dialyzed and lyophilized.
The synthetic peptide of gp120 of HTLV-IIIMN
strain and peptide-KLH conjugate prepared above are used as an immunogen and antigen for assay.
(2) Cultivation of HTLV-IIIMN-producing cells and preparation of HTLV-IIIMN particles:
The H9/HTLV-IIIMN strain is used as HTLV-IIIMN-producing cells. A culture medium is RPMI1640 supplemented with 20 o FCS and 2 mM L-glutamine to be used in a 50 L
scale. The H9/HTLV-IIIMN strain is cultivated in said culture medium in a 36 liter SpinnerTM flask with a cultivation controller (manufactured by Wakenyaku Kogyo K.K.) and the resulting cells-floating mixture is centrifuged at 3,000 r.p.m. for 5 minutes to separate the culture supernatant. The culture supernatant is subjected to sucrose density-gradient centrifugation (25 0, 50 0, discontinuing, 89,000 x g, 20 hrs.) with a continuous rotater (RPC35TTM, manufactured by Hitachi Ltd.) at a rate of 2 liter/hr. to separate viral particles, wherein the viral particles are collected in 30 - 45 % sucrose layer.
The viral particles thus-obtained are used as an immunogen and an antigen for assay.
Purified gp120 is prepared by collecting the cells from the above H9/HTLV-IIIMN culture broth by centrifugation, lysing the cells with 1 o TritonGX-100, centrifuging the mixture and then purifying the supernatant by affinity chromatography with ConA - Sepharose°4B column.
The eluted solution is further purified by affinity chromatography with HIV antibody (IgG) - Sepharose 4B
column. The purified gp120 thus obtained is used as an immunogen and an antigen for assay.
(3) Preparation of recombinant expression peptide of HTLV-IIIMN gp120 V3 domain:
H9/HTLV-IIIMN cells (106 - 10' cells) are floated in 1 x RSB buffer and thereto are added sodium dodecyl sulfate (SDS, at final concentration of 1 0) and Proteinase K (at final concentration of 1 mg/ml), and the mixture is incubated at 37°C for 2 hours. The resulting mixture is repeatedly subjected to extraction with phenol and precipitation with ethanol to give a high molecular weight DNA (genomic DNA). HTLV-IIIMN gp120 V3 domain (amino acid 247 - 370) is amplified by conventional PCR method by using a template of the above high molecular weight DNA and the following A primer and C primer:
A primer: (5')TGTACACATGGAATTAGGCCAG(3') C primer: (3')GAAGTCCTCCCCTGGGTCTTTA(5') The amplification is carried out with Taq polymerase for 30 to 35 cycles.
The amplified DNA fragment is cloned with pUCl8 plasmid, and the cloned DNA fragment is inserted into pUEX2 expression vector (manufactured by Amersham, Code No.
RPN1515; Bressan, G. and Stanley, Y., Nucleic Acid Research, 15, p. 10056, 1987). Escherichia coli are transfected with the expression vector and then subjected to heat induction at 42°C to express the peptide. The expressed HTLV-IIIMN gp120 V3 domain (amino acid 247 - 370) is a fusion protein with I~-galactosidase, which is then purified in the form of E. coli-inclusion body as follows.
After expression, E. coli are fractured with glass beads and treated with lysozyme (final concentration, 0.1 mg/ml) at 4°C. The resulting precipitate separated by centrifugation is treated with Triton X-100 (final concentration, 0.5 0). The precipitate is solubilized with 8 M urea and is used as an immunogen and an antigen for assay.
Immuno-sensitization of mouse An example of immuno-sensitization of mouse with the synthetic peptides prepared hereinabove is illustrated below.
BALB/c mice (4 - 8 weeks age) are inoculated with the synthetic peptide and synthetic peptide-KLH conjugated antigen mixture (each 100 ug) three times via an intraperitoneal route and one time via an intravenous route, on the first day i.p. in the presence of Freund's complete adjuvant, on 14th day i.p. in the presence of Freund's incomplete adjuvant, on 28th day i.p. in the presence of Freund's incomplete adjuvant, and on 42nd day i.v. in the absence of an adjuvant.
Cell fusion and cultivation of hybridoma Three days after the immunization, the spleen cells are collected from the mice in a usual manner.
The spleen cells are mixed with myeloma cells p3X63Ag8-Ul in a ratio of cells of 1 . 5, and the mixture is centrifuged (1,200 r.p.m./5 minutes) to remove the supernatant. The precipitated mass of cells is well untangled and is added to a mixture (1 ml) of polyethylene glycol-4000 (2 g), minimum essential medium (MEM) (2 ml) and dimethylsulfoxide, and the mixture is incubated at 37°C
for 5 minutes, and thereto is slowly added further MEM to a total volume of 50 ml. The mixture is centrifuged (900 r.p.m./5 minutes) to remove the supernatant fluid and the cells are untangled mildly. To the cells is added a normal medium (RPMI1640 medium with 10 o FCS) (100 ml), and the cells are gradually suspended therein with a measuring pipette.
The suspension is poured into each well of a 24-well culture plate (1 ml/well) and the plate is incubated in an incubator containing 5 o COz at 37°C for 24 hours. Then, 1 ml/well of HAT medium [a normal medium supplemented with hypoxanthine (1 x 10-9 M), thymidine (1.5 x 10-3 M) and aminopterin (4 x 10-' M) ] is added and the plate is incubated for an additional 24 hours. The culture is continued for 10 to 14 days in the same manner while exchanging the culture supernatant (1 ml) with the same volume of a HT medium (HAT medium depleted with aminopterin) every 24 hours for 2 days.
Each well with the fused cells (about 300 cells per well) growing in a colonial shape is selected. The culture supernatant (1 ml) of the selected well is exchanged with the same volume of the HT medium and then the exchange is repeated every 24 hours for 2 days.
After 3 to 4 days culture with the HT medium, a part of the culture supernatant is collected and used for selection of the desired hybridoma by screening method as described below.
Screening of hybridoma The desired hybridoma is selected by a combination of enzyme immunoassay (EIA), immunofluorescence and Western blotting methods. The thus selected clone is measured for its neutralizing activity.
(1) EIA:
To each well of a 96-well microtest plate is added 100 ul/well of the synthetic peptide antigen, purified gp120 antigen, or recombinant peptide (protein concentration: 2 ug/ml), prepared as mentioned above, and the plate is incubated at 4°C overnight for immobilization.

Then, 2 o bovine serum albumin (BSA) solution (100 u1) is added to each well and the plate is incubated in the same manner for masking. To each well of the thus prepared antigen-immobilized plate are added the hybridomas obtained by the cell fusion and the culture supernatant of hybridomas after cloning, and the plate is incubated at 37°C for 2 hours. The plate is washed with 0.1 0 Tween~'20/PBS three times and 100 ul/well of a solution of peroxidase-labelled anti-mouse immunoglobulin (manufactured by Cappel, x 5,000 dilution). After incubation at 37°C for 1 hour, the plate is washed with 0.1 o Tween 20/PBS five times. Then, a substrate solution of 3,3',5,5'-tetramethylbenzidine (TMBZ) is added to each well for color development and an optical density is measured at 450 nm.
A hybridoma clone is thus selected which strongly reacts only with the synthetic peptide derived from HTLV-IIIMN but not with the synthetic peptide derived from HTLV-IIIB.
(2) Immunofluorescence:
H9/HTLV-IIIMN cells or uninfected H9 cells (5 x 105 cells) suspended in the culture supernatant to be tested (100 ~1) are cultured at 4°C for 30 minutes. The cultured cells are washed twice with a PBS solution containing BSA (2 0) and azide (0.1 0) (PBS-BSA-Az). After washing, 100 u1 of anti-mouse IgG labelled with fluorescein-isothiocyanate (FITC) (manufactured by Sigma, diluted to 1 . 40 with PBS-BSA-Az) and the mixture is reacted at 4°C for 30 minutes. The reaction mixture is washed with PBS-BSA-Az three times and then fixed with PBS

containing 0.1 o paraformaldehyde.
Using laser flow-cytometry (Spectrum III°
manufactured by Ortho Diagnostics), the reactivity of the antibody is measured based on the strength of fluorescence.
A hybridoma showing a maximum binding ability to the surface of H9/HTLV-IIIMN cells is selected and cloned by limiting dilution method. The hybridoma clone after cloning is also selected in the same manner.
(3) Western blotting:
Western blotting is carried out in accordance with Towbin et al. [Proc. Natl. Acad. Sci. U.S.A., 76, p. 4350 (1979) ] .
A purified HTLV-IIIMN virus is prepared by the method described in the literature [Science, 224, p. 497 (1984)] and electrophoresed by 12 o sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The gel is then transferred to nitrocellulose membrane to transfer the virus to the membrane and the membrane is cut into strips with 0.4 to 0.5 cm width. Each strip is immersed in a hybridoma culture supernatant and incubated at room temperature overnight. After washing with PBS three times, each strip is warmed in a solution of biotin-labelled anti-mouse IgG (manufactured by TACO) diluted to 1 . 750. After washing with PBS three times, each strip is immersed in a solution of horseradish peroxidase-conjugated avidin (manufactured by Sigma) diluted to 1 . 1,000 and warmed for 1 hour. After washing with PBS three times, a coloring reagent containing 4-chloro-1-naphthol (manufactured by BIO-RAD) is used for color development. A hybridoma showing a colored band of HTLV-IIIMN gp120 is selected and cloned. The hybridoma clone after cloning is also selected in the same manner.
(4) Measurement of neutralizing activity:
The culture supernatant of H9/HTLV-IIIMN is used as an original viral solution (104'5 to 105 TCIDSO) .
The viral solution adjusted to 10 TCIDSO/50 u1 and 50 u1 of the hybridoma clone culture supernatant or purified ascites, which are diluted in series, are inoculated into each well of a 96-well flat-bottomed plate and the plate is incubated at 37°C for 1 hour. Then, MT4 cells are added to each well at 10q cells/100 u1/well, said cells being floated in RPMI1640 medium supplemented with 10 o FCS, L-glutamine (3.5 to 4.0 g/1), penicillin (50 U/ml) and streptomycin (50 ug/ml), and cultured at 37°C
for 5 days.
The neutralizing activity is evaluated based on an ability of the antibody to inhibit the syncytium formation observed during infection. The neutralization titer is expressed as a minimum effective concentration of the antibody showing 100 o inhibition of syncitium formation.
The above selection procedure provides hybridomas (u39.1 and X5.5) capable of producing the desired monoclonal antibody.
Preparation of monoclonal antibodies with hybridomas u39.1 and u5.5:

Each 5 x 106 cells/animal of the hybridoma u39.1 or u5.5 obtained above is intraperitoneally administered to Pristane-treated female BALB/c mice (8 weeks age). After 10 to 21 days, ascites cancer is induced. Ascites are taken out from the mice and centrifuged at 3,000 r.p.m. for 5 minutes to remove solid components. Then, the antibody is purified by subjecting the supernatant to affinity chromatography using Affigel Protein A MAPS-II kit (manufactured by BIO-RAD).
Example 2 Analysis of monoclonal antibodies u39.1 and u5.5 (1) Reactivity to gp120 synthetic peptide derived from various HIV mutants:
Synthetic peptides of gp120 (amino acid sequence 303-325 or 308-329) derived from HTLV-IIIMN, HTLV-IIIB, HTLV-IIIRF and HIV-2 are employed. The reactivity is tested in the same manner as described in the above Screening of hybridoma, (1) EIA.
As shown in Fig. l, it is clear that the control 0.5f~ antibody strongly reacts with the peptide derived from HTLV-IIIB but not with the peptide derived from HTLV-IIIMN
at a lower concentration, although it cross-reacts with the peptide derived from HTLV-IIIMN at a higher concentration.
On the other hand, it is seen that the monoclonal antibody, u39.1 is a HTLV-IIIMN-specific antibody, which strongly reacts with the peptide derived from HTLV-IIIMN.
It is also seen that the u39.1 monoclonal antibody reacts neither with the synthetic peptides derived from HTLV-IIIRe nor with those from HIV-2 (data is not shown in Fig. 1).
The reactivity of the monoclonal antibody u5.5 is completely the same as that of X39.1, i.e. this monoclonal antibody is a HTLV-IIIMN-specific antibody which strongly reacts only with the peptide derived from HTLV-IIIMN.
(2) Reactivity to gp120 derived from infected cells (Western blotting):
In order to determine the reactivity of the monoclonal antibodies u39.1 and u5.5 to the external envelope glycoprotein gp120 derived from infected cells, Western blotting was carried out of H9/HTLV-IIIMN cell lysate. The procedure is the same as that described for "Screening of hybridoma, (3) Western blotting".
As shown in Fig. 2, strip A is a positive control in which HIV antibody positive human serum is employed, wherein a gp120 band is observed. The monoclonal antibody 0.513 does not react with gp120 derived from HTLV-IIIMN
(strip B) while the monoclonal antibodies u39.1 and X5.5 recognize gp120 derived from HTLV-IIIMN (strips C and D).
It is also found that the reactivity of the monoclonal antibody X5.5 is stronger than that of the monoclonal antibody X39.1 as shown in Fig. 2.
(3) Neutralizing property of monoclonal antibodies u39.1 and u5.5:
The neutralizing property of the monoclonal antibodies u39.1 and u5.5 is examined according to the procedure described in the above "Screening of hybridoma, (4) measurement of neutralizing activity". The results are shown in the following Table 1.
m~rio , Inhibitory activity Virus-neutralizing on cell-to-cell activityz infect. by infected cellsl MoAb u5.5 u39.1 0.513 H5.5 u39.1 0.513 Virus IIIMN 16 63 >500 1 63 >500 IIIB/LAV >500 >500 31 >500 >500 4 IIIRE >500 >500 >500 >500 >500 >500 (Note): 1. Minimum effective concentration (ug/ml) of the antibody showing 80 % inhibition of cell-to-cell infection by infected cells 2. Minimum effective concentration (~g/ml) of the antibody showing 100 o inhibition of viral infection The right column in Table 1 shows a minimum effective concentration of the antibody showing 100 0 inhibition of infection of each variant viral species. The control monoclonal antibody 0.513 shows a neutralizing activity specific to HTLV-IIIB/LAV. On the other hand, the monoclonal antibody u39.1 is a monoclonal antibody capable of specifically neutralizing HTLV-IIIMN which completely inhibits the infection of HTLV-IIIMN at a concentration of 63 ug/ml, but not the infection of the other HTLV strains IIIB and IIIRE. The monoclonal antibody u5.5, likewise u39.1, shows a neutralizing activity specific to the strain IIIMN. It is seen that the neutralizing activity of the monoclonal antibody u5.5 is more than 50 times higher than that of u39.1 and is a strong neutralizing antibody which can completely inhibit the infection of the strain IIIMN at a concentration of 1 ug/ml.
The left column of Table 1 indicates a minimum effective concentration of the antibody showing 80 0 inhibition of cell-to-cell infection by infected cells.
The control monoclonal antibody 0.513 shows a neutralizing activity specific to IIIB/LAV infected cells. On the other hand, the monoclonal antibody u39.1 inhibits the cell-to-cell infection by IIIMN infected cells at a concentration of 63 ug/ml but not the infection by IIIB or IIIRF infected cells. That is, it is found that the monoclonal antibody u39.1 is a neutralizing antibody specific to the strain IIIMN in the cell-to-cell infection by the infected cells.
The monoclonal antibody u5.5, likewise X39.1, also shows a neutralizing activity specific to the strain IIIMN. It is seen that the neutralizing activity of the monoclonal antibody u5.5 is more than about 4 times higher than that of X39.1 and is a strong neutralizing antibody which inhibits the cell-to-cell infection by the infected cells at a concentration of 16 ~g/ml.

Claims (4)

1. A monoclonal antibody being capable of specifically binding to a glycoprotein antigen having a molecular weight of about 12 x 10 4 daltons (gp120) present in the envelope of human T-lymphotropic virus III MN
(HTLV-III MN) and capable of substantially neutralizing the HTLV-III MN or fragments thereof.

2. The monoclonal antibody or fragments thereof of Claim 1 which has the following characteristics:
(a) immunoglobulin class: IgG, k (b) being capable of specifically binding to a glycoprotein antigen having a molecular weight of about 12 x 10 4 daltons (gp120) present in the envelope of human T-lymphotropic virus III MN (HTLV-III MN), (c) being capable of recognizing at least one epitope which is present in the region of the amino acid sequence 303 to 325 (Tyr Ash Lys Arg Lys Arg Ile His Ile Gly Pro Gly Arg Ala Phe Tyr Thr Thr Lys Asn Ile Ile Gly) of gp120 of HTLV-III MN.
(d) being capable of specifically binding to the surface of HTLV-III MN viral particles and thereby inhibiting the infection of CD4-positive cells by HTLV-III MN, and (e) being capable of specifically binding to the surface of cells infected with HTLV-III MN and thereby inhibiting the syncytium formation induced by interaction between the infected cells and uninfected cells.

3. The monoclonal antibody or fragments thereof of Claim 1 or 2 which is produced by the hybridoma FERM BP-3402.

4. The monoclonal antibody or fragments thereof of any one of Claims 1 to 3 wherein said monoclonal antibody is a murine antibody.