PAPILLOMAVIRUS VACCINES

Abstract: Recombinant expression vectors encoding the L1 and L2 proteins of papillomavirus, methods of making and using the recombinant proteins and purified virus-like particles comprised of the recombinant proteins are provided.

Description: TITLE OF THE INVENTION PAPILLOMAVIRUS VACCINES CROSS-RELATED TO OTHER APPLICATIONS This is a continuation-in-part of U. S. S. N. 08/242,794, filed May 16, 1994, now pending. HELD OF THE INVENTION Recombinant expression vectors encoding the LI and L2 proteins of papillomavirus, methods of making the recombinant proteins and methods of using the recombinant proteins are provided. BACKGROUND OF THE INVENTION Papillomavirus infections occur in a variety of animals, including humans, sheep, dogs, cats, rabbits, monkeys, snakes and cows. Papillomaviruses infect epithelial cells, generally inducing benign epithelial or fibroepithelial tumors at the site of infection. Papillomaviruses are species specific infective agents; a human papillomavirus cannot infect a nonhuman animal. Papillomaviruses may be classified into distinct groups based on the host that they infect. Human papillomaviruses (HPV) are further classified into more than 60 types based on DNA sequence homology (for a review, see Papillomaviruses and Human Cancer, H. Pfister (ed.), CRC Press, Inc., 1990). Papillomavirus types appear to be type-specific immunogens in that a neutralizing immunity to infection to one type of papillomavirus does not confer immunity against another type of papillomavirus. In humans, different HPV types cause distinct diseases. HPV types 1 , 2, 3, 4, 7, 10 and 26-29 cause benign warts in both normal and immunocompromised individuals. HPV types 5, 8, 9, 12, 14, 15, 17, 19-25, 36 and 46-50 cause flat lesions in immunocompromised individuals. HPV types 6, 1 1, 34, 39, 41-44 and 51-55 cause nonmalignant condylomata of the genital or respiratory mucosa. HPV types 16 and 18 cause epithelial dysplasia of the genital mucosa and are associated with the majority of in situ and invasive carcinomas of the cervix, vagina, vulva and anal canal. HPV6 and HPVl 1 are the causative agents for more than 90% of all condyloma (genital warts) and laryngeal papillomas. The most abundant subtype of HPV type 6 is HPV6a. Immunological studies in animals have shown that the production of neutralizing antibodies to papillomavirus antigens prevents infection with the homologous virus. The development of effective papillomavirus vaccines has been slowed by difficulties associated with the cultivation of papillomaviruses in vitro. The development of an effective HPV vaccine has been particularly slowed by the absence of a suitable animal model. Neutralization of papillomavirus by antibodies appears to be type-specific and dependent upon conformational epitopes on the surface of the virus. Papillomaviruses are small (50-60 run), nonenveloped, icosahedral DNA viruses that encode for up to eight early and two late genes. The open reading frames (ORFs) of the virus genomes are designated El to E7 and LI and L2, where "E" denotes early and "L" denotes late. LI and L2 code for virus capsid proteins. The early (E) genes are associated with functions such as viral replication and cellular transformation. The LI protein is the major capsid protein and has a molecular weight of 55-60 kDa. L2 protein is a minor capsid protein which has a predicted molecular weight of 55-60 kDa and an apparent molecular weight of 75-100 kDa as determined by polyacrylamide gel electrophoresis. Immunologic data suggest that most of the L2 protein is internal to the LI protein. The L2 proteins are highly conserved among different papillomaviruses, especially the 10 basic amino acids at the C- terminus. The LI ORF is highly conserved among different papillomaviruses. The LI and L2 genes have been used to generate vaccines for the prevention and treatment of papillomavirus infections in animals. Zhou et al., (1991; 1992) cloned HPV type 16 LI and L2 genes into a vaccinia virus vector and infected CV-1 mammalian cells with the recombinant vector to produce virus-like particles (VLP). Bacterially-derived recombinant bovine papillomavirus LI and L2 have been generated. Neutralizing sera to the recombinant bacterial proteins cross-reacted with native virus at low levels, presumably due to differences in the conformations of the native and bacterially-derived proteins. Recombinant baculo viruses expressing HPV6 LI, HPVl 1 L1, HPV16 L1, HPV18 L1, HPV31 LI or HPV 16 L2 ORFs have been used to infect insect SF9 cells and produce LI and L2 proteins. Western blot analyses showed that the baculovirus-derived LI and L2 proteins reacted with antibody to HPV 16. The baculovirus derived LI forms VLPs. Carter et al. , ( 1991 ) demonstrated the production of HPV 16 LI and HPV 16 L2 proteins by recombinant strains of Saccharomvces cerevisiae. Carter et al. also demonstrated the production of HPV6b LI and L2 proteins. The HPV6b LI protein was not full-length LI protein. The recombinant proteins were produced as intracellular as well as secreted products. The recombinant LI and L2 proteins were of molecular weights similar to the native proteins. When the proteins were expressed intracellularly, the majority of the protein was found to be insoluble when the cells were lysed in the absence of denaturing reagents. Although this insolubility may facilitate purification of the protein, it may hamper analysis of the native epitopes of the protein. Recombinant proteins secreted from yeast were shown to contain yeast-derived carbohydrates. The presence of these N-linked oligosaccharides may mask native epitopes. In addition, the secreted recombinant proteins may contain other modifications, such as retention of the secretory leader sequence. It would be useful to develop methods of producing large quantities of papillomavirus proteins of any species and type by cultivation of recombinant yeasts. It would also be useful to produce large quantities of papillomavirus proteins having the immunity- conferring properties of the native proteins, such as the conformation of the native protein. The present invention is directed to the production of recombinant papillomavirus proteins having the immunity conferring properties of the native papillomavirus proteins as well as methods for their production and use. The present invention is directed to the production of a prophylactic and possibly therapeutic vaccine for papillomavirus infection. The recombinant proteins of the present invention are capable of forming virus-like particles. These VLP are immunogenic and prevent formation of warts in an animal model. The present invention uses the cottontail rabbit papillomavirus (CRPV) and HPV type 6 (subtype 6a) as model systems. SUMMARY OF THE INVENTION Recombinant expression vectors encoding the LI and L2 proteins of papillomavirus, methods of making the recombinant proteins and methods of using the recombinant proteins are provided. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows bidirectional yeast expression vector used to express papillomavirus LI and/or L2 capsid proteins. Figure 2 shows expression of HPV6a LI in yeast (immunoblot). Figure 3 shows expression of HPV6a L2 in yeast. Immunoblot of HPV6a L2 expressed in yeast; lane 1, molecular weight markers; lane 2, trpE-L2 fusion protein expressed in coh as positive control; lane 4, HPV6a LI expressed in yeast as negative control; lane 5, HPV6a L2 expressed in yeast (for experimental details see text). Figure 4 is an electron micrograph of HPV6a LI VLPs expressed in yeast. Figure 5 is an electron micrograph of HPV6a L1/L2 VLPs expressed in yeast. Figure 6 Immunoblots of CRPV LI, L2, and L1+L2 proteins expressed in yeast. Panel (A): Expression of CRPV LI as measured by reactivity with anti-CRPV LI antiserum. Panel (B): Expression of CRPV L2 as measured by reactivity with anti-CRPV L2 antiserum. Lane 1, molecular weight markers in kDa (Amersham Rainbow™ Markers, 14,300-200,000 daltons); Lane 2, BJ5462 containing the CRPV LI expression vector; Lane 3, strain 1569 containing the CRPV L2 expression vector; Lanes 4 and 5, two isolates of strain 1569 cotransformed with two plasmids for expression of CRPV LI and CRPV L2; Lanes 6-8, three isolates of strain 1569 containing single vector for coexpression of CRPV LI and L2 proteins; Lanes 9 and 10, two isolates of BJ5462 containing single vector for coexpression of CRPV LI and L2 proteins. The position of migration of LI and L2 are marked on the right axis of the appropriate panel.Figure 6 is Figure 7 is a schematic overview of the construction of S cerevisiae strain 1558. Figure 8 is a schematic overview of the construction of S . cerevisiae strain 1569. Figure 9 outlines major steps in a purification procedure. Figure 10 is list of strains. Figure 11 shows a set of SDS-PAGE analyses of HPVl 6 L1+L2 purified from yeast. In addition to the final purified VLP, retains from intermediate steps in the purification process are included. The table provides identification of the sample in each lane. A gel stained with colloidal Coomassie as well as Western blots probed with antisera to LI and L2 proteins are included. Figure 12 is a schematic of alternative cottontail rabbit papillomavirus LI purification processes. Figures 13 and 14 are SDS/PAGE analyses of purified VLP. DETAILED DESCRIPTION OF THE INVENTION Methods, compositions and processes for the prevention, characterization, detection and treatment of papillomavirus (PV) infection are provided. The methods are based on the production of recombinant LI or recombinant L2 or recombinant LI and L2 proteins in yeast. The recombinant proteins are capable of mimicking the conformational neutralizing epitopes of native PV. The recombinant LI or LI and L2 proteins may also be capable of forming virus-like particles (VLP). The compositions of the invention include but are not limited to recombinant DNA molecules encoding the LI or L2 or LI and L2 proteins, the recombinant proteins either alone or in combination with other recombinant proteins, VLP comprised of at least one recombinant protein, fragments of the recombinant proteins, pharmaceutical compositions comprising the recombinant proteins, vaccine compositions comprising the recombinant proteins, antibodies to the recombinant proteins or VLP, immunogenic compositions comprising at least one recombinant protein, and diagnostic kits comprising the recombinant DNA molecules or the recombinant proteins. The processes of the present invention include but are not limited to the process of producing a recombinant protein comprising the transformation of an appropriate yeast host cell with a recombinant DNA molecule, cultivating the transformed yeast under conditions that permit the expression of the DNA encoding the recombinant protein, and purifying the recombinant protein. The processes of the present invention also include the administration of the recombinant protein, recombinant protein compositions or VLP to an animal, including but not limited to humans. Appropriate host cells include, but are not limited yeast strains of the genera Saccharomvces. Pichia, Kluwermvces. Schizo saccharomvces and Hansenula. Papillomavirus infections occur in a variety of animals, including humans, sheep, dogs, cats, rabbits, monkeys, snakes and cows. Papillomaviruses infect epithelial cells, generally inducing benign epithelial or iϊbroepithelial tumors at the site of infection. Papillomaviruses may be classified into distinct groups based on the host that they infect. Human papillomaviruses (HPV) are further classified into more than 60 types based on DNA sequence homology (for a review, see Papillomaviruses and Human Cancer, H. Pfister (ed.), CRC Press, Inc., 1990). Papillomavirus types appear to be type-specific immunogens in that a neutralizing immunity to infection to one type of papillomavirus does not confer immunity against another type of papillomavirus. In humans, different HPV types cause distinct diseases. HPV types 1, 2, 3, 4, 7, 10 and 26-29 cause benign warts in both normal and immunocompromised individuals. HPV types 5, 8, 9, 12, 14, 15, 17, 19-25, 36 and 46-50 cause flat lesions in immunocompromised individuals. HPV types 6, 11, 34, 39, 41-44 and 51-55 cause nonmalignant condylomata of the genital and respiratory mucosa. HPV types 16 and 18 cause epithelial dysplasia of the genital tract and are associated with the majority of in situ and invasive carcinomas of the cervix, vagina, vulva and anal canal. HPV6 and HPVl 1 cause the majority of genital warts and laryngeal papillomas. Immunological studies in animals have shown that the production of neutralizing antibodies to papillomavirus capsid proteins prevents infection with the homologous virus. The development of effective papillomavirus vaccines has been slowed by difficulties associated with the cultivation of papillomaviruses in vitro. The development of an effective HPV vaccine has been particularly slowed by the absence of a suitable animal model. Neutralization of papillomavirus by antibodies appears to be type-specific and dependent upon conformational epitopes on the surface of the virus. Papillomaviruses are small (50-60 nm), nonenveloped, icosahedral DNA viruses that encode for up to eight early and two late genes. The open reading frames (ORFs) of the virus genomes are designated El to E7 and LI and L2, where "E" denotes early and "L" denotes late. LI and L2 code for virus capsid proteins. The early (E) genes are associated with functions such as viral replication and transformation. The LI protein is the major capsid protein and has a molecular weight of 55-60 kDa. L2 protein is a minor capsid protein which has a predicted molecular weight of 55-60 kDa and an apparent molecular weight of 75-100 kDa as determined by polyacrylamide gel electrophoresis. The production of HPV 16 LI, HPV 16 L2, and HPV type 6 LI proteins by recombinant strains of Saccharomvces cerevisiae has been reported. It would be useful to develop methods of producing large quantities of papillomavirus proteins of any species and type by cultivation of recombinant yeasts. It would also be useful to produce large quantities of papillomavirus proteins having the immunity- conferring properties of the native proteins, such as the conformation of the native protein. The present invention is directed to the production of recombinant papillomavirus proteins having the immunity conferring properties of the native papillomavirus proteins as well as methods for their production and use. The present invention is particularly directed to the production of a prophylactic vaccine for papillomavirus infection. The present invention is exemplified by cottontail rabbit papillomavirus (CRPV) and human papillomavirus type 6 (HPV type 6 or HPV6) as model systems. The exemplification does not limit the scope of the invention, which includes other types and subtypes of papillomavirus (P V), including but not limited to HPV type 11 , HPV type 16 and HPV type 18 as well as HPV subtype 6a and HPV subtype 6b. Pharmaceutically useful compositions comprising the proteins or VLP may be formulated according to known methods such as by the admixture of a pharmaceutically acceptable carrier. Examples of such carriers and methods of formulation may be found in Remington's Pharmaceutical Sciences. To form a pharmaceutically acceptable composition suitable for effective administration, such compositions will contain an effective amount of the protein or VLP. Such compositions may contain proteins or VLP derived from more than one type of HPV. Therapeutic or diagnostic compositions of the invention are administered to an individual in amounts sufficient to treat or diagnose PV infections. The effective amount may vary according to a variety of factors such as the individual's condition, weight, sex and age. Other factors include the mode of administration. Generally, the compositions will be administered in dosages ranging from about 1 μg to about 250 μg. The pharmaceutical compositions may be provided to the individual by a variety of routes such as subcutaneous, topical, oral, mucosal, and intramuscular. The vaccines of the invention comprise recombinant proteins or VLP that contain the antigenic determinants necessary to induce the formation of neutralizing antibodies in the host. Such vaccines are also safe enough to be administered without danger of clinical infection; do not have toxic side effects; can be administered by an effective route; are stable; and are compatible with vaccine carriers. The vaccines may be administered by a variety of routes, such as orally, parenterally, subcutaneously, mucosally or intramuscularly. The dosage administered may vary with the condition, sex, weight, and age of the individual; the route of administration; and the type PV of the vaccine. The vaccine may be used in dosage forms such as capsules, suspensions, elixirs, or liquid solutions. The vaccine may be formulated with an immunologically acceptable carrier. The vaccines are administered in therapeutically effective amounts, that is, in amounts sufficient to generate a immunologically protective response. The therapeutically effective amount may vary according to the type of PV. The vaccine may be administered in single or multiple doses. The methods of the present invention make possible the formulation of subviral vaccines for preventing PV infection. Using the methods, either monovalent or multivalent PV vaccines may be made. For example, a monovalent HPV type 16 vaccine may be made by formulating recombinant HPV 16 LI protein or L2 protein or LI and L2 proteins. Alternatively, a multivalent HPV vaccine may be formulated by mixing LI or L2 or LI and L2 proteins or VLP from different HPV types. The recombinant proteins and VLP of the present invention may be used in the formulation of immunogenic compositions. Such compositions, when introduced into a suitable host, are capable of inducing an immunologic response in the host. The recombinant proteins and VLP may be used to generate antibodies. The term "antibody" as used herein includes both polyclonal and monoclonal antibodies, as well as fragments thereof, such as, Fv, Fab and F(ab)2 fragments that are capable of binding antigen or hapten. The recombinant proteins, VLP and antibodies of the present invention may be used to serotype HPV infection and HPV screening. The recombinant proteins, VLP and antibodies lend themselves to the formulation of kits suitable for the detection and serotyping of HPV. Such a kit would comprise a compartmentalized carrier suitable to hold in close confinement at least one container. The carrier would further comprise reagents such as recombinant HPV protein or VLP or anti-HPV antibodies suitable for detecting a variety of HPV types. The carrier may also contain means for detection such as labeled antigen or enzyme substrates or the like. The recombinant proteins and VLP of the present invention are also useful as molecular weight and molecular size markers. The following examples are provided to further define the invention without, however, limiting the invention to the particulars of these examples. EXAMPLE 1 Preparation of Yeast Strain U9 Saccharomvces cerevisiae strain 2150-2-3 (MATa, leu2-04, adel, cir°) was obtained from Dr. Leland Hartwell (University of Washington, Seattle, WA). Cells of strain 2150-2-3 were propagated overnight at 30°C in 5 mL of YEHD medium (Carty et al., Ind. Micro. 2 (1987) 1 17-121). The cells were washed 3 times in sterile, distilled water, resuspended in 2 mL of sterile distilled water, and 0.1 mL of cell suspension was plated onto each of six 5-fluoro-orotic acid (FOA) plates in order to select for ura3 mutants (Cold Spring Harbor Laboratory Manual for Yeast Genetics). The plates were incubated at 30°C. The medium contained per 250 mL distilled water: 3.5 g, Difco Yeast Nitrogen Base without amino acids and ammonium sulfate; 0.5 g 5- Fluoro-orotic acid; 25 mg Uracil; and 10.0 g Dextrose. The medium was sterilized by filtration through 0.2 μm membranes and then mixed with 250 mL of 4% Bacto-Agar (Difco) maintained at 50°C, 10 mL of a 1.2 mg/mL solution of adenine, and 5 mL of L-leucine solution (180 mg/ 50 mL). The resulting medium was dispensed at 20 mL per petri dish. After 5 days of incubation, numerous colonies had appeared. Single colonies were isolated by restreaking colonies from the initial FOA plates onto fresh FOA plates which were then incubated at 30°C. A number of colonies from the second set of FOA plates were tested for the presence of the ura3 mutation by replica-plating onto both YEHD plates and uracil-minus plates. The desired result was good growth on YEHD and no growth on uracil-minus medium. One isolate (U9) was obtained which showed these properties. It was stored as a frozen glycerol stock (strain #325) at -70°C for later use. EXAMPLE 2 Preparation of a Vector for disruption of the Yeast MNN9 gene In order to prepare a vector for disruption of the MNN9 gene, it was necessary to first clone the MNN9 gene from S. cerevisiae genomic DNA. This was accomplished by standard Polymerase Chain Reaction (PCR) technology. A 5' sense primer and 3 ' antisense primer for PCR of the full-length MNN9 coding sequence were designed based on the published sequence for the yeast MNN9 gene (Zymogenetics: EPO Patent Application No. 88117834.7, Publication No. 0-314-096-A2). The following ohgodeoxynucleotide primers containing flanking Hindlll sites (underlined) were used: sense primer: 5'-CTT AAA GCT TAT GTC ACT TTC TCT TGT ATC G-3'(SEQ ID NO:l ) antisense primer: 5'-TGA TAA GCT TGC TCA ATG GTT CTC TTC CTC-3'(SEQ ID NO:2). The initiating methionine codon for the MNN9 gene is highlighted in bold print. The PCR was conducted using genomic DNA from S. cerevisiae strain JRY188 as template, Taq DNA polymerase (Perkin Elmer) and 25 cycles of amplification (94°C 1 min., 37°C 2 min., 72°C 3 min.). The resulting 1.2 kbp PCR fragment was digested with Hindlll, gel-purified, and ligated with Hindlll-digested, alkaline- phosphatase treated pUC13 (Pharmacia). The resulting plasmid was designated pi 183. In order to disrupt the MNN9 gene with the yeast URA3 gene, the plasmid pBR322-URA3 (which contains the 1.1 Kbp Hindlll fragment encoding the S. cerevisiae URA3 gene subcloned into the Hindlll site of pBR322) was digested with Hindlll and the 1.1 kbp DNA fragment bearing the functional URΛ3 gene was gel -purified, made blunt- ended with T4 DNA polymerase, and then ligated with Pmll-digested plasmid pi 183 (Pmll cuts within the MNN9 coding sequence). The resulting plasmid pi 199 contains a disruption of the MNN9 gene by the functional URA3 gene. EXAMPLE 3 Construction of U9-derivative strain 1372 containing disruption of MNN9 gene For disruption of the MNN9 gene in strain U9(#325), 30 μg of plasmid pi 199 were digested with Hindlll to create a linear mnn9::URA3 disruption cassette. Cells of strain 325 were transformed with the Hindπi-digested pi 199 DNA by the spheroplast method (Hinnen et al., 1978, Proc. Natl. Acad. Sci. USA &5: 1929- 1933) and transformants were selected on a synthetic agar medium lacking uracil and containing 1.0 M sorbitol. The synthetic medium contained, per liter of distilled water: Agar, 20 g; Yeast nitrogen base w/o amino acids, 6.7 g; Adenine, 0.04 g; L-tyrosine, 0.05 g; Sorbitol, 182 g; Glucose, 20 g; and Leucine Minus Solution #2, 10 ml. Leucine Minus Solution #2 contains per liter of distilled water: L-arginine, 2 g; L-histidine, 1 g; L-Leucine, 6 g; L-Isoleucine, 6 g; L-lysine, 4 g; L-methionine, 1 g; L-phenylalanine, 6 g; L-threonine, 6 g; L-tryptophan, 4 g. The plates were incubated at 30°C for five days at which time numerous colonies had appeared. Chromosomal DNA preparations were made from 10 colonies and then digested with EcoRI plus HindHI. The DNA digests were then evaluated by Southern blots (J. Sambrook et al.. Molecular Cloning: A Laboratorv Manual. 2nd edition. Cold Spring Harbor Laboratory Press, 1989) using the 1.2 kbp HindUI fragment bearing the MNN9 gene (isolated from plasmid pi 199) as a probe. An isolate was identified (strain #1372) which showed the expected DNA band shifts on the Southern blot as well as the extreme clumpiness typically shown by MNN9 mutants. EXAMPLE 4 Construction of a Vector for Disruption of Yeast HIS3 Gene In order to construct a disruption cassette in which the S. cerevisiae HIS3 gene is disrupted by the URA3 gene, plasmid YEp6 (K. Struhl et al., 1979, Proc. Natl. Acad. Sci., USA 76:1035) was digested with BamHI. The 1.7 kbp BamHI fragment bearing the HIS3 gene was gel-purified, made blunt-ended with T4 DNA polymerase, and ligated with pUCl 8 which had been previously digested with BamHI and treated with T4 DNA polymerase. The resulting plasmid (designated pi 501 or pUC18-HIS3) was digested with Nhel (which cuts in the HIS3 coding sequence), and the vector fragment was gel-purified, made blunt-ended with T4 DNA polymerase, and then treated with calf intestine alkaline phosphatase. The URA3 gene was isolated from the plasmid pBR322- URA3 by digestion with Hindlll and the 1.1 kbp fragment bearing the URA3 gene was gel-purified, made blunt-ended with T4 DNA polymerase, and ligated with the above pUC18-HIS3 Nhel fragment. The resulting plasmid (designated pUC18-his3::URA3 or pi 505) contains a disruption cassette in which the yeast HIS3 gene is disrupted by the functional URA3 gene. EXAMPLE 5 Construction of Vector for Disruption of Yeast PRBl Gene by the HIS3 Gene Plasmid FP8ΔH bearing the S. cerevisiae PRBl gene was provided by Dr. E. Jones of Carnegie-Mellon Univ. (C. M. Moehle et al., 1 87, Genetics 115:255-263). It was digested with Hindlll plus Xhol and the 3.2 kbp DNA fragment bearing the PRBl gene was gel-purified and made blunt-ended by treatment with T4 DNA polymerase. The plasmid pUC18 was digested with BamHI, gel-purified and made blunt-ended by treatment with T4 DNA polymerase. The resulting vector fragment was ligated with the above PRBl gene fragment to yield the plasmid pUC18- PRB 1. Plasmid YEp6, which contains the HIS3 gene, which was digested with BamHI. The resulting 1.7 kbp BamHI fragment bearing the functional HIS 3 gene was gel-purified and then made blunt-ended by treatment with T4 DNA polymerase. The pUC18-PRBl was digested with EcoRV plus Ncol which cut within the PRBl coding sequence and removes the protease B active site and flanking sequence. The 5.7 kbp EcoRV-NcoI fragment bearing the residual 5' and 3 '-portions of the PRBl coding sequence in pUC18 was gel-purified, made blunt-ended by treatment with T4 DNA polymerase, dephosphorylated with calf intestine alkaline phosphatase, and ligated with the blunt-ended HIS3 fragment described above. The resulting plasmid (designated pUC18-prbl::HIS3, stock #1245) contains the functional HIS3 gene in place of the portion of the PRBl gene which had been deleted above. EXAMPLE 6 Construction of a U9-related Yeast Strain containing disruptions of both the MNN9 and PRBl Genes The U9-related strain 1372 which contains a MNN9 gene disruption was described in Example 3. Clonal isolates of strain 1372 were passaged on FOA plates to select ura3 mutants. A number of ura3 isolates of strain 1372 were obtained, and one isolate (strain 12930-190- Sl -1) was selected for subsequent disruption of the HIS3 gene. The pUC18-his3::URA3 gene disruption vector (pi 505) was digested with Xbal plus EcoRI to generate a linear his3::URA3 disruption cassette and used for transformation of strain 12930-190-S1-1 by the lithium acetate method (Methods in Enzvmologv. 194:290 ( 1991 ). Ura + transformants were selected on synthetic agar medium lacking uracil, restreaked for clonal isolates on the same medium, and then replica-plated onto medium lacking either uracil or histidine to screen for those isolates that were both Ura + and His-. One isolate (strain 12930-230-1) was selected for subsequent disruption of the PRBl gene. The PRBl gene disruption vector (pUC18-prbl ::HIS3, stock #1245) was digested with Sad plus Xbal to generate a linear prbl ::HIS3 disruption cassette and used for transformation of strain 12930-230- 1 by the Lithium Acetate method. His + transformants were selected on agar medium lacking histidine and restreaked on the same medium for clonal isolates. Genomic DNA was prepared from a number of the resulting His + isolates, digested with EcoRI, and then electrophoresed on 0.8% agarose gels. Southern blot analyses were then performed using a radio-labeled 617 bp probe for the PRBl gene which had been prepared by PCR using the following oligodeoxynucleotide primers: 5'TGGTCATCCCAAATCTTGAAA3 * (SEQIDNO:3) 5'CACCGTAGTGTTTGGAAGCGA3'(SEQIDNO:4) Eleven isolates were obtained which showed the expected hybridization of the probe with a 2.44 kbp prbl ::HIS3 DNA fragment. This was in contrast to hybridization of the probe with the 1.59 kbp fragment for the wild-type PRBl gene. One of these isolates containing the desired prbl ::HIS3 disruption was selected for further use and was designated strain #1558. EXAMPLE 7 Construction of a Vector for Disruption of Yeast PEP4 Gene The S. cerevisiae PEP 4 gene was cloned from a yeast genomic library in the following manner. E. coli cells containing the yeast genomic library pLSlOl (Schultz and Friesen, 1983, J. Bacteriol. 155: 8-14)) were propagated overnight in 5 mL of LB medium containing 100 μg/mL ampicillin. From this culture, 10 ~ 4 and 10 ~ 5 dilutions were plated on LB plus ampicillin plates. Colony plates lifts were prepared using nitrocellulose filters. A 600 bp probe for the yeast PEP4 gene was prepared by PCR using Taq DNA polymerase, total plasmid DNA from the pLSlOl yeast library, and the following oligodeoxynucleotide primers designed based on the published DNA sequence for PEP4 (C. A. Woolford et al., Mol. Cell. Biol. 6:2500 (1986)). Sense Primer: 5'-GAG GCT ACC AGC GAG CCG GGC-3'(SEQ ID NO:5) Antisense Primer: 5 ' -GGC C AG TGG GCC AAC AGG TTC-3 ' (SEQ ID NO:6). The PCR was conducted with 25 cycles of amplification (94°C 1 min., 37°C 2 min., 72°C 3 min.). The PCR probe was gel-purified, radio- labeled, and hybridized with the above colony filters. Several colonies were positive for hybridization with the PEP4 probe and were restreaked on LB plus ampicillin plates for single colonies. Plasmid DNA was prepared by the alkaline-SDS lysis (Sambrook et al., supra) from several of the isolates and digested with BamHI. The expected 14 kbp vector band and 6.9 kbp PEP4 insert band were observed. Upon double digestion with EcoRI plus Xhol, the expected 1.5 kbp band for PEP4 was observed. One isolate (strain #860) showing the expected results was selected for further use. Plasmid DNA from strain #860 was digested with BamHI and the 6.9 kbp BamHI DNA fragment carrying the chromosomal PEP4 gene was subcloned into the BamHI site of pUC13 to yield the plasmid p890. The plasmid p890 was then digested with Ncol (which cuts within the PEP4 coding sequence), gel-purified, made blunt - ended by treatment with T4 DNA polymerase, and ligated with the 1.1 kbp blunt-ended fragment bearing the functional URA3 gene (prepared as in Example 2). The resulting plasmid containing the PEP 4 gene disrupted by the URA3 gene was designated pUC13-pep4::URA3 (strain #906). EXAMPLE 8 Construction of Yeast Strain #1569 which is Derivative of Strain U9 Containing both prbl and pep4 Mutations In order to disrupt the HIS3 gene in strain U9, the disruption vector pUC18-his3::URA3 was digested with EcoRI plus Xbal and then used to transform strain U9 by the lithium acetate method. Ura + transformants were selected on agar medium lacking uracil and restreaked on the same medium for clonal isolates. A number of the resulting Ura + isolates were then replica-plated onto agar medium lacking either uracil or histidine and screened for those that were both Ura + and His". One isolate (strain #1524) was selected for subsequent disruption of the PRBl gene. The PRBl gene disruption vector pUC18-prbl ::HIS3 was digested with Sad plus Xbal and then used for transformation of strain #1524 by the lithium acetate method. His + transformants were selected on agar medium lacking histidine and restreaked for clonal isolates on the same medium. Genomic DNA was prepared from a number of the His+ isolates and evaluated by Southern blot hybridization with a radio-labeled PRBl probe. One of the isolates (strain #1537) showing the desired disruption of the PRBl gene by HIS3 (i.e., prbl ::HIS3) was selected for subsequent disruption of the PEP4 gene. Strain #1537 was passaged on FOA plates in order to obtain ura3 isolates and one isolate (strain #1541) was selected for further use. In order to disrupt the PEP4 gene in strain #1541 , the PEP4 gene disruption vector pUC13-pep4::UR A3 was digested with Xhol to generate a linear pep4::URA3 disruption cassette and used for transformation of strain #1541 by the lithium acetate method. Ura + transformants were selected on uracil-minus agar medium and streaked for clonal isolates on the same medium. Genomic DNA was prepared from a number of the Ura+ transformants and evaluated by Southern blots using a radio-labeled probe for the PEP4 gene. One isolate (strain #1569) showing the desired disruption of the PEP4 gene by the URA3 gene was selected for further use. EXAMPLE 9 Construction of CRPV LI Expression Vector The CRPV LI gene was amplified by PCR from plasmid pLAII which contains the complete CRPV viral genome (Dr. Peter Howley, NCI) using Vent polymerase (New England Biolabs, Inc.); 35 cycles of amplification (94°C, 1 min; 50°C, 1 min; 72°C, 2 min) and the following oligonucleotide primers which contain flanking Bgiπ sites (underlined) were used: sense primer: 5'- GAA GAT CTT CAA AAC AAA ATG GCA GTG TGG CTG TCT AC-3'(SEQ ID NO:7) antisense primer: 5'-GAA GAT CTT TAT TAA GTA CGT CTC TTG CGT TTAG-3'(SEQ ID NO:8) The sense primer introduces a yeast non-translated leader sequence immediately upstream of the CRPV LI initiating methionine codon (highlighted in bold print). The 1.6 kb LI PCR product was digested with Bgiπ, gel-purified and subcloned into the Bgl II site of vector pSP72 (Promega) to yield the plasmid pSP72-CRPV-Ll (p 12930- 314-4-1). One subclone was sequenced completely and found to be different in 4 nucleotides from the published CRPV LI sequence. The changes do not result in amiηo acid changes. The LI gene was cut out of pSP72-CRPV-Ll as a Bgl ϋ fragment and subcloned into the unique BamHI site located between the yeast GAL10 promoter and ADH1 transcriptional terminator in the yeast expression vector pCl/l-GAL10p- ADH 11 which contains the GAL 10 promoter from YEp52 (Broach et al., Exp. Manipulation of Gene Expression. 1983, 83:81-116) and ADH1 transcriptional terminator in a pCl/1 vector backbone). The resulting plasmid was designated pi 2930-323-6-1. EXAMPLE 10 Construction of CRPV L2 Expression Vector The CRPV L2 gene was amplified by PCR using Vent polymerase (New England Biolabs, Inc.) from plasmid pLAII after digesting the plasmid with Sail, gel purifying the 7.9 Kb fragment and ligating it with itself. Thirty-five cycles of amplification (90°C, 1 min; 50°C, 1 min; 72°C, 2 min) and oligonucleotide primers which contain flanking EcoRI sites (underlined) were used: sense primer: 5'-GGA ATT CAC AAA ACA AAA TGG TTG CAC GGT CAC GAA AAC-3'(SEQ ID NO:9) antisense primer: 5'-GGA ATT CTT ATT CTG CGT AGA CAG CCA CAC TG-3' (SEQ ID NO:10) The sense primer introduces a yeast non-translated leader sequence immediately upstream of the CRPV LI initiating methionine codon (highlighted in bold print). The 1.5 kb PCR product was digested with EcoRI, gel-purified and subcloned into the EcoRI site of the bidirectional promoter vector pUCl 8-GALlp-GAL10p containing the divergent yeast GAL1/GAL 10 promoter. This vector contains a unique BamHI site between the GAL1 promoter and a first copy of the ADH1 transcription terminator, unique EcoRI and Smal sites located between the GAL 10 promoter, and a second copy of the ADH1 transcriptional terminator. The resulting expression cassette is carried on a 1.4 kb SphI fragment. One clone (pi 2930-295-2-2) containing the desired L2 insert adjacent to the GAL 10 promoter was completely sequenced and shown to contain 6 nucleotide changes from the published sequence, 4 of which result in amino acid changes. Sequence analysis of the original template DNA confirmed that the changes were also present in pLAII and not introduced by the PCR. The pUCl 8-GALlp-GAL10p vector containing the L2 gene was cut with SphI and the 2.9 kb fragment harboring the ADHlt-GALlp-GAL10p-L2-ADHlt expression cassette was ligated with the large SphI fragment of the yeast shuttle vector pCl/1. The resulting plasmid was designated pl2930-323-2-3 (pCl/l-GALlp-GAL10p- CRPV-L2). EXAMPLE 11 Expression of CRPV LI and CRPV L2 Capsid Protein in Yeast Plasmids pi 2930-323-6-1 and pi 2930-323-2-3 (pCl/1- GALlOp-CRPV/Ll and pCl/l-GALlp-GAL10p-CRPV/L2) were used to transform S. cerevisiae strains #1569, BJ5462 [E. W. Jones, Methods in Enzymologv J94 (1991) 428-453] and BJ1995 [Jones, ibid.]. Clonal isolates were grown at 30°C in YEHD medium containing 2% galactose for 48-72 hours. After harvesting the cells, the cell pellets were broken with glass beads, Triton X-100 was added to 0.5% final concentration and the resulting cell lysates were evaluated for the expression of CRPV LI and L2 by immunoblot analyses. Samples containing 40 μg of total cellular protein were electrophoresed on 12% Tris-Glycine gels (Novex) under reducing and denaturing conditions and electroblotted onto PVDF membranes (Novex). CRPV LI and L2 proteins were detected using polyclonal rabbit anti-Ll or anti-L2 antisera (gift of Dr. John Kreider, Hershey Medical Center) as primary antibodies and protein A coupled to horseradish peroxidase (Amersham, Inc.) as the secondary antibody. The membranes were processed using the chemiluminescent ECL™ Detection Kit (Amersham, Inc.). A 55-61 kDa LI protein band was detected in all samples harboring the LI expression plasmid and a ~90 kDa L2 protein band was detected in all samples from yeast clones harboring the L2 expression plasmid. No signal was detected in samples derived from yeast clones harboring the LI expression plasmid with anti-L2 antisera or vice versa. EXAMPLE 12 A. Purification of Recombinant CRPV LI Capsid Protein All steps were performed at 4°C unless specified. Cells, stored at -70°C, were thawed and suspended in an equal volume of "LI Buffer" (20 niM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed by 10 passes in a microfluidizer. The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% sucrose (w/v) in LI buffer, and LI was pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/10 volume of LI buffer and clarified by centrifugation at 5000 x g for 10 minutes. Tween-80 was added to the supernatant to a final concentration of 0.01 % (v/v) and the supernatant was fractionated at room temperature by size-exclusion chromatography on a 1700 ml column (5 cm ID) of Sephacryl S-1000 resin (Pharmacia). Running buffer for this column was 10 mM sodium phosphate, pH 7.2, 150 mM NaCl, 0.01% (v/v) Tween-80. Fractions containing immunoreactive material by immuno-dot blot were pooled and concentrated to 1/6 volume by ultrafiltration using an Amicon stirred cell with a 76 mm diameter YM-100 flat-sheet membrane (100,000 MWCO). The product was sterile filtered through a Millex-GV 0.22 μm membrane (Millipore). Purified CRPV LI Capsid Protein was adsorbed to aluminum hydroxide at a concentration of 100 μg/ml. B. Characterization of Recombinant CRPV LI Capsid Protein The identity of the final product was confirmed by Western blotting and by N-terminal sequence analysis. Purity was assessed by SDS/PAGE with Coomassie and silver staining, and by Solution Sieving Capillary Electrophoresis (SSCE) with optical detection at 215 nm. The preparation was 75% pure LI by SSCE. EXAMPLE 13 Purification of Recombinant CRPV L2 Capsid Protein All steps were performed at 4°C unless specified. Cells, stored at -70°C, were thawed and suspended in an equal volume of "LI Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed by 10 passes in a microfluidizer. The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% sucrose (w/v) in LI buffer, and L2 was pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/10 volume of LI buffer. The resuspended pellet was clarified by centrifugation at 5000 x g for 10 minutes. Tween-80 was added to the supernatant to a final concentration of 0.01 % (v/v) and the supernatant was fractionated at room temperature by size-exclusion chromatography on a 1700 ml column (5 cm ID) of Sephacryl S-1000 resin (Pharmacia). Running buffer for this column was 10 mM sodium phosphate, pH 7.2, 150 mM NaCl, 0.01 % (v/v) Tween-80. Fractions containing immunoreactive material by immuno-dot blot were pooled. Pooled fractions were analyzed by SDS/PAGE (silver) and by Western blotting. EXAMPLE 14 A. Purification of Recombinant CRPV LI Capsid Protein-Scheme 1 Cells stored at -70°C, were thawed and suspended in an equal volume of Breaking buffer (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed by 10 passes in a microfluidizer. The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% sucrose (w/v) in LI buffer, and LI was pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/lOth volume of LI buffer. The resuspended pellet was clarified by centrifugation at 5000 x g for 10 minutes. Tween-80 was added to the supernatant to a final concentration of 0.01% and the supernatant was fractionated at room temperature by size-exclusion chromatography on a 1700 ml column (5 cm ID) of Sephacryl S-1000 resin (Pharmacia). Running buffer for this column was 10 mM sodium phosphate, pH 7.2, 150 mM NaCl, 0.01% Tween-80. Fractions containing immunoreactive material by immunodot blot assay were pooled and concentrated to l/6th volume by ultrafiltration using an Amicon stirred cell with a 76 mm diameter YM-100 flat-sheet membrane (100,000 MWCO). The product was sterile filtered through a Millex-GV 0.22 μm membrane (Millipore). B. Characterization of Recombinant CRPV LI Capsid Protein The identity of the final product was confirmed by Western blotting and by N-terminal sequence analysis. Purity was assessed by SDS/PAGE with Coomassie and silver staining, and by Solution Sieving Capillary Electrophoresis (SSCE) with optical detection at 215 nm. LI was 75% pure by SSCE. Electron microscopy showed that VLP in the 50 - 55 nm diameter size range were present. C. Analytical Size-Exclusion HPLC To assay for VLP, samples were fractionated according to size by size-exclusion chromatography. Chromatography was performed with a Perkin-Elmer Series 410 Biopump HPLC with an ISS 100 autoinjector fitted with a 200 microliter injection loop. The column was a TSK-gel G5000PW, 7.5 x 600 mm (TOSOHAAS, Montgomeryville, PA). To monitor elution of protein from the column, optical detection at 280 nm was accomplished with a Perkin-Elmer LC-235 diode array detector. The mobile phase was 0.5 M NaCl in 10 mM sodium phosphate buffer, pH 7.2. The flow rate was 0.5 rnL/min, and one milliliter fractions were collected. Column calibration was performed with protein standards from Sigma as well as recombinant hepatitis B surface antigen (Recombivax, Merck & Co., West Point, PA). Detection of antigen in fractions collected during elution is accomplished by immunodot blot assay. D. Immunodot Blot Assay A 10 microliter sample of each fraction was applied to a strip of PVDF membrane (Immobilon-P, Millipore Corp., Bedford, MA) which was pre-wetted and placed on dampened blotting paper. The sample was allowed to soak into the membrane, and the membrane was placed in a Blocking Solution (5% (w/v) of non-fat dry milk dissolved in 0.15 M NaCl, 0.02% (w/v) sodium azide, and 0.01M sodium phosphate, pH 7.2) and incubated at room temperature with gentle agitation for a minimum of three hours. Blocking solution was decanted and replaced with primary antibody solution. Primary antibody used varied depending on the antigen to be detected: CRPV LI was probed with rabbit anti-CRPV serum "late response" (Biodesign International, Kennebunk, ME). CRPV L2 was probed with rabbit anti-CRPV L2 serum. HPV6a LI was probed with monoclonal antibody MAB 837 (Chemicon International, Inc., Temecula, CA). HPV6a L2 was probed with mouse anti-HPV6a L2-t E fusion serum. Visualization of the immune complexes was by standard methods using a second antibody conjugated to alkaline phosphatase and the chromogenic substrate NBT/BCIP. E. Solution Sieving Capillary Electrophoresis (SSCE") Samples of CRPV VLP (-0.2 milligram/milliliter) were heated for 15 minutes at 100°C in 1 % 2-mercaptoethanol and 1% (w/v) SDS. The sample was applied electrokinetically along with a reference marker, mellitic acid, to a silica fused capillary, 42 cm (22 cm to detector) x 0.05 mm I.D., pre-equilibrated with 10 lumen volumes of 0.1 N NaOH, water, and ProSort sieving reagent (Applied Biosystems, Foster City, CA). A separation voltage of 300 volts/cm was applied using an Applied Biosystems Model 270A-HT CE instrument. Elution of sample was monitored by absorbance at 215 nm, and data was collected using Nelson Turbochrom 3 software. F. Preparation of Vaccine from Recombinant CRPV LI Capsid Protein Purified CRPV LI Capsid Protein was adsorbed to Al(OH)3 at a concentration of 100 μg/ml. EXAMPLE 15 Protection Against Papilloma Development Caused by CRPV by Vaccination with Yeast Derived CRPV LI VLPs 5 New Zealand White rabbits were immunized intramuscularly with either 135 mg of LI VLPs (75% pure, see Example 17) adsorbed to alum or 100 mg recombinant hepatitis B surface antigen (99% pure) adsorbed to aluminum hydroxide as a negative control. Animals received 2 more boosts over 8 weeks before they were challenged with CRPV 10 days after the last boost. Sera taken before immunization, at each boost, and before challenge were analyzed by an LI -VLP specific ELISA. An indirect ELISA assay was used to determine semm antibody responses to yeast-expressed CRPV LI VLPs. The antigens used in the ELISA were CRPV LI VLPs expressed in insect cells with a recombinant baculovims essentially as described by Christensen et al. (J. Virol. 64:3151-3156, 1990; J. Gen. Virol. 75:2271- 2276 (1994). Goat anti-rabbit IgG-alkaline phosphatase was used as second antibody and p-nitrophenyl phosphate as substrate (Kirkegaard and Perry Labs., Inc.). Absorbance was measured at 405 nm. The titer was determined by endpoint-dilution (3 -fold dilutions of sera starting at 1 :100) and was considered positive if the LI -specific absorbance exceeded the mean absorbance readings plus 2 standard deviations of rabbit preimmune sera. Exact titers were calculated from these data using the SOFTmax program version 2.3 (Molecular Devices Inc., Menlo Park, CA). Anti-Ll VLP antibody titers were present 4 weeks after the first immunization, and they increased with each additional boost. Control animals were negative. 6 weeks after CRPV challenge the vaccinated animals were wart-free in 15 out of 15 sites (1 :2 diluted or 1:12 diluted vims stock) while the control animals show wart formation in 12 out of 15 sites (1:2 diluted vims) or 9 out of 15 (1 :12 diluted vims). After 15 weeks, the vaccinated animals were still wart-free. Vims neutralization assays were performed (essentially according to method of Christensen et al., 1991. Virology 181 :572-579 by mixing rabbit sera with CRPV and subsequently challenging rabbits with the treated CRPV. The standard for determining neutralizing antibody was complete vims neutralization (3/3 sites negative for wart formation). Sera from the 5 vaccinated animals and 5 control animals were analyzed. Sera collected after 1 dose of CRPV LI VLPs contained antibodies which completely neutralized undiluted vims in 80% of rabbits (4/5). After 2 or 3 doses of CRPV LI VLPs 100% of rabbits (5/5) had vims neutralizing antibodies. Control sera did not show any vims neutralizing activity. Depending on final titers sera of selected vaccinated animals could be diluted between 10-1000 fold and were still 100% neutralizing. To test whether the neutralizing antibody response was specific for native CRPV LI VLPs , one immune semm was chosen and incubated with nitrocellulose squares which had been coated with either native or denatured yeast-derived CRPV LI VLPs. Nitrocellulose squares (1 cm^) were coated with either native or denatured (reduced and alkylated with iodoacetic acid in 8 M urea) yeast-expressed CRPV LI VLPs. Native or denatured yeast extracts were used as controls. Rabbit immune semm was incubated serially 4 times with the nitrocellulose squares for 8-14 hours at 4°C, before it was tested in the virus- neutralization assay as described above. Only native CRPV LI VLPs were able to absorb the antibodies responsible for neutralizing CRPV, while denatured or control yeast proteins did not absorb these antibodies. In addition, native CRPV LI VLPs also removed the ELISA reactivity to CRPV LI VLPs expressed in insect cells (data not shown). EXAMPLE 16 Constmction of Vector for Coexpression of CRPV L1/L2 from a Single Plasmid Plasmid pSP72-CRPV-Ll (pi 2930-314-4-1) was digested with Bgiπ and the 1.5 kbp Bgiπ fragment bearing the CRPV LI ORF with a yeast 5'-nontranslated leader was gel-purified. Plasmid p 12930- 323-2-3 (pCl/l-GALlp-GAL10p-CRPV-L2) was digested with BamHI which cuts between the GAL1 promoter and the ADH1 transcriptional terminator. The linear vector fragment was gel-purified and then ligated with the aforementioned CRPV-Ll Bglll fragment to yield the plasmid pl2930-366-l-2 (pCl/l-GALl/10p-CRPV/Ll+L2). This resulting plasmid contains the CRPV-Ll ORF under control of the GAL1 promoter and the CRPV-L2 ORF under control of the GAL 10 promoter. EX AMPLE 17 Constmction of Vector for Coexpression of CRPV L1/L2 from Two Plasmids The pUC18-GALlp-GAL10p vector containing the L2 gene was cut with SphI and the 2.9 kb fragment harboring the ADHlt-GALlp- GAL10p-L2-ADH It expression cassette was gel-purified and made blunt-ended by treatment with T4 DNA polymerase. The yeast shuttle vector YEp24 [Botstein et al., Gene 8: 17 (1979)] was digested with BamHI, made blunt-ended by treatment with T4 DNA polymerase, dephosphorylated with calf intestine alkaline phosphatase and then ligated with the above blunt-ended L2 expression cassette to yield the plasmid pi 594. EXAMPLE 18 Coexpression of CRPV LI and L2 in Yeast Plasmid pl2930-366-l-2 (pCl/l-GALl/10p-CRPV/Ll+L2) was used to transform S cerevisiae strains #1569 and BJ5462 (one plasmid system) and the resulting transformants were selected on leucine- minus synthetic agar medium. In a parallel experiment, strain 1569 was cotransformed with the pCl/1-GALlOp-CRPV-Ll expression vector pl2930-323-6-l plus the YEp24-GAL10p-L2 expression vector pl594 (two plasmid system) and the resulting transformants containing both vectors were selected on synthetic agar medium lacking both leucine and uracil. Clonal isolates for both the one plasmid system and two plasmid system were grown at 30°C in YEHD complex medium containing 2% galactose for 48-72 hours. After harvesting the cells, the cell pellets were broken with glass beads. Triton X-100 was added to 0.5% final concentration and cell lysates were analyzed for the expression of CRPV LI and L2 by immunoblot analysis. Samples containing 50 μg of total cellular protein were electrophoresed on 8-16% Tris-Glycine gradient gels (Novex) under reducing and denaturing conditions and electroblotted onto PVDF membranes (Novex). CRPV LI and L2 proteins were detected using polyclonal rabbit anti-Ll or anti-L2 antisera (gift of Dr. John Kreider, Hershey Medical Center) as primary antibodies and protein A coupled to horseradish peroxidase (Amersham, Inc.) as the secondary antibody. The membranes were processed using the chemiluminescent ECL™ Detection Kit (Amersham, Inc.). A 55-61 kDa LI protein band and a -90 kDa L2 protein band was detected in all samples from yeast clones harboring the LI + L2 expression plasmid. No signal for L2 was detected in samples derived from yeast clones harboring the expression plasmid for LI . No signal for LI was detected in samples from cells containing only the L2 expression vector. EXAMPLE 19 Purification of CRPV LI and CRPV LI + L2 VLPs for EM studies The yeast expressed CRPV LI and CRPV LI and L2 proteins were partially purified and concentrated for electron microscopy (EM) studies. One to 1.5 liters of YEHD medium containing 2% galactose were inoculated with S. cerevisiae strain #1569 or BJ5462 transformed with the LI + L2 coexpression vector pi 2930-366- 1-2 (pCl/1-GALl/lOp-CRPV/Ll + L2) and grown at 30°C for 48-72 hours. In a parallel experiment, cells of strain #1569 co-transformed with the GALlOp-CRPV-Ll expression vector pi 2930-323-6-1 plus the YEp24- GAL10p-L2 plasmid pi 594 were grown in a similar fashion. The cells were harvested and cell pellets frozen at -70°C. All following steps were performed at 4°C. Cell pellets were thawed and suspended in an equal volume of "LI buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protein inhibitors PMSF and Pepstatin A were added to the slurry at a final concentration of 2 mM and 1.7 μM respectively. Cells were lysed by 3-5 passages in a microfluidizer. The lysates were clarified by centrifugation at 5000 x g for 10 min. The supernatant was layered on top of a 5 cm cushion of 45% (v/v) sucrose in LI buffer and the LI , L2 or LI and L2 proteins were pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/10th the volume of LI buffer. The resuspended pellet was clarified by centrifugation at 5000 x g for 10 min. For EM analysis (Stmcture Probe, West Chester, PA), an aliquot of each sample was placed on 200 mesh carbon coated copper grids. A drop of 2% phosphotungstic acid (PTA), pH 7.0 was placed on the grid for 20 seconds. The grids were allowed to air dry prior to TEM examination. All microscopy was done using a JEOL 100CX transmission electron microscope (JEOL USA, Inc.) at an accelerating voltage of 100 KV. The micrographs generated have a final magnification of 100,000X. In all yeast samples harboring either the CRPV LI expression plasmid or plasmids for the co-expression of CRPV LI and L2, VLP were observed in the 50-55 nm diameter size range. No VLP were observed in yeast control samples or yeast samples harboring the L2 expression plasmid alone. (Figures 7,8, 9). EXAMPLE 20 Purification of Recombinant CRPV LI Capsid Protein - Scheme 2 All steps were performed at 4°C unless specified. Cells stored at -70°C were thawed and suspended in an equal volume of Breaking buffer (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed using a BioNeb Cell Dismptor system (Glas-Col Apparatus Co., Terra Haute, IN). The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% sucrose (w/v) in LI buffer, and LI was pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/10 volume of LI buffer. The resuspended pellet was clarified by centrifugation at 5000 x g for 10 minutes. Supernatant was diluted 1 :5 with PBS, reclarified by centrifugation in Sorvall SA-600 rotor at 6500 rpm for 10 minutes at 4°C. The supernatant was filtered through a 0.22 micron syringe filter and fractionated by anion-exchange chromatography. 31 - Anion-exchange chromatography was performed with a Perkin-Elmer Series 410 Biopump HPLC with a 5 milliliter injection loop. The chromatography medium was a Fractogel EMF TMAE-650 (S) 25-40 micron resin (EM Separations, Gibbstown, NJ) in a 150 mm x 10 mm ID glass column. To monitor elution of protein from the column, optical detection at 280 nm was accomplished with a Perkin-Elmer LC- 235 diode array detector. The column was pre-equilibrated with 0.15M NaCl in 0.01M sodium phosphate buffer, pH 7.2 (Buffer A). The column was mn at a flow rate of 0.75 ml/min. The sample was loaded on the column, and the column was washed with Buffer A to remove unbound material. Bound material was eluted with a linear concentration gradient of sodium chloride, 0.15 M to 0.65 M for 5 minutes, followed by a 0.65 M to 1.15 M linear gradient for 30 minutes. Detection of antigen in fractions collected during elution was accomplished by immuno dot blot assay. Fractions containing immunoreactive material (i.e., fractions eluting between 0.81M and 1.05M NaCl) were pooled. The pooled fractions were concentrated in Macrosep centrifugal concentration devices (Filtron Technology Corp., Northborough, MA) to 1/5 volume. The concentrate was fractionated by size-exclusion chromatography using Sephacryl S-1000 SF resin (Pharmacia, Piscataway, NJ) in a 87 cm x 27 mm ID column. The column was run at a flow rate of 2.5 ml/min. Elution of protein was monitored by absorbance at 280nm. Antigen was detected by immunoblot. Fractions containing immunoreactive material were pooled and concentrated by ultrafiltration using a stirred cell (Amicon, Inc., Beverly, MA) with a 43 mm diameter YM-100 flat sheet membrane (Amicon, Inc., Beverly, MA) under nitrogen at 10 psi pressure. The final product was characterized by SDS/PAGE with Coomassie staining, and by solution-sieving capillary electrophoresis (SSCE). The final product from Scheme 2 was 88% pure by SSCE. EXAMPLE 21 A. Purification of Recombinant CRPV LI Capsid Protein - Scheme 3 All steps were performed at 4°C unless specified. Cells stored at -70°C were thawed and suspended in an equal volume of Breaking buffer (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed using a BioNeb Cell Dismptor system (Glas-Col Apparatus Co., Terra Haute, IN). The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% sucrose (w/v) in LI buffer, and LI was pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/10th volume of LI buffer. The resuspended pellet was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was extracted with 1/2 volume of chloroform. The aqueous layer was removed and clarified by centrifugation at 12,000 rpm in a Beckman microfuge for 5 minutes at room temperature. Supernatant was diluted 1 :5 with PBS, reclarified by centrifugation in Sorvall SA-600 rotor at 6500 rpm for 10 minutes at 4°C. The supernatant was filtered through a 0.22 micron syringe filter and fractionated by anion-exchange chromatography. Anion-exchange chromatography was performed with a Perkin-Elmer Series 410 Biopump HPLC with a 5 milliliter injection loop. The chromatography medium was a Fractogel EMF TMAE-650 (S) 25-40 micron resin (EM Separations, Gibbstown, NJ) in a 150 mm x 10 mm ID glass column. To monitor elution of protein from the column, optical detection at 280 nm was accomplished with a Perkin-Elmer LC- 235 diode array detector. The column was pre-equilibrated with 0.15M NaCl in 0.01 M sodium phosphate buffer , pH 7.2 (Buffer A). The column was run at a flow rate of 0.75 ml/min. The sample was loaded on the column, and the column was washed with Buffer A to remove unbound material. Bound material was eluted with a linear concentration gradient of sodium chloride, 0.15 M to 0.65 M for 5 minutes, followed by a 0.65 M to 1.15 M linear gradient for 30 minutes. Detection of antigen in fractions collected during elution was accomplished by immuno dot blot assay. Fractions containing immunoreactive material (i.e., fractions eluting between 0.81 M and 1.05M NaCl) were pooled. The pooled fractions were concentrated in Macrosep centrifugal concentration devices (Filtron Technology Corp., Northborough, MA) to 1/5 volume. The concentrate was fractionated by size-exclusion chromatography using Sephacryl S-1000 SF resin (Pharmacia, Piscataway, NJ) in a 87 cm x 27 mm ID column. The column was run at a flow rate of 2.5 ml/min. Elution of protein was monitored by A280nm. Antigen was detected by immunoblot. Fractions containing immunoreactive material were pooled and concentrated by ultrafiltration using a stirred cell (Amicon, Inc., Beverly, MA) with a 43 mm diameter YM-100 flat sheet membrane (Amicon, Inc., Beverly, MA) under nitrogen at 10 psi pressure. The final product was characterized by SDS/PAGE with Coomassie staining, and by solution-sieving capillary electrophoresis (SSCE). The final product from Scheme 3 was 95% pure by SSCE. EXAMPLE 22 Expression of CRPV LI and HPV Type 6a LI (strain 1644) in enriched complex and chemicallv-defined media. Inocula for these strains were developed in leucine-free synthetic medium as described above for transfer to shake flask cultures. The shake flasks used were baffled for high aeration capacity (70 mL liquid per 300 mL flask, Tunair Labware) and media were supplemented with ca. 0.5 mL/L of an antifoam (UCON LB-625, Union Carbide). Enriched complex medium contained (per L): 40 g Difco yeast extract; 20 g Sheffield HySoy peptone; 30 g glucose; 50 g galactose; the medium was adjusted to pH 5.3 prior to sterilization. The chemically-defined medium used was similar to that described by Oura (Biotechnol. Bioengineer.16: 1197-1212. 1974) but supplemented with (per L): 0.1 g choline Cl; 0.4 g adenine; 30 g monosodium glutamate as nitrogen source; 0.2 g uracil; 20 g glucose; 40 g galactose. Flasks were inoculated with 3 mL inoculum and incubated for 66 hr at 28 C, 250 rpm on a rotary shaker. Flasks were sampled at intervals for verification of expression by immunoblot using anti-CRPV LI and anti-HPV 6a LI antisera. EXAMPLE 23 Cloning of HPV-6a Genome Tissue from a patient diagnosed with severe condylomata acuminata (provided by Dr. Darron Brown, Indiana University School of Medicine) was typed by restriction enzyme digestion and polymerase chain reaction (PCR) and was shown to contain HPV type 6a. DNA was extracted from the tissue sample and digested with Hindffl enzyme. Following size-fractionation through a 0.8% low melting temperature agarose prep gel, the 8-kb region was excised from the gel and the agarose was digested with Gelase™ enzyme (Epicentre Technologies, Inc.). The sample was ligated with pUCl 8 which had been digested with Hind in and dephosphorylated (Pharmacia, Inc). Following transformation of competent R, coH DH5 cells (BRL), the plasmid library was screened for HPV-6a positive clones using a 32p_ι a beled oligodeoxynucleotide that was complementary to the HPV-6a LI gene. A pUC18 plasmid containing the 8-kb HPV-6a genome was isolated and characterized by restriction enzyme and Southern blot analyses. This plasmid was designated, pUCl 8-HPV-6a. The complete 8-kb HPV-6a genome was sequenced using the ABI automated sequencer (#373A) according to the manufacturer's instructions. A large vulvar condyloma acuminatum lesion was obtained from a 25 year old, postpartum female patient. A fragment of the lesion was frozen in liquid nitrogen, then processed with a Braun mikro- dismembrator H (B. Braun Instruments, Melsungen , Germany). The resulting material was solubilized with 0.6% (w/v) sodium dodecyl sulfate (SDS), treated with proteinase K (50 mcg/ml), and extracted with phenol/chloroform/isoamyl alcohol. DNA was ethanol-precipitated and quantified by UV spectrophotometry. The presence of high-molecular- weight DNA was established by agarose gel electrophoresis followed by staining with ethidium bromide. The HPV DNA type was determined using the hybrid capture assay marketed as ViraType Plus (Digene Diagnostics, Beltsville, MD). The HPV probes used were divided into two pools whose composition is based on the association of each type with genital tract malignancies. Probe group A contained the "low-risk" types HPV6, 11 , 42, 43, and 44 while probe B contained the "high-risk" types 16, 18, 31, 33, 35, 45, 51, 52, and 56. Total DNA was digested with PstI, BamHI, and Hindiπ and Southern blots were performed under high stringency conditions (T m - 15°C) to determine the HPV subtype. To determine the complete HPV6a sequence, sequencing primers were synthesized based on the published HPV6b sequence. Both strands of the complete 8.1 -kbp HPV6a genome were sequenced by the dideoxy chain termination method using the PRISMTM ι_it and an Applied Biosystems (ABI) automated sequencer (#373 A) according to the manufacturers' instructions (ABI, Inc., Foster City, CA). In cases where the sense and antisense sequence did not match, additional HPV6a specific primers were synthesized to resequence in both directions over the area in question to obtain a consensus. The DNA sequences of HPV6a and HPV6b exhibited over 97% identity with a total of 229 bp changes identified out of 8010 bp. The most significant differences compared to the HPV6b sequence were found in the long control region (LCR; nt 7205 - nt 106). Apart from several single nucleotide (nt) changes in the HPV6a LCR, a 94-bp insertion at nt 7350 and another 19-bp insertion at nt 7804 were found. At nt 7615, six base pairs were deleted from the HPV6a genome. EXAMPLE 24 Constmction of HPV6a LI Yeast Expression Vector HPV type 6a DNA was used as a template for PCR. The HPV6a LI gene was amplified by PCR using Vent polymerase (New England Biolabs, Inc.), 35 cycles of amplification (94°C 1 min, 48°C 1 min, 72°C 1 min 45 sec), and the following oligodeoxynucleotide primers which contain flanking Bgl II sites (underlined): sense primer: 5'-CTC AGA TCT CAC AAA ACA AAA TGT GGC GGC CTA GCG ACA GCA CAG-3'(SEQ ID NO:l l) antisense primer: 5'-GAG AGA TCT TAC CTT TTA GTT TTG GCG CGC TTA C-3'(SEQ ID NO:12) The sense primer introduces a yeast non-translated leader sequence immediately upstream to the HPV6a LI initiating methionine codon (highlighted in bold print). The 1.5-kbP LI PCR product was digested with Bgiπ and gel-purified. The pC 1/1 -GAL expression vector was constmcted by isolating the 1.4 kbp SphI fragment from the bidirectional promoter vector pUC18-GALlp-GAL10p which contains the divergent GAL1/GAL10 promoter from the plasmid pBM272 (provided by Dr. Mark Johnston, Washington University, St. Louis) flanked on each side by a copy of the yeast ADH1 transcriptional terminator [Bennetzen, J.L. and Hall, B.D. (1982) J. Biol. Chem. 257:3018-3025]. In the resulting expression cassette, a BamHI site is located between the GAL1 promoter and the first copy of the ADH1 transcriptional terminator and a Smal cloning site is located between the divergent GAL 10 promoter and the second copy of the ADH1 transcriptional terminator. The yeast shuttle vector pCl/1 (Rosenberg et al., Nature 312 (1984) 77-80) was digested with SphI and ligated with the 1.4-kbp SphI GAL promoter fragment. The resulting vector, pCl/1-GAL, was linearized with BamHI which cuts between the GAL1 promoter and the ADH1 transcription terminator. The BamHI digested pC 1/1 -GAL vector and the Bglll digested HPV6a LI PCR fragment were ligated and used to transform E. coli DH5 cells (BRL). A pCl/1-GAL plasmid was isolated which contains the HPV-6a LI gene and was designated pl3173- 357-6. The LI gene in pi 3173-357-6 was sequenced (ABI Sequencer #373 A) and shown to be identical to the LI gene in the pUC18-HPV6a clone. EXAMPLE 25 Constmction of the HPV6a LI and L2 Yeast Expression Vector Plasmid pl3173-357-6 (pCl/l-GAL+ HPV6a LI ) was digested with Smal, which cuts between the GAL10 promoter and the ADH1 transcription terminator. The 1.4-kbp HPV6a L2 gene was amplified by PCR using the pUC18-HPV6a DNA as template, Vent polymerase (New England Biolabs, Inc.), 10 cycles of PCR amplification (94°C, 1 min; 48°C, 1 min; 72°C, 1 min 45 sec) and the following oligodeoxynucleotide primers which contain flanking Smal sites (underlined): sense primer: 5'-TCC CCC GGG CAC AAA ACA AAA TGG CAC ATA GTA GGG CCC GAC GAC-3' (SEQ ID NO: 13) antisense primer: 5'-TCC CCC GGG CTA GGC CGC CAC ATC TGA AAA AAA TAA GG-3' (SEQ ID NO:14) The sense primer introduces a yeast non-translated leader sequence immediately upstream to the HPV6a L2 initiating methionine codon (highlighted in bold print). The PCR fragment was digested with Smal, gel purified and ligated with the Smal digested pl3173-357-6 plasmid. A pC 1/1 -GAL plasmid containing both the HPV6a LI and L2 genes was isolated and designated, pi 4049-7-2. The L2 gene was sequenced (ABI Sequencer #373 A) and found to be identical to the L2 gene in the pUC18-HPV6a clone. EXAMPLE 26 Expression of HPV6a LI and Co-Expression of HPV6a LI and L2 in Yeast Plasmids pl3173-357-6 (pCl/1-GAL + HPV6a LI) and pl4049-7-2 (pCl/1-GAL + HPV6a LI and L2) were used to transform J cerevisiae strains #1569 (MATa, Ieu2-Q4, prbl, adel, pep4, cir°) and #1558 (MATa, leu2-04 , prbl , mnn9, adel Λ cir°). The resulting recombinant strains obtained using host strain #1558 were strains #1644 (HPV6a LI ) and #1670 (HPV6a L1+L2) as shown in the table. Clonal isolates were grown at 30°C in YEHD medium containing 2% galactose for 68-78 hours. After harvesting the cells, the cell pellets were broken with glass beads and cell lysates analyzed for the expression of HPV6a LI or HPV6a L2 protein by immunoblot analysis. Samples containing 40 μg of total cellular protein were electrophoresed on 10% Tris-Glycine gels under reducing and denaturing conditions and electroblotted onto nitrocellulose filters. The LI protein was immunodetected using rabbit antisera raised against a trpE-HPVl 1 fusion protein (Brown, D. R. et al., Virology 201:46-54) as primary antibody and donkey anti-rabbit IgG horseradish peroxidase-linked (HRP) whole antibody (Amersham, Inc.) as the secondary antibody. The filters were processed using the chemiluminescent ECL™ Detection Kit (Amersham, Inc.). A 50-55 kDa LI protein band was detected in all samples except the negative control (pCl/1 without LI or L2 gene). The L2 protein was detected as a 70 kDa protein band by Western analysis using 1 :250 diluted sera from mice which had been immunized 3 times with a trpE-HPV6a L2 fusion protein prepared essentially according to the method of Carter et al. as the primary antibody and HRP-linked, sheep anti-mouse IgG (Amersham, Inc.) as a second antibody (1 :1000 dilution). For EM analysis (Structure Probe, West Chester, PA), an aliquot of each sample was placed on 200 mesh carbon coated copper grids. A drop of 2% phosphotungstic acid (PTA), pH 7.0 was placed on the grid for 20 seconds. The grids were allowed to air dry prior to TEM examination. All microscopy was done using a JEOL 100CX transmission electron microscope (JEOL USA, Inc.) at an accelerating voltage of 100 KV. The micrographs generated have a final magnification of 100,000X. VLP were observed in the 50-55 nm diameter size range in all yeast samples harboring either the HPV6a LI or HPV6a LI and L2 coexpression plasmids. No VLP were observed in yeast control samples. EXAMPLE 27 Fermentation of HPV6a L1+L2 (Strain #1670). Surface growth of a plate culture of strain 1670 was aseptically transferred to a leucine-free liquid medium containing (per L): 8.5 g Difco yeast nitrogen base without amino acids and ammonium sulfate; 0.2 g adenine; 0.2 g uracil; 10 g succinic acid; 5 g ammonium sulfate; and 0.25 g L tyrosine; this medium was adjusted to pH 5.0-5.3 with NaOH prior to sterilization. After growth for 25 hr at 28 °C, 250 rpm on a rotary shaker, frozen culture vials were prepared by adding sterile glycerol to a final concentration of 17% (w/v) prior to storage at - 70 C (1 mL per cryovial). Inoculum for fermentation of strain 1670 was developed in the same medium (500 mL per 2-L flask) and was started by transferring the thawed contents of two frozen culture vials to the 2-L flasks and incubating at 28 °C, 250 rpm on a rotary shaker for 25 hr. Fermentation of strain 1670 used a New Bmnswick SF-116 fermentor with a working volume of 10 L after inoculation. The production medium used contained (per L): 20 g Difco yeast extract; 10 g Sheffield HySoy peptone; 20 g glucose; 20 g galactose; the medium was adjusted to pH 5.3 prior to sterilization. The entire contents (500 mL) of the 2-L inoculum flask was transferred to the fermentor which was incubated at 28 °C, 5 L air per min, 400 rpm, 3.5 psi pressure. Agitation was increased as needed to maintain dissolved oxygen levels of greater than 40% of saturation. Progress of the fermentation was monitored by offline glucose measurements (Beckman Glucose 2 Analyzer) and online mass spectrometry (Perkin-Elmer 1200). After 69 hr incubation, a cell density of 9.9 g dry cell weight per L was reached. The culture was concentrated by hollow fiber filtration (Amicon H5MP01-43 cartridge in an Amicon DC- 10 filtration system) to ca. 2 L, diafiltered with 2 L phosphate- buffered saline, and concentrated further (to ca. 1 L) before dispensing into 500 mL centrifuge bottles. Cell pellets were collected by centrifugation at 8,000 rpm (Sorval GS3 rotor) for 20 min at 4 °C. After decanting the supernatant, the pellets (total 225 g wet cells) were stored at - 70 °C until use. EXAMPLE 28 Purification of Recombinant HPV6a LI + L2 Capsid Proteins All steps performed at 4 ° C unless noted. Cells of strain #1670 were stored frozen at -70 ° C. Frozen cells (wet weight = 38.0 g) were thawed at 20-23 ° C and resuspended in 50 mL "LI Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). The protease inhibitors PMSF and pepstatin A were added to final concentrations of 2 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 8,000 psi by 3 passes in a Ml 10 Microfluidizer (Microfluidics Corp., Newton, MA). The broken cell slurry was centrifuged at 5,000 x g for 10 min to remove cellular debris. The supernatant liquid containing LI + L2 antigen was recovered. The supernatant liquid was diluted 1 :5 by addition of Buffer A (20 mM MOPS, pH 7.0) and applied to an anion exchange capture column (5.0 cm ID x 4.0 cm) of Fractogel ® EMD TMAE-650 (S) resin (EM Separations, Gibbstown, NJ) equilibrated in Buffer A. Following a wash with Buffer A, the antigen was eluted with a gradient of 0 - 1.0 M NaCl in Buffer A. Immuno-dot blotting was performed to determine which fractions from the column contained LI protein. Fractions containing LI protein as determined by immuno- dot blot were assayed for total protein by the Bradford method followed by SDS-PAGE using silver staining and Western blotting. TMAE fractions showing comparable purity and enrichment of LI protein were pooled. The antigen was concentrated by ammonium sulfate fractionation. The solution was adjusted to 63% saturated ammonium sulfate by adding solid reagent while gently stirring over 30 min. The sample was placed on ice and precipitation allowed to proceed for 30 min. The sample was centrifuged at 12,000 x g. The pellet was resuspended in 20.0 mL PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). The resuspended pellet was chromatographed on a size exclusion column (2.6 cm ID x 89 cm) of Sephacryl 500 HR resin (Pharmacia, Piscataway, NJ). Running buffer was PBS. Chromatography performed at 20-23 ° C. Fractions were analyzed by SDS-PAGE using silver staining and western blot detection. The purest fractions were pooled. The resulting pool was concentrated. Final product was analyzed by SDS-PAGE using colloidal Coomassie staining. The LI and L2 proteins were estimated to be 85% homogeneous. The identity of LI and L2 proteins was confirmed by western blotting using the appropriate antisera. The final product was aliquoted and stored at -70 ° C. This process resulted in a total of 3.0 mg protein. Electron microscopy analysis was performed by Stmcture Probe (West Chester, PA). An aliquot of sample was placed on a 200 mesh carbon-coated copper grid. A drop of 2% phosphotungstic acid, pH 7.0 was placed on the grid for 20 seconds. The grid was allowed to air dry prior to TEM examination. All microscopy was performed using a JEOL 100 CX transmission electron microscope (JEOL USA, Inc.) at an accelerating voltage of 100 kV. The micrographs generated have a final magnification of 100,000 x. The presence of vims-like particles in the 50-55 nm size range was confirmed. EXAMPLE 29 Purification of HPV-6a LI and LI /L2 VLPs for EM Studies The yeast-expressed HPV-6a LI and HPV-6a LI + L2 proteins were partially purified and concentrated for electron microscopy (EM) studies. One to 1.5 liters of YEHD medium containing 2% galactose and 0.1 M sorbitol were inoculated with J . cerevisiae strain #1558 harboring either plasmid pl3173-357-6 (LI expression vector) or plasmid pi 4049-7-2 (LI and L2 co-expression vector) and grown at 30°C for 68-78 hours. The cells were harvested by centrifugation at 4,000 g for 10 min, and cell pellets were frozen at -70°C. All following steps were performed at 4°C. Cell pellets were thawed and suspended in an equal volume of "LI buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). Protease inhibitors PMSF and Pepstatin A were added to the slurry to final concentrations of 2 mM and 1.7 μM respectively. Cells were lysed by 3-5 passes in a microfluidizer. The lysate was clarified by centrifugation at 5000 x g for 10 minutes. The supernatant was layered on top of a 5 cm cushion of 45% (w/v) sucrose in LI buffer, and the LI or Ll + L2 proteins were pelleted by centrifugation at 100,000 x g for 4 hours. The pellet was resuspended in 1/lOth volume of Ll buffer and clarified by centrifugation at 5000 x g for 10 minutes. Samples were studied by EM and shown to contain vims-like particles. EXAMPLE 30 Cloning of HPV 16 Ll and L2 Genes Total genomic DNA was extracted from Caski cells (ATCC #CRL 1550) by standard techniques (Sambrook et al., supra). The DNA was digested with Bstl 1071 and SphI endonucleases and electrophoresed through a 0.8% low-melting-temperature agarose preparative gel. A region corresponding to DNA of ~3.5-kbp was excised from the gel and the agarose was digested with GelaseTM enzyme (Epicentre Technologies, Inc.). The gel-purified DNA was made blunt-ended with T4 DNA polymerase and ligated with blunt-ended, phosphorylated oligodeoxynucleotide linkers that contain a buried Hindiπ site. The ligation mixture was digested to completion with Hindiπ and the ~ 3.5- kbp DNA was size-fractionated through an agarose gel as described above. The gel-purified DNA was ligated with pUC18 plasmid DNA that had been digested with Hindiπ and dephosphorylated. Following transformation of competent E.coli DH5 cells (BRL), the plasmid library was screened for HPV16-positive clones by colony hybridization using an antisense 32p_j a beled oligodeoxynucleotide that is complementary to the 3'-end of the HPV-16 Ll gene (5 -GAG AGA TCT TAC AGC TTA CGT TTT TTG CGT TTA GC-3'). A pUC18 plasmid containing a 3.3- kbp HPV 16 genomic fragment was isolated and characterized by restriction enzyme and Southern blot analyses. This plasmid was designated pUC18-HPV16 L1/L2 and contains all of the Ll and L2 coding DNA sequences. Plasmid DNA was prepared using the QiagenTM Plasmid Maxi kit (Qiagen, Inc.). EXAMPLE 31 Constmction of HPV 16 Ll Yeast Expression Vector The clone, pUC18-HPV16 L1/L2 was used as a template for PCR. The HPV 16 Ll gene was amplified by PCR using Vent polymerase (New England Biolabs, Inc.), 10 cycles of amplification (940C, 1 min; 48«C, 1 min; 72<>C, 1 min 45 sec), and the following oligodeoxynucleotide primers which contain flanking Bgiπ sites (underlined): sense primer: 5'-CTC AGA TCT CAC AAA ACA AAA TGT CTC TTT GGC TGC CTA TGT AGG CC- 3'(SEQ ID NO:15) antisense primer: 5'-GAG AGA TCT TAC AGC TTA CGT TTT TTG CGT TTA GC-3' (SEQ ID NO: 16) The sense primer introduces a yeast non-translated leader sequence immediately upstream to the HPV 16 Ll initiating methionine codon (highlighted in bold print). The 1.5-kbp Ll PCR product was digested with Bgiπ, gel-purified, and ligated with the BamHI digested pCl/1-GAL vector. A pCl/1-GAL plasmid was isolated containing the HPV16 Ll gene and designated, p 14049-37-1. The Ll gene in pl4049- 37-1 was sequenced using the PRISM™ kit (ABI, Inc.) and an ABI Sequencer Model #373A according to the manufacturer's directions. The Ll gene in this isolate was shown to contain 3 nucleotide changes from the corrected, published prototype sequence (Kimbauer, R. et al. (1993) J. Virol. 67: 6929-6936), resulting in two amino acid changes: His-202 to Asp; Thr-266 to Ala. Sequence analysis of the original template DNA confirmed that these changes were also present in the genomic clone pUC18-HPV16 L1/L2 and were not introduced by the PCR. EXAMPLE 32 Constmction of the HPV 16 Ll and L2 Yeast Expression Vector Plasmid pl4049-37-l (pCl/l-GAL+HPV16 Ll) was digested with Smal, which cuts between the GAL10 promoter and the ADH1 transcription terminator. The 1.4-kbp HPV 16 L2 gene was amplified by PCR using the pUC18-HPV16 L1/L2 DNA as template, Vent polymerase (New England Biolabs, Inc.), 10 cycles of PCR amplification (94°C, 1 min; 48«C, 1 min; 72 0 C, 1 min 45 sec) and the following oligodeoxynucleotide primers which contain flanking Smal sites (underlined): sense primer: 5'-TCC CCC GGG CAC AAA ACA AAA TGC GAC ACA AAC GTT CTG CAA AAC- 3'(SEQ ID NO:17) antisense primer: 5'-TCC CCC GGG CTA GGC AGC CAA AGA GAC ATC TGA-3'(SEQ ID NO:18) The sense primer introduces a yeast non-translated leader sequence immediately upstream to the HPV 16 L2 initiating methionine codon (highlighted in bold print). The 1.4-kbp L2 PCR product was digested with Smal, gel-purified, and ligated with the Smal digested pl4049-37-l vector. A pCl/1 -GAL plasmid containing both the HPV16 Ll and L2 genes was isolated and designated, pi 4049-42-2. The L2 gene in pi 4049-42-2 was sequenced using the PRISM™ kit (ABI, Inc.) and an ABI Sequencer Model #373A according to the manufacturer's directions. The L2 gene in this isolate was shown to contain 5 nucleotide changes from the corrected, published prototype sequence (Kimbauer, R. et al. (1993) supra), resulting in one amino acid change: Ser-269 to Pro. Sequence analysis of the genomic clone pUCl 8-HPV16 L1/L2 confirmed that this change was also present in the original template DNA and was not introduced by the PCR. EXAMPLE 33 A. Expression of HPV 16 Ll and Co-Expression of HPV 16 Ll and L2 in Yeast Plasmids pl4049-37-l (pCl/l-GAL+HPV16 Ll) and pl4049-42-2 (pCl/l-GAL+HPV16 Ll and L2) were used to transform S. cerevisiae strain #1558. The resulting recombinant strains were #1678 (HPV16-L1) and #1679 (HPV16 L1+L2) as shown in the table. Clonal isolates were grown at 30°C in YEHD medium containing 2% galactose for 68-78 hours. After harvesting the cells, the cell pellets were broken with glass beads and cell ly sates analyzed for the expression of HPV 16 Ll or HPV 16 L2 protein by immunoblot analysis. Samples containing 40 meg of total cellular protein were electrophoresed on 10% Tris-Glycine gels under reducing and denaturing conditions and electroblotted onto nitrocellulose filters. The HPV 16 Ll protein was immunodetected using rabbit polyclonal antisera raised against a trpE-HPVl 1 Ll fusion protein (D. Brown et al., Virology 201 :46-54) as primary antibody and HRP- linked, donkey anti-rabbit IgG antibody (Amersham, Inc.) as the secondary antibody. The filters were processed using the chemiluminescent ECL Detection kit (Amersham, Inc.). A 50-55 kDa Ll protein band was detected in all samples except the negative control (pCl/1 without Ll or L2 gene). The L2 protein was detected as a 70 kDa protein band by immunoblot using mouse anti-HPV16 L2 sera raised against trpE-L2 fusion proteins expressed in E. coli as primary antibody. Goat anti-mouse IgG HRP-linked (Amersham, Inc.) was used as secondary antibody and the filters were processed as described above. B. Purification of Recombinant HPV Type 16 Ll + L2 Capsid Proteins All steps performed at 4 ° C unless noted. Cells were stored frozen at -70 ° C. Frozen cells (wet weight = 27.6 g) were thawed at 20-23 ° C and resuspended in 40 mL "Ll Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). The protease inhibitors PMSF and pepstatin A were added to final concentrations of 2 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 8,000 psi by 3 passes in a Ml 10 Microfluidizer (Microfluidics Corp., Newton, MA). The broken cell slurry was centrifuged at 5,000 x g for 10 min to remove cellular debris. The supematant liquid containing Ll + L2 antigen was recovered. The supematant liquid was diluted 1 :5 by addition of Buffer A (20 mM MOPS, pH 7.0) and applied to an anion exchange capture column (5.0 cm ID x 4.8 cm) of Fractogel ® EMD TMAE-650 (S) resin (EM Separations, Gibbstown, NJ) equilibrated in Buffer A. Following a wash with Buffer A, the antigen was eluted with a gradient of 0 - 1.0 M NaCl in Buffer A. Immuno-dot blotting was performed to determine which fractions from the column contained Ll protein. Fractions containing Ll protein as determined by immuno¬ dot blot were assayed for total protein by the Bradford method followed by SDS-PAGE using silver staining and Western blotting. TMAE fractions showing comparable purity and enrichment of Ll protein were pooled. The antigen was concentrated by ammonium sulfate fractionation. Samples were adjusted to 48% saturated ammonium sulfate by addition of solid reagent while gently stirring over 30 min. The samples were placed on ice and precipitation allowed to proceed overnight. The samples were centrifuged at 12,000 x g. The pellet was resuspended in 20.0 mL PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). Resuspended pellets were chromatographed separately on a size-exclusion column (2.6 cm ID x 89 cm) of Sephacryl 500 HR resin (Pharmacia, Piscataway, NJ) at 20-23 ° C. Running buffer was PBS. Fractions were analyzed by SDS-PAGE using silver staining and Westem blot detection. The purest fractions were pooled. Resulting pools were concentrated in a 50 mL stirred cell using 43 mm YM-100 flat-sheet membranes (Amicon, Beverly, MA) at a N2 pressure of 4-6 psi. Final product was analyzed by SDS-PAGE using colloidal Coomassie staining. The Ll and L2 proteins were estimated to be 70% homogeneous. The identity of Ll and L2 proteins was confirmed by Westem blotting using the appropriate antisera. The final product was aliquoted and stored at -70 ° C. This process resulted in a total of 0.53 mg protein. Electron microscopy analysis was performed by Stmcture Probe (West Chester, PA). An aliquot of sample was placed on a 200 mesh carbon-coated copper grid. A drop of 2% phosphotungstic acid, pH 7.0 was placed on the grid for 20 seconds. The grid was allowed to air dry prior to TEM examination. All microscopy was performed using a JEOL 100 CX transmission electron microscope (JEOL USA, Inc.) at an accelerating voltage of 100 kV. The micrographs generated have a final magnification of 100,000 x. The presence of vims-like particles in the 50-55 nm size range was confirmed. C. Purification of Recombinant HPV Type 16 Ll + L2 Capsid Proteins All steps performed at 4 ° C unless noted. Cells were stored frozen at -70 ° C. Frozen cells (wet weight = 92.8 g) were thawed at 20-23 ° C and resuspended in 105 mL "Ll Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl, 1.7 mM EDTA). The protease inhibitors PMSF and pepstatin A were added to final concentrations of 2 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 16,000 psi by 3 passes in a Ml 10-Y Microfluidizer (Microfluidics Corp., Newton, MA). The broken cell slurry was centrifuged at 6,100 x g for 15 min to remove cellular debris. The supematant liquid containing Ll + L2 antigen was recovered. The supematant liquid was diluted 1 :5 by addition of Buffer A (20 mM MOPS, pH 7.0) and applied to an anion exchange capture column (5.0 cm ID x 4.2 cm) of Fractogel ® EMD TMAE-650 (S) resin (EM Separations, Gibbstown, NJ) equilibrated in Buffer A. Following a wash with Buffer A, the antigen was eluted with a gradient of 0 - 1.0 M NaCl in Buffer A. Immuno-dot blotting was performed to determine which fractions from the column contained Ll protein. Fractions containing Ll protein as determined by immuno¬ dot blot were assayed for total protein by the Bradford method followed by SDS-PAGE using silver staining and Westem blotting. TMAE fractions showing comparable purity and enrichment of Ll protein were pooled. The antigen was concentrated by ammonium sulfate fractionation. Samples was adjusted to 35% saturated ammonium sulfate by addition of solid reagent while gently stirring over 10 min. The samples were placed on ice and precipitation allowed to proceed for 4 hours. The samples were centrifuged at 12,000 x g. The pellet was resuspended in 20.0 mL PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl) which contained 1 mM EDTA. Resuspended pellets were chromatographed separately on a size-exclusion column (2.6 cm ID x 89 cm) of Sephacryl 500 HR resin (Pharmacia, Piscataway, NJ). Running buffer was PBS + 1 mM EDTA. Fractions were analyzed by SDS-PAGE using silver staining and westem blot detection. The purest fractions were pooled. Resulting pools were concentrated in a 50 mL stirred cell using 43 mm YM-100 flat-sheet membranes (Amicon, Beverly, MA) at a N2 pressure of 4-6 psi. Final product was analyzed by SDS-PAGE using colloidal Coomassie staining. The Ll and L2 proteins were estimated to be 70% homogeneous. The identity of Ll and L2 proteins was confirmed by Westem blotting using the appropriate antisera. The final product was aliquoted and stored at -70 ° C. This process resulted in a total of 3.8 mg protein. EXAMPLE 34 A. Fermentation of Strain 1679 (HPV type 16 L1+L2) Procedures used for preparation frozen stock cultures, inoculum development, fermentation, and cell recovery of strain 1679 were essentially as described above. After 67 hr incubation, a cell density of 4.2 g dry cell weight per L was reached and yielded a total of 93 g wet cell pellet after recovery. B. Fermentation of Strain 1678 (HPV type 16 Ll). Procedures used for preparation frozen stock cultures, inoculum development, fermentation, and cell recovery of strain 1678 were essentially as described above. After 70.5 hr incubation, the contents of two 10 L fermentations were pooled (a cell density of 8.7 g dry cell weight per L) which yielded a total of 258 g wet cell pellet after recovery. C. Purification of Recombinant HPV Type 16 Ll Capsid Proteins All steps performed at 4 ° C unless noted. Cells of strain #1678 were stored frozen at -70 ° C. Frozen cells (wet weight = 128 g) were thawed at 20-23 ° C and resuspended in 140 mL "Modified Ll Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl). The protease inhibitors PMSF and pepstatin A were added to final concentrations of 2 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 16,000 psi by 3 passes in a Ml lO-Y Microfluidizer (Microfluidics Corp., Newton, MA). The broken cell slurry was centrifuged at 1 1 ,000 x g for 40 min to remove cellular debris. The supematant liquid containing Ll antigen was recovered. The supematant liquid was diluted 1 :5 by addition of Buffer A (20 mM MOPS, pH 7.0) and applied to an anion exchange capture column (5.0 cm ID x 6.4 cm) of Fractogel ® EMD TMAE-650 (S) resin (EM Separations, Gibbstown, NJ) equilibrated in Buffer A. Following a wash with Buffer A, the antigen was eluted with a gradient of 0 - 1.0 M NaCl in Buffer A. Immuno-dot blotting was performed to determine which fractions from the column contained Ll protein. Fractions containing Ll protein as determined by immuno¬ dot blot were assayed for total protein by the Bradford method followed by SDS-PAGE using silver staining and Westem blotting. TMAE fractions showing comparable purity and enrichment of Ll protein were pooled. The antigen was concentrated by ammonium sulfate fractionation. Samples were adjusted to 35% saturated ammonium sulfate by addition of solid reagent while gently stirring over 10 min. The samples were placed on ice and precipitation allowed to proceed for 5 hours. The samples were centrifuged at 12,000 x g. The pellet was resuspended in 20.0 mL PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). Resuspended pellets were chromatographed separately on a size-exclusion column (2.6 cm ID x 89 cm) of Sephacryl 500 HR resin (Pharmacia, Piscataway, NJ). Running buffer was PBS. Fractions were analyzed by SDS-PAGE using silver staining and Westem blot detection. The purest fractions were pooled. Resulting pools were concentrated in a 50 mL stirred cell using 43 mm YM-100 flat-sheet membranes (Amicon, Beverly, MA) at a N2 pressure of 4-6 psi. Final product was analyzed by SDS-PAGE using colloidal Coomassie staining. The Ll protein was estimated to be 70% homogeneous. The identity of Ll was confirmed by Westem blotting using the appropriate antisera. The final product was aliquoted and stored at -70 ° C. This process resulted in a total of 7.4 mg protein. D. Analytical Procedures Immuno-Dot Blot Procedure Samples were diluted (when necessary) 1:10 in Milli-Q-H2θ and 10 mcL of sample was spotted onto PolyScreen™ PVDF membranes (NEN Research Products, Boston, MA). After spots had dried, the membranes were washed in water and allowed to dry. Primary antibody solution was prepared by dilution of the appropriate antisemm in blotting buffer (5% non-fat milk in 6.25 mM Na phosphate, pH 7.2, 150 mM NaCl, 0.02% NaN3). Incubation was for at least 1 hour at 20-23 ° C. The blot was washed for 1 min each in three changes of PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). Secondary antibody solution was prepared by diluting the appropriate alkaline phosphatase-linked conjugate antisemm in blotting buffer. Incubation proceeded under the same conditions for at least 1 hour. Blots were washed as before and detected using a 1 step NBT/BCIP substrate (Pierce, Rockford, IL). Antibodies used for detection were as follows: HPV6a Ll was detected by MAB 837 (Chemicon International, Inc., Temecula, CA). HPV 6a L2 was detected by mouse anti-HPV6a L2-trpE fusion semm pool # 641 and 647. HPV 16 Ll was detected by MAB 885 (Chemicon International, Inc., Temecula, CA). HPV 16 L2 was detected by mouse anti-HPV16 L2-trpE fusion serum pool # 611. Bradford Assay for Total Protein Total protein was assayed using a commercially available Coomassie Plus ® kit (Pierce, Rockford, IL). Samples were diluted to appropriate levels in Milli-Q-H2θ. Volumes required were 0.1 mL and 1.0 mL for the standard and microassay protocols, respectively. For both protocols, BSA (Pierce, Rockford, IL) was used to generate the standard curve. The assay was performed according to manufacturer's recommendations. Standard curves were plotted using CricketGraph ® software on a Macintosh πci computer. EXAMPLE 35 Purification of Recombinant HPV Type 1 1 Ll Capsid Proteins All steps were performed at 4 ° C unless noted. Cells were stored frozen at -70 ° C. Frozen cells (wet weight = 180 g) were thawed at 20-23 ° C and resuspended in 900 mL "Breaking Buffer" (50 mM MOPS, pH 7.2, 500 mM NaCl, 1 mM CaCl2). The protease inhibitors AEBSF and pepstatin A were added to final concentrations of 1 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 16,000 psi by 4 passes in a Ml 10- Y Microfluidizer (Microfluidics Corp., Newton, MA). A sufficient volume of 10% Triton XI 00 ® detergent (Pierce, -Rockford, IL) was added to the broken cell slurry to bring the concentration of TXlOO to 0.5%. The slurry was stirred for 20 hours. The Triton XI 00-treated lysate was centrifuged at 12,000 x g for 40 min to remove cellular debris. The supematant liquid containing Ll protein was recovered. The supematant liquid was diafiltered against five volumes of 20 mM sodium phosphate, pH 7.2, 0.5 M NaCl using a 300K tangential flow membrane cassette (Filtron, Northborough, MA). The material retained by the membrane was shown by radioimmunoassay and westem blotting to contain the Ll protein. The retentate was applied to a high resolution affinity column (11.0 cm ID x 5.3 cm) of SP Spherodex (M) ® resin (IBF, Villeneuve-la-Garenne, France) equilibrated in 20 mM sodium phosphate, pH 7.2, 0.5 M NaCl. Following a wash with equilibration buffer and a step wash with 20 mM sodium phosphate, pH 7.2, 1.0 M NaCl, the Ll protein was eluted with a step wash of 20 mM sodium phosphate, pH 7.2, 2.5 M NaCl. Fractions were collected during the washes and elution. Column fractions were assayed for total protein by the Bradford method. Fractions were then analyzed by Westem blotting and SDS-PAGE with colloidal Coomassie detection. Fractions were also analyzed by radioimmunoassay. SP Spherodex fractions showing comparable purity and enrichment of Ll protein were pooled. Final product was analyzed by westem blotting and SDS- PAGE with colloidal Coomassie detection. The Ll protein was shown by densitometry of the Coomassie-stained gels to be > 90% homogeneous. The identity of Ll protein was confirmed by Westem blotting. The final product was filtered aseptically through a 0.22 μm membrane and stored at 4 ° C. This process resulted in a total of 202 mg protein. Electron microscopy analysis is performed by Structure Probe (West Chester, PA). An aliquot of sample is placed on a 200 mesh carbon-coated copper grid. A drop of 2% phosphotungstic acid, pH 7.0 is placed on the grid for 20 seconds. The grid is allowed to air dry prior to TEM examination. All microscopy is performed using a JEOL 100 CX transmission electron microscope (JEOL USA, Inc.) at an accelerating voltage of 100 kV. The micrographs generated have a final magnification of 100,000 x. SDS-PAGE and Westem Blot Assays All gels, buffers, and electrophoretic apparatus were obtained from Novex (San Diego, CA) and were run according to manufacturer's recommendations. Briefly, samples were diluted to equal protein concentrations in Milli-Q-H2θ and mixed 1 : 1 with sample incubation buffer containing 200 mM DTT. Samples were incubated 15 min at 100 ° C and loaded onto pre-cast 12% Tris-glycine gels. The samples were electrophoresed at 125V for 1 hr 45 min. Gels were developed by colloidal Coomassie staining using a commercially obtained kit (Integrated Separation Systems, Natick, MA). For Westem blots, proteins were transferred to PVDF membranes at 25V for 40 min. Membranes were washed with Milli-Q- H2θ and air-dried. Primary antibody was polyclonal rabbit antiserum raised against a TrpE-HPVl 1L1 fusion protein (gift of Dr. D. Brown). The antibody solution was prepared by dilution of antiserum in blotting buffer (5% non-fat milk in 6.25 mM Na phosphate, pH 7.2, 150 mM NaCl, 0.02% NaN3). Incubation was for at least 1 hour at 20-23 ° C. The blot was washed for 1 min each in three changes of PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). Secondary antibody solution was prepared by diluting goat anti-rabbit IgG alkaline phosphatase-linked conjugate antisemm (Pierce, Rockford, IL) in blotting buffer. Incubation proceeded under the same conditions for at least 1 hour. Blots were washed as before and detected using a 1 step NBT/BCIP substrate (Pierce, Rockford, IL). EXAMPLE 36 Expression of HPV 18 Ll and L2 in Yeast Plasmids pl91-6 (pGALl-10 + HPV18 Ll) and pl95-l 1 (pGALl -10 + HPV 18 Ll + L2) were used to transform S. cerevisiae strain #1558 (MATa, leu2-04, prbl ::HIS3, mnn9::URA3, adel , cirO). Clonal isolates were grown at 30°C in YEHD medium containing 2% galactose for 88 hours. After harvesting the cells, the cell pellets were broken with glass beads and cell lysates analyzed for the expression of HPV 18 Ll and/or HPV 18 L2 protein by immunoblot analysis. Samples containing 25 ug of total cellular protein were electrophoresed through 10% Tris-Glycine gels (Novex, Inc.) under denaturing conditions and electroblotted onto nitrocellulose filters. Ll protein was immunodetected using rabbit antisemm raised against a trpE-HPWl 1 Ll fusion protein as primary antibody (Brown et al., 1994, Virology 201 :46-54) and horseradish peroxidase (HRP)-linked donkey anti-rabbit IgG (Amersham, Inc.) as secondary antibody. The filters were processed using the chemiluminescent ECL^M Detection Kit (Amersham, Inc.). A 50-55 KDa Ll protein band was detected in both the Ll and Ll + L2 coexpressor yeast clones (strains 1725 and 1727, respectively) and not in the negative control (pGALl-10 without Ll or L2 genes). The HPV 18 L2 protein was detected by Westem analysis using goat polyclonal antisemm raised against a trpE-HWlR L2 fusion protein as primary antibody followed by HRP-conjugated, rabbit anti- goat IgG (Kirkegaard and Perry Laboratories, Gaithersburg, MD). The filters were processed as described above.The L2 protein was detected as a 75 kDa protein band in the Ll + L2 coexpressor yeast clone (strain 1727) but not in either the negative control or the Ll expressor clone. EXAMPLE 37 Fermentation of HPV 18 Ll (strain 1725) and 18 L1+ΔL2 (strain 1727). Surface growth of a plate culture of strains 1725 and 1727 was aseptically transferred to a leucine-free liquid medium containing (per L): 8.5 g Difco yeast nitrogen base without amino acids and ammonium sulfate; 0.2 g adenine; 0.2 g uracil; 10 g succinic acid; 5 g ammonium sulfate; 40 g glucose; 0.25 g L-tyrosine; 0.1 g L-arginine; 0.3 g L-isoleucine; 0.05 g L-methionine; 0.2 g L-tryptophan; 0.05 g L- histidine; 0.2 g L-lysine; 0.3 g L-phenylalanine; this medium was adjusted to pH 5.0-5.3 with NaOH prior to sterilization. After growth at 28 °C, 250 rpm on a rotary shaker, frozen culture vials were prepared by adding sterile glycerol to a final concentration of 17% (w/v) prior to storage at - 70 °C (1 mL per cryovial). Inocula were developed in the same medium (500 mL per 2-L flask) and were started by transferring the thawed contents of a frozen culture vial and incubating at 28 °C, 250 rpm on a rotary shaker for 29 hr. Fermentations of each strain used a New Brunswick SF-116 fermentor with a working volume of 10 L after inoculation. The production medium contained (per L): 20 g Difco yeast extract; 10 g Sheffield HySoy peptone; 20 g glucose; 20 g galactose; 0.3 mL Union Carbide UCON LB-625 antifoam; the medium was adjusted to pH 5.3 prior to sterilization. The entire contents (500 mL) of the 2-L inoculum flask was transferred to the fermentor which was incubated at 28 °C, 5 L air per min, 400 rpm, 3.5 psi pressure. Agitation was increased as needed to maintain dissolved oxygen levels of greater than 40% of saturation. Progress of the fermentation was monitored by off¬ line glucose measurements (Beckman Glucose 2 Analyzer) and on-line mass spectrometry (Perkin-Elmer 1200). After incubation for 66 hr, cell densities of 9.5 to 9.7 g dry cell weight per L were reached. The cultures were concentrated by hollow fiber filtration (Amicon H5MP01-43 cartridge in an Amicon DC-10 filtration system) to ca. 2 L, diafiltered with 2 L phosphate-buffered saline, and concentrated further (to ca. 1 L) before dispensing into 500-mL centrifuge bottles. Cell pellets were collected by centrifugation at 8,000 rpm (Sorval GS-3 rotor) for 20 min at 4 °C. After decanting the supematant, the pellets (total 191 to 208 g wet cells) were stored at - 70 °C until use. EXAMPLE 38 Purification of Recombinant HPV Type 18 Ll Capsid Proteins All steps performed at 4 ° C unless noted. Cells were stored frozen at -70 ° C. Frozen cells (wet weight = 126 g) were thawed at 20-23 ° C and resuspended in 70 mL "Breaking Buffer" (20 mM sodium phosphate, pH 7.2, 100 mM NaCl). The protease inhibitors PMSF and pepstatin A were added to final concentrations of 2 mM and 1.7 μM, respectively. The cell slurry was broken at a pressure of approximately 16,000 psi by 4 passes in a Ml 10- Y Microfluidizer (Microfluidics Corp., Newton, MA). The broken cell slurry was centrifuged at 12,000 x g for 40 min to remove cellular debris. The supematant liquid containing Ll antigen was recovered. The supematant liquid was diluted 1 :5 by addition of Buffer A (20 mM MOPS, pH 7.0) and applied to an anion exchange capture column (9.0 cm ID x 3.9 cm) of Fractogel ® EMD TMAE-650 (M) resin (EM Separations, Gibbstown, NJ) equilibrated in Buffer A. Following a wash with Buffer A, the antigen was eluted with a gradient of 0 - 1.0 M NaCl in Buffer A. Column fractions were assayed for total protein by the Bradford method. Fractions were then analyzed at equal total protein loadings by Westem blotting and SDS-PAGE with silver stain detection. TMAE fractions showing comparable purity and enrichment of Ll protein were pooled. The antigen was concentrated by ammonium sulfate fractionation. The solution was adjusted to 35% saturated ammonium sulfate by adding solid reagent while gently stirring over 10 min. The sample was placed on ice and precipitation allowed to proceed for 4 hours. The sample was centrifuged at 16,000 x g for 45 min. The pellet was resuspended in 20.0 mL PBS (6.25 mM Na phosphate, pH 7.2, 150 mM NaCl). The resuspended pellet was chromatographed on a size exclusion column (2.6 cm ID x 89 cm) of Sephacryl 500 HR resin (Pharmacia, Piscataway, NJ). Running buffer was PBS. Fractions were analyzed by westem blotting and SDS-PAGE with silver stain detection. The purest fractions were pooled. The resulting pool was concentrated in a 50 mL stirred cell using 43 mm YM-100 flat-sheet membranes (Amicon, Beverly, MA) at a N2 pressure of 4-6 psi. Final product was analyzed by westem blotting and SDS- PAGE with colloidal Coomassie detection. The Ll protein was estimated to be 50-60% homogeneous. The identity of Ll protein was confirmed by westem blotting. The final product was aliquoted and stored at -70 ° C. This process resulted in a total of 12.5 mg protein. EXAMPLE 39 Preparation of Immunogenic Compositions Purified VLP are formulated according to known methods, such as by the admixture of pharmaceutically acceptable carriers, stabilizers, or a vaccine adjuvant. The immunogenic VLP of the present invention may be prepared for vaccine use by combining with a physiologically acceptable composition such as, e.g. PBS, saline or distilled water. The immunogenic VLP are administered in a dosage range of about 0.1 to 100 μg, preferably about 1 to about 20 μg, in order to obtain the desired immunogenic effect. The amount of VLP per formulation may vary according to a variety of factors, including but not limited to the individual's condition, weight, age and sex. Administration of the VLP formulation may be by a variety of routes, including but not limited to oral, subcutaneous, topical, mucosal and intramuscular. Such VLP formulations may be comprised of a single type of VLP (i.e., VLP from HPV6a) or a mixture of VLP (i.e, VLP from HPV6a, HPVl 1, HPV16 and HPV18). An antimicrobial preservative, e.g. thimerosal, optionally may be present. The immunogenic antigens of the present invention may be employed, if desired, in combination with vaccine stabilizers and vaccine adjuvants. Typical stabilizers are specific compounds, e.g. polyanions such as heparin, inositol hexasulfate, sulfated beta- cyclodextrin, less specific excipients, e.g. amino acids, sorbitol, mannitol, xylitol, glycerol, sucrose, dextrose, trehalose, and variations in solution conditions, e.g. neutral pH, high ionic strength (ca. 0.5-2.0 M salts), divalent cations (Ca^ + , Mg2+). Examples of adjuvants are Al(OH)3 and Al(Pθ4). The vaccine of the present invention may be stored under refrigeration or in lyophilized form. EXAMPLE 40 Preparation of Antibodies to VLP Purified VLP are used to generate antibodies. The term "antibody" as used herein includes both polyclonal and monoclonal antibodies as well as fragments thereof, such as Fv, Fab and F(ab)2 fragments that are capable of binding antigen or hapten. The antibodies are used in a variety of ways, including but not limited to the purification of recombinant VLP, the purification of native Ll or L2 proteins, and kits. Kits would comprise a compartmentalized carrier suitable to hold in close confinement at least one container. The carrier would further comprise reagents such as the anti-VLP antibody or the VLP suitable for detecting HPV or fragments of HPV or antibodies to HPV. The carrier may also contain means for detection such as labeled antigen or enzyme substrates or the like. The antibodies or VLP or kits are useful for a variety of purposes, including but not limited to forensic analyses and epidemiological studies.

Claims: WHAT IS CLAIMED IS: 1. Isolated and purified protein of papillomavims selected from Ll protein, L2 protein, Ll + L2 protein, and functional derivatives thereof, the proteins being at least 60% pure. 2. The protein of Claim 1 wherein the papillomavims is selected from the group consisting of human papillomavims and cottontail rabbit papillomavims. 3. The protein of Claim 2 wherein the human papillomavims is selected from the group consisting of HPV6a, HPV6b, HPVl 1, HPV16, HPV18, HPV31 , HPV33, HPV35, HPV41, HPV45, and HPV58 . 4. The protein of Claim 1 wherein the protein is produced by a synthetic system, the synthetic system comprising a recombinant host. 5. Capsids comprised of the protein of Claim 1. 6. Vims-like particles comprised of the protein of Claim 1. 7. A method of producing the purified protein of Claim 1, comprising: (a) transforming a host with a recombinant DNA molecule, the recombinant DNA molecule encoding a protein selected from papillomavims Ll protein, papillomavims L2 protein, papillomavims Ll + L2 proteins, and functional derivatives thereof; (b) cultivating the transformed host under conditions that permit expression of the recombinant DNA molecule to produce cmde recombinant papillomavims protein; and (c) purifying the cmde recombinant papillomavims protein to produce the purified protein. 8. Recombinant papillomavims protein produced by the method of Claim 7. 9. Capsids comprised of the protein of Claim 7. 10. Vims-like particles comprised of the protein of Claim 7. 11. A vaccine comprising the protein of Claim 1. 12. Pharmaceutical compositions comprising the protein of Claim 1. 13. A method of treating or preventing papillomavims infection comprising administering the vaccine of Claim 1 1 to a host. 14. A kit for the detection of papillomavims or antibodies to papillomavims comprising a reagent selected from a DNA molecule encoding the papillomavims protein of Claim 1 , the protein of Claim 1 , vims-like particles comprised of the protein of Claim 1 , antibody to protein of Claim 1, and antibody to vims-like particles comprised of the protein of Claim 1. 15. A method for producing a recombinant papillomavims capsid protein assembled into a capsid or vims-like particle, comprising: a) cloning a papillomavims gene that codes for at least one papillomavims capsid protein into a vector; b) transferring the vector into a host cell to produce a recombinant host cell; c) cultivating the recombinant host cell under conditions that permit production of papillomavims capsid protein; and d) purifying the papillomavims capsid protein. 16. Capsids produced by the method of Claim 15. 17. Vims-like particles produced by the method of Claim 15. 18. A method for inducing an immune response in a vertebrate animal comprising administering the purified protein of Claim 15, or the capsid of Claim 15 or the vims-like particle of Claim 15 to an animal. 19. A method for inducing an immune response in an animal comprising administering the protein of Claim 1 to an animal. 20. The synthetic system of Claim 4 wherein the system selected from transformed insect cells, transformed yeast cells, transformed bacterial cells, transformed fungal cells, transformed plant cells and transformed animal cells. 21. The system of Claim 20 wherein the yeast is selected from the group consisting of Saccharomyces cerevisiae, Saccharomyces carlsbergensis, Hansenula polymorpha, Pichia pastor is, Kluyvermyces fragilis, and Schizosaccharomyces pombe.. 22. The system of Claim 21 wherein the Saccharomyces cerevisiae is selected from the group consisting of strains 2150-2-3, U9, 1372, 1372-ura3, 1372-his3, 1558, 1524, 1537, 1541, 1582 and 1569.

Inventors: COOK JAMES C III, GEORGE HUGH A, HOFMANN KATHRYN J, JANSEN KATHRIN U, JOYCE JOSEPH G, LEHMAN ERNEST DALE, MARKUS HENRY Z, ROSOLOWSKY MARK, SCHULTZ LOREN D, COOK, JAMES, C., III, GEORGE, HUGH, A., HOFMANN, KATHRYN, J., JANSEN, KATHRIN, U., JOYCE, JOSEPH, G., LEHMAN, ERNEST, DALE, MARKUS, HENRY, Z., ROSOLOWSKY, MARK, SCHULTZ, LOREN, D.
Applicants: COOK JAMES C III, GEORGE HUGH A, HOFMANN KATHRYN J, JANSEN KATHRIN U, JOYCE JOSEPH G, LEHMAN ERNEST DALE, MARKUS HENRY Z, MERCK & CO INC, ROSOLOWSKY MARK, SCHULTZ LOREN D, COOK, JAMES, C., III, GEORGE, HUGH, A., HOFMANN, KATHRYN, J., JANSEN, KATHRIN, U., JOYCE, JOSEPH, G., LEHMAN, ERNEST, DALE, MARKUS, HENRY, Z., MERCK & CO., INC., ROSOLOWSKY, MARK, SCHULTZ, LOREN, D.
Application year: 1995
Main classification: C12N7
IPC codes: A61K35, A61K38, A61K39, A61P17, A61P31, C07H21, C07K14, C12N1, C12N5, C12N7, C12N15, C12P21, G01N33