Characterization of murine polyclonal antisera and monoclonal antibodies generated against intact and denatured human papillomavirus type 1 virions

Cross-neutralizing antibody titres against non-vaccine types induced by a recombinant trivalent HPV vaccine (16/18/58) in rhesus macaques

Human papillomavirus (HPV) causes not only most cervical cancers but also cancers of the vagina, vulva, penis, anus, rectum, and oropharynx. Every year, 200,000 women die of cervical cancer in the world, and China accounts for about 10%. HPV vaccines are effective in preventing HPV infections thus HPV-related cancers worldwide. Studies on the clinical trials of the 2v Cervarix™ and the 4v Gardasil® have suggested that immunization with either of these vaccines provided some level of protection against other HPV types that are closely related to the types contained in the vaccines. Here we conducted a preliminary evaluation on the ability to induce cross-neutralizing antibodies in rhesus monkeys by a 3v HPV vaccine that targets HPV16, 18, and 58 and it is specifically designed for Chinese women. We found that this vaccine is no less than Gardasil® in terms of the ability to induce NAbs against non-vaccine types of HPV in rhesus macaques. These results provided evidence from the immunogenicity point of view that the KLWS 3v HPV vaccine is a strong competitor to the imported 2v and 4v HPV vaccines currently available on the market.

Production and characterization of a novel HPV anti-L2 monoclonal antibody panel

The major capsid protein of HPV, L1, assembles into pentamers that form a T = 7 icosahedral particle, but the location of the co-assembled minor capsid protein, L2, remains controversial. Several researchers have developed useful monoclonal antibodies targeting L2, but most react with linear epitopes toward the N-terminus. As a means to better define the virus capsid and better assess the localization and exposure of L2 epitopes in the context of assembled HPV, we have developed a panel of 30 monoclonal antibodies (mAbs) which target the N-terminus of L2 amino acids 11-200, previously defined as a broadly protective immunogen. Select mAbs were processed with enzymes and anti-L2 Fabs were generated. These new mAb/Fab probes will be beneficial in future studies to unravel the placement of L2 and to help better define the role of L2 in the HPV lifecycle and the nature of the broadly protective epitopes.

Development and characterization of an HPV18 detection kit using two novel HPV18 type-specific monoclonal antibodies

Background

HPV 18 is one of the most prevalent oncogenic types, only second to HPV 16, and included in the licensed vaccines on the market. In this study, we describe the production and characterization of a panel of monoclonal antibodies (mAb) to HPV18.

Methods

The immunocompetence of 1B1 and 4C2 mAbs for HPV L1 protein was evaluated by SDS-PAGE analysis, neutralization assays, affinity identification, and ELISA. The 1B1 and 4C2 genes were sequenced and analyzed. Finally, the detection kit with the two mAbs was assessed for linearity, repeatability and specificity.

Results

Both mAbs specifically recognized HPV18 L1 and virus-like particles (VLPs). These mAbs are conformation-neutralizing antibodies that have high affinity and type specificity. Based on these characteristics of these mAbs, we developed an ELISA kit for specifically detecting HPV 18 antigen. We showed that this kit displayed good linearity, repeatability and sensitivity for detecting HPV18 L1 pentamer and HPV18 VLP.

Conclusions

We characterized two monoclonal neutralizing antibodies for HPV L1 protein, and developed an ELISA kit for specifically detecting HPV 18 antigen. This newly developed kit can be used to monitor the potency of HPV vaccines throughout the entire production process as well as preliminary analysis of HPV18 infections.

A human monoclonal antibody against HPV16 recognizes an immunodominant and neutralizing epitope partially overlapping with that of H16.V5

The presence of neutralizing epitopes in human papillomavirus (HPV) L1 virus-like particles (VLPs) is the structural basis of prophylactic vaccines. An anti-HPV16 neutralizing monoclonal antibody (N-mAb) 26D1 was isolated from a memory B cell of a human vaccinee. The pre-binding of heparan sulfate to VLPs inhibited the binding of both N-mAbs to the antigen, indicating that the epitopes are critical for viral cell attachment/entry. Hybrid VLP binding with surface loop swapping between types indicated the essential roles of the DE and FG loops for both 26D1 (DEa in particular) and H16.V5 binding. Specifically, Tyr(135) and Val(141) on the DEa loop were shown to be critical residues for 26D1 binding via site-directed mutagenesis. Partially overlap between the epitopes between 26D1 and H16.V5 was shown using pairwise epitope mapping, and their binding difference is demonstrated to be predominantly in DE loop region. In addition, 26D1 epitope is immunodominant epitope recognized by both antibodies elicited by the authentic virus from infected individuals and polyclonal antibodies from vaccinees. Overall, a partially overlapping but distinct neutralizing epitope from that of H16.V5 was identified using a human N-mAb, shedding lights to the antibody arrays as part of human immune response to vaccination and infection.

Identification of neutralizing conformational epitopes on the human papillomavirus type 31 major capsid protein and functional implications

The aim of this study was to characterize the conformational neutralizing epitopes of the major capsid protein of human papillomavirus type 31. Analysis of the epitopes was performed by competitive epitope mapping using 15 anti-HPV31 and by reactivity analysis using a HPV31 mutant with an insertion of a seven-amino acid motif within the FG loop of the capsid protein. Fine mapping of neutralizing conformational epitopes on HPV L1 was analyzed by a new approach using a system displaying a combinatorial library of constrained peptides exposed on E. coli flagella. The findings demonstrate that the HPV31 FG loop is dense in neutralizing epitopes and suggest that HPV31 MAbs bind to overlapping but distinct epitopes on the central part of the FG loop, in agreement with the exposure of the FG loop on the surface of HPV VLPs, and thus confirming that neutralizing antibodies are mainly located on the tip of capsomeres. In addition, we identified a crossreacting and partially crossneutralizing conformational epitope on the relatively well conserved N-terminal part of the FG loop. Moreover, our findings support the hypothesis that there is no correlation between neutralization and the ability of MAbs to inhibit VLP binding to heparan sulfate, and confirm that the blocking of virus attachment to the extracellular matrix is an important mechanism of neutralization.

Identification of type-specific and cross-reactive neutralizing conformational epitopes on the major capsid protein of human papillomavirus type 31

The majority of the neutralizing epitopes of papillomaviruses (PV) are conformation-specific and have not been fully characterised. Studies have, to date, been limited to a few HPV types only. We analysed the epitopes on the major capsid protein (L1) of Human papillomavirus (HPV) type 31 using monoclonal antibodies (MAbs) generated against HPV-31 virus-like particles (VLPs). The type-specific MAbs against HPV-31 were all found to be neutralizing and recognized conformation-dependent epitopes. Two other MAbs directed against a conformational epitope were found to be cross-reactive with other HPV types, and one of them was found to be cross-neutralizing. Cross-reactive antibodies were further investigated using wild-type HPV-16 L1 VLPs and two mutants. The results obtained suggested the existence of a cross-neutralizing conformational epitope at the N-terminal part of the FG loop of the major capsid protein, and the other four cross-reactive MAbs recognized epitopes also located at the N-terminal part of the FG loop.

Immunohistochemical demonstration of multiple HPV types in laryngeal squamous cell carcinoma

The aim of this study was to determine the prevalence of human papillomaviruses (HPV) types 6, 11, 16, 18, 31, 33, 42, 51, 52, 56 and 58 in laryngeal squamous cell carcinoma specimens using immunohistochemical reactions and to correlate the presence of HPV with the clinical and pathological characteristics of these patients. Tissue samples were collected from 40 patients with primary laryngeal squamous cell carcinoma (LSCC) and from 33 subjects with non-neoplastic laryngeal lesions or laryngeal nodules, which served as a control group. Human papilloma virus was detected in 6 (15%) of the 40 patients. Five (83.4%) of six patients with HPV positive tumors had G2 (moderately differentiated), one patient (16.6%) had G3 (poorly differentiated), and no patient with HPV positive tumor had a G1 (well-differentiated) tumor. Four (66.6%) of the six HPV positive tumors were in the supraglottic region, one (16.6%) tumor was located in the glottis, and one (16.6%) HPV positive tumor was in the subglotic region. Five (83.4%) of six HPV positive tumors were T3-T4, and one was T2. Three of six HPV positive patients had no clinically evident cervical lymph nodes (N0), and three of the HPV positive patients were N1 or N2. Human papillomavirus was not detected in any of the samples from the control group. The presence of HPV infection in 15% of the cases may suggest a possible role in the etiology of laryngeal squamous cell carcinoma. However, no significant correlation between HPV incidence and histological grading and clinical staging could be demonstrated.

Mutations on the FG surface loop of human papillomavirus type 16 major capsid protein affect recognition by both type-specific neutralizing antibodies and cross-reactive antibodies

The aim of this study was to further characterize the conformational neutralizing epitopes present on the surface-exposed FG loop of human papillomavirus (HPV) type 16 L1 major capsid protein. We have generated previously two chimeric L1 proteins by insertion of a foreign peptide encoding an epitope of the hepatitis B core (HBc) antigen within the FG loop. In addition, three other chimeric L1 proteins were obtained by replacing three different FG loop sequences by the HBc motif and three others by point mutations. All these chimeric L1 proteins retained the ability to self-assemble into virus-like particles (VLPs), with the exception of the mutant with substitution of the L1 sequence 274-279 by the HBc motif. The eight chimeric VLPs were then analyzed for differential reactivity with a set of six HPV-16 and HPV-31 monoclonal antibodies that bound to conformational and linear epitopes. The binding patterns of these monoclonal antibodies confirmed that the FG loop contained or contributed to neutralizing conformational epitopes. The results obtained suggested that the H31.F7 antibody, an anti-HPV-31 cross-reacting and neutralizing antibody, recognized a conformational epitope situated before the 266-271 sequence. In addition, H16.E70 neutralizing antibody reactivity was reduced with L1 VLPs with an Asn to Ala point mutation at position 270, suggesting that Asn is a part of the epitope recognized by this antibody. This study contributes to the understanding of the antigenic structure of HPV-16 and -31 L1 proteins by confirming that the FG loop contributes to neutralizing epitopes and suggesting the existence of both type-specific and cross-reactive conformational epitopes within the FG loop.

A surface immunodeterminant of human papillomavirus type 16 minor capsid protein L2

We used human papillomavirus type 16 (HPV-16) particles composed of capsid proteins L1 and L2 (L1/L2 capsids) as an antigen to produce mouse monoclonal antibodies (MAbs). Of 18 MAbs recognizing surface epitopes of L1/L2 capsids, 1 was an anti-L1 MAb and 17 were anti-L2 MAbs. Seven of 11 anti-L2 MAbs recognizing linear epitopes wer found to bind to a synthetic peptide with an HPV-16 L2 sequence of amino acids (aa) 69-81, which is within a highly conserved region among different HPVs. The synthetic peptide reacted with the human sera that had been shown to be positive for an antibody against HPV-16, -18, -58, or -6b capsids composed of L1 alone. The data suggest that the HPV-16 L2 region of aa 69-81 contains a type-common immunodeterminant exposed on the surface of HPV virions.

Human papillomavirus type 16 variant lineages in United States populations characterized by nucleotide sequence analysis of the E6, L2, and L1 coding segments

Human papillomavirus type 16 (HPV16) nucleotide sequence variations in the E6 (nucleotide positions [nt] 104 to 559), L2 (nt 4272 to 5657), and L1 (nt 5665 to 7148) open reading frames (ORFs), and the long control region (nt 7479 to 7842), were examined in 29 selected United States isolates. Of 3,690 nucleotide positions, 129 (3.5%) varied. The maximum pairwise distance was 66 nucleotide differences, or 1.8%. Nucleotide variations within different genome segments were phylogenetically compatible, and nucleotide changes within E6, L2, and L1 contained phylogenetic information beyond that provided in the long control region. Most isolates were classified as members of HPV16 lineages that have been described previously. However, two novel phylogenetic branches were identified. The L2 ORF was the most variable coding segment. L2 synonymous and nonsynonymous nucleotide changes were distributed asymmetrically. The amino-terminal half of the L2 protein was remarkably conserved among all isolates, suggesting that the region is under evolutionary constraint. The amino-terminal region of the E6 ORF was relatively varied, especially at E6 amino acid positions 10 and 14. Several amino acid difference in the L1 ORF were observed between lineages. Forty-nine amino acid variations across all sequenced coding regions were observed. These amino acid differences may be relevant to differences in the generation of humoral or cell-mediated immune responses to HPV16 variants. Our data form a basis for considering HPV16 sequence variation in the rational design of vaccine strategies and as an epidemiologic correlate of cervical cancer risk.

Human papillomavirus (HPV) type distribution and serological response to HPV type 6 virus-like particles in patients with genital warts

Thirty-nine patients with condylomas (12 women and 27 men) attending a dermatology clinic were tested for genital human papillomavirus (HPV) DNA and for seroprevalence to HPV type 6 (HPV6) L1 virus-like particles. The L1 consensus PCR system (with primers MY09 and MY11) was used to determine the presence and types of HPV in sample specimens. All 37 (100%) patients with sufficient DNA specimens were positive for HPV DNA, and 35 (94%) had HPV6 DNA detected at the wart site. Three patients (8%) had HPV11 detected at the wart site, and one patient had both HPV6 and -11 detected at the wart site. Thirteen additional HPV types were detected among the patients; the most frequent were HPV54 (8%) and HPV58 (8%). Baculovirus-expressed HPV6 L1 virus-like particles were used in enzyme-linked immunosorbent assays to determine seroprevalence among the patients with warts. Seronegativity was defined by a control group of 21 women who were consistently PCR negative for HPV DNA. Seroprevalence was also determined for reference groups that included cytologically normal women who had detectable DNA from either HPV6 or HPV16 and women with HPV16-associated cervical intraepithelial neoplasia. Among the asymptomatic women with HPV6, only 2 of 9 (22%) were seropositive, compared with 12 of 12 (100%) female patients with warts. A similar trend in increased HPV6 seropositivity with increased grade of disease was found with the HPV16 DNA-positive women, whose seroprevalence increased from 1 in 11 (9%) in cytologically normal women to 6 in 15 (40%) among women with cervical intraepithelial neoplasia 1 or 3. However, only 4 of 25 (16%) male patients were seropositive. No factors examined, such as age, sexual behavior, or a history of warts, were found to definitively account for the gender difference in seroresponse.

Immunization of mice with HPV vaccinia virus recombinants generates serum IgG, IgM, and mucosal IgA antibodies

To assess the utility of vaccinia virus recombinants in the development of an immune response against HPV capsid antigens, 5-week-old C57B16 female mice were administered either purified HPV 1 capsids produced by a vaccinia virus recombinant or the recombinant vaccinia virus itself. Animals were boosted at Week 4 with either agent. Mice developed a serum IgG antibody response in all the administration protocols that was directed mainly against native L1 epitopes. Mice injected initially with the vaccinia virus recombinant and boosted with purified capsids had a higher titer antibody response (P = 0.024) with more mice responding to a greater extent. All mice produced a serum IgM response that preceded the IgG response by approximately 2 weeks and lasted 1-3 weeks. The IgM response was directed against native L1 epitopes. Although no serum IgA was detected, IgA could be detected in vaginal secretions of mice that were immunized or boosted with the vaccinia virus vector. These results indicate that an extensive humoral immune response to HPV can be elicited using vaccinia virus recombinants.

Self-assembly of human papillomavirus type 1 capsids by expression of the L1 protein alone or by coexpression of the L1 and L2 capsid proteins

Vaccinia virus vectors were used to express the major (L1) and minor (L2) capsid proteins of human papillomavirus type 1 (HPV-1) with the vaccinia virus early (p7.5K) or late (pSynth, p11K) promoters. All constructs expressed the appropriate-sized HPV proteins, and both L1 and L2, singly or in combination, localized to the nucleus. Capsids were purified by cesium chloride density gradient centrifugation from nuclei of cells infected with a vaccinia virus-L1 (vac-L1) recombinant or a vac-L1-L2 recombinant but not from vac-L2-infected cells. Electron microscopy showed that the particles were 55 nm in diameter and had icosahedral symmetry. Immunogold-labeled antibodies confirmed the presence of the L1 and L2 proteins in the HPV-1 capsids. Capsids containing L1 alone were fewer and more variable in size and shape than capsids containing the L1 and L2 proteins. The L1-plus-L2 capsids were indistinguishable in appearance from HPV-1 virions obtained from plantar warts. The ability to produce HPV capsids in vitro will be useful in many studies of HPV pathogenicity.

Detection of capsid antigen of human papillomavirus (HPV) in benign lesions of female genital tract using anti-HPV monoclonal antibody

We established a murine monoclonal antibody (K1H8) to human papillomavirus (HPV) using alkaline-disrupted virions of HPV type 1 (HPV-1) as the immunogen. K1H8 recognized a 57 kD capsid protein of HPV-1 and detected the antigen in paraffin sections of formalin-fixed tissue. With K1H8, we examined immunohistochemically 68 biopsy specimens obtained from the female genital tract. The specimens were histologically condyloma acuminatum or koilocytotic lesions with or without dysplasia and each specimen was found to harbour a single type of genital HPV, such as types 6, 11, 16, 18, 31, 33, 42, 51, 52, 56, and 58, by Southern blot hybridization analysis. The antigen was localized in the nuclei and occasionally in the cytoplasm of squamous cells showing koilocytotic changes. Eighty-four per cent of the specimens (57 cases) showed positivity for the antigen, indicating that K1H8 is a broadly-reactive antibody to various genital HPVs. The results suggest that benign mucosal lesions of the female genital tract are more frequently associated with viral production and are a potential source of transmission.

HPV-1 L1 protein expressed in cos cells displays conformational epitopes found on intact virions

Seven polyclonal and monoclonal antibodies were characterized for their ability to react specifically with either conformational or nonconformational epitopes of the HPV-1 virion. Using these antibodies, it was shown that the HPV-1 L1 protein (when expressed by an SV40 vector in cos cells) displayed conformational epitopes characteristic of intact viral particles. In addition, the L1 capsid protein was translocated normally into cell nuclei, was of appropriate size (57 kDa), and could be isolated in native form by immunoprecipitation techniques. Most importantly, the screening of expressed papillomavirus capsid proteins for reactivity with conformation-dependent antibodies represents a new, general methodology for ensuring that such proteins will be suitable for use in vaccine development or in the serologic detection/typing of human papillomavirus infections.

Human antibodies recognize multiple distinct type-specific and cross-reactive regions of the minor capsid proteins of human papillomavirus types 6 and 11

Human serum samples derived from a case-control study of patients with cervical carcinoma (n = 174) or condyloma acuminatum (n = 25) were tested for the presence of immunoglobulin G antibodies to human papillomavirus type 6 (HPV6) L2 and HPV11 L2 recombinant proteins in a Western immunoblot assay. Thirty-six samples (18%) were positive for HPV6 L2 antibodies alone, 25 (13%) were positive for HPV11 L2 antibodies alone, and 34 (17%) were positive for both HPV6 L2 and HPV11 L2 antibodies. Thirty samples that were positive for both antibodies were tested for the presence of HPV6-HPV11 L2 cross-reactive antibodies. Fifteen (50%) serum samples contained HPV6-HPV11 L2 cross-reactive antibodies, and 15 (50%) contained independent, type-specific HPV6 L2 and HPV11 L2 antibodies. Altogether, 82% of the HPV6 L2 and HPV11 L2 antibody reactivities were type specific and 18% were HPV6-HPV11 cross-reactive. There was no significant difference in the prevalence of antibody reactivities between samples from patients with cervical carcinoma and those with condyloma acuminatum. Deletion mapping identified five HPV6 L2 regions that reacted with HPV6 type-specific antibodies: 6U1 (amino acids [aa] 152 to 173), 6U2 (aa 175 to 191), 6U3 (aa 187 to 199), 6U4 (aa 201 to 217), and 6U5 (aa 351 to 367). Five HPV11 L2 regions that reacted with HPV11 type-specific antibodies were identified: 11U1 (aa 49 to 84), 11U2 (aa 147 to 162), 11U3 (aa 179 to 188), 11U4 (aa 180 to 200), and 11U5 (aa 355 to 367). Two HPV6-HPV11 cross-reactive regions were identified: 6CR1 (HPV6 L2 aa 106 to 128)/11CR1 (HPV11 L2 aa 103 to 127) and 6CR2 (HPV6 L2 aa 187 to 199)/11CR2 (HPV11 L2 aa 180 to 200).

Expression of human papillomavirus proteins in yeast Saccharomyces cerevisiae

The L1 and L2 proteins of human papillomavirus (HPV) types 1, 6, and 16 and the E6 and E7 proteins of HPV 16 were expressed in Saccharomyces cerevisiae. The yeast expressed proteins were readily detected by immune blotting and were generally intact. The HPV 1 L1 and L2 proteins expressed in yeast were indistinguishable from the major and minor capsid proteins purified from HPV 1 virions as judged by gel electrophoresis and immunoblotting. The HPV 6 and HPV 16 L2 proteins and HPV 16 E7 proteins were secreted from yeast by fusion to the yeast pre-pro-alpha-factor leader sequence. Following secretion of the HPV 16 E7 protein a rapid method of purification was developed. The yeast expressed proteins were used as antigen targets to study the human immune response in Western blot assay, ELISA, and immune precipitation. One human serum reacted with intact, but not denatured HPV 16 L2 proteins, suggesting that the yeast expressed proteins will be useful to detect antibodies reactive with conformational epitopes.