POLYPEPTIDES USEFUL AS IMMUNOTHERAPEUTIC AGENTS AND METHODS OF POLYPEPTIDE PREPARATION

Abstract: Fusion polypeptides and aggregates of polypeptides comprising papillomavirus-derived antigens, and compositions thereof and their use e.g. with adjuvants for immunogenic and vaccine purposes in eliciting e.g. HPV-specific immune responses. The polypeptides can be purified to result in aggregates which when in solution or dispersion can pass through a sterilisation filter, and in amorphous aggregates. An example of such a polypeptide is a fusion protein of human papillomavirus proteins L2 and E7.

Description: Polypeptides useful as Iπinunotherapeutic Agents and Methods of Pol peptide Preparation Field of the Invention: The present invention relates to HPV polypeptide preparations and their use in prophylactic or therapeutic treatment of chronic HPV infection. Methods of preparing these combinations, including protein purification techniques and the engineering of nucleic acid sequences by recombinant DNA techniques in order to enhance and achieve high level expression of a particular protein in heterologous cells, in particular E. coli bacterial cells, are generally applicable in the field of protein production and form a further aspect of the invention. Background of the Invention, and Prior Art: Human papillomaviruses (HPV) are agents responsible for several benign and malignant lesions which proliferate in the skin and mucosal surfaces of humans. They are a genetically diverse group of DNA viruses which infect epithelial tissue, and can cause a range of different human diseases. Over 60 different types of HPV have been distinguished, based on the extent of cross hybridisation between their genomes, and of those, different subgroups are associated primarily with different types of disease. For example HPVs of types 1, 2. etc are associated with cutaneous warts of the hands and feet. HPVs 5 and 8 are associated with the rare disorder epidermodysplasia verruciformis. Approximately twenty HPV types infect the genital mucosa. and can be divided into two subsets on the basis of severity of the disease with which they are associated. The first group include viruses such as HPV-6 and HPV-11 which are associated with the majority of benign condylomas (warts), including genital warts. The second group includes HPVs 16. 18. 31. 33 and 45. associated with flat warts of the cervix, and involved in malignant conversions leading to carcinomas of the uterine cervix (zur Hausen. Cancer Res.49 (1989) pp 4677-4681). Diseases associated with HPV are generally characterised by benign proliferations of epithelial tissue (warts) caused directly by virus infection. The virus infects the basal non-keratinised cells of the epithelium but cannot complete its replication cycle in these cells. Instead virus gene expression is limited to a set of early proteins which can induce the infected cell to proliferate, giving rise to the characteristic wart. In the upper layers of the wart however, the infected cells begin to undergo terminal differentiation towards their final keratinised state, and this differentiation is sufficient to allow the virus to complete its replication cycle with the production of virus proteins and ultimately new virus particles. These lesions, although proliferative. are at low risk of malignant conversion, and in most cases the warts remain benign. However, in some cases, over a period of years, cells carrying HPV sequences may become tumorigenie. In this case it appears that the bulk of the virus genome is likely to be lost, and a residual portion of the genome, usually including the virus E6 and E7 genes becomes integrated into the genome. This progression to malignant cancer is. however, associated primarily with a limited range of HPV types, namely HPVs 16. 18, 31.33.35.45 and with particular tissues such as the cervix and penis. It is known that the immune system can play a role in controlling HPV infection. It is well known that the incidence of HPV-induced skin warts and HPV-associated diseases increases in those who are receiving immunosuppressive treatment, suggesting that in many cases virus infection is kept under control by imunological mechanisms. Further evidence for the capacity of the immune system to control infection has come from study of spontaneous wart regression. A common observation is that in some individuals with genital warts, the warts suddenly disappear. Such regressingwarts have been studied histologically. revealing a substantial influx of T lymphocytes in the lesions. Regression is believed to be mediated by the immune system. Effective immune responses to HPV infections are thought to be mainly cell-mediated since disease can persist in individuals with serum antibodies against HPV. Moreover, it is known that spontaneous regression of warts is often accompanied by lymphocytic infiltration, itching, reddening of the affected area and other symptoms characteristic of cell- mediated immune reaction. HPV infections are also common in patients with impaired cellular immunity, where persistence of viral disease suggests poor immune surveillance. Studies on regression of papillomavirus-associated disease in vaccinated animal models also support the concept of an immune effector in combatting disease. For example, cattle vaccinated against Bovine papillomavirus (BPV) produced antibodies reported not to be neutralising, yet vaccination with a fusion protein comprising sequences of BPV L2 and non-HPV sequences (beta galactosidase) has been shown to produce both prophylactic and therapeutic responses in these animals: (see W093/00436, of Cancer Research Campaign Technology Limited: Jarrett et al. and Jarrett et al. Virology. 184 (1991) pp33-42). The use of HPV proteins such as LI. L2 in the preparation of vaccines is known for example from WO 93/02184 (Univ of Queensland & CLS Ltd: I Frazer et al: Papilloma virus vaccine). Other HPV proteins have been decribed for use in imunodiagnostics, e.g. in WO 91/18294 (Medscand AB: J Dillner et al: Synthetic peptides of various human papi11o aviruses, for diagnostic immunossay); and EP 0375555 (Medgenix: G De Martynoff et al: Peptides, antibodies against them, and methods for detection and dosage of papilloma virus). EP 0 456 197 (1991) (Behringwerke: C Bleu! et al) discloses peptides with one or more seroreactive epitopes of defined sequence from HPV18 proteins El. E6. and E7. EP 0451 550 (1991) (Behringwerke: M Mueller et al) discloses peptides with one or more seroreactive epitopes of defined sequence from HPV16 proteins E4. E6. E7. or LI. The disclosures are for screening test purposes, and also mention vaccine use. WO 93/00436 (Cancer Research Campaign Technology: WFH Jarrett et al) disclose papillomavirus proteins and fragments related to L2 protein for prophylaxis and therapy of papillomavirus tumours, also mentioning preparation of E7 protein. WO 92/16636 (Immunology Ltd: MEG Boursnell et al) discloses genetic sequences of HPV16 and HPV18 E6 and E7 as fused genes inserted in a recombinant vaccinia virus vector, causing in-vivo expression of antigens after administration of the live virus vector. WO 92/05248 (Bristol-Myers Squibb: EK Thomas et al) proposes materials for inhibiting and treating human papillomavirus infection and cell transformation, mentioning recombinant cells (including virus vectors) containing a gene encoding a peptide substantially corresponding to a region of the E6 and/or E7 gene product or a chimeric peptide compound of one or more regions of HPV proteins. CP Crum et al. Virology 178 (1990) pp 238-246. describe expression of fused part-sequences of HPV-16 LI and E4 and the use of the proteins with Freund's complete adjuvant to immunise rabbits to make antisera for diagnostic or other test purposes. Summary and description of the Invention: The present invention provides fusion polypeptides and aggregates of polypeptides having papillomavirus-derived antigens as described more particularly below, and compositions thereof and their use for immunogenic and vaccine purposes in eliciting papillomavirus-specific immune responses. Also provided are methods of producing, treating and and purifying such polypeptides and compositions, as described below. According to the invention there are provided polypeptides and polypeptide compositions comprising an antigenie determinant of a papillomavirus protein, in aggregated form which when in solution or dispersion can pass through a sterilisation filter, or in amorphous aggregated form. The invention also provides fusion polypeptides that combine papilloma-virus-derived antigens, e.g. from each of at least two different papillomavirus proteins, e.g. comprising (a) at least an antigenie determinant of a papillomavirus L2 protein, and (b) at least an antigenie determinant selected from El. E2. E4, E5. E6 and E7 papillomavirus proteins and L2 papillomavirus proteins of different papillomavirus type than in (a). Further fusion polypeptides provided hereby comprise antigenie determinants from at least two papillomavirus proteins selected from El. E2. E4, E5. E6 and E7 papillomavirus proteins e.g. where the said proteins are from different papillomavirus types. Particularly preferred polypeptides and compositions hereof comprise antigenie determinants of human papillomavirus proteins, e.g. of HPV type 6.11.16.18. Antigenie determinants of proteins from other HPV types and proteins of non-human animal papi11omaviruses can also be made and used. In further detail, the invention provides for example polypeptides comprising antigenie determinants from each of at least two different HPV proteins. An antigenie determinant of a papillomavirus protein can for example be represented and provided in connection with the invention either by the full sequence of the papillomavirus protein concerned, or by such sub-sequences as may be desired, e.g. a sequence fragment comprising at least 25*. e.g. at least 50* or 75* of the full sequence of the protein concerned, e.g. a N-terminal or C-terminal sequence fragment. Sequences can be taken from clinical papillomavirus isolates or published sequences or muteins thereof. The HPV proteins, of which antigenie determinants can form part of such a fusion polypeptide. can be selected for example from the LI. L2, El. E2. E4. E5. E6 and E7 proteins. Proteins of for example (human) papillomavirus types HPV 6.11, 16 and 18, as well as from other human or animal papillomavirus types can be used. Thus antigenie determinants of at least two papillomavirus proteins can for example be L2 and another, and/or E7 and another. In particular examples, the polypeptide can comprise at least an antigenie determinant from each of at least two different papillomavirus proteins, and from the same or from different papillomavirus types. For example, at least one of the proteins can be selected from LI or L2 and/or at least one of the proteins can be selected from El, E2, E4. E5, E6 and E7. In particular examples the invention provides a polypeptide comprising an antigenie determinant of HPV L2 protein and an antigenie determinant of HPV E7 protein, suitably comprising for example a substantially full length L2 and/or E7 protein of HPV. or antigenie fragments or muteins thereof. A fusion protein comprising L2 and E7 proteins of HPV. can comprise a sequence fragment of at least 50* of the full sequence of each of L2 protein and E7 protein, e.g. substantially the full sequence of L2 and of E7: optionally further including a sequence of LI protein. The polypeptide may further include antigenie determinants of other HPV proteins or be in admixture or aggregated with other HPV proteins or protein fragments, such as LI or another member or members of the L or E series of papillomavirus-encoded proteins. The polypeptide can comprise a single protein consisting of a fusion of L2 and E7 or a fusion of L2. E7 and LI. Alternatively the polypeptide can comprise an L2-E7 fusion combined with LI protein for prophylactic or therapeutic application. The polypeptide may comprise a fusion molecule or can be derived from individual polypeptides coupled or aggregated together. Soluble or solubiUsed forms of the polypeptide fall within the scope of the invention. In certain embodiments the polypeptide can be coupled by chemical crosslinking, in per se known manner, e.g. by standard techniques involving covalent attachment for example to exposed tyrosine residues or to the epsilon-amino groups of lysine residues or the carboxyl groups of aspartate and glutamate residues. Preferred embodiments are however fusion proteins each resulting from expression in a recombinant host cell of a polynucleotide sequence of which part encodes part of all of the amino acid sequence of a first papillomavirus protein and another part encodes part or all of the amino acid sequence of a second papillomavirus protein. In particular, the invention provides for example a polypeptide comprising an antigenie determinant from each of at least two different papillomavirus proteins, in an aggregated form which when in solution or dispersion can pass through a sterilisation filter, e.g. a filter with pore size in the range 0.16-0.22 micron, e.g. 0.2 micron. It can be seen that the invention provides for example a polypeptide comprising an antigenie determinant from each of at least two different papillomavirus proteins, e.g. L2 or LI and at least one other of LI. L2. El, E2. E4. E6 and E7. in a reaggregated form that when in solution or dispersion can pass through a sterilisation filter, e.g. a filter with a pore size in the range 0.16 - 0.22 micron, e.g.0.2 micron. Suitable forms of preparation can result for example by denaturation. or denaturation with reduction, e.g. with subsequent reaggregation of a polypeptide which can be a fusion protein or other papillomavirus protein, e.g. a single papillomavirus protein, expressed in the form of inclusion bodies in a recombinant host cell. Such a form can offer an advantage in that it can be relatively easily purified, e.g. for vaccine use. Alternative aggregated preparations of the polypeptides need not be filterable to sterilise them and can be prepared and purified by aseptic technique. Aggregated or reaggregated polypeptides as described herein can have for example masses in the range about 100.000. e.g. 160,000 to 10.000.000 dalton. The molecular weight of a dimer of L2E7 can be about 130.000. The aggregates can for example have diameters on electron microscopy in the range about 4 to 50 nm. e.g. 10 to 15 nm. An example of a polypeptide provided by the invention as descri ed in detail in the example below contains a reaggregated L2E7 fusion polypeptide containing aggregates of about 500.000 dalton. about 10-15 or 15-20 nm in diameter upon electron microscopy, with about 7-10. e.g. about 8 L2E7 fusion polypeptide chains per aggregate. More generally, the product can have about 2 to 200, e.g.5-50 chains per aggregate particle, and the preparations of aggregate can comprise particles with a range of particle sizes within the composition. Suitable reaggregation is obtainable for example as a result of slow or gradual removal of urea and thiol-reducing agent (often e.g. dithiothreitol. or other acceptable thiol-reducing agent such as glutathione) from a denatured and reduced preparation of the fusion polypeptide in urea (e.g. about 8M urea) and thiol-reducing agent e.g. about 10 M dithiothreitol (preferably lowered to about 0.1 mM or less, e.g. about 0.04 mM or less in the reaggregated product). Such gradual removal can for example result from the column chromatography procedure described in detail below. The denatured and reduced preparation of the fusion polypeptide is obtainable for example by solubilising, in urea and thiol-reducing agent, initially-insoluble inclusion bodies as produced by expression of the polypeptides in a E.coli T7 system. Such aggregated soluble or disperse products are often amorphous, can lack LI protein, and are otherwise distinct from virus-like particles based on papillomavirus LI protein (and sometimes including other papillomavirus proteins), as reported to result from expression of HPV genes (including LI) in systems such as e.g. recombinant baculoviruses in insect cells or in yeast cells. For example, the virus-like particles have not been disclosed as having undergone solubiusing denaturation and thiol-reduction followed by reaggregation. The polypeptides mentioned above can suitably be prepared using recombinant DNA techniques. Thus the invention also provides nucleic acids which encode the above mentioned polypeptides. cloning and expression vectors incorporating them and parts of them, and transfected and transduced host cells incorporating such nucleic acids and able to express them as protein. In a preferred example, the nucleic acid comprises a fusion gene comprising for example the L2 and E7 genes isolated for example from an isolate of HPV-6 obtained from a clinical specimen of genital wart. Preferably the polypeptides described above are prepared by expression of the nucleic acid in a prokaryotic or eukaryotie host using recombinant DNA techniques. Specifically, a nucleic acid which encodes the desired polypeptide is incorporated into a suitable vector system as a suitable open reading frame with any accessory sequences proper for its expression in a chosen system. The host cell is transformed with the vector. Transformed host cells are then cultured and the desired polypeptide isolated from the culture, either from the supernatant or from the cells, as in examples given below. The above-mentioned vectors as well as transformed host cells form a further aspect of the invention. Expression of polypeptides provided by the invention has been examined in yeast and baculovirus expression systems, which have been previously reported to allow expression of HPV-derived genes. It was found that in both cases it was possible to obtain expression of a full- length molecule, but that expression levels were sometimes low. It is presently preferred, for the sake of optimising expression levels, to use a prokaryotic host expression system (particularly a E.coli T7 system), rather than the two tested eukaryotie systems (yeast or baculovirus). Immunogenic polypeptides and vaccine compositions provided hereby are useful in eliciting HPV-specific immune responses e.g. as vaccines for prophylaxis or therapy of papi11omavirus-associated conditions. The immunogens. e.g. immuno-therapeutic or prophylactic vaccines for use in the prophylaxis or treatment of HPV-associated diseases can be used to generate immune responses, e.g. responses involving cellular immunity capable of mediating the regression of chronic HPV infections including genital warts (especially where the products and the infections are based on HPV of types 6 and/or 11) or cervical intra-epithelial neoplasia (especially where the products and the infections are based on HPV of types 16 and/or 18) in infected patients. Such immune response can be targeted towards T-cells, e.g. CD4+ cells, e.g. by the use of appropriate ad uvants. Thus the invention further provides a method for preventing or treating HPV infection or lesions associated therewith, which method comprises administering to a patient an effective amount of a polypeptide as described herein. Embodiments provided by the invention include vaccine preparations based on polypeptides as mentioned herein, which according to specificity are intended for use in eliciting immune responses to papillomavirus. particularly for example of papi11omaviruses of types HPV 6 and 11, and of types HPV 16 and 18. for use in prophylaxis and therapy of human genital warts and of cervical intra-epithelial neoplasia. Cross-reactivity between HPVs of different types has been observed, and according to such observable cross-reactivity the polypeptides and vaccines produced hereby can be used in eliciting useful immune responses against papillomavirus types other than the types from which they were derived. The invention provides immunogenic compositions of the polypeptides mentioned above, suitable for administration by injection, comprising a carrier such as an immunological adjuvant. In certain preferred examples the adjuvant comprises alumimium hydroxide and/or monophosphoryl lipid A as decribed more particularly below. Such immunogenic compositions, e.g. for use as a therapeutic or prophylactic vaccine in humans or non-human animals, can comprise an adsorption complex comprising "alum" (i.e. aluminium hydroxide usually Alhydrogel (IT.) or Rehydrogel (TM) as conventionally used as vaccine adjuvant) having adsorbed thereon a polypeptide obtainable as mentioned above. The adsorption complex can be a binary complex consisting of the alum and the polypeptide. or there may be further constituents, e.g. MPL as described below, making for example a ternary complex of MPL. alum and polypeptide. The polypeptide. either soluble or aggregated, may be used as vaccine directly or may be administered as a pharmaceutical composition comprising also a pharmaceutically acceptable vehicle, buffer, adjuvant or other acceptable material. Hence the invention further provides a vaccine or pharmaceutical composition which comprises a polypeptide as described above in combination with a suitable carrier or excipient. The polypeptide can be either a soluble monomer, for example of L2E7, or a polypeptide aggregate. Preferably the polypeptide, e.g. an L2E7 fusion protein, is formulated by combining with an adjuvant or other accessory substance such as an immunostimulatory molecule in order to enhance its effect as a therapeutic antigen, and also to stimulate a preferred type of immune response in the recipient patient. Useful adjuvants include, but are not limited to; aluminium hydroxide ("alum"). e.g. in the form of Alhydrogel(TM) or Rehydrogel(TM); 3D-MPL (3- deacylated monophosphoryl lipid A) e.g. as described in US 4.912.094 (Ribi Immunochem Research: KR Myers and AT Truchot: describing adjuvants based on modified lipopoly-saccharide. de-3-0-acyl monophosphoryl lipid A), which can be applied for example as described in US 4.912.094 or as in specification WO 94/21292 (Smithkline Beecha : P Hauser et al: Vaccine compositions containing 3-0-deacylated monophosphoryl Lipid A). Where both alum and MPL are used, the protein is preferably adsorbed first to alum and MPL added afterwards. Also usable are trehalose diesters such as trehalose dimyeolate; saponins and their derivatives such as Quil A or QS-21. as for example described in specifications WO 88/09336 (Cambridge Bioscience: CA ensil et al : Saponin adjuvant) and WO 93/05789 (Cambridge Biotech: CA Kensil et al: Saponin-antigen conjugates): ISCOMS or ISCOM matrices, as for example described in specifications WO 90/03184 (B Morein et al: Iscom matrix with immunomodulating activity, comprising lipid and optionally also adjuvants) and WO 92/21331 (Kabi Pharmacia AB: B Morein et al: Pharmaceutical carriers comprising sterol and saponin); or muramyl dipeptide, or cholera toxin B. Further accessory or immunostimulatory molecules useful in this connection include cytokines, such as interleukins, including but not limited to GM-CSF. IL-3. IL-2. IL- 12 and IL-7. Such adjuvants and/or other accessory substances, can be used separately or in combinations as desired. Pharmaceutical compositions such as vaccines provided hereby can e.g. be: emulsified in acceptable mineral or hydrocarbon oil. including but not limited to squalene, or biodegradable mineral oils as described in specifications WO 91/00106 and WO 91/00107 (SEPPIC: B Brancq et al: describing injectable multi-phase emulsions and emulsion vectors with continuous oily phase); or encapsulated, e.g. by encapsulation in biodegradable microparticles or liposomes or nonionic surfactant vesicles: for these techniques see respectively e.g. specifications WO 94/27718 (DT O'Hagan et al: microparticles containing entrapped antigens and their use in immunization) and WO 93/19781 (PCT/GB93/00716) (Proteus Molecular Design: J Alexander et al: Vaccines containing non-ionic surfactant vesicles with entrapped antigen). The polypeptides may be given for therapeutic or prophylactic purposes. Routes and procedures of administration include, but are not limitedto standard intramuscular, subcutaneous, intradermal, intravenous, oral or rectal routes and procedures. The amount of polypeptide administered can be chosen according to the formulation and the condition to be treated. Generally it is expected that doses will be between l-2000μg of the protein, preferably 10-300μg. e.g. 10-250μg. Optimal amounts can readily be determined in subjects. One or more doses of the vaccine may be administered at intervals (see e.g. Example 13). This regime can readily be optimised in subjects. Alternatively, a nucleic acid encoding said polypeptide can be incorporated into a suitable recombinant virus vector and introduced into a host organism, such as a human, in order that expression of the nucleic acid can give rise to the polypeptide in situ. Examples of viruses suitable for use as basis of recombinant virus vectors in this way are for example viruses as described in WO 92/05263 (Immunology Ltd: SC Inglis et al) and WO 92/16636 (Immunology Ltd: MEG Boursnell et al). Vaccines containing HPV-related polypeptides as described herein may activate broad HPV-specific immune responses. Such immune responses can include: specific antibody, including HPV6 and HPV11 neutralising antibodies, cell mediated immunity including HPV6 and HPV11 specific lyphoproliferative responses, delayed type hypersensitivity responses, cytotoxic T cells, and cytokine production. In the course of preparing a suitable vector for expression of the polypeptide of the invention, the applicants have arranged a technique which can enhance and achieve high level expression of a particular polypeptide in heterologous cells, in particular E. coli bacterial cells. Thus in a further aspect the invention provides a method for preparing a recombinant polypeptide which method comprises expressing in a bacterial cell a nucleic acid sequence which encodes the desired polypeptide but which has been mutated such that codons or groups of codons which cause premature termination of transcription or translation have been replaced by degenerate codons. In particular, applicants have found that in the T7 expression system of E. coli. the incidence of premature termination of transcription or translation can effectively be prevented or reduced by removal of at least one poly-T sequence such as [TTT]n where n is 2 or more, e.g. by replacing such a sequence with an acceptable alternative, e.g. a [TTC]n sequence which encodes the same amino acids, leading to higher yield of desired polypeptide. In bacterial expression systems such as the 17 system, recombinant polypeptides are found in insoluble aggregates or 'inclusion bodies' (IBs) within the cell. The applicants have arranged a improved technique for the recovery of said recombinant polypeptides. Thus in a further aspect of the invention there is provided a method of recovering a recombinant polypeptide from an inclusion body within a prokaryotic host cell, said method comprising subjecting a suspension comprising said inclusion bodies along with unwanted material e.g. broken-cell debris to cross-flow filtration and recovering recombinant polypeptide from inclusion bodies separated therefrom. This technique has the combined effect of separating inclusion bodies present in a cell homogenate from other cell debris and at the same time washing them, hence providing a useful degree of purification. In a preferred embodiment of this process, the separated inclusion bodies are subsequently solubiused in situ and the polypeptide is recovered from the solution. Examples of solubiusing reagents include urea and mixtures of urea and dithiothreitol or other sulphydryl reducing agent, e.g. at about 8M-10M concentration. It can be particularly convenient to carry out cross-flow filtration of a crude suspension resulting from disruption of host cells, containing a desired expressed polypeptide in the form of inclusion bodies, in two stages in the same filtration apparatus, a first stage in which the desired inclusion bodies are retained and washed in the filter retentate under non-solubiusing conditions, and a second stage in which said inclusion bodies are contacted with a solubiUsing liquid and collected in a filtrate in such liquid (e.g. in 8-10M urea optionally with sulphydryl reducer such as dithiothreitol). Removal of the solubiuser, and re-aggregation, can usefully follow. A particular example of a protein preparation of the invention would comprise a fusion protein comprising L2E7 proteins based on HPV-6. The protein is suitably expressed in E. coli cells, purified to homogeneity and then formulated with an adjuvant, for example alum. The preparation would be of use in treating genital warts and would be formulated so as to be in a form suitable for administration by parenteral injection to the recipient patient. The invention is further described below by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a nucleotide sequence for a vector expressing a HPV L2E7 fusion protein according to an embodiment of the invention; Figures la and lb show sequences of the vector that precede the start codon and follow the stop codon in the sequence of Figure 1; Figure 2 shows a corresponding aminoacid sequence; and Figure 3 illustrates a protein purification procedure for use according to an embodiment of the invention in purifying the L2E7 fusion protein of Figures 1 and 2. The applicants have isolated certain HPV genes, in particular the LI. L2 and E7 genes from the HPV-6 virus. The gene sequences have been used as described herein to construct gene fusions for expression of HPV-6 proteins to high levels in prokaryotic and eukaryotie systems. For this purpose, plasmid vectors for the expression of the above- described polypeptides such as HPV-6, L2 and E7 as a single fusion protein in E. coli have been constructed. Genes from the HPV-6 virus were amplified by Polymerase Chain Reaction (PCR) from a viral DNA sample prepared from a single clinical isolate of wart tissue infected with HPV-6. The genes isolated were used to construct a gene fusion cassette for the expression of HPV-6 derived protein in a heterologous system. A number of modifications to the gene construct were made in order to improve the production process. Particularly useful modifications were as follows: 1. Introduction of a leader sequence ("pelB leader") at the N terminus of the encoded protein sequence in order to enhance the expression of the protein in E. coli cells (but not to direct the expression to the periplasma). 2. Introduction of a sequence ("His-Tag") at the C terminus of the encoded protein sequence in order to allow purification of the protein by metal chelation chromatography. 3. Mutation of stretches of thyππdine residues to eradicate sequences implicated in the premature termination of transcription of the fusion gene. The mutation affects solely the DNA sequence of the gene construct, but does not effect the sequence of the encoded protein, since it involved the mutation of the degenerate third position in the codon. Constructs were assayed by transcription and translation of the protein open reading frames, in vitro. In the case of the HPV-6 L2E7 fusion protein, both a full-length protein (80 kD) and a truncated protein product (70 kD) were seen when using an HPV-6 L2E7 gene fusion construct expressed in vitro,, and this pattern was repeated in vivo. The appearance of a truncated form of the target protein was correlated with the presence in the HPV-6 L2 sequence of a long run of Thyidine (T) residues. A second T-rich region containing 6 thymidine residues was also identified. These regions were subjected to mutagenesis. in vitro, using obligonucleotides which altered the DNA sequence but not the amino acid sequence of the HPV-6 L2 protein. The mutated HPV-6 L2E7 gene fusion was subcloned into a plasmid expression vector driving expression of cloned sequences from a bacteriophage T7 promoter (pET expression system, Novagen). The plasmid construct obtained, designated pGW53, chosen for HPV-6 L2E7 expression, encoded an upstream leader sequence, pelB, the HPV- 6 L2E7 ORF's and a downstream sequence encoding 6 histidine residues (His Tag) "in frame" with the C-terminus of the HPV-6 fusion protein. Figures 1-2: The sequence data in Figures 1 and 2 indicate, without limitation, nucleotide and encoded aminoacid sequence of a preferred example of the L2E7 fusion protein produced by the techniques described herein, including an upstream leader and a downstream tag sequence. The leader sequence as well as the tag sequence (aa 591-601) can be omitted if desired. Figures la and lb show non-coding sequences in the preferred T7 expression vector, which precede the start codon and follow the stop codon in Figure 1. Figure 2 shows the sequence of the preferred fusion protein of L2 and E7. In the DNA sequence of 1827 base pairs, locations 7 to 1812 (inclusive of stop codon) encode a L2E7 fusion protein and tags. The sequence regions corresponding to L2 and E7 in Figures 1-2 have been found to incorporate a few differences by comparison with published separate aminoacid sequences of L2 and E7. The differences are as follows (with reference first to an aminoacid residue in the sequence numbering of Figures 1-2 herein, and then to the (different) aminoacid in the corresponding position of the published sequence): 105 Gly was Gin in the published sequence; 215 He was Val; 230 He was Val; 373 Glu was Asp; 381 Lys was Glu; 386 Asp was Gly; 422 lie was Leu; 544 Tyr was Phe. In addition a few 'silent' differences were found in polynucleotide sequence, i.e. differences not leading to any difference in translated aminoacid sequence. These are believed to be without significance for the present invention. Two silent mutations from TTTTTT to TTCTTC. produced for reasons as discussed in the present text, are located at aminoacid positions 83-4 and 483-4. A fusion protein expressed with precise correspondence with the published sequences, and incorporated in compositions as disclosed herein would be highly cross-reactive with the preferred L2E7 fusion protein shown in Figures 1 and 2 and would elicit equi alently similar or highly cross-reactive immune responses. Also functionally similar would be L2E7 fusion proteins derived from the sequences of other clinical isolates of HPV: such further isolates from the clinical environment could possibly have discrepancies of sequence as compared with the sequences given here, but these are expected not to be significant to the performance of the invention. If desired, any discrepancies found in a particular clinical isolate could readily be eliminated e.g. by site-specific mutagenesis of the corresponding cloning vectors prepared therefrom. The gene construct obtained as described herein was inserted in an expression system optimised for high level expression of heterologous proteins in E. coli cells. This expression system was based on the growth of E. coli cells to a significant density followed by induction of the T7 polymerase within the cells, which leads to the high level transcription of the gene construct. The protein product which was then expressed and accumulated within inclusion bodies inside the E. coli cells. Following harvest of the cells, the protein was purified away from bacterial proteins, and prepared as a solubiused protein extract. This protein extract comprises a high molecular mass aggregate of protein molecules, which is soluble in an aqueous solution. The purified protein thus obtained can be used to form the basis of a therapeutic antigen product in particular for the treatment of genital warts. The following Examples and the sequence data given herein illustrate the invention but without intent to limit the scope of the present disclosure. EXAMPLE 1: Amplification and Cloning of HPV-6 Genes Viral DNA of the HPV type in the infected tissue was originally deduced by PCR using a method based on a modification of the method of Snijders et al . . 1990, Journal of General Virology, 71: pp 173-191 with standard primers for HPV-6. HPV-6 LI, L2 and E7 genes were amplified by Polymerase Chain Reaction (PCR) from a viral DNA sample prepared from a single clinical isolate (H26) selected as the basis for development of the therapeutic entity on the basis of the ease of isolation of genes. The identity of the clinical isolate is not important and any ordinary clinical isolate of HPV-6 would be practically equivalent even though not identical. Initial PCR was performed using Taq DNA polymerase. Oligonucleotide primers used in the PCR reactions encoded 24 nucleotides of exact homology to the gene sequence of interest as well as additional nucleotides where these encoded restriction enzyme sites or were added to maintain the reading frame between eventual gene fusions or to introduce stop codons in the final expression constructs. An example of the oligonucleotide used is as follows: JPC08 CAGTGTCGACGGTCπCGGTGCGCAGATGGGACA SEQ ID NO 1 Non-coding strand oligonucleotide primer for amplification of HPV 7 E7 gene and Sail site for directional cloning. The single PCR products from the amplification reactions of the LI. L2 and E7 genes were used as template DNA in sequencing reactions to generate a consensus sequence for each of the three genes. The consensus DNA sequence was assumed to be an accurate reflection of the actual DNA sequences of the genes in the viral DNA extracts because it was a sequence generated from many individual template molecules. The HPV-6 L2 gene was amplified by PCR from HPV-6 viral DNA as a single product of approximately 1400 bp. The product was purified from agarose and used as a template for DNA sequence analysis, and a consensus sequence for the amplified L2 gene was generated using oligonucleotde primers. The purified L2 product was directly subcloned into the vector pGEM-T to create plasmid pGW12. The full DNA sequence of the subcloned L2 gene was generated from the pGW12 template DNA using the same oligonucleotide primers as for the consensus sequence. The DNA sequence of the cloned L2 gene was shown to be identical to that of the consensus. The HPV-6 E7 gene was amplified by PCR from HPV-6 viral DNA as a single product of approximately 300 bp. This was purified from agarose and used as template for DNA sequence analysis, and a consensus sequence for the amplified gene was generated using oligonucleotide primers. The purified E7 PCR product was directly subcloned into the vector pGEM-T to create plasmid pGW04. The full DNA sequence of the subcloned E7 gene was generated from the pGW04 template using the same oligonucleotide primers as for the consensus sequence. The sequence of the cloned E7 gene was shown to be identical to that of the consensus. The HPV-6 LI gene was amplified by PCR from HPV-6 viral DNA as a single product of approximately 1500 bp. This was purified from agarose and used as a template for DNA sequence analysis, and a consensus sequence for the amplified gene was generated using oligonucleotide primers. The purified LI PCR product was directly subcloned into the vector pGEM-T to create plasmid pGW-A. The full DNA sequence of the subcloned LI gene was generated from the pGW-A template using the same oligonucleotide primers as for the consensus sequence. The sequence of the cloned E7 gene was shown to be identical to that of the consensus. PCR products were purified from agarose gels by binding to silica matrix and ligated to pGEM-T vector DNA. The products of these ligation reactions were used to transform E. coli DH5a cells. Recombinant clones were isolated and further screened for the correct HPV-6 gene inserts using a method based on PCR. The DNA sequences of the cloned HPV-6 L2 and E7 genes were obtained and compared with the consensus sequence generated directly from the original PCR products. Clones whose sequences agreed with the consensus were used for the construction of recombinant protein expression cassettes. Example 2: Comparison of HPV-6 Sequences with EMBL Database The consensus sequence was compared to that of closely related HPV types including HPV-11. HPV-16 and HPV-18 as well as the published sequence of HPV-6b from the European Molecular Biology Laboratory (EMBL) DNA database to ensure that the genes amplified were from an HPV-6 type virus. Comparisons were made with the help of Lasergene Navigator software (DNAStarlnc.) using the EditSeq, SeqMan, Megalign and Protean programs. Comparisons wre made at the DNA level and from the predicted amino acid sequences of the three genes. This analysis indicated that the amplified L2, LI and E7 genes were derived from an HPV-6 type virus. The results demonstrate that although the gene sequence is highly conserved, a number of changes from the predicted sequence were observed. Accordingly, it is considered that suitable constructs for use in this invention can be made on the basis of DNA from wild-type clinical HPV isolates. EXAMPLE 3: Construction of Expression Cassette The individual genes for L2 and E7 were assembled to generate the fusion molecule in the following manner: Both the L2 and E7 genes were cloned by PCR amplification to introduce novel N- and C-terminal restriction enzyme sites, whilst maintaining the integrity of the protein sequence. These gene sequences were then ligated together into a cloning vector, using standard recombinant DNA techniques, to create a L2E7 fusion gene, so that the open reading frames of the two sequences were maintained. The L2E7 fusion gene was constructed as follows. The HPV-6 L2 gene was initially generated as a l.lkb PCR fragment flanked by BaHI and Nco I sites. This PCR fragment was sub-cloned into the pGEM-T cloning vector. Clones possessing the required insert were digested with the two enzymes in order to liberate the L2 gene, which was then purified by separation on an agarose gel followed by extraction onto glass milk. Similarly the HPV-6 E7 gene was generated as a 300 bp Nco I - Sal I fragment, sub-cloned into pGEM-T. These two gene fragments were ligated together to produce a 1.4kb BamH I - Sal I DNA fragment which encoded an L2E7 fusion protein. The resulting BamH I - Sal I DNA fragment was then ligated into a derivative of pETlδb. a non-expressing cloning vector possessing kanamycin resistance. The resulting construct was named pGW48. The L2E7 gene fusion was subsequently transferred to an expressing pET vector in order to analyse the expression of the protein in E. coli. Following analysis of the expression of the fusion gene in E. coli, mutation of the gene was performed as described to eliminate stretches of T residues, which were believed to be causing permature termination of transcription. The L2E7 fusion gene was then modified by PCR to generate BamH I and Not I termini capable of allowing the insertion of the gene cassette into an expression vector containing an in frame pelB leader sequence at the 5' end and an in frame His Tag at the 3' end. The PCR fragment was cloned through the pGEM-T vector, and finally transferred to a pET vector derived from pET22b. This final construct was named pGW53. Following assembly, the fusion construct was transferred to a series of prokaryotic expression vectors known as pET vectors. These well known vectors comprise strong bacteriophage T7 transcription and translation signals. Expression may then be induced by providing a source of T7 RNA polymerase in the host cell, under the control of the inducible lacUVδ promoter. Addition of the inducer. IPTG, then results in conversion of the cell's resources into target gene expression. Potentially the desired product can then comprise more than 50* of the total cell protein. Moreover, because the system is inducible, it can maintain the target gene sequence in a transcriptionally silent state prior to induction, allowing the expression of gene sequences which are potentially toxic to the host cell. Addition of IPTG to a rapidly growing culture of cells transformed with the pET vector containing the target gene therefore leads to induction of the polymerase enzyme and concomitant expression of the cloned gene. The protein product may either be secreted, or in the case of these HPV gene products directed into inclusion bodies. The cloning step was performed by the introduction of a Bgl II restriction enzyme site at each end of the gene fragment by PCR mutagenesis. using the following oligonucleotide: NRW170 GTCGACAGATCTGGCACATAGTAGGGCCCGA SEQ ID NO 2 (Oligonucleotide for PCR cloning of HPV 6 L2E7 into pET vector. Introduction of Bgl11 site into N-terminus of HPV 6 L2. No methionine codon is required for fusion into pET leader sequence (pelB). DNA sequencing followed. The L2E7 fusion gene was then ligated into the following vectors: pETllb. pET12b. pET16b and pET22b. which differ in the nature of their N-terminal and C-terminal sequences. The recombinant plasmids were then used to transform an appropriate host cell, HMS174, which contains the gene for 17 polymerase. Other host cells that differ in their stringency of suppressing basal expression are available and have been successfully used in this method. EXAMPLE 4: Expression of L2E7 Construct in E.coli Individual bacterial colonies were picked from the transformation plate and used to inoculate 2 ml aliquots of 2YT medium. These aliquots were grown up for 2 hours, then used to inoculate a 12 ml culture of warmed medium, adjusting the volume of inoculum to provide a consistent number of bacteria as determined by measurement of optical density at 600 nm. These cultures were grown up until the optical density reached 0.6. at which point the cultures were split into two 5.0 ml aliquots. IPTG at the recommended concentration of 1.0 mM was added to one culture, and both cultures were incubated under identical conditions for 3 hours. At the end of this period, the bacteria were transferred to ice and the optical density was measured. The bacterial cultures were harvested by centrifugation in a 15 ml Falcon tube for 10 minutes at 4.000 rpm. The supernatant was removed and the bacteria resuspended in TE at a final volume of 0.5 ml. Analysis by SDS-PAGE was carried out as follows: The sample was then added to an equal volume of reducing electrophoresis sample buffer, and heated at 100°C for 10 minutes. 50μl of sample was then loaded on a 5 - 15 * polyacrylamide gel. and electrophoresed at 10mA for 12 hours. The protein bands were visualised by staining in Coomassie Brilliant Blue in 10* acetic acid. 10* methanol for 30 minutes, followed by destaining. A major protein band of molecular weight 90kD. corresponding to the full-length L2E7 protein, could be detected by staining the gel in Coomassie. in addition to at least one other band, of 80kD. corresponding to a product of either proteolytic degradation or premature termination of transcription or translation. Following modification of the gene sequence by site-directed mutagenesis as described e.g. in Example 6. the 80kD band was no longer detectable following staining by Coomassie Blue, suggesting that the hypothesis of premature termination of transcription or translocation was correct. Comparison of the amount of protein present on the gel with a known standard allowed an estimate of the level of expression within the bacteria. The levels appeared to be consistently within the range 10- 30mg/L. For more detailed characterisation of the expressed protein products, the gel was subjected to Western transfer, followed by probing with anti-L2 antisera generated by immunisation of sheep with E. coli- derived L2 fusion protein. Western blotting allowed the visulisation of a large number of bands of molecular weight below that of the full-length species, presumably all of which are again generated by proteolytic degradation or premature termination of transcription or translation. The initial SDS-PAGE analyses demonstrated the presence of a Coomassie-staining protein band with a size corresponding to that expected for the full-length L2E7 gene product. In addition, there were a number of other bands visible, which may correspond to either proteolytic fragments of L2E7 or to premature termination artifacts. This was investigated by Western blotting, using either anti-L2 or anti-E7 anti-sera. The results confirmed that the major product was L2E7. and suggested that the minor bands were lacking C-terminal regions. Further characterisation was performed by protein sequencing, which confirmed that the two major bands contained intact N-terminal sequences. including an uncleaved pelB leader sequence. EXAMPLE 5: In Vitro Transcription and Translation In order to characterise the products further the genes were analysed in a series of coupled in vitro transcription and translation experiments. This system uses an introduced T7 polymerase enzyme to generate an mRNA transcript from the cloned gene in the expression vector, which is then translated in vitro to generate a synthetic protein product. By incorporation of a radio-label into the protein product, its synthesis can be monitored using SDS-PAGE analysis. In vitro transcription and translation revealed a similar pattern of protein synthesis to that found in the E.coli heterologous system. The L2E7 fusion protein consisted of two major bands of 80 kD and 70 kD. while the LI product contained two major bands at 30 and 32 kD in addition to the presumed full length product of 60 kD. DNA sequence analysis revealed that in both the sequences for LI and L2 there were stretches of poly-T consisting of between seven and nine T residues, which appeared to coincide with the positions of prematurely terminated fragments of both the LI and L2E7 molecules. It was suggested that these regions caused premature termination of either transcription or translation, most probably the former. This belief was supported by the observation of a poly-T tract in the terminator sequence for the T7 polymerase. EXAMPLE 6: Mutagenesis of DNA Sequences In order to eliminate potential termination artifacts, it was decided to mutate two stretches of T-rich regions. The codon TTT encodes the amino acid phenylalanine (Phe). for which an alternative codon (TTC) exists. It was therefore decided to replace the TTT codon by mutation to generate the sequence TTC. thereby maintaining the reading frame and the natural protein sequence. This was chosen so as to leave unaffected, in this example, the properties of the product, by leaving unchanged the protein sequence of the immunotherapeutic reagent. However, the mutation should increase yield of expressed protein product by minimising the level of artifacts due to premature ending of transcription or translation. Mutation was performed by the PCR technique of gene overlap extension using oligonucleotides JCT61, JPC81 defined below, in which the natural DNA sequence is replaced by the mutant sequence in the relevant area. The following oligonucleotides were employed in the mutagenesis: JCT61 CCAACCCTCCGAAGAACACCCCCAAAC SEQ ID NO 3 (Non-coding strand oligonucleotide primer for mutagenesis of HPV 6 L2 at DNA sequence positions 159 and 162 (MINI to TTCTTO). JPC81 (^TCAAATAT[AAAATGGGGAAGπTGGGGGTGπcπCGGAGGG SEQ ID NO 4: (Coding strand oligonucleotide primer for HPV 6 L2 incorporating a mutagenes s of the sequence TTTTTT to TTCTTC at position 159 and 162. The oligonucleotide encodes an Sspl site AATATT. A second site was also mutated by site-directed mutagenesis using the following oligonucleotide: JPC90 CGTAπCCCπAπCTTCTCAGATGTGGCGGC SEQ ID No 5 (Coding strand oligonucleotide primer for HPV 6 L2 incorporating in vitro mutagenesis of the sequence at position 1359 and 1362) The final gene product was then inserted in order to create a final expression vector designed as pGW53 and analysed by in vitro and in vivo expression. EXAMPLE 7: Expression of Mutated Sequences Following mutagenesis of the L2E7 construct the effect was monitored by in vitro and in vivo expression followed by SDS-PAGE analysis, and Western blot analysis where appropriate. Initial experiments were performed to analyse the in vitro transcription and translation products of both mutated L2E7 and LI genes. The in vivo expression of the mutated L2E7 and the LI gene were examined as before. Individual colonies were selected and grown up to an optical density of 0.6, at which point IPTG was used to induce half the culture; three hours post-induction the cells were harvested and aliquots prepared for analysis by SDS-PAGE. The expression cassette was found to be translated satisfactorily. Both in vitro and in vivo experiments confirmed that mutagenesis of the poly-T-regions leads to a diminution in the yield of prematurely terminated fragments of both L2E7 and LI. and an enhancement of the yield of full-length product. The net result was a diminution in the yield of the 70 kD product from expression of L2E7 and a loss of the 30-32 kD fragments from expression of LI. It is therefore clear that mutation of the poly-T regions leads to an enhanced expression of the full-length species in this expression system. This result has not previously been described for a 17 polymerase-based expression system, and may have wide applications in other areas of expression work. EXAMPLE 8: Protein production and purification process Dedicated master and working cell banks of E.coli HMS174 cells containing the pGW53 plasmid and derived as described herein are laid down and stored at -80°C. For production an ampoule from the working cell bank is thawed and cultured in 2YT medium to an appropriate volume for fermenter inoculation. Fermentation scale can range from 1.3L to 50L and further scale up may be envisaged. Cells were cultured until cell density reaches a preset point (typically 0.3g per L). At this point the culture is induced with IPTG after which the cells are harvested some 2 hours later. Yields of 24-50 mg L2E7 per g dry wt cells have been obtained on occasions using standard fermentation conditions. Cell disruption and protein purification are then carried out as indicated below and in Figure 3 of the accompanying drawings. Cell breakage is performed to release insoluble L2E7 stored as intracellular inclusion bodies (IB's). This is done using a hydraulic press which causes cell lysis by passing the cells through a narrow aperture under a pressure of 5000 psi. Lysis of approx 95* efficiency can be achieved by standard methods and is virtually complete after 3 passes. E.coli cell lysate containing insoluble L2E7 in the form of inclusion bodies is centrifuged. The sedimented pellet, containing inclusion bodies and cell debris was resuspended in a buffer containing Triton X-100 detergent. In such tangential cross-flow filtration, which is a per-se standard technique carried out in commercially-obtainable "Filtron" (TM) apparatus, a flow of liquid or suspension to be ultrafiltered or filtered is passed across an ultrafiltration or filtration membrane under a transmembrane pressure sufficient to drive filtrate through the membrane. In the present embodiment, tangential cross-flow filtration is used to concentrate the inclusion body suspension against a 0.16|L/m filter. Inclusion bodies are concentrated in the retentate and contaminants are removed in the filtrate. The concentrate is then diluted to reduce the Triton X-100 concentration, and concentrated again. Urea and DTT (dithiothreitol) are then added to a final concentration of 8M. and lOmM respectively, which solubilises the L2E7. Denatured, reduced L2E7 protein then passes through the 0.16μ filter into further filtrate where it is collected. The L2E7 in denatured, reduced, filtered form is then purified using ion exchange chromatography. 8.0M urea solubiused L2E7 protein is first purified by anion exchange chromatography using conditions indicated in Figure 3. Typically l-2g of the product are purified on a 250-350mL column. Urea-solubiused L2E7 is loaded onto the anion exchange resin, and weakly bound contaminants removed by elution with 4 column volumes of Urea DTT Tris buffer (pH 8.0) containing 50mM NaCl. Finally. L2E7 protein is eluted from the column using a maximum of 5 column volumes of urea DTT Tris buffer (pH 8.0) containing 350mM salt. Flow rate throughout the step is about 5ml cm ' Vminute. The anion exchange chromatography peak product is loaded onto a cation exchanger. Typically l-2g of product are purified on about 250ml of column material. Product is loaded onto the resin at 2.5ml in cm '1 which is then washed with 4 column volumes of 8.0M urea DTT phosphate (pH 6.2) containing 210mM sodium chloride followed by L2E7 peak elution with wash buffer containing 500mM sodium chloride into approximately 1.5 column volumes. The cation exchanger peak product was loaded onto a size exclusion matrix (as indicated in Figure 3) using a running buffer of 25mM Tris pH 8.0 containing 75mM sodium chloride. Typically 100ml containing 200-400mg of L2E7 is loaded (at 0.2ml cm ' Vmin) onto 6.5L of matrix with a bed height of 100cm. The peak corresponding to the major product and minor N terminal clipped fragments was peak cut at an approximate elution volume of 0.46 column volumes. The size exclusion chromatography peak at this stage of the process is dilute, at an approximate concentration of 0.25-0.5mg ml "1 . The product (1-2L) is concentrated by loading onto a small volume of anion exchange matrix (- 75ml) at a flow rate of 0.5ml cm '2 /min. The product is eluted using urea DTT phosphate buffer pH 8.0 containing 1.0M sodium chloride. The peak volume is 1-2 column volumes. The concentrated Q anion cartridge peak was buffer exchanged into a final formulation buffer at 48.9mM Tris pH 8.0 containing 5mM DTT. The column matrix is Sepharose medium G25 with a volume of -2.5 litres. A 'slug' of buffer containing 8M urea equal to the product volume is preloaded onto the column. The product is then loaded at a -100-150 mis load. The formulated buffer exchanged product peak is typically eluted at 0.5 column volumes using a flow rate of 0.06ml cm ' Vmin. The final product bulk is then -80°C stored. A solution or dispersion of the product L2E7 protein obtainable in this way is in an aggregated (reaggregated) form, which can nevertheless pass through a sterilising filter, e.g. a filter of gauge in the range 0.16-0.22 micron, e.g. 0.2 micron. EXAMPLE 9: Cloning and Expression of HPV-6 Genes in Yeast - Saccharomyces cerevisiae In order to examine the ability of other heterologous systems to express high levels of the HPV-6 genes, the genes for the L2E7 fusion construct and for LI have been cloned into a generally available S. cerevisiae autonomously replicating expression vector. This vector, based on elements of the 2μ plasmid. allows expression of heterologous in-frames genes driven by the GAL7 promoter. The vector also contains the LEU-2d marker, for selection of increased copy numbers in yeast cells, and the kana ycin resistance gene enabling selection in Escherichia coli. The Saccharomyces host strain used for expression was S150-2B (genotype: a. leu2-3. 112. Δ his3. trpl-289. ura3-52). Yeast were transformed with the HPV-6L2-E7 construct and grown up in medium containing 2* glucose as the sole carbon source, in order to repress transcription from the GAL7 promoter. Gene expression was induced in the presence of 2* galactose in the medium, as the sole carbon source. Cell extracts were produced by disruption of the cell membranes in the presence of glass beads. The extraction buffer was Tris-based and contained a broad range protease inhibitors; PMSF. pepstatin, leupeptin, antipain and chymostatin. Cell extracts were processed by SDS PAGE and the resolved proteins were Western blotted using polyclonal antisera raised in sheep against HPV-6 L2 and HPV-6 E7. Yields of HPV-6 L2-E7 fusion protein produced from Saccharomyces cerevisiae in this way have been estimated to be lOμg per litre of culture in certain embodiments. EXAMPLE 10 Cloning and Expression of HPV-6 Genes in Yeast - Pichia pastoris An L2E7 fusion molecule (see Example 3 above) can be created as a BamH I - Not I DNA fragment, and cloned into a suitable expression vector such as a Pichia expression vector pPIC3K (obtained under license from Phillips Petroleum). The gene can be placed under the control of the Alcohol Oxidase promoter. AOXI. in order to allow high level expression of the fusion protein. Following linearisation of the expression construct, the DNA can be transfected into yeast cells by spheroplast fusion. Transformants can be selected by their ability to grow in minimal media in the absence of histidine, unlike untransfected cells which retain the requirement for histidine in the growth medium. A second round of screening on the basis of slow growth on a methanol substrate can be performed to select for those clones containing an L2E7 gene integrated at the correct locus. EXAMPLE 11: Cloning and Expression of HPV-6 Genes in Baculovirus In order to investigate expression of the L2E7 fusion gene in baculovirus. two constructs were generated, each coding for an HPV-6 L2E7 fusion protein, either with or without a HisTag tail. Neither construct contained a leader sequence, as on this occasion it was wished to examine the level of intracellular expression. The two constructs were cloned by PCR amplification, which introduced terminal Bgl II sites, into the pGEM-T vector. The L2E7 genes were then isolated as Bgl II - Bgl II fragments and subcloned into the BamHI cloning site of the transfer vector pBacPAKl (Clontech). The orientation of the inserts were then determined by PCR analysis, and DNA was prepared from clones containing the correct orientation. DNA from the pBacPAKl transfer vector containing either L2E7 construct was transfected. using the standard lipofectin mediated procedure, into Spodoptera frugiperda (type Sf9) cells along with Bsu36 1 cut PBacPAKl viral DNA (Clontech). In vivo homologous recombination between the plasmid and viral DNA then occurs to rescue the viral DNA, and in the process the target gene is transferred to the viral genome. The progeny viruses generated in the co-transfection supernatant were then amplified by infecting fresh cells. A fraction of the infected cells were harvested and genomic DNA was prepared. PCR amplification using the above primers indicated that recombinant virus was present in the cells. The passage one virus stock was then used to further infect cells at a high multiplicity of infection to characterise gene expression by determining the time course of protein production: Confluent Sf9 cells in 6 well dishes were infected at a high multiplicity of infection, cells and supernatant were harvested 24 hrs, 48 hrs and 72 hrs post infection. The results of the experiment were observed by SDS-PAGE analysis and Western blotting in order to detect synthesis of the protein. Recombinant protein was not observed on a Coomassie stained SDS/PAGE gel but was detected at low levels by Western blotting. As expected the protein was not secreted due to the absence of a leader sequence. The amplified genes were sequenced in full and subcloned into plasmid vectors. The gene sequences have been used to contruct gene fusions for expression of HPV-6 proteins to high levels in prokaryotic and eukaryotie systems. EXAMPLE 12: Immunogenicity of L2E7 in mice The immunogenicity of an aggregate of L2E7 has been examined in mice. It was found that when an aggregate of L2E7 adsorbed onto aluminium hydroxide ('alum') was injected into B6CBA mice L2E7 specific immunity was elicited. This L2E7 specific immunity included serum antibodies, of immunoglobulin G (IgG) class and immunoglobulin Gl subclass (IgGl). L2E7 specific delayed type hypersensitivity responses and lymphoproliferative responses in vitro were also found. The immunogenicity of L2E7 adsorbed onto alum was examined in B6CBA mice. Mice were given two subcutaneous injections of 180μg L2E7/Alum 14 days apart. Serum was collected 7. 14 and 56 days after the 2nd injection of L2E7/Alum. Serum anti-L2E7 antibody levels were determined in an L2E7 specific enzyme linked imunosorbent assay. Serum anti-L2E7 responses peaked 14 days after the 2nd injection of L2E7 (mid point titre 4.572 loglO) and persisted to 56 days (mid point titre 4.127 loglO). In vivo delayed type hypersensitivity responses (DTH) to L2E7 were measured in a second group of mice immunized as above. 7 days after their 2nd injection with L2E7/Alum mice were challenged with l.βμg L2E7 in their right ear and an equal volume of buffer in their left ear. L2E7 specific increase in ear thickness were measured with an engineers micrometer 24, 48 & 72 hours after the ear challenge. Mice immunized with L2E7/Alum made in-vivo DTH responses. In-vitro lymphoproliferative responses were measured with draining lymph node cells (axillary lymph node cells) taken from a third group of mice, seven days after their second injection with L2E7 / alum product (as above). A single lymph node cell suspension was made and 2xl0"6 viable lymphocytes/ml were plated out in medium (Iscove's modified Dulbecco's medium) supplemented with 1* normal mouse serum, glutamine. beta- mercaptoethanol and antibiotics. L2E7 was titrated into the cultures (from 91 micro-g/ml) and cell proliferation was assessed by incorporation of tritiated thymidine for the final 24 hours of the 72 hour culture. Lymph node cells from mice were immunized with L2E7/Alum proliferated in vitro in response to L2E7 (42000 cpm. stimulation index 50). EXAMPLE 13: Immune responses in humans: A vaccine as described above, an aluminium hydroxide gel complex of L2E7 prepared equivalently as indicated above, has been shown to induce an appropriate dose-related immune response in healthy male volunteers. Cells from all of 36 vaccinated volunteers showed a L2E7-specific in-vitro lymphoproliferative response (CD4+ T cells) indicative of immune response to the product. The volunteers had been given the product by intramuscular injection in doses of 3, 30 or 300 μg. an initial dose at day 0 and repeated doses on day 7 and day 28 (accelerated schedule). (An alternative, slower, schedule for vaccination on days 0, 28 and 56 was also tried, and found less preferable.) Lymphoproliferative responses were seen from day 7 at dose levels including the lowest dose, 3 μg. L2E7 specific antibody response was also shown in 29 of 32 assessable samples from the volunteers (the three non-responders in the antibody test had been given the lowest dose). Increased in-vitro production of IL-5. consistent with the antibody production, was also seen. The two higher doses elicited T-cell proliferation sooner than the lowest dose. The highest dose, 300μg. stimulated more IFN-gamma production than the lower doses. The observations made, of rapid T-cell proliferation and associated production of IFN-gamma. are appropriately consistent with the intended use of the product as a therapeutic vaccine for genital warts. Regression of long-established human plantar warts, considered to be due to human papillomavirus, has been seen in a recipient of the product at a dose of 3 micro-g, whose cells were among those showing lymphoproliferative response. Regression was observable at day 7 and disappearance of warts occurred by day 14. The invention described and the disclosure made herein are susceptible to many modifications and variations as will be apparent to. and readily performable by, the skilled reader in the light of this disclosure; and the disclosure extends to adaptations, combinations and subcombinations of the features mentioned and/or described herein. Documents cited herein are hereby incorporated by reference.

Claims: CLAIMS 1: A polypeptide or polypeptide composition comprising an antigenie determinant of a papillomavirus protein, in an aggregated form which when in solution or dispersion can pass through a sterilisation filter, or in an amorphous aggregated form. 2: A polypeptide or polypeptide composition according to claim 1, comprising antigenie determinants of at least two papillomavirus proteins, e.g. L2 and another, or E7 and another. 3: A polypeptide or polypeptide composition according to claim 1 or 2, comprising at least one antigenie determinant of papillomavirus L2 protein and at least one antigenie determinant of papillomavirus El. E2. E4. E6 or E7 protein. 4: A polypeptide or polypeptide composition according to claim 1, 2. or 3, comprising antigenie determinants of L2 and E7 proteins of HPV. e.g. comprising a sequence fragment of at least 50* of the full sequence of each of L2 protein and E7 protein, e.g. comprising substantially the full sequence of L2 and of E7: optionally further including a sequence of LI protein. 5: A polypeptide or polypeptide composition according to any preceding claim, wherein the antigenic determinant is of a papillomavirus protein of HPV type 6, 11, 16, 18, or of a non-human animal papillomavirus. 6: A polypeptide or polypeptide composition according to any preceding claim, in the form of a denatured, reduced, and reaggregated preparation. 7: A polypeptide or polypeptide composition according to any preceding claim, obtainable by denaturation, or denaturation with reduction, and subsequent reaggregation of a polypeptide expressed in the form of inclusion bodies in a recombinant host cell. 8: A polypeptide or polypeptide composition according to claim 7, which has a molecular mass per aggregate in the range about 100,000 to about 10.000.000 dalton. 9: A polypeptide or polypeptide composition according to claim 7, which comprises aggregate particles with diameters on electron microscopy in the range about 4 to 50 nm, e.g. about 10-15 nm. 10: A polypeptide or polypeptide composition according to claim 7, which comprises aggregate particles having 2-200. e.g. 5-50, polypeptide chains per aggregate. 11: A polypeptide or polypeptide composition comprising a fusion polypeptide comprising (a) at least an antigenic determinant of a papillomavirus L2 protein, and (b) at least an antigenic determinant selected from El. E2, E4. E5. E6 and E7 papillomavirus proteins and L2 papillomavirus proteins of different papillomavirus type than in (a); or comprising antigenic determinants from at least two papillomavirus proteins selected from El. E2, E4. E5. E6 and E7 papillomavirus proteins e.g. where the said proteins are from different papillomavirus types. 12: A polypeptide or polypeptide composition according to claim 11, comprising a fusion polypeptide comprising an antigenic determinant of L2 protein and an antigenic determinant from at least one of El, E2, E4. E6 and E7 proteins. 13: An immunogenic composition suitable for administration by injection, comprising a polypeptide according to any preceding claim together with an immunological adjuvant. 14: An immunogenic composition according to claim 13. wherein the adjuvant comprises alumimium hydroxide and/or monophosphoryl lipid A. 15: Use of a polypeptide or immunogenic composition according to any preceding claim as an immunogen, e.g. as a vaccine for prophylaxis or therapy of a papi11omavirus-associated condition.

Inventors: CARMICHAEL JEREMY PADDON, CONNOR STEPHEN EDWARD, THOMPSON HENRY STEPHEN GRAMMER, WHITTLE NIGEL RICHARD, WILSON MARK JONATHAN, CARMICHAEL, JEREMY, PADDON, CONNOR, STEPHEN, EDWARD, THOMPSON, HENRY, STEPHEN, GRAMMER, WHITTLE, NIGEL, RICHARD, WILSON, MARK, JONATHAN
Applicants: CANTAB PHARMA RES, CARMICHAEL JEREMY PADDON, CONNOR STEPHEN EDWARD, THOMPSON HENRY STEPHEN GRAMMER, WHITTLE NIGEL RICHARD, WILSON MARK JONATHAN, CANTAB PHARMACEUTICALS RESEARCH LIMITED, CARMICHAEL, JEREMY, PADDON, CONNOR, STEPHEN, EDWARD, THOMPSON, HENRY, STEPHEN, GRAMMER, WHITTLE, NIGEL, RICHARD, WILSON, MARK, JONATHAN
Application year: 1996
Main classification: C12N15
IPC codes: A61K39, A61P31, C07K14, C07K19, C12N15, C12P21, C12R1