FR2698271A1 - Vaccine against bovine leukaemia virus - contg. peptide(s), derived from the viral gp 51 glyco:protein, esp. useful for booster vaccination. - Google Patents

Abstract

Vaccine against bovine leukaemia virus (BLV) contains as active ingredient a peptide (I) corresponding to the amino acid sequences 64-73, 98-117 or 177-192 of the gp 51 viral glycoprotein, in a suitable vehicle or excipient. Partic. (I) are of formula: (Arg)3PheGlyAlaArgAlaMetVal (Ia); SerGlnAlaAspGlnGly SerPheThrVal AsnHisGlnIleLeuPhe LeuHisLeuLys (Ib); or ProAspCysAlaIle CysTrpGluProSer ProProTrpAlaProGlu (Ic). Also new is synthetic peptide (Ic). USE/ADVANTAGE - This vaccine is esp. useful as a booster (following prim. vaccination with a live recombinant virus expressing both gp 51 and gp 30 of BLV). (I) are free of undesirable sequences esp. those that induce antibodies facilitating penetration of the virus into cells. They induce both a neutralising B-cell response and an auxiliary T-cell response.

Description

 Bovine leukemia virus vaccine, new immunogenic peptide and vaccination kit.

 The present invention relates to a vaccine against bovine leukemia based on the use of peptide fragments of the glycoprotein gp51 of the bovine leukemia virus. It also relates to a new fragment of gp51 useful in the invention, as well as a vaccination kit.

Bovine leukemia virus (BLV) is an oncovirus structurally and functionally related to human viruses HTLV-1 and HTLV-2 (NR RICE et al., 1987, in "Enzootic leukosis and bovine leukemia virus", editions
A. Burny and M. Mammerickx, pages 115 to 144, Nijhoff, Boston) and constitutes the etiological agent of bovine leukemia and lymphoma (A. BURNY et al., 1990, in "Retrovirus biology and human diseases", editions R. Gallo and F.

Wong-Staal, pages 9 to 25, Dekker, New-York). The BLV envelope (env) complex comprises the external membrane glycoprotein gp51 and the transmembrane glycoprotein gp30 and is directly involved in the infectious process, for example in receptor recognition and membrane fusion (V. VONECHE et al., 1992 ,
Proc. Natl. Acad. Sci. USA 89, 3810-3814).

Three monoclonal antibodies directed against conformational antigenic sites F, G and H of gp51 have been shown to inhibit syncytia formation and neutralize the pseudotypes VSV (vesicular stomatitis virus) - BLV (C. Bruck et al., 1982, Virology 122, 342-352). Obtaining an effective vaccine on the basis of these three epitopes requires their presentation in native configuration. This was recently achieved during the vaccination of sheep with a recombinant vaccine incorporating the env gene of BLV (D. PORTETELLE et al., 1991,
Vaccine 9, 194-200). All the animals which reacted significantly to the vaccine preparation (estimate on the basis of the titer of induced neutralizing antibodies) actually proved to be protected against a virulent test (1,500 times the infectious dose in sheep).

 In general, a successful vaccine must include protective epitopes and avoid harmful genomic parts. As recently reported in connection with the human immunodeficiency virus HIV-1 (J.A.

BERZOFSKY et al., 1991, FASEB J. 5, 2412-2418), undesirable epitopes can induce facilitating antibodies, which can thus facilitate the introduction of the virus into the cell via Fc receptors or complement receptors (A. TAKEDA et al., 1988, Science 242, 4710-4714 and WE ROBINSON et al., 1990, Proc. Natl.

Acad. Sci. USA 87, 3185-3189). Antibodies which cross-react with self antigens have also been described (H. GOLDING et al., 1989, J. Clin. Invest.

83, 1430-1435) or preventing the recognition of adjacent "protective" determinants. We can also expect harmful consequences from the stimulation of suppressive T cells or, as is the case for peptides of retrovirus transmembrane proteins, from the inhibition of several immune functions, such as lymphocyte proliferation (GJ CIANCOLO et al., 1985,
Science 230, 453-455 and CL RUEGG et al., 1989, J. Virol.

63, 3250-3256).

 Obtaining immunogenic candidates therefore requires the choice of interesting determinants and their delimitation excluding any undesirable part.

 European patent application EP-A-0 284 492 (see also D. PORTETELLE et al., 1989, Virology 169, 34-41) discloses a number of peptides and proposes using those corresponding to residues as a vaccine 39 to 48, 78 to 92 and 144 to 157 of the gp51 glycoprotein.

 I. CALLEBAUT et al. r 1991 (FEBS Letters, Volume 392, no. 1, 2, pages 148 to 150) carried out an antigenic study of the gp51 glycoprotein using 27 synthetic peptides corresponding to fragments of the gp51 glycoprotein, among which are fragments 64-73 and 98-117 See also in this sense I. CALLEBAUT et al., 1991, Virology 185, pages 48 to 55. No immunogenic candidate is proposed in these articles.

 The object of the present invention is to provide a vaccine based on peptides which correspond to fragments of the gp51 glycoprotein and which are free of undesirable, in particular facilitating, parts.

 The subject of the invention is therefore a vaccine against the bovine leukemia virus comprising, as active principle, a peptide essentially comprising an amino acid sequence chosen from the group consisting of sequences which correspond to residues 64 to 73, 98 to 117 and 177 to 192 of the bovine leukemia virus glycoprotein gp51, in a vehicle or excipient for a vaccine, in particular of the type usually used for making vaccines.

 N. SAGATA et al. (Proc. Natl. Acad. Sci. USA 1985, 82, 677-681) determined the sequence of the x-BLV-1 variant.

The fragments defined by residues 64 to 73, 98 to 117 and 177 to 192 have the following sequences (the numbering is carried out without taking account of the signal peptide)
64 to 73
Arg - Arg - Arg - Phe - Gly - Ala - Arg - Ala - Met - Val
98 to 117
Ser - Gln - Ala - Asp - Gln - Gly - Ser - Phe - Tyr - Val
Asn - His - Gln - Ile - Leu - Phe - Leu - His - Leu - Lys
177 to 192
Pro - Asp - Cys - Ala - Ile - Cys - Trp - Glu - Pro - Ser
Pro - Pro - Trp - Ala - Pro - Glu.

 The vaccine according to the invention therefore advantageously contains a peptide essentially comprising one of these sequences.

 The invention naturally includes the sequences of other variants which could differ without modifying the immunogenic properties of the peptides as well as the sequences modified by addition, deletion or substitution of amino acids and also retaining the properties specific to the sequences 64-73 , 98-117 and 177-192.

By way of examples, the following sequences fall within the scope of the invention
- sequences 62-73 or 63-73 residue 63: Gly residue 62: Gln (or Lys in the case of the VdM 7628 variant)
- sequence 177-192 extended from 1 to 8 amino acids on the N-terminal side; for example sequence 169-192
- sequences 62-73, 63-73 or 64-73 from which one or more amino acids would be removed from the side
C-terminal
- sequence 98-117 in which residue 111 (Ile for variants T15-2, LB 285, VdM7628, FLK, lBLV-1 and pBLB-A1) is Thr (variant LB59).

 The vaccine according to the invention can therefore comprise a peptide comprising the sequence 62-73 or 63-73 of the glycoprotein gp51 or else the major part of the sequence 169-192 of gp51, preferably then with the part 177-192 preserved. , elongated by about 1 to 8 N-terminal amino acids.

 Of course, the vaccine according to the invention can comprise two or three peptides corresponding to the different sequences of the group, including variant peptides within the meaning of the invention.

 The peptides according to the invention can advantageously be obtained by chemical synthesis.

 According to the invention, the revelation of the protective power of the peptide can be obtained by various means.

 The peptide can be coupled to a usual immunogenic carrier molecule, which can in particular be a carrier protein1 such as, in particular, keyhole limpet hemocyanin (Keyhole Limpet Hemocyanin or KLH). The coupling of the peptide to the carrier protein is preferably carried out in the presence of a coupling agent such as in particular glutaraldehyde or the maleimidocaproic ester N-succinimide.

In the case where the vaccine comprises two or three peptides corresponding to the different sequences and / or variant sequences of the group, these are in the form of a conjugate including an immunogenic carrier molecule. It is understood that, in this case, each peptide can be conjugated to its own carrier molecule or else in the form of a single entity comprising the peptides and the conjugate.

The invention therefore relates to vaccines in which the peptide according to the invention is thus conjugated.

 In addition, to facilitate coupling, a cysteine residue (Cys) can be added to the N-terminal end of the peptide, in particular in the case of peptide 64-73, to facilitate coupling to the immunogenic carrier molecule.

 Alternatively, a plurality of molecules of the peptide "candelabrum" can be connected to a polylysine matrix, for example by the method described by TAM J.P.

(1988) Proc. Natl. Acad. Sci. USA 85, 5409-5413, POSNETT
DN et al, (1988) J. Biol. Chem. 263, 1719-1725.

 According to another embodiment of the invention, the vaccine can comprise a live virus recombined to express one or more peptides. The virus can advantageously be a Poxvirus, in particular the vaccinia virus. This type of vaccine can also be carried out with such a recombinant live virus which is incapable of replicating in cattle. One can thus advantageously use an Avipox, in particular fowlpox or canarypox (D. BAXBY and E. PAOLETTI, Vaccine, volume 10, 1, pages 8 and 9, 1992).

Many other viruses are possible, for example adenoviruses. The vaccine according to the invention can also include several recombinant viruses to express different peptides.

 According to another embodiment of the invention, the vaccine can comprise chimeric viral pseudo-particles formed from a viral particle devoid of its genetic material and carrying the peptide (s) on its surface. Preferably then, the viral pseudo-particle can advantageously be derived from the blue tongue virus (P. ROY et al., 1992, Vaccine, volume 10, 1, pages 28 to 32).

The vaccine may also include combinations of viral pseudo-particles carrying different peptides.

 In another embodiment of the invention, the vaccine can comprise living mammalian cells producing one or more peptides, or combinations of such cells, in particular according to the technique described by C.

ALTANER et al., In Vaccine1 volume 9, December 1991, pages 889 to 895.

The vaccine can also comprise, in another embodiment, an ISCOM preparation incorporating one or more peptides, in particular according to the technique described by
MS MERZA et al., 1989, Vaccine, 7, page 22. Combinations with different peptides are also possible.

 The vaccine according to the invention can advantageously constitute a booster vaccine.

 Under these conditions, the subject of the invention is also a vaccination kit against the bovine leukemia virus comprising a vaccine of first administration and a vaccine according to the invention constituting a booster vaccine. Preferably then, as a vaccine for first administration, the kit can advantageously comprise a recombinant live virus to express both the glycoprotein gp51 and the glycoprotein gp30 of the bovine leukemia virus, as described in the European patent application EP- A-0 431 156.

The peptide corresponding to residue 177-192 of the gp51 glycoprotein is new. A subject of the invention is therefore also a peptide essentially comprising the amino acid sequence corresponding to residues 177 to 192 of the glycoprotein gp51 of the bovine leukemia virus, for the production of a vaccine or a vaccination kit according to the invention. Preferably, the peptide essentially comprises the sequence Pro - Asp - Cys - Ala - Ile
Cys - Trp - Glu - Pro - Ser - Pro - Pro - Trp - Ala - Pro
Glue. The sequence can be lengthened on the N-terminal side, in particular from 1 to 8 amino acids approximately, and the peptide according to the invention can therefore also comprise the major part of the sequence 169-192 of gp51, the part 177-192 being preferably kept.

 A further subject of the invention is the synthetic peptide consisting of the sequence described above.

DETAILED DESCRIPTION
PREPARATION OF SYNTHETIC PEPTIDES
The peptides are conventionally synthesized in solid phase according to the technique described by Merrifield, RB

(J. Am. Chem. Soc. (1963) 85, 2149-2154).

 Solid support: p-methylbenzhydrylamine resin (polystyrene resin crosslinked with 1% divinylbenzene).

 The synthesis is carried out in "continuous flow" (method described by V. Krchnak and J. Vagner, Pept. Res.

(1990) 3, 182-193) using a protection strategy
Fmoc (amine a) / t-Bu (side chains).

The efficiency of the coupling is controlled by reaction with bromophenol blue (V. Krchnak et al., Collet
Czech. Chem. Common. (1988) 53, 2542-2548).

 After cleavage of the protective groups of the side chains (by treatment with trifluoroacetic acid) and release of the resin (by treatment with hydrofluoric acid), the peptides are purified by reverse-phase high performance liquid chromatography (RP-HPLC) .

 Their amino acid composition can be verified by amino acid analysis after total acid hydrolysis.

 Three peptides having the sequences 64-73, 98-117 and 177-192 detailed above were thus synthesized. The peptide of sequence 64-73 additionally contains a cysteine residue (Cys) at its N-terminal end.

RESULTS
The results are divided into two parts taking up two ways in which peptides can play a role in the acquisition of immunity against the virus.

1. NEUTRALIZING RESPONSE B (ANTIBODIES) 1.1 Preparation of antipeptide antibodies
Three antipeptide antibodies were prepared.

The three peptides were coupled to a carrier protein, KLH (for Keyhole Limpet Hemocyanin or
Keyhole limpet hemocyanin).

 The coupling agents are glutaraldehyde for peptide 98-117 (1 conjugate), glutaraldehyde or maleimidocaproic ester N-succinimide for peptide 177-192 (2 conjugates) and this same ester for peptide 64-73 (1 conjugate) ).

 Glutaraldehyde coupling: At 5 mg of KLH in 1 ml of 0.1 M phosphate buffer (0.9% NaCl, pH 8), 40 μl of 25% glutaraldehyde and 1 mg of peptide are added simultaneously. After 5 hours with stirring, the conjugate solution is divided into aliquots (aliquots containing 1 mg of KLH per ml) and the aliquots are stored at -20 C.

 Coupling to the maleimidoeaproic ester Nsuccinimide: To 5 mg of KLH in 1 ml of 0.1 M phosphate buffer (0.1 M NaCl, pH 7), 128 μg of maleimidocaproic ester N-succinimide dissolved in dimethylformamide are added . The mixture is incubated for 1 hour at 30 ° C. After dialysis on a Millipore membrane (0.025 μm) against the phosphate buffer, 2.5 mg of peptide is added to the activated solution. After stirring overnight, the conjugate solution is distributed in aliquots (aliquots containing 1 mg of KLH per ml) and the aliquots are stored at -20 C.

 Rabbits were injected intradermally and 15 days apart each time with an aliquot of conjugate (see above) emulsified in full (first 2 injections) or incomplete (third injection) Freund's adjuvant. Blood was collected before each injection and 8 to 12 days after the last injection. The sera samples extracted from these blood samples were stored at -20 C.

 It is on the last samples (bloodletting 8 to 12 days after the last injection), characterized by the highest titers of antipeptide antibodies (see below), that the biological tests were carried out (neutralizing power, recognition of the gp51).

Table 1
Peptides and anti-peptide antibodies (GA = glutaraldehyde, MCS = maleimidocaproic ester N-succinimide)
Peptide Coupling n "rabbit
98-117 GA 90 117-192 GA 64 177-192 MCS 66
64-73 MCS 16 1.2. Antiserum titer determination
This titer is determined by ELISA test in which the peptide is adsorbed on the plate (100 ng per well). Antiserum dilutions are then made
The titer of an antiserum is defined as being the inverse of the dilution for which the optical density observed for the reaction of the serum with the peptide is still equal to at least twice the optical density observed for the reaction of the peptide with the serum control (serum before injection of the peptide).

Table 2
Antipeptide peptides and antibodies: ante serum titer
Peptide n "rabbit title
98-117 90 44,000 177-192 64 1 100,000 177-192 66 3,300,000
64-93 16 180 1.3. Recognition of gp51 by antiserum
The ability of the antipeptide antibodies to recognize the protein from which their sequences are derived was determined by ELISA tests (recognition of the denatured BLV virion with octelglucoside FELISA BLVJ / recognition of gp51 presented by the monoclonal antibody directed against the E site (ELISA E-gpJ) or by Western Blot FWB].

 The results show that the different sera recognize gp51, in a pronounced manner for sera No. 16, 64 and 66 and weak for serum No. 90.

Table 3
Peptides and Antipeptide Antibodies: Recognition of gp51
Peptide nt rabbit ELISA BLV ELISA E-gp WB
98-117 90 - ++ 177-192 64 +++ +++ +++ +++ 177-192 66
64-73 16 + +++ 1.4. Antiserum neutralizing power
Defining the "neutralizing" power of an antiserum amounts to estimating the capacity of antipeptide antibodies to inhibit the entry of the virus into a cell. This estimate uses the two tests described below.

1 "Inhibition of syncytia formation
The Early Fusion Test (Early
Polykaryocytosis), also known as SIA (Syncytia
Infectivity Assay), consists in coculturing bovine kidney cells infected with BLV (FLK for
Lamb Kidney Fetal) and cells indicative of cell fusion (CC81, cat cells transformed by
MSV). Many syncytia then appear within 24 hours in these cultures. In order to decrease the number of syncytia, which cannot be determined in this case with precision, "filling" cells (OVK) are added at the same time as the FLK and CC81.

The inhibition test was slightly modified compared to that described by C. BRUCK et al., 1982 (Virology
122, 342-352). BLV virus-producing cells (10,000 FLK cells, Van der Maaten and Miller, 1976, Bibl.

Haematol. 43, 360-362) and uninfected cells (100,000 OVK cells) in 100 µl of complete MEM medium (MEM
Gibco including non-essential amino acids and glutamine, kanamycin and 10% fetal calf serum
inactivated) are added to dilutions (three in three from 1/12) of antiserum (50 μl) prepared in 96-well microplates (flat bottoms) for cell culture (Nunc). The microplates are then incubated for 4 h at 37 ° C. in an atmosphere at 5% CO 2. Transformed CC81 cat cells (400,000 cells) are then added to each well (PJ Fischinger et al.,
1974, J. Virol. 14, 177-179) and incubated overnight.

The cells are then fixed with a methanol / acetic acid solution (3 vol./1 vol.), They are washed and then they are stained, for example, with Giemsa dye. Cells containing more than 5 nuclei are considered syncytia.

 Syncytia formation can be inhibited in the presence of the various antipeptide antibodies of the invention (sera n "16, n" 90, n "64, n" 66). The titer of inhibition is defined as being the inverse of the dilution of serum giving another 50% of inhibition.

Table 4
Peptides and antipeptide antibodies: titer in inhibition of syncytia (the titles of negative control sera are less than 12).

Peptide n "rabbit title
98-117 90 108 177-192 64 36 177-192 66 36
64-73 16 36 2 "Neutralization of VSV-BLV pseudotypes
Vesicular stomatitis virus (VSV) pseudotype particles carrying the BLV envelope proteins on their surface are lytic to cells
VERO (indicator cells). We proceed as described by J.

ZAVADA et al., 1978, (Acta Virol. 22, 91-96). The neutralizing power of antibodies is assessed by the inhibition of the lysis of these cells. Lysis plate counts were made at a 1/30 serum dilution. Only serum No. 64 still produces 50% inhibition at this dilution. Serums No. 16, No. 90 and No. 66 do not demonstrate any obvious neutralization properties of the pseudotypes.

1.5 Conclusion
The antisera directed against the peptides, all recognizing gp51, all have properties that inhibit the formation of syncytia. Only the serum directed against the peptide 177-192 (when the latter is coupled to KLH by means of glutaraldehyde) also neutralizes pseudotypes VSV-BLV.

2. AUXILIARY RESPONSE
The helper T response manifests itself in vitro by a proliferation of cells following the specific recognition of an antigen (here peptides).

In this context, a system capable of judging the in vitro proliferation of infected bovine cells brought into contact with different peptides derived from the sequence of gp51 has been developed. This involves the use of autologous serum (serum inactivated by the heat of the animal whose cells are tested) and the elimination of B cells (these express the virus in vitro). In parallel, the proliferation, induced by peptides, of mouse cells of different haplotypes which have been immunized with gap 1 has been studied.

 The results for peptides 64-73, 98-117 and 177-192 are shown in the table below in terms of stimulation index: ratio of cpm * of the culture with peptide and of the culture without peptide (*: the cpm are directly proportional to the proliferative state of the culture and therefore the indices are a function of the proliferation rate). Indexes greater than 2 are considered significant.

Table 5
Stimulation index
Peptide Cattle infected Immune mouse
68 71 73 79 80 BALB / c C57 / BL C3H
98-117 2.5 2.1 - 2.6 - 3.1 - 177-192 - - - - 7.6
64 - 73 - - 3.8 - - - -
NB: these stimulation indexes are the highest that we have observed (tests carried out several times).

 It appears from these experiments that the peptide 98-117 has an epic topical character with respect to various infected cows ** and a haplotype of mice, while the peptide 177-192 induces very high indexes of stimulation of 'an infected cattle. None of the peptides induced a stimulation index> 2 with cells from healthy bovine or non-immune mice. (** The haplotypes of the different cows cannot be determined for lack of tools).

TESTS CONCERNING THE PROTECTIVE POWER OF PEPTIDE 98-117 IN
VIVO
Peptide 98-117, alone or in combination with a recombinant vaccinia virus (VP459 carrying and expressing gp51 and gp30 in accordance with European patent application EP-A-0 431 156), was injected into sheep.

 The cells of sheep no. 175, having received three injections of the peptide 98-117 (coupled to a carrier protein), were tested for the proliferative response induced in vitro in the presence of the same peptide (cf. single figure). The cells are found to respond strongly to the presence of the peptide in the culture. The peptide 98-117 therefore appears to induce an auxiliary response in vivo, however, after superinfection with infected bovine cells, an appearance is observed. anti-p24 antibodies, which is a sign of infection.

A protective power (no appearance of anti-p24 antibodies after challenge) is however observed for a sheep (No. 11) to which the peptide has been injected and
VP459.

REMARKS 1 "The peptide 177-192 was synthesized and tested in an auxiliary response following the observation of very high stimulation indices (up to 12) obtained with the cells of bovine 80 in the presence of a peptide overlapping the peptide 177-192 and comprising residues 169-188 (sequence Leu Asn
Gln Thr Ala Arg Ala Phe Pro Asp Cys Ala Ile Cys Trp Glu Ser
Pro Pro). As bovine 80 cells do not respond to another peptide (residues 168-180) covering the part
N-terminal of peptide 169-188, the epitopic site must be located in the C-terminal part of peptide 169-188. I1 has therefore been synthesized peptides incorporating this part
C-terminal (however extending it by a few residues).

These are peptides 177-192, 179-192 and 181-192. In view of the results shown in Table 6, it appears that only the longest of these peptides induces a proliferative response in bovine 80 cells. It can therefore be concluded that residues P (177) and / or D (178) are essential obtaining a proliferative response, if however the epitopes included in peptides 169-188 and 177-192 are identical. It also appears from Table 6 that peptides 177-192, 179-192 and 181-192 are at the origin of neutralizing antibodies unlike peptide 169-188, which shows the need for one or more of the four residues WAPE for obtaining an effective response B.

Table 6: Peptides located in the region 168-192 immunological properties
168-180 169-188 177-192 179-192 181-192
Response B (neutralizers) - - + + +
Auxiliary T response (cattle 80) - + + -
The peptide 177-192 therefore has a double neutralizing character. We can say that its C-terminal part is essential for obtaining the neutralizing response B while its N-terminal part is essential for the auxiliary T response. An extension of this peptide in its N-terminal part can however be achieved since the stimulation indices obtained with the peptide 169-188 are higher than those obtained with the peptide 177-192 (12 against 7.6).

2 "The peptides according to the invention are located in very constant regions of gp51, which constitutes a considerable asset for the design of a vaccine. Indeed, the peptide 177-192 is completely invariant on all the variants listed up to 'now (Daniel Portetelle,
Thesis of aggregation of higher education, Gembloux, 1989). The same is true for peptide 169-188. For peptide 98-117, only residue 111 (Ile for variants
T15-2, LB285, VdM7628, FLK, lBLV-1, pBLB-A1) is substituted by Thr in the sequence of the variant LB59.

 3 Peptides 64-73, 98-117 and 177-192 are capable of inducing a neutralizing B response and an auxiliary T response. If under the experimental conditions (in particular concentration, vector of immunogenicity, adjuvant), the peptide 98-117 proves to be a good booster vaccine after a first administration of the vaccine VP459, the peptides according to the invention have the properties required for constitute the active principle of a vaccine.

Claims (25)

 1. Vaccine against the bovine leukemia virus, comprising as active ingredient. a peptide comprising an amino acid sequence chosen from the group of sequences which correspond to residues 64 to 73, 98 to 117 and 177 to 192 of the bovine leukemia virus glycoprotein gp51, in a vehicle or excipient for vaccine.  2. Vaccine according to claim 1, characterized in that the peptide essentially comprises one of the following sequences 1) Arg - Arg - Arg - Phe - Gly - Ala - Arg - Ala - Met - Val 2) Ser - Gln - Ala - Asp - Gln - Gly - Ser - Phe - Tyr  Val - Asn - His - Gln - Ile - Leu - Phe - Leu - His  Leu - Lys 3) Pro - Asp - Cys - Ala - Ile - Cys - Trp - Glu - Pro  Ser - Pro - Pro - Trp - Ala - Pro - Glu.  3. Vaccine according to claim 1, characterized in that the peptide comprises the sequence 62 to 73 or 63 to 73 of the glycoprotein gp51 of the bovine leukemia virus.  4. Vaccine according to claim 1, characterized in that the peptide comprises the major part of the sequence 169-192 of the glycoprotein gp51 of the bovine leukemia virus.  5. Vaccine according to any one of claims 1 to 4, characterized in that it comprises two or three peptides corresponding to the different sequences of the group.  6. Vaccine according to any one of claims 1 to <characterized in that the peptides are obtained by chemical synthesis.  7. Vaccine according to any one of claims 1 to 6, characterized in that the peptide is coupled to an immunogenic carrier molecule.  8. Vaccine according to claim 5, characterized in that the vaccine peptides are in the form of a conjugate including an immunogenic carrier molecule.  9. Vaccine according to claim 7 or 8, characterized in that the immunogenic carrier molecule is a carrier protein, such as in particular keyhole limpet hemocyanin.  10. Vaccine according to claim 9, characterized in that the carrier protein is coupled to the peptide in the presence of glutaraldehyde or maleimidocaproic ester N-succinimide.  11. Vaccine according to any one of claims 1 to 6, characterized in that it comprises a live virus recombined to express the peptide.  12. Vaccine according to claim 11, characterized in that the virus is a Poxvirus, in particular vaccinia.  13. Vaccine according to claim 11, characterized in that the virus is incapable of replicating in cattle.  14. Vaccine according to claim 13, characterized in that the virus is an Avipox, in particular fowlpox or canarypox.  15. Vaccine according to any one of claims 1 to 6, characterized in that it comprises chimeric viral pseudo-particles formed of a viral particle devoid of its genetic material and carrying the peptide on its surface.  16. Vaccine according to claim 15, characterized in that the viral pseudo-particle is derived from the blue tongue virus.  17. Vaccine according to any one of claims 1 to 6, characterized in that it comprises living mammalian cells producing the peptide.  18. Vaccine according to any one of claims 1 to 6, characterized in that it comprises an ISCOM preparation incorporating the peptide.  19. Vaccine according to any one of claims 1 to 18, characterized in that it constitutes a booster vaccine.  20. Vaccination kit against the bovine leukemia virus comprising a first administration vaccine and a booster vaccine according to claim 19.  21. Vaccination kit according to claim 20, characterized in that, as a first administration vaccine, the kit comprises a live recombinant virus to express both the gp51 and the gp30 of the bovine leukemia virus.  22. Peptide essentially comprising the amino acid sequence corresponding to residues 177 to 192 of the glycoprotein gp51 of the bovine leukemia virus, for the production of a vaccine or a vaccination kit according to any one of claims 1 at 21.  23. Peptide according to claim 22, characterized in that it essentially comprises the following sequence Pro - Asp - Cys - Ala - Ile - Cys - Trp - Glu - Pro - Ser Pro - Pro - Trp - Ala - Pro - Glu.  24. Peptide according to claim 22 or 23, characterized in that it comprises the major part of the sequence 169-192 of the glycoprotein gp51, the part 177-192 being preserved.  25. Synthetic peptide consisting of the sequence Pro - Asp - Cys - Ala - Ile - Cys - Trp - Glu - Pro - Ser Pro - Pro - Trp - Ala - Pro - Glu and intended for the production of a vaccine according to any one of claims 1 to 21.