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

Comparison of HPV neutralizing and IgG antibodies in unvaccinated female adolescents

Aims: To analyze the consistency between HPV neutralizing antibodies and specific total IgG antibodies in unvaccinated females. Materials & methods: Serum samples from 978 unvaccinated Chinese females aged 9-26 years were measured for antibodies against HPV-16 and HPV-18 using simultaneous pseudovirus-based neutralization assay and ELISA. Results: There was a moderate level of consistency between HPV neutralizing antibodies and specific IgG in females aged 18-26 years (Cohen's κ coefficient for HPV-16 and HPV-18: 0.52 and 0.38) and poor consistency in those aged 9-17 years (Cohen's κ coefficient <0.05). However, Cohen's κ coefficient remained almost unchanged in sensitivity analysis when the IgG antibody cut-off value was raised. Conclusion: HPV neutralizing antibodies are a more specific indicator for the evaluation of HPV natural humoral immunity.

Contribution of Surface-Exposed Loops on the HPV16 Capsid to Antigenic Domains Recognized by Vaccine or Natural Infection Induced Neutralizing Antibodies

Human papillomavirus (HPV) is the causative agent of cervical and other cancers and represents a significant global health burden. HPV vaccines demonstrate excellent efficacy in clinical trials and effectiveness in national immunization programmes against the most prevalent genotype, HPV16. It is unclear whether the greater protection conferred by vaccine-induced antibodies, compared to natural infection antibodies, is due to differences in antibody magnitude and/or specificity. We explore the contribution of the surface-exposed loops of the major capsid protein to antigenic domains recognized by vaccine and natural infection neutralizing antibodies. Chimeric pseudoviruses incorporating individual (BC, DE, EF, FG, HI) or combined (All: BC/DE/EF/FG/HI) loop swaps between the target (HPV16) and control (HPV35) genotypes were generated, purified by ultracentrifugation and characterized by SDS-PAGE and electron microscopy. Neutralizing antibody data were subjected to hierarchical clustering and outcomes modeled on the HPV16 capsomer crystal model. Vaccine antibodies exhibited an FG loop preference followed by the EF and HI loops while natural infection antibodies displayed a more diverse pattern, most frequently against the EF loop followed by BC and FG. Both vaccine and natural infection antibodies demonstrated a clear requirement for multiple loops. Crystal modeling of these neutralizing antibody patterns suggested natural infection antibodies typically target the outer rim of the capsomer while vaccine antibodies target the central ring around the capsomer lumen. Chimeric pseudoviruses are useful tools for probing vaccine and natural infection antibody specificity. These data add to the evidence base for the effectiveness of an important public health intervention. IMPORTANCE The human papillomavirus type 16 (HPV16) major virus coat (capsid) protein is a target for antibodies induced by both natural infection and vaccination. Vaccine-induced immunity is highly protective against HPV16-related infection and disease while natural infection associated immunity significantly less so. For this study, we created chimeric functional pseudoviruses based upon an antigenically distant HPV genotype (HPV35) resistant to HPV16-specific antibodies with inserted capsid surface fragments (external loops) from HPV16. By using these chimeric pseudoviruses in functional neutralization assays we were able to highlight specific and distinct areas on the capsid surface recognized by both natural infection and vaccine induced antibodies. These data improve our understanding of the difference between natural infection and vaccine induced HPV16-specific immunity.

Investigation of the diversity of human papillomavirus 16 variants and L1 antigenic regions relevant for the prevention of human papillomavirus-related oropharyngeal cancer in Japan

OBJECTIVE

This study aimed to investigate the distribution of human papillomavirus 16 (HPV16) variants that contribute to the development of HPV-related oropharyngeal carcinoma (HPV-OPC) in the Japanese population and to evaluate genetic variations in the sequence encoding the L1 antigen region of the viral outer shell that is targeted by existing vaccines and is relevant for designing a prevention strategy to combat the exponential increase in HPV-OPC cases in Japan.

METHODS

Seventy Japanese HPV-OPC patients treated at Tohoku University Hospital were included in the study. DNA was extracted from formalin-fixed, paraffin-embedded tissue samples. Polymerase chain reaction and direct nucleotide sequencing were performed to determine the nucleotide polymorphisms necessary for the classification of HPV16 variants and to assess genetic diversity in the HPV16 L1 antigen region, including the BC, DE, EF, FG, and HI loops.

RESULTS

The most common variant of HPV16 was the A4 sublineage (88.6%), conventionally called the Asian type, followed by the A1/2/3 (10.0%) sublineage, classified as the European type. The only nonsynonymous substitution detected in the L1 antigen loop region was p.N181T in the EF loop, which was found in 28/70 (40%) cases. In contrast, no nonsynonymous substitutions were observed in the DE, FG, and HI loops, which are particularly important regions in the antigen loop targeted by existing HPV vaccines.

CONCLUSION

The most common HPV16 variant in Japanese HPV-OPC patients was the A4 subtype. The L1 antigen region is highly conserved, suggesting sufficient efficacy of existing HPV vaccines. These findings provide important information that will aid in the design of an HPV16 infection control strategy using existing HPV vaccines to prevent the spread of HPV-OPC in Japan.

Structural basis for the shared neutralization mechanism of three classes of human papillomavirus type 58 antibodies with disparate modes of binding

Human papillomavirus type 58 (HPV58) is associated with cervical cancer and poses a significant health burden worldwide. Although the commercial 9-valent HPV vaccine covers HPV58, the structural and molecular-level neutralization sites of the HPV58 complete virion are not fully understood. Here, we report the high-resolution (∼3.5 Å) structure of the complete HPV58 pseudovirus (PsV58) using cryo-electron microscopy (cryo-EM). Three representative neutralizing monoclonal antibodies (nAbs 5G9, 2H3 and A4B4) were selected through clustering from a nAb panel against HPV58. Bypassing the steric hindrance and symmetry-mismatch in the HPV Fab-capsid immune-complex, we present three different neutralizing epitopes in the PsV58, and show that, despite differences in binding, these nAbs share a common neutralization mechanism. These results offer insight into HPV58 genotype specificity and broaden our understanding of HPV58 neutralization sites for antiviral research.IMPORTANCE Cervical cancer primarily results from persistent infection with high-risk types of human papillomavirus (HPV). HPV type 58 (HPV58) is an important causative agent, especially within Asia. Despite this, we still have limited data pertaining to the structural and neutralizing epitopes of HPV58, and this encumbers our in-depth understanding of the virus mode of infection. Here, we show that representative nAbs (5G9, 10B11, 2H3, 5H2 and A4B4) from three different groups share a common neutralization mechanism that appears to prohibit the virus from associating with the extracellular matrix and cell surface. Furthermore, we identify that the nAbs engage via three different binding patterns: top-center binding (5G9 and 10B11), top-fringe binding (2H3 and 5H2), and fringe binding (A4B4). Our work shows that, despite differences in the pattern in binding, nAbs against HPV58 share a common neutralization mechanism. These results provide new insight into the understanding of HPV58 infection.

Prevalence of antibodies against a cyclic peptide mimicking the FG loop of the human papillomavirus type 16 capsid among Tunisian women

Background

In the past decade, cervical cancer has gone from being the second to the fourth most common cancer in women worldwide, but remains the second most common in developing countries. This cancer is most commonly caused by high-risk types of human papillomavirus (HPV), mainly type 16 (HPV16), which are sexually transmitted. This study aimed to investigate the usefulness of a cyclic synthetic peptide designed from the major L1 capsid protein of HPV16 for detecting anti-HPV16 antibodies.

Methods

We designed and synthetized a peptide that corresponds to the full sequence of the surface-exposed FG loop. We tested the antigenicity of the linear and the cyclic peptides against HPV16 L1 monoclonal antibodies. We used ELISA to detect anti-peptide antibodies in sera and cervical secretions of 179 Tunisian women, and we applied polymerase chain reaction and direct sequencing methods to detect and genotype HPV DNA.

Results

Both the linear and the cyclic peptides were recognized by the same neutralizing monoclonal antibodies, but the cyclic peptide was more reactive with human sera. The prevalence of the anti-peptide antibodies in sera was higher in women with low-grade squamous intraepithelial lesions (LGSIL) than in women with high-grade squamous intraepithelial lesions (HGSIL) (44% and 15%, respectively). This contrasts with HPV16 DNA prevalence. Compared to women from the general population, systemic IgG prevalence was significantly higher among sex workers (25%; P = 0.002) and women with LGSIL (44%; P = 0.001). In addition, systemic IgA and cervical IgG prevalence was higher among sex workers only (P = 0.002 and P = 0.001, respectively). We did not observe anti-peptide IgG antibodies in women with a current HPV16 infection.

Conclusion

Anti-peptide IgG in sera or in cervical secretions could be markers of an effective natural immunization against HPV16. This may open novel perspectives for monitoring vaccinated women and for the design of synthetic peptide-based vaccines.

HPV16 L1 diversity and its potential impact on the vaccination-induced immunity

Human Papillomavirus 16 (HPV16) is the most oncogenic HPV and the most associated genotype with cervical cancer development and progression. Currently, all developed vaccines are targeting HPV16 and were designed based on the major L1 capsid protein. Thus, evaluation of the diversity of HPV16 L1 sequence, mainly in the antigenic regions, will be of a great interest to assess the efficacy of the prophylactic vaccines and to predict the impact of genetic variations in these regions on the vaccination-induced immunity. A total of 377 HPV16 L1 sequences, published in public domain GenBank database, from the Americas, Africa, Asia, and Europe were collected and assembled. A total of 626 mutation events affecting 83 distinct nucleotides into the five antigenic regions of L1 gene of HPV16 were reported, and most SNPs were located in DE (27.38%, 23/83) and FG (31%, 26/83) loops. Overall, 4 mutations were frequently found in HPV16 sequences: T176N and N181T in EF loop; A266T in the FG loop and T353P/I/N HI loop. Of particular interest, some SNPs are ubiquitous and were found in all populations whereas others were population specific and their presence was limited to one or 2 at the maximum. Association between mutations in the antigenic regions and ethnicity was also investigated and showed that mutations in BC and DE loops were present with no significant difference in sequences from Europe, Asia, America and Africa. However, most mutations in FG loop are reported in sequences from European cases and are less pronounced in cases from America and Asia, whereas mutations EF and HI loops prevail in Asian cases. These data highlight a high number of variant amino acid residues that could affect the vaccination-induced immunity and impact the effectiveness of the prophylactic vaccination to fight against HPV, warranting the need of further investigation for vaccines and natural history studies of HPV16.

Substitution of Human Papillomavirus Type 16 L2 Neutralizing Epitopes Into L1 Surface Loops: The Effect on Virus-Like Particle Assembly and Immunogenicity

Cervical cancer caused by infection with human papillomaviruses (HPVs) is the fourth most common cancer in women globally, with the burden mainly in developing countries due to limited healthcare resources. Current vaccines based on virus-like particles (VLPs) assembled from recombinant expression of the immunodominant L1 protein are highly effective in the prevention of cervical infection; however, these vaccines are expensive and type-specific. Therefore, there is a need for more broadly protective and affordable vaccines. The HPV-16 L2 peptide sequences 108-120, 65-81, 56-81, and 17-36 are highly conserved across several HPV types and have been shown to elicit cross-neutralizing antibodies. To increase L2 immunogenicity, L1:L2 chimeric VLPs (cVLP) vaccine candidates were developed. The four L2 peptides mentioned above were substituted into the DE loop of HPV-16 L1 at position 131 (SAC) or in the C-terminal region at position 431 (SAE) to generate HPV-16-derived L1:L2 chimeras. All eight chimeras were transiently expressed in Nicotiana benthamiana via Agrobacterium tumefaciens-mediated DNA transfer. SAC chimeras predominantly assembled into higher order structures (T = 1 and T = 7 VLPs), whereas SAE chimeras assembled into capsomeres or formed aggregates. Four SAC and one SAE chimeras were used in vaccination studies in mice, and their ability to generate cross-neutralizing antibodies was analyzed in HPV pseudovirion-based neutralization assays. Of the seven heterologous HPVs tested, cross-neutralization with antisera specific to chimeras was observed for HPV-11 (SAE 65-18), HPV-18 (SAC 108-120, SAC 65-81, SAC 56-81, SAE 65-81), and HPV-58 (SAC 108-120). Interestingly, only anti-SAE 65-81 antiserum showed neutralization of homologous HPV-16, suggesting that the position of the L2 epitope display is critical for maintaining L1-specific neutralizing epitopes.

Genetic variability of human papillomavirus type 66 L1 gene among women presenting for cervical cancer screening in Chile

The high-risk human papillomaviruses (HR-HPVs) are involved in the development of cervical cancer. Nevertheless, there are differences in the oncogenic potential among them. HPV-16 and HPV-18 are associated with approximately 70% of cancer worldwide, and both types are the most extensively studied HR-HPV. Great variations in the prevalence of HR-HPV have been described in different countries. The impact of these variations on the epidemiology of lesions and cervical cancer is currently unknown. A high prevalence of HPV-66 has been detected in Chile. Here, we have analyzed the genetic variability of the L1 gene from HPV-66-infected Chilean women. Higher order interactions between identified mutations were analyzed by co-variation and cluster analyses. Antigenic-index alterations following L1 mutations and B-cell epitopes were predicted by BcePred algorithm. HPV-66 L1 sequences clustered phylogenetically into two main clades. The genetic variability in the HPV-66 L1 gene involved thirty nucleotide changes. Four of these were for the first time identified in this study. Some of these variants are embedded in the B-cell epitope regions. Amino acid homology in the immunodominant epitopes of HPV-66 L1 protein (DE, FG and H1 loops) was 42.9-59.1% and 28.6-68.9% compared with HPV-16 and HPV-18, respectively. The results of this research suggest that the neutralizing epitopes of HPV-66 are antigenically different compared to HPV-16 and HPV-18. Our findings show the need to perform new structural and immunological studies on HPV-66 L1 protein to evaluate the cross-protection conferred by current HPV vaccines.

Sulfotransferase and Heparanase: Remodeling Engines in Promoting Virus Infection and Disease Development

An extraordinary binding site generated in heparan sulfate (HS) structures, during its biosynthesis, provides a unique opportunity to interact with multiple protein ligands including viral proteins, and therefore adds tremendous value to this master molecule. An example of such a moiety is the sulfation at the C3 position of glucosamine residues in HS chain via 3-O sulfotransferase (3-OST) enzymes, which generates a unique virus-cell fusion receptor during herpes simplex virus (HSV) entry and spread. Emerging evidence now suggests that the unique patterns in HS sulfation assist multiple viruses in invading host cells at various steps of their life cycles. In addition, sulfated-HS structures are known to assist in invading host defense mechanisms and initiating multiple inflammatory processes; a critical event in the disease development. All these processes are detrimental for the host and therefore raise the question of how HS-sulfation is regulated. Epigenetic modulations have been shown to be implicated in these reactions during HSV infection as well as in HS modifying enzyme sulfotransferases, and therefore pose a critical component in answering it. Interestingly, heparanase (HPSE) activity is shown to be upregulated during virus infection and multiple other diseases assisting in virus replication to promote cell and tissue damage. These phenomena suggest that sulfotransferases and HPSE serve as key players in extracellular matrix remodeling and possibly generating unique signatures in a given disease. Therefore, identifying the epigenetic regulation of OST genes, and HPSE resulting in altered yet specific sulfation patterns in HS chain during virus infection, will be a significant a step toward developing potential diagnostic markers and designing novel therapies.

Epitope clustering analysis for vaccine-induced human antibodies in relationship to a panel of murine monoclonal antibodies against HPV16 viral capsid

Human papillomavirus (HPV) type 16 is the most common type implicated as the etiological agent that causes cervical cancer. The marketed prophylactic vaccines against HPV infection are composed of virus-like particles (VLPs) assembled from the recombinant major capsid protein L1. Elicitation of functional and neutralizing antibodies by vaccination is the mode of action by which the vaccines prevent the viral infection. In this study, a panel of murine mAbs against HPV16 L1 were generated and comprehensively characterized with respect to their mapping to the epitope spectrum on the viral capsid. These mAbs were categorized into five epitope bins by two different methods based on the pairwise cross-inhibition and competition with human polyclonal antibodies. In addition, a preliminary demonstration of the spatial relationship of the epitopes recognized by these mAbs was performed using a cross-blocking assay with a well-characterized human mAb, 26D1. Interestingly, two mAbs recognizing different epitopes were found to act synergistically in the pseudovirion-based neutralization assay (PBNA). To facilitate cross-lab and cross-study comparison, the international standard (IS) serum 05/134 was used to calibrate the mAbs as well as the human serum samples from the HPV16/18 vaccine recipients. The neutralizing mAbs, particularly those that recognizing immunodominant epitopes, would be useful in developing epitope-specific assays for monitoring the vaccine production process and for serological assessment.

Naturally Occurring Single Amino Acid Substitution in the L1 Major Capsid Protein of Human Papillomavirus Type 16: Alteration of Susceptibility to Antibody-Mediated Neutralization

Background

Each vaccine for human papillomavirus type 16 (HPV16) has been developed on the basis of a single variant, and whether these vaccines can prevent infection due to naturally occurring variants was not clear.

Methods

To examine this question, constructs of 39 naturally occurring single amino acid substitutions in L1 were generated for pseudovirion production, based on the analysis of 1204 HPV16 L1 protein sequences from the National Center for Biotechnology Information and Papilloma Virus Episteme.

Results

Thirty-one of 39 HPV16 L1 mutants produced infectious pseudovirions that exhibited similar particle-to-infectivity ratios, compared with reference pseudovirions. Twenty-one of 31 pseudovirion-producing mutants showed different susceptibilities to monoclonal antibodies, with 6 resulting in complete loss of reactivity to some of the tested monoclonal antibodies. The vaccinated sera neutralized all 31 variants. Mean neutralization titers of most variants changed by approximately 4-fold, compared with the reference pseudovirions, with the C428W and K430Q mutations displaying 9-fold and 11-fold lower susceptibilities, respectively, to neutralization by the sera than the reference pseudovirions.

Conclusions

These results suggest that the current HPV vaccines may not offer equal protection against all of the naturally occurring HPV16 variants discovered so far.

Cryoelectron Microscopy Maps of Human Papillomavirus 16 Reveal L2 Densities and Heparin Binding Site

Human papillomavirus (HPV) is a significant health burden and leading cause of virus-induced cancers. The current commercial vaccines are genotype specific and provide little therapeutic benefit to patients with existing HPV infections. Host entry mechanisms represent an excellent target for alternative therapeutics, but HPV receptor use, the details of cell attachment, and host entry are inadequately understood. Here we present near-atomic resolution structures of the HPV16 capsid and HPV16 in complex with heparin, both determined from cryoelectron micrographs collected with direct electron detection technology. The structures clarify details of capsid architecture for the first time, including variation in L1 major capsid protein conformation and putative location of L2 minor protein. Heparin binds specifically around the capsid icosahedral vertices and may recapitulate the earliest stage of infection, providing a framework for continuing biochemical, genetic, and biophysical studies.

The DE and FG loops of the HPV major capsid protein contribute to the epitopes of vaccine-induced cross-neutralising antibodies

The human papillomavirus (HPV) vaccines consist of major capsid protein (L1) virus-like particles (VLP) and are highly efficacious against the development of cervical cancer precursors attributable to oncogenic genotypes, HPV16 and HPV18. A degree of vaccine-induced cross-protection has also been demonstrated against genetically-related genotypes in the Alpha-7 (HPV18-like) and Alpha-9 (HPV16-like) species groups which is coincident with the detection of L1 cross-neutralising antibodies. In this study the L1 domains recognised by inter-genotype cross-neutralising antibodies were delineated. L1 crystallographic homology models predicted a degree of structural diversity between the L1 loops of HPV16 and the non-vaccine Alpha-9 genotypes. These structural predictions informed the design of chimeric pseudovirions with inter-genotype loop swaps which demonstrated that the L1 domains recognised by inter-genotype cross-neutralising antibodies comprise residues within the DE loop and the late region of the FG loop. These data contribute to our understanding of the L1 domains recognised by vaccine-induced cross-neutralising antibodies. Such specificities may play a critical role in vaccine-induced cross-protection.