We generated a monoclonal antibody, RG-1, that binds to highly conserved L2 residues 17 to 36 and neutralizes human papillomavirus 16 (HPV16) and HPV18. Passive immunotherapy with RG-1 was protective in mice. Antiserum to the HPV16 L2 peptide comprising residues 17 to 36 (peptide 17-36) neutralized pseudoviruses HPV5, HPV6, HPV16, HPV 18, HPV31, HPV 45, HPV 52, HPV 58, bovine papillomavirus 1, and HPV11 native virions. Depletion of HPV16 L2 peptide 17-36-reactive antibodies from cross-neutralizing rabbit and human L2-specific sera abolished cross-neutralization and drastically reduced neutralization of the cognate type. This cross-neutralization of diverse HPVs associated with cervical cancer, genital warts, and epidermodysplasia verruciformis suggests the possibility of a broadly protective, peptide-based vaccine.Minor capsid antigen L2 is a possible alternative to highly multivalent L1 virus-like-particle (VLP) vaccines to obtain broad protection against oncogenic human papillomaviruses (HPVs) (16). Vaccination with L2 as a full-length protein or as polypeptides protects animals against homologous-type viral challenges at both cutaneous and mucosal sites (2-4, 6, 12). Protection is not mediated by cellular immunity, suggesting the importance of neutralizing antibodies (5, 7). L2 is subdominant in the context of L1/L2 VLPs (19), but antibodies elicited by recombinant L2 immunogens are able to neutralize a remarkably broad range of HPV genotypes (15). This suggests that neutralizing epitopes of L2 may be conserved across HPV types due to some critical viral function (13). Furthermore, it raises the possibility that a single L2 protein-or peptide-based vaccine might provide comprehensive protection against the HPV types causing genital cancer and genital warts and possibly even those associated with cutaneous warts and epidermodysplasia verruciformis (EV).Identification of neutralizing epitopes within HPV16 L2. The rational design of a broadly protective L2-based preventive vaccine requires knowledge of the relevant neutralizing epitopes. To identify the neutralizing epitopes in L2, we vaccinated BALB/c mice with full-length six-His-tagged HPV16 L2 protein and produced hybridomas by using standard procedures (18). Of the 100 supernatants reactive with L2 protein, only 45 reacted with HPV16 L1/L2 pseudovirions, and only one (RG-1) neutralized HPV16 pseudovirus and was cloned. The RG-1 supernatant exhibited a neutralizing titer of 1,280 and also reacted with HPV16 L1/L2 pseudivirions by an enzyme-linked immunosorbent assay (ELISA). RG-1 and another four monoclonal antibodies (MAbs) that showed the highest ELISA reactivities with HPV16 pseudovirions were all the immunoglobulin G1() [IgG1()] isotype and reacted with HPV16 L2 protein by Western blotting (Table 1).Each MAb was screened for reactivity with 56 20-mer peptides of HPV16 L2 that overlapped each other by 12 amino acids ( Table 1). The neutralizing MAb RG-1 reacted with a peptide comprising residues 17 to 36 of HPV 16 L2 (peptide 17-36) (Fig. 1A) but not the ...

A panel of 24 monoclonal antibodies (MAbs) was generated against human papillomavirus (HPV) types 16 and 18 L1 virus-like particles (VLPs). The MAbs were screened for reactivity to a variety of VLPs prepared from HPV-6, -11, -16, -18, -31, -33, -35, and -45, cottontail rabbit papillomavirus, bovine papillomavirus type 1, and a set of 35 overlapping 20-amino-acid peptides spanning the entire HPV-16 L1 gene. Type-specific linear and conformational surface epitopes were detected as well as several cross-reactive linear epitopes that showed various levels of cross-reactivity between different genital HPV and animal papillomavirus L1s. Most of the linear epitopes were mapped using synthetic peptides, and the epitopes were identified as being either surface or buried within the VLP as defined by the pattern of reactivity in ELISA using intact and disrupted VLP antigen. These MAbs may be useful reagents to help define neutralizing epitopes of HPV-16 and -18 when infectivity assays become available, and to define the regions of L1 that are exposed on the surface or buried within the assembled capsid.

To study the temporal relationship between serum antibody response and human papillomavirus type 16 (HPV-16) infection, a cohort of 325 university women were scheduled for examinations at 4-month intervals. At every examination, interviews were completed, cells were obtained for polymerase chain reaction-based testing and for Pap screening, and serum was obtained for testing with a HPV-16 capsid-capture ELISA. Seroreactivity was associated with detection of HPV-16 DNA and with increased numbers of sex partners. The median time to seroconversion was 8.3 months among women with incident HPV-16 infections. Within 16 months following HPV-16 DNA detection, 93.7% of women with prevalent and 67.1% of women with incident infections seroconverted. After seroconversion, antibody responses were maintained during follow-up among HPV-16 DNA-positive women. Women who seroconverted were 5.7 times (95% confidence interval = 2.4-13.4) more likely to have squamous intraepithelial lesions associated with the detection of HPV-16 DNA than were women who did not seroconvert.

Papillomavirus capsids are composed of 72 pentamers reinforced through inter-and intrapentameric disulfide bonds. Recent research suggests that virus-like particles and pseudovirions (PsV) can undergo a redox-dependent conformational change involving disulfide interactions. We present here evidence that native virions exploit a tissue-spanning redox gradient that facilitates assembly events in the context of the complete papillomavirus life cycle. DNA encapsidation and infectivity titers are redox dependent in that they can be temporally modulated via treatment of organotypic cultures with oxidized glutathione. These data provide evidence that papillomavirus assembly and maturation is redox-dependent, utilizing multiple steps within both suprabasal and cornified layers.Human papillomaviruses (HPVs) exclusively infect cutaneous or mucosal epithelial tissues (14,15,30). HPV types that infect the mucosal epithelia can lead to the development of benign or malignant neoplasms, thus allowing for their categorization into low-risk or high-risk HPV types, respectively (14,15,30). A small subset of the more than 200 HPV types now identified are the causative agents of over 75% of all cervical cancers. HPV16 is the most prevalent type worldwide, found in ca. 50 to 62% of squamous cell carcinomas (14, 50).HPV16 virions contain a single, circular double-stranded DNA genome of ϳ8 kb which associates with histones to form a chromatin-like structure. This minichromosome is packaged within a nonenveloped, icosahedral capsid composed of the major capsid protein L1 and the minor capsid protein L2. Similar to polyomaviruses, 72 capsomeres of L1 are geometrically arranged on a Tϭ7 icosahedral lattice (2,9,17,19,36,42). Recent cryoelectron microscopy images of HPV16 pseudovirions (PsV) suggest that L2 is arranged near the inner conical hollow of each L1 pentamer, although it is not known whether each L1 pentamer is occupied with a single L2 protein (5, 42).Due to technical constraints in the production of native HPV virions in organotypic culture, assembly studies of HPV particles have largely been restricted to the utilization of in vitro-derived particles such as virus-like particles (VLPs), PsV, and quasivirions (QV) (6,12,25,40,43). Recent research suggests that HPV and bovine papillomavirus PsV can undergo a redox-dependent conformational change that takes place over the course of many hours. This conformational change is characterized by resistance to proteolysis and chemical reduction and the appearance of a more orderly capsid structure via transmission electron microscopy (TEM) (7,20).We present evidence that native virions, in the context of the complete papillomavirus life cycle, utilize a tissue-spanning redox gradient that facilitates multiple redox-dependent assembly and maturation events over the course of many days. We show that stability and specific infectivity of 20-day virions increases over 10-day virions, 20-day virions are more susceptible to neutralization than 10-day virions, and both viral DNA encapsidation...

Animal papillomaviruses are widely used as models to study papillomavirus infection in humans despite differences in genome organization and tissue tropism. Here, we have investigated the extent to which animal models of papillomavirus infection resemble human disease by comparing the life cycles of 10 different papillomavirus types. Three phases in the life cycles of all viruses were apparent using antibodies that distinguish between early events, the onset of viral genome amplification, and the expression of capsid proteins. The initiation of these phases follows a highly ordered pattern that appears important for the production of virus particles. The viruses examined included canine oral papillomavirus, rabbit oral papillomavirus (ROPV), cottontail rabbit papillomavirus (CRPV), bovine papillomavirus type 1, and human papillomavirus types 1, 2, 11, and 16. Each papillomavirus type showed a distinctive gene expression pattern that could be explained in part by differences in tissue tropism, transmission route, and persistence. As the timing of life cycle events affects the accessibility of viral antigens to the immune system, the ideal model system should resemble human mucosal infection if vaccine design is to be effective. Of the model systems examined here, only ROPV had a tissue tropism and a life cycle organization that resembled those of the human mucosal types. ROPV appears most appropriate for studies of the life cycles of mucosal papillomavirus types and for the development of prophylactic vaccines. The persistence of abortive infections caused by CRPV offers advantages for the development of therapeutic vaccines.

We introduced a novel humanized HLA-A*0201 transgenic (HLA Tg) rabbit model to assess the protective efficacy of a human CD8+ T cell epitope-based vaccine against primary ocular herpes infection and disease. Each of the three immunodominant human CD8+ T cell peptide epitopes from HSV-1 glycoprotein D (gD53–61, gD70–78, and gD278–286) were joined with a promiscuous human CD4+ T cell peptide epitope (gD49–82) to construct three separate pairs of CD4–CD8 peptides. Each CD4–CD8 peptide pair was then covalently linked to an Nε-palmitoyl–lysine residue via a functional base lysine amino group to construct CD4–CD8 lipopeptides. HLA Tg rabbits were immunized s.c. with a mixture of the three CD4–CD8 HSV-1 gD lipopeptides. The HSV-gD–specific T cell responses induced by the mixture of CD4–CD8 lipopeptide vaccine and the protective efficacy against acute virus replication and ocular disease were determined. Immunization induced HSV-gD49–82–specific CD4+ T cells in draining lymph node (DLN); induced HLA-restricted HSV-gD53–61, gD70–78, and gD278–286–specific CD8+ T cells in DLN, conjunctiva, and trigeminal ganglia and reduced HSV-1 replication in tears and corneal eye disease after ocular HSV-1 challenge. In addition, the HSV-1 epitope-specific CD8+ T cells induced in DLNs, conjunctiva, and the trigeminal ganglia were inversely proportional with corneal disease. The humanized HLA Tg rabbits appeared to be a useful preclinical animal model for investigating the immunogenicity and protective efficacy of human CD8+ T cell epitope-based prophylactic vaccines against ocular herpes. The relevance of HLA Tg rabbits for future investigation of human CD4–CD8 epitope-based therapeutic vaccines against recurrent HSV-1 is discussed.

Vaccination with papillomavirus L2 has been shown to induce neutralizing antibodies that protect against homologous type infection and cross-neutralize a limited number of genital HPVs. Surprisingly, we found that antibodies to bovine papillomavirus (BPV1) L2 amino acids 1-88 induced similar titers of neutralizing antibodies against Human papillomavirus (HPV)16 and 18 and BPV1 pseudoviruses and also neutralized HPV11 native virions. These antibodies also neutralized each of the other pseudovirus types tested, HPV31, HPV6 and Cottontail rabbit papillomavirus (CRPV) pseudoviruses, albeit with lower titers. HPV16, HPV18, HPV31, HPV6 and CRPV L2 anti-sera also displayed some cross-neutralization, but the titers were lower and did not encompass all pseudoviruses tested. This study demonstrates the presence of broadly cross-neutralizing epitopes at the N-terminus of L2 that are shared by cutaneous and mucosal types and by types that infect divergent species. BPV1 L2 was exceptionally effective at inducing cross-neutralizing antibodies to these shared epitopes.

Cell surface heparan sulfate proteoglycans (HSPGs) serve as primary attachment receptors for human papillomaviruses (HPVs). To demonstrate that a biologically functional HPV-receptor interaction is restricted to a specific subset of HSPGs, we first explored the role of HSPG glucosaminoglycan side chain modifications. We demonstrate that HSPG O sulfation is essential for HPV binding and infection, whereas de-N-sulfated heparin interfered with VLP binding but not with HPV pseudoinfection. This points to differences in VLP-HSPG and pseudovirion-HSPG interactions. Interestingly, internalization kinetics of VLPs and pseudovirions, as measured by fluorescence-activated cell sorting analysis, also differ significantly with approximate half times of 3.5 and 7.5 h, respectively. These data suggest that differences in HSPG binding significantly influence postbinding events. We also present evidence that pseudovirions undergo a conformational change after cell attachment. A monoclonal antibody (H33.J3), which displays negligible effectiveness in preattachment neutralization assays, efficiently neutralizes cell-bound virions. However, no difference in H33.J3 binding to pseudovirions and VLPs was observed in enzyme-linked immunosorbent assay and virus capture assays. In contrast to antibody H33.B6, which displays equal efficiencies in pre-and postattachment neutralization assays, H33.J3 does not block VLP binding to heparin, demonstrating that it interferes with steps subsequent to virus binding. Our data strongly suggest that H33.J3 recognizes a conformation-dependent epitope in capsid protein L1, which undergoes a structural change after cell attachment.Human papillomaviruses (HPVs) are highly species-specific epitheliotropic DNA viruses. Of the more than 100 different genotypes, HPV type 16 (HPV16), HPV18, HPV31, HPV33, HPV35, HPV45, and HPV58 are most closely associated with cervical epithelial neoplasias and members of the group of HPV imposing a "high risk" for malignant progression to invasive genital carcinomas (30). The nonenveloped papillomavirus is composed of 360 copies of the major capsid protein L1, organized in 72 capsomeres, and probably 12 copies of the minor capsid protein L2 (1, 43). The encapsidated genome is an 8,000-bp circularized double-stranded DNA associated with cellular histones.Despite their considerable clinical significance, the initial steps leading to infection with these viruses, as well as the mechanisms involved in virus entry into host cells, have not yet been completely elucidated due to the limited growth properties of HPV in cell cultures and the ubiquitous expression of HPV-binding proteins. The use of virus-like particles (VLPs) (20,25,36,46,49) has helped in the study of the initial interaction of papillomavirus particles with cell surfaces. It was established that VLPs of many HPV types compete for binding to the same highly conserved proteinaceous attachment receptor. In contrast to L1, L2 protein was not essential for binding, since L1 VLPs bound as efficiently as L1L2 VLPs (32,3...