Neutralization of HPV16, 18, 31, and 58 pseudovirions with antisera induced by immunizing rabbits with synthetic peptides representing segments of the HPV16 minor capsid protein L2 surface region

Vaccination with a Human Papillomavirus L2 Multimer Provides Broad Protection against 17 Human Papillomavirus Types in the Mouse Cervicovaginal Challenge Model

Human papillomavirus (HPV) is a prevalent cause of mucosal and cutaneous infections and underlying conditions ranging from benign warts to anogenital and oropharyngeal cancers affecting both males and females, notably cervical cancer. Cervical cancer is the fourth leading cause of cancer deaths among women globally and is the most impactful in low- and middle-income countries (LMICs), where the costs of screening and licensed L1-based HPV vaccines pose significant barriers to comprehensive administration. Additionally, the licensed L1-based HPV vaccines fail to protect against all oncogenic HPV types. This study generated three independent lots of an L2-based target antigen (LBTA), which was engineered from conserved linear L2-protective epitopes (aa11-88) from five human alphapapillomavirus genotypes in E. coli under cGMP conditions and adjuvanted with aluminum phosphate. Vaccination of rabbits with LBTA generated high neutralizing antibody titers against all 17 HPV types tested, surpassing the nine types covered by Gardasil®9. Passive transfer of naïve mice with LBTA antiserum revealed its capacity to confer protection against vaginal challenge with all 17 αHPV types tested. LBTA shows stability at room temperature over >1 month. Standard in vitro and in vivo toxicology studies suggest a promising safety profile. These findings suggest LBTA's promise as a next-generation vaccine with comprehensive coverage aimed at reducing the economic and healthcare burden of cervical and other HPV+ cancers in LMICs, and it has received regulatory approval for a first-in-human clinical study (NCT05672966).

Risedronate-functionalized manganese-hydroxyapatite amorphous particles: A potent adjuvant for subunit vaccines and cancer immunotherapy

The cGAS-STING pathway and the Mevalonate Pathway are druggable targets for vaccine adjuvant discovery. Manganese (Mn) and bisphosphonates are known to exert adjuvant effects by targeting these two pathways, respectively. This study found the synergistic potential of the two pathways in enhancing immune response. Risedronate (Ris) significantly amplified the Mn adjuvant early antibody response by 166-fold and fortified its cellular immunity. However, direct combination of Mn2+ and Ris resulted in increased adjuvant toxicity (40% mouse mortality). By the combination of doping property of hydroxyapatite (HA) and its high affinity for Ris, we designed Ris-functionalized Mn-HA micro-nanoparticles as an organic-inorganic hybrid adjuvant, named MnHARis. MnHARis alleviated adjuvant toxicity (100% vs. 60% survival rate) and exhibited good long-term stability. When formulated with the varicella-zoster virus glycoprotein E (gE) antigen, MnHARis triggered a 274.3-fold increase in IgG titers and a 61.3-fold surge in neutralization titers while maintaining a better long-term humoral immunity compared to the aluminum adjuvant. Its efficacy spanned other antigens, including ovalbumin, HPV18 VLP, and SARS-CoV-2 spike protein. Notably, the cellular immunity elicited by the group of gE + MnHARis was comparable to the renowned Shingrix®. Moreover, intratumoral co-administration with an anti-trophoblast cell surface antigen 2 nanobody revealed synergistic antitumor capabilities. These findings underscore the potential of MnHARis as a potent adjuvant for augmenting vaccine immune responses and improving cancer immunotherapy outcomes.

Folliculin Prevents Lysosomal Degradation of Human Papillomavirus To Support Infectious Cell Entry

Human papillomavirus (HPV) infects epithelial basal cells in the mucosa and either proliferates with the differentiation of the basal cells or persists in them. Multiple host factors are required to support the HPV life cycle; however, the molecular mechanisms involved in cell entry are not yet fully understood. In this study, we performed a genome-wide clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein 9 (Cas9) knockout (KO) screen in HeLa cells and identified folliculin (FLCN), a GTPase-activating protein for Rag GTPases, as an important host factor for HPV infection. The introduction of single guide RNAs for the FLCN gene into HeLa, HaCaT, and ectocervical Ect1 cells reduced infection by HPV18 pseudovirions (18PsVs) and 16PsVs. FLCN KO HeLa cells also exhibited strong resistance to infection with 18PsVs and 16PsVs; nevertheless, they remained highly susceptible to infections with vesicular stomatitis virus glycoprotein-pseudotyped lentivirus and adeno-associated virus. Immunofluorescence microscopy revealed that the numbers of virions binding to the cell surface were slightly increased in FLCN KO cells. However, virion internalization analysis showed that the internalized virions were rapidly degraded in FLCN KO cells. This degradation was blocked by treatment with the lysosome inhibitor bafilomycin A1. Furthermore, the virion degradation phenotype was also observed in Ras-related GTP-binding protein C (RagC) KO cells. These results suggest that FLCN prevents the lysosomal degradation of incoming HPV virions by enhancing lysosomal RagC activity. IMPORTANCE Cell entry by human papillomavirus (HPV) involves a cellular retrograde transport pathway from the endosome to the trans-Golgi network/Golgi apparatus. However, the mechanism by which this viral trafficking is safeguarded is poorly understood. This is the first study showing that the GTPase-activating protein folliculin (FLCN) protects incoming HPV virions from lysosomal degradation and supports infectious cell entry by activating the Rag GTPases, presumably through the suppression of excessive lysosomal biosynthesis. These findings provide new insights into the effects of small GTPase activity regulation on HPV cell entry and enhance our understanding of the HPV degradation pathway.

Critical Residues Involved in the Coassembly of L1 and L2 Capsid Proteins of Human Papillomavirus 16

Human papillomaviruses (HPV) are small DNA viruses associated with cervical cancer, warts, and other epithelial tumors. Structural studies have shown that the HPV capsid consists of 360 copies of the major capsid protein, L1, arranged as 72 pentamers in a T=7 icosahedral lattice, coassembling with substoichiometric amounts of the minor capsid protein, L2. However, the residues involved in the coassembly of L1 and L2 remain undefined due to the lack of structure information. Here, we investigated the solvent accessibility surfaces (SASs) of the central cavity residues of the HPV16 L1 pentamer in the crystal structure because those internal exposed residues might mediate the association with L2. Twenty residues in L1 protein were selected to be analyzed, with four residues in the lumen of the L1 pentamer identified as important: F256, R315, Q317, and T340. Mutations to these four residues reduced the PsV (pseudovirus) infection capacity in 293FT cells, and mutations to R315, Q317, and T340 substantially perturb L2 from coassembling into L1 capsid. Compared with wild-type (WT) PsVs, these mutant PsVs also have a reduced ability to become internalized into host cells. Finally, we identified a stretch of negatively charged residues on L2 (amino acids [aa] 337 to 340 [EEIE]), mutations to which completely abrogate L2 assembly into L1 capsid and subsequently impair the endocytosis and infectivity of HPV16 PsVs. These findings shed light on the elusive coassembly between HPV L1 and L2. IMPORTANCE Over 200 types of HPV have been isolated, with several high-risk types correlated with the occurrence of cervical cancer. The HPV major capsid protein, L1, assembles into a T=7 icosahedral viral shell, and associates with the minor capsid protein, L2, which plays a critical role in the HPV life cycle. Despite the important role of the L2 protein, its structure and coassembly with L1 remain elusive. In this study, we analyzed the amino acid residues at the proposed interface between L1 and L2. Certain mutations at these sites decreased the amount of L2 protein assembled into the capsid, which, in turn, led to a decrease in viral infectivity. Knowledge about these residues and the coassembly of L1 and L2 could help to expand our understanding of HPV biology and aid in the development of countermeasures against a wide range of HPV types by targeting the L2 protein.

Prevention and Treatment of HPV-Induced Skin Tumors

Non-melanoma skin cancer (NMSC) is the most common cancer in humans with increasing incidence. Meanwhile, a growing body of evidence has provided a link between skin infections with HPV of the genus beta (betaHPV) and the development of cutaneous squamous cell carcinomas (cSCCs). Based on this association, the development of vaccines against betaHPV has become an important research topic. This review summarizes the current advances in prophylactic and therapeutic betaHPV vaccines, including progresses made in preclinical testing and clinical trials.

Mutation Profile of HPV16 L1 and L2 Genes in Different Geographic Areas

The causal relationship between HPV and cervical cancer in association with the high prevalence of high risk HPV genotypes led to the design of HPV vaccines based on the major capsid L1 protein. In recent years, capsid protein L2 has also become a focal point in the field of vaccine research. The present review focuses on the variability of HPV16 L1 and L2 genes, emphasizing the distribution of specific amino acid changes in the epitopes of capsid proteins. Moreover, a substantial bioinformatics analysis was conducted to describe the worldwide distribution of amino acid substitutions throughout HPV16 L1, L2 proteins. Five amino acid changes (T176N, N181T; EF loop), (T266A; FG loop), (T353P, T389S; HI loop) are frequently observed in the L1 hypervariable surface loops, while two amino acid substitutions (D43E, S122P) are adjacent to L2 specific epitopes. These changes have a high prevalence in certain geographic regions. The present review suggests that the extensive analysis of the amino acid substitutions in the HPV16 L1 immunodominant loops may provide insights concerning the ability of the virus in evading host immune response in certain populations. The genetic variability of the HPV16 L1 and L2 epitopes should be extensively analyzed in a given population.

A bacterially expressed triple-type chimeric vaccine against human papillomavirus types 51, 69, and 26

Persistent infection of high-risk human papillomavirus (HPV) is a leading cause of some cancers, including cervical cancer. However, with over 20 carcinogenic HPV types, it is difficult to design a multivalent vaccine that can offer complete protection. Here, we describe the design and optimization of a HPV51/69/26 triple-type chimeric virus-like particle (VLP) for vaccine development. Using E. coli and a serial N-terminal truncation strategy, we created double- and triple-type chimeric VLPs through loop-swapping at equivalent surface loops. The lead candidate, H69-51BC-26FG, conferred similar particulate properties as that of its parental VLPs and comparable immunogenicity against HPV51, -69 and -26. When produced in a GMP-like facility, these H69-51BC-26FG VLPs were verified to have excellent qualities for the development of a multivalent HPV vaccine. This study showcases an amenable way to create a single VLP using type-specific epitope clustering for the design of a triple-type vaccine.

Human Papillomavirus Minor Capsid Protein L2 Mediates Intracellular Trafficking into and Passage beyond the Endoplasmic Reticulum

Human papillomaviruses (HPVs) consist of two capsid proteins: major capsid protein L1 and minor capsid protein L2. The L2 protein has been shown to be involved in intracellular trafficking events that lead to the deposition of the viral DNA into the nucleus. In this study, we investigate the role of HPV16 L2 residues 43-DQILQ-47 during intracellular trafficking in human keratinocytes. We demonstrate that the highly conserved amino acids aspartic acid, isoleucine, and leucine are involved with the intracellular trafficking of the virus. Amino acid substitution of the isoleucine and leucine residues with alanine residues results in a significant decrease in infectivity of the pseudovirions without any changes to the binding or internalization of the virus. The pseudovirions containing these substitutions exhibit an altered trafficking pattern and do not deposit the viral pseudogenome into the nucleus. Instead, these mutated pseudovirions display a lack of interaction with syntaxin 18, an ER SNARE protein, are unable to progress past the endoplasmic reticulum (ER) and are redirected to the lysosomes. The results of this study help to elucidate the role and potential involvement of the 43-DQILQ-47 sequence during intracellular trafficking, specifically during trafficking beyond the ER. IMPORTANCE High-risk types of human papillomaviruses (HPVs), such as HPV16, are highly associated with cervical, anogenital, and oropharyngeal cancers. The minor capsid protein L2 is essential for the intracellular trafficking of the viral DNA to the nucleus. This study investigates the role of amino acid residues 43-DQILQ-47 of the HPV16 L2 protein in the intracellular trafficking of the virus. Understanding how the virus traffics through the cell is a key factor in the development of additional preventative antiviral therapies. This study illustrates, through modification of the 43-DQILQ-47 sequence in pseudovirions, the importance of the 43-DQILQ-47 sequence in the trafficking of the virus beyond the endoplasmic reticulum.

In vitro inhibitory activity against HPV of the monoterpenoid zinc tetra-ascorbo-camphorate

Zinc tetra-ascorbo-camphorate (or drug "C14") is a synthetic monoterpenoid derivative that has potent anti-HIV-1 activity in vitro. In this study, we evaluated the in vitro antiviral properties of C14 against human papillomavirus (HPV). Inhibition assay of HPV-16-pseudovirus (PsVs) adsorption on COS-7 cells by C14 was used. C14 inhibited HPV-16-PsVs adsorption with IC₅₀ ranging between 2.9 and 8.3 μM and therapeutic indexes between >410 to >3,300. Pretreatment of COS-7 cells with C14 before addition of HPV-16-PsV was associated with more potent anti-HPV activity than simultaneous deposition on COS-7 of HPV-16-PsV and C14, suggesting that C14 is more effective in preventing HPV attachment to target cells than post-HPV adsorption viral events. Overall, these in vitro studies suggest that the monoterpenoid zinc tetra-ascorbo-camphorate molecule may be suitable for further clinical evaluations as potential microbicide or therapeutic drug.

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.

RG1-VLP and Other L2-Based, Broad-Spectrum HPV Vaccine Candidates

Licensed human papillomavirus (HPV) vaccines contain virus-like particles (VLPs) self-assembled from L1 major-capsid proteins that are remarkably effective prophylactic immunogens. However, the induced type-restricted immune response limits coverage to the included vaccine types, and costly multiplex formulations, restrictive storage and distribution conditions drive the need for next generation HPV vaccines. Vaccine candidates based upon the minor structural protein L2 are particularly promising because conserved N-terminal epitopes induce broadly cross-type neutralizing and protective antibodies. Several strategies to increase the immunological potency of such epitopes are being investigated, including concatemeric multimers, fusion to toll-like receptors ligands or T cell epitopes, as well as immunodominant presentation by different nanoparticle or VLP structures. Several promising L2-based vaccine candidates have reached or will soon enter first-in-man clinical studies. RG1-VLP present the HPV16L2 amino-acid 17–36 conserved neutralization epitope “RG1” repetitively and closely spaced on an immunodominant surface loop of HPV16 L1-VLP and small animal immunizations provide cross-protection against challenge with all medically-significant high-risk and several low-risk HPV types. With a successful current good manufacturing practice (cGMP) campaign and this promising breadth of activity, even encompassing cross-neutralization of several cutaneous HPV types, RG1-VLP are ready for a first-in-human clinical study. This review aims to provide a general overview of these candidates with a special focus on the RG1-VLP vaccine and its road to the clinic.

Progress in L2-Based Prophylactic Vaccine Development for Protection against Diverse Human Papillomavirus Genotypes and Associated Diseases

The human papillomaviruses (HPVs) are a family of small DNA tumor viruses including over 200 genotypes classified by phylogeny into several genera. Different genera of HPVs cause ano-genital and oropharyngeal cancers, skin cancers, as well as benign diseases including skin and genital warts. Licensed vaccines composed of L1 virus-like particles (VLPs) confer protection generally restricted to the ≤9 HPV types targeted. Here, we examine approaches aimed at broadening the protection against diverse HPV types by targeting conserved epitopes of the minor capsid protein, L2. Compared to L1 VLP, L2 is less immunogenic. However, with appropriate presentation to the immune system, L2 can elicit durable, broadly cross-neutralizing antibody responses and protection against skin and genital challenge with diverse HPV types. Such approaches to enhance the strength and breadth of the humoral response include the display of L2 peptides on VLPs or viral capsids, bacteria, thioredoxin and other platforms for multimerization. Neither L2 nor L1 vaccinations elicit a therapeutic response. However, fusion of L2 with early viral antigens has the potential to elicit both prophylactic and therapeutic immunity. This review of cross-protective HPV vaccines based on L2 is timely as several candidates have recently entered early-phase clinical trials.

Rational design of a multi-valent human papillomavirus vaccine by capsomere-hybrid co-assembly of virus-like particles

The capsid of human papillomavirus (HPV) spontaneously arranges into a T = 7 icosahedral particle with 72 L1 pentameric capsomeres associating via disulfide bonds between Cys175 and Cys428. Here, we design a capsomere-hybrid virus-like particle (chVLP) to accommodate multiple types of L1 pentamers by the reciprocal assembly of single C175A and C428A L1 mutants, either of which alone encumbers L1 pentamer particle self-assembly. We show that co-assembly between any pair of C175A and C428A mutants across at least nine HPV genotypes occurs at a preferred equal molar stoichiometry, irrespective of the type or number of L1 sequences. A nine-valent chVLP vaccine-formed through the structural clustering of HPV epitopes-confers neutralization titers that are comparable with that of Gardasil 9 and elicits minor cross-neutralizing antibodies against some heterologous HPV types. These findings may pave the way for a new vaccine design that targets multiple pathogenic variants or cancer cells bearing diverse neoantigens.

Serum and cervicovaginal IgG immune responses against α7 and α9 HPV in non-vaccinated women at risk for cervical cancer: Implication for catch-up prophylactic HPV vaccination

BACKGROUND

Cervical cancer associated with high risk-human papillomavirus (HR-HPV) infection is becoming the one of the most common female cancer in many sub-Saharan African countries. First-generation immigrant African women living in Europe are at-risk for cervical cancer, in a context of social vulnerability, with frequent lack of cervical cancer screening and HPV vaccination.

OBJECTIVE

Our objective was to address immunologically the issue of catch-up prophylactic HPV vaccination in first-generation African immigrant women living in France.

METHODS

IgG immune responses and cross-reactivities to α7 (HPV-18, -45 and -68) and α9 (HPV-16, -31, -33, -35, -52 and -58) HPV types, including 7 HR-HPV targeted by the Gardasil-9® prophylactic vaccine, were evaluated in paired serum and cervicovaginal secretions (CVS) by HPV L1-virus-like particles-based ELISA. Genital HPV were detected by multiplex real time PCR (Seegene, Seoul, South Korea).

RESULTS

Fifty-one immigrant women (mean age, 41.7 years; 72.5% HIV-infected) were prospectively included. More than two-third (68.6%) of them carried genital HPV (group I) while 31.4% were negative (group II). The majority (90.2%) exhibited serum IgG to at least one α7/α9 HR-HPV. Serum HPV-specific IgG were more frequently detected in group I than group II (100% versus 68.7%; P = 0.002). The distribution of serum and genital HPV-specific IgG was similar, but mean number of IgG reactivities to α7/α9 HR-HPV was higher in serum than CVS (5.6 IgG per woman in serum versus 3.2 in CVS; P<0.001). Rates of IgG cross-reactivities against HPV different from detected cervicovaginal HPV were higher in serum and CVS in group I than group II. Finally, the majority of groups I and II women (68.6% and 68.7%, respectively) exhibited serum or cervicovaginal IgG to Gardasil-9® HR-HPV, with higher mean rates in group I than group II (6.1 Gardasil-9® HR-HPV per woman versus 1.4; P<0.01). One-third (31.2%) of group II women did not show any serum and genital HPV-specific IgG.

CONCLUSIONS

Around two-third of first-generation African immigrant women living in France showed frequent ongoing genital HPV infection and high rates of circulating and genital IgG to α7/α9 HPV, generally cross-reacting, avoiding the possibility of catch-up vaccination. Nevertheless, about one-third of women had no evidence of previous HPV infection, or showed only low levels of genital and circulating HR-HPV-specific IgG and could therefore be eligible for catch-up vaccination.

Development of a β-HPV vaccine: Updates on an emerging frontier of skin cancer prevention

Human papillomaviruses (HPVs) are small, non-enveloped, doublestranded DNA viruses. Over 200 subtypes of HPV have been identified, organized into five major genera. β-HPVs are a group of approximately 50 HPV subtypes that preferentially infect cutaneous sites. While α-HPVs are primarily responsible for genital lesions and mucosal cancers, growing evidence has established an association between β-HPVs and the development of cutaneous squamous cell carcinomas. Given this association, the development of a vaccine against β-HPVs has become an important topic of research; however, currently licensed vaccines only provide coverage for genital HPVs, leaving β-HPV infections and their associated skin cancers unaddressed. In this review, we summarize the current advances in β-HPV vaccine development, including progress made in preclinical testing and limited clinical data. We also discuss novel findings in the viral pathomechanisms involved in β-HPV cutaneous tumorigenesis that may play a large role in future vaccine development. We hope that synthesizing the available data and advances surrounding β- HPV vaccine development will not only lead to increased dedication to vaccine development, but also heightened awareness of a future vaccine among clinicians and the public.

α-Defensin HD5 Stabilizes Human Papillomavirus 16 Capsid/Core Interactions

Background:

Human papillomavirus (HPV) is linked to nearly all cases of cervical cancer. Despite available vaccines, a deeper understanding of the immune response to HPV is needed. Human α-defensin 5 (HD5), an innate immune effector peptide, blocks infection of multiple sero-types of HPV, including high-risk HPV16. While a common mechanism of α-defensin anti-viral activity against nonenveloped viruses such as HPV has emerged, there is limited understanding of how α-defensins bind to viral capsids to block infection.

Methods:

We have used cryo-electron microscopy (cryoEM), mass spectrometry (MS) crosslinking and differential lysine modification studies, and molecular dynamics (MD) simulations to probe the interaction of HPV16 pseudovirions (PsVs) with HD5.

Results:

CryoEM single particle reconstruction did not reveal HD5 density on the capsid surface. Rather, increased density was observed under the capsid shell in the presence of HD5. MS studies indicate that HD5 binds near the L1 and L2 capsid proteins and specifically near the C-terminal region of L1. MD simulations indicate that favorable electrostatic interactions can be formed between HD5 and the L1 C-terminal tail.

Conclusions:

A model is presented for how HD5 affects HPV16 structure and cell entry. In this model, HD5 binds to disordered regions of L1 and L2 protruding from the icosahedrally ordered capsid. HD5 acts to cement interactions between L1 and L2 and leads to a closer association of the L2/genome core with the L1 capsid. This model provides a structural rationale for our prior observation that HD5 interferes with the separation of L1 from the L2/genome complex during cell entry.

Graphical Abstract

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.

Genome-wide association study of cervical cancer suggests a role for ARRDC3 gene in human papillomavirus infection

The development of cervical cancer is initiated by human papillomavirus (HPV) infection and involves both viral and host genetic factors. Genome-wide association studies (GWAS) of cervical cancer have identified associations in the HLA locus and two loci outside HLA, but the principal genes that control infection and pathogenesis have not been identified. In the present study, we performed GWAS of cervical cancer in East Asian populations, involving 2609 cases and 4712 controls in the discovery stage and 1461 cases and 3295 controls in the follow-up stage. We identified novel-significant associations at 5q14 with the lead single nucleotide polymorphism (SNP) rs59661306 (P = 2.4 × 10-11) and at 7p11 with the lead SNP rs7457728 (P = 1.2 × 10-8). In 5q14, the chromatin region of the GWAS-significant SNPs was found to be in contact with the promoter of the ARRDC3 (arrestin domain-containing 3) gene. In our functional studies, ARRDC3 knockdown in HeLa cells caused significant reductions in both cell growth and susceptibility to HPV16 pseudovirion infection, suggesting that ARRDC3 is involved in the infectious entry of HPV into the cell. Our study advances the understanding of host genes that are responsible for cervical cancer susceptibility and guides future research on HPV infection and cancer development.

Oral immunization with bacteriophage MS2-L2 VLPs protects against oral and genital infection with multiple HPV types associated with head & neck cancers and cervical cancer

Human papillomaviruses (HPVs) are the most common sexually transmitted infections. HPVs are transmitted through anogenital sex or oral sex. Anogenital transmission/infection is associated with anogenital cancers and genital warts while oral transmission/infection is associated with head and neck cancers (HNCs) including recurrent respiratory papillomatosis. Current HPV vaccines protect against HPV types associated with ∼90% of cervical cancers and are expected to protect against a percentage of HNCs. However, only a few studies have assessed the efficacy of current vaccines against oral HPV infections. We had previously developed a mixed MS2-L2 candidate HPV vaccine based on bacteriophage MS2 virus-like particles (VLPs). The mixed MS2-L2 VLPs consisted of a mixture of two MS2-L2 VLPs displaying: i) a concatemer of L2 peptide (epitope 20-31) from HPV31 & L2 peptide (epitope 17-31) from HPV16 and ii) a consensus L2 peptide representing epitope 69-86. The mixed MS2-L2 VLPs neutralized/protected mice against six HPV types associated with ∼87% of cervical cancer. Here, we show that the mixed MS2-L2 VLPs can protect mice against additional HPV types; at the genital region, the VLPs protect against HPV53, 56, 11 and at the oral region, the VLPs protect against HPV16, 35, 39, 52, and 58. Thus, mixed MS2-L2 VLPs protect against eleven oncogenic HPV types associated with ∼95% of cervical cancer. The VLPs also have the potential to protect, orally, against the same oncogenic HPVs, associated with ∼99% of HNCs, including HPV11, which is associated with up to 32% of recurrent respiratory papillomatosis. Moreover, mixed MS2-L2 VLPs are thermostable at room temperature for up to 60 days after spray-freeze drying and they are protective against oral HPV infection.

Vaccine synergy with virus-like particle and immune complex platforms for delivery of human papillomavirus L2 antigen

Diverse HPV subtypes are responsible for considerable disease burden worldwide, necessitating safe, cheap, and effective vaccines. The HPV minor capsid protein L2 is a promising candidate to create broadly protective HPV vaccines, though it is poorly immunogenic by itself. To create highly immunogenic and safe vaccine candidates targeting L2, we employed a plant-based recombinant protein expression system to produce two different vaccine candidates: L2 displayed on the surface of hepatitis B core (HBc) virus-like particles (VLPs) or L2 genetically fused to an immunoglobulin capable of forming recombinant immune complexes (RIC). Both vaccine candidates were potently immunogenic in mice, but were especially so when delivered together, generating very consistent and high antibody titers directed against HPV L2 (>1,000,000) that correlated with virus neutralization. These data indicate a novel immune response synergy upon co-delivery of VLP and RIC platforms, a strategy that can be adapted generally for many different antigens.

N-terminal truncations on L1 proteins of human papillomaviruses promote their soluble expression in Escherichia coli and self-assembly in vitro

Human papillomavirus (HPV) is the causative agent in genital warts and nearly all cervical, anogenital, and oropharyngeal cancers. Nine HPV types (6, 11, 16, 18, 31, 33, 45, 52, and 58) are associated with about 90% of cervical cancers and 90% of genital warts. HPV neutralization by vaccine-elicited neutralizing antibodies can block viral infection and prevent HPV-associated diseases. However, there is only one commercially available HPV vaccine, Gardasil 9, produced from Saccharomyces cerevisiae that covers all nine types, raising the need for microbial production of broad-spectrum HPV vaccines. Here, we investigated whether N-terminal truncations of the major HPV capsid proteins L1, improve their soluble expression in Escherichia coli. We found that N-terminal truncations promoted the soluble expression of HPV 33 (truncated by 10 amino acids [aa]), 52 (15 aa), and 58 (10 aa). The resultant HPV L1 proteins were purified in pentamer form and extensively characterized with biochemical, biophysical, and immunochemical methods. The pentamers self-assembled into virus-like particles (VLPs) in vitro, and 3D cryo-EM reconstructions revealed that all formed T = 7 icosahedral particles having 50–60-nm diameters. Moreover, we formulated a nine-valent HPV vaccine candidate with aluminum adjuvant and L1 VLPs from four genotypes used in this study and five from previous work. Immunogenicity assays in mice and non-human primates indicated that this HPV nine-valent vaccine candidate elicits neutralizing antibody titers comparable to those induced by Gardasil 9. Our study provides a method for producing a nine-valent HPV vaccine in E. coli and may inform strategies for the soluble expression of other vaccine candidates.

• N-terminal truncations promote the soluble expression of HPV L1 proteins in E. coli and their self-assembly of T = 7 icosahedral particle in vitro

• An HPV 9-valent vaccine candidate was formulated with E. coli-derived HPV 6, 11, 16, 18, 31, 33, 45, 52, and 58 VLPs, and conferred comparable immunogenicity with Gardasil 9

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.

Roles of Fc Domain and Exudation in L2 Antibody-Mediated Protection against Human Papillomavirus

To address how L2-specific antibodies prevent human papillomavirus (HPV) infection of the genital tract, we generated neutralizing monoclonal antibodies (MAbs) WW1, a rat IgG2a that binds L2 residues 17 to 36 (like mouse MAb RG1), and JWW3, a mouse IgG2b derivative of Mab24 specific for L2 residues 58 to 64. By Western blotting, WW1 recognized L2 of 29/34 HPV genotypes tested, compared to only 13/34 for RG1 and 25/34 for JWW3. WW1 IgG and F(ab')₂ bound HPV16 pseudovirions similarly; however, whole IgG provided better protection against HPV vaginal challenge. Passive transfer of WW1 IgG was similarly protective in wild-type and neonatal Fc receptor (FcRn)-deficient mice, suggesting that protection by WW1 IgG is not mediated by FcRn-dependent transcytosis. Rather, local epithelial disruption, required for genital infection and induced by either brushing or nonoxynol-9 treatment, released serum IgG in the genital tract, suggesting Fc-independent exudation. Depletion of neutrophils and macrophages reduced protection of mice upon passive transfer of whole WW1 or JWW3 IgGs. Similarly, IgG-mediated protection by L2 MAbs WW1, JWW3, and RG1 was reduced in Fc receptor knockout compared to wild-type mice. However, levels of in vitro neutralization by WW1 IgG were similar in TRIM21 knockout and wild-type cells, indicating that Fc does not contribute to antibody-dependent intracellular neutralization (ADIN). In conclusion, the Fc domain of L2-specific IgGs is not active for ADIN, but it opsonizes bound extracellular pseudovirions for phagocytes in protecting mice from intravaginal HPV challenge. Systemically administered neutralizing IgG can access the site of infection in an abrasion via exudation without the need for FcRn-mediated transcytosis.IMPORTANCE At least 15 alpha HPV types are causative agents for 5% of all cancers worldwide, and beta types have been implicated in nonmelanoma skin cancer, whereas others produce benign papillomas, such as genital warts, associated with considerable morbidity and health systems costs. Vaccines targeting the minor capsid protein L2 have the potential to provide broad-spectrum immunity against medically relevant HPVs of divergent genera via the induction of broadly cross-neutralizing serum IgG. Here we examine the mechanisms by which L2-specific serum IgG reaches the viral inoculum in the genital tract to effect protection. Abrasion of the vaginal epithelium allows the virus to access and infect basal keratinocytes, and our findings suggest that this also permits the local exudation of neutralizing IgG and vaccine-induced sterilizing immunity. We also demonstrate the importance of Fc-mediated phagocytosis of L2 antibody-virion complexes for humoral immunity, a protective mechanism that is not detected by current in vitro neutralization assays.

Minor Capsid Protein L2 Polytope Induces Broad Protection against Oncogenic and Mucosal Human Papillomaviruses

The amino terminus of the human papillomavirus (HPV) minor capsid protein L2 contains a major cross-neutralization epitope which provides the basis for the development of a broadly protecting HPV vaccine. A wide range of protection against different HPV types would eliminate one of the major drawbacks of the commercial, L1-based prophylactic vaccines. Previously, we have reported that insertion of the L2 epitope into a scaffold composed of bacterial thioredoxin protein generates a potent antigen inducing comprehensive protection against different animal and human papillomaviruses. We also reported, however, that although protection is broad, some oncogenic HPV types escape the neutralizing antibody response, if L2 epitopes from single HPV types are used as immunogen. We were able to compensate for this by applying a mix of thioredoxin proteins carrying L2 epitopes from HPV16, -31, and -51. As the development of a cost-efficient HPV prophylactic vaccines is one of our objectives, this approach is not feasible as it requires the development of multiple good manufacturing production processes in combination with a complex vaccine formulation. Here, we report the development of a thermostable thioredoxin-based single-peptide vaccine carrying an L2 polytope of up to 11 different HPV types. The L2 polytope antigens have excellent abilities in respect to broadness of protection and robustness of induced immune responses. To further increase immunogenicity, we fused the thioredoxin L2 polytope antigen with a heptamerization domain. In the final vaccine design, we achieve protective responses against all 14 oncogenic HPV types that we have analyzed plus the low-risk HPVs 6 and 11 and a number of cutaneous HPVs.IMPORTANCE Infections by a large number of human papillomaviruses lead to malignant and nonmalignant disease. Current commercial vaccines based on virus-like particles (VLPs) effectively protect against some HPV types but fail to do so for most others. Further, only about a third of all countries have access to the VLP vaccines. The minor capsid protein L2 has been shown to contain so-called neutralization epitopes within its N terminus. We designed polytopes comprising the L2 epitope amino acids 20 to 38 of up to 11 different mucosal HPV types and inserted them into the scaffold of thioredoxin derived from a thermophile archaebacterium. The antigen induced neutralizing antibody responses in mice and guinea pigs against 26 mucosal and cutaneous HPV types. Further, addition of a heptamerization domain significantly increased the immunogenicity. The final vaccine design comprising a heptamerized L2 8-mer thioredoxin single-peptide antigen with excellent thermal stability might overcome some of the limitations of the current VLP vaccines.

Subcellular Trafficking of the Papillomavirus Genome during Initial Infection: The Remarkable Abilities of Minor Capsid Protein L2

Since 2012, our understanding of human papillomavirus (HPV) subcellular trafficking has undergone a drastic paradigm shift. Work from multiple laboratories has revealed that HPV has evolved a unique means to deliver its viral genome (vDNA) to the cell nucleus, relying on myriad host cell proteins and processes. The major breakthrough finding from these recent endeavors has been the realization of L2-dependent utilization of cellular sorting factors for the retrograde transport of vDNA away from degradative endo/lysosomal compartments to the Golgi, prior to mitosis-dependent nuclear accumulation of L2/vDNA. An overview of current models of HPV entry, subcellular trafficking, and the role of L2 during initial infection is provided below, highlighting unresolved questions and gaps in knowledge.

Antibody Competition Reveals Surface Location of HPV L2 Minor Capsid Protein Residues 17-36

The currently available nonavalent human papillomavirus (HPV) vaccine exploits the highly antigenic L1 major capsid protein to promote high-titer neutralizing antibodies, but is limited to the HPV types included in the vaccine since the responses are highly type-specific. The limited cross-protection offered by the L1 virus-like particle (VLP) vaccine warrants further investigation into cross-protective L2 epitopes. The L2 proteins are yet to be fully characterized as to their precise placement in the virion. Adding to the difficulties in localizing L2, studies have suggested that L2 epitopes are not well exposed on the surface of the mature capsid prior to cellular engagement. Using a series of competition assays between previously mapped anti-L1 monoclonal antibodies (mAbs) (H16.V5, H16.U4 and H16.7E) and novel anti-L2 mAbs, we probed the capsid surface for the location of an L2 epitope (aa17-36). The previously characterized L1 epitopes together with our competition data is consistent with a proposed L2 epitope within the canyons of pentavalent capsomers.

Crystal Structures of Two Immune Complexes Identify Determinants for Viral Infectivity and Type-Specific Neutralization of Human Papillomavirus

Persistent, high-risk human papillomavirus (HPV) infection is the primary cause of cervical cancer. Neutralizing antibodies elicited by L1-only virus-like particles (VLPs) can block HPV infection; however, the lack of high-resolution structures has limited our understanding of the mode of virus infection and the requirement for type specificity at the molecular level. Here, we describe two antibodies, A12A3 and 28F10, that specifically bind to and neutralize HPV58 and HPV59, respectively, through two distinct binding stoichiometries. We show that the epitopes of A12A3 are clustered in the DE loops of two adjacent HPV58 L1 monomers, whereas 28F10 recognizes the HPV59 FG loop of a single monomer. Via structure-based mutagenesis and analysis of antibody binding, we further identified the residues HPV58 D154, S168, and N170 and HPV59 M267, Q270, E273, Y276, K278, and R283, which play critical roles in virus infection. By substituting these strategic epitope residues into other HPV genotypes, we could then redirect the type-specific binding of the antibodies to these genotypes, thus highlighting the importance of these specific residues, HPV58 R161, S168, and N308 and HPV59 Q270, E273, and D281. Overall, our findings provide molecular insights into potential structural determinants of HPV required for infectivity and type specificity.

High-risk human papillomaviruses (HPVs) are considered the major causative pathogens of cancers that affect epithelial mucosa, such as cervical cancer. However, because of the lack of high-resolution structural information on the sites of neutralization, we have yet to determine the precise mode of HPV infection and how different types of HPV cause infection. Our crystal structures in this study have uncovered discrete binding stoichiometries for two different antibodies. We show that one A12A3 Fab binds to the center of one HPV58 pentamer, whereas five 28F10 Fabs bind along the top fringe of one HPV59 pentamer. Furthermore, through targeted epitope analysis, we show that 6 to 7 discontinuous residues of the L1 major capsid protein of HPV are determinants, at least in part, for virus infection and type specificity. This knowledge will help us to unravel the process of HPV infection and can potentially be used to drive the development of therapeutics that target neutralization-sensitive sites.

A novel candidate HPV vaccine: MS2 phage VLP displaying a tandem HPV L2 peptide offers similar protection in mice to Gardasil-9

Human papillomaviruses (HPVs) cause approximately 5% of cancer cases worldwide. Fortunately, three prophylactic vaccines have been approved to protect against HPV infections. Gardasil-9, the most recent HPV vaccine, is predicted to offer protection against the HPV types that cause ∼90% of cervical cancer, 86% of HPV-associated penile cancers, and ∼93% of HPV-associated head & neck cancers. As an alternative to Gardasil-9, we developed and tested a novel candidate vaccine targeting conserved epitopes in the HPV minor capsid protein, L2. We displayed a tandem HPV31/16L2 peptide (amino acid 17-31) or consensus peptides from HPV L2 (amino acid 69-86 or 108-122) on the surface of bacteriophage MS2 virus-like particles (VLPs). Mice immunized with the MS2 VLPs displaying the tandem peptide or immunized with a mixture of VLPs (displaying the tandem peptide and consensus peptide 69-86) elicited high titer antibodies against individual L2 epitopes. Moreover, vaccinated mice were protected from cervicovaginal infection with HPV pseudoviruses 16, 31, 45, 58 and sera from immunized mice neutralized HPV pseudoviruses 18 and 33 at levels similar to mice immunized with Gardasil-9. These results suggest that immunization with a tandem, L2 peptide or a low valency mixture of L2 peptide-displaying VLPs can provide broad protection against multiple HPV types.

Characterization of an Escherichia coli-derived human papillomavirus type 16 and 18 bivalent vaccine

Human papillomavirus (HPV) types 16 and 18 account for approximately 70% of cervical cancer worldwide. Neutralizing HPV prophylactic vaccines offer significant benefit, as they block HPV infection and prevent subsequent disease. However, the three licensed HPV vaccines that cover these two genotypes were produced in eukaryotic cells, which is expensive, particularly for low-income countries where HPV is highest. Here, we report a new HPV16 and -18 bivalent candidate vaccine produced from Escherichia coli. We used two strategies of N-terminal truncation of HPV L1 proteins and soluble non-fusion expression to generate HPV16 and HPV18 L1-only virus-like particles (VLPs) in a scalable process. Through comprehensive characterization of the bivalent candidate vaccine, we confirm lot consistency in a pilot scale-up of 30L, 100L and 500L. Using cryo-EM 3D reconstruction, we found that HPV16 and -18VLPs present in a T=7 icosahedral arrangement, similar in shape and size to that of the native virions. This HPV16/18 bivalent vaccine shares comparable immunogenicity with the licensed vaccines. Overall, we show that the production of a HPV16/18 bivalent vaccine from an E. coli expression system is robust and scalable, with potentially good accessibility worldwide as a population-based immunization strategy.

HPV entry into cells

Human papillomavirus (HPV) is a sexually transmitted virus responsible for the development of cervical cancer, anal cancer, head and throat cancers, as well as genital area warts. A major focus of current HPV research is on preventing the virus from entering a cell and transferring its genetic material to the nucleus, thus potentially preventing the development of cancer. Although the available HPV vaccines are extremely successful, approximately 15 additional cancer-causing HPVs have been identified that the vaccines do not protect against. Therefore, roughly 150,000 cancer cases will not be prevented annually with the current vaccines. Research efforts focused on the basic cell biology of HPV infection have a goal of identifying common infectious events that may lead to inexpensive vaccines or anti-virals to prevent infection by most, if not all, HPVs. In this review we attempt to summarize what is known regarding the process of HPV binding, entry, and intracellular trafficking.

Stop codon mutagenesis for homogenous expression of human papillomavirus L1 protein in Escherichia coli

Human papillomavirus (HPV) is widely accepted to be the major causative pathogen of cervical cancer, warts, and other epithelial tumors. Virus infection and subsequent disease development can be prevented by vaccination with HPV vaccines derived from eukaryotic expression systems. Here, we report the soluble expression of the major capsid protein L1 of HPV31, a dominant carcinogenic HPV genotype, in Escherichia coli. HPV31 L1 protein and its elongated form (L1+) were observed in SDS-PAGE and CE-SDS analysis, generated by the native HPV31 L1 gene with a TAA stop codon. Replacing the TAA with TAG but not TGA could completely terminate protein translation. Mass spectrometry sequencing showed that L1+ comprised L1 with a C-terminal extension of 38 amino acids (aa). RNA folding analysis revealed that the unfaithful L1+ expression may result from translational read-through, as TAG is more stable and accessible than the other stop codons. The 38-aa elongated fragment perturbs self-assembly of HPV31 L1+, as shown in size and morphology analyses. By 3D cryo-electron microscopy structure determination, we show self-assembly of purified HPV31 L1 (TAG) VLPs into T = 7 icosahedral symmetry particles, resembling the native HPV virion. Finally, through additional characterization and antigenicity/immunogenicity assays, we verified that the E.coli-derived HPV31 VLPs are an ideal immunogen for HPV vaccine development. Our findings outline a codon optimization stratagem for protein expression and provide a method for the in-depth investigation of prokaryotic translation regulation.

Chimeric L2-Based Virus-Like Particle (VLP) Vaccines Targeting Cutaneous Human Papillomaviruses (HPV)

Common cutaneous human papillomavirus (HPV) types induce skin warts, whereas species beta HPV are implicated, together with UV-radiation, in the development of non-melanoma skin cancer (NMSC) in immunosuppressed patients. Licensed HPV vaccines contain virus-like particles (VLP) self-assembled from L1 major capsid proteins that provide type-restricted protection against mucosal HPV infections causing cervical and other ano-genital and oro-pharyngeal carcinomas and warts (condylomas), but do not target heterologous HPV. Experimental papillomavirus vaccines have been designed based on L2 minor capsid proteins that contain type-common neutralization epitopes, to broaden protection to heterologous mucosal and cutaneous HPV types. Repetitive display of the HPV16 L2 cross-neutralization epitope RG1 (amino acids (aa) 17-36) on the surface of HPV16 L1 VLP has greatly enhanced immunogenicity of the L2 peptide. To more directly target cutaneous HPV, L1 fusion proteins were designed that incorporate the RG1 homolog of beta HPV17, the beta HPV5 L2 peptide aa53-72, or the common cutaneous HPV4 RG1 homolog, inserted into DE surface loops of HPV1, 5, 16 or 18 L1 VLP scaffolds. Baculovirus expressed chimeric proteins self-assembled into VLP and VLP-raised NZW rabbit immune sera were evaluated by ELISA and L1- and L2-based pseudovirion (PsV) neutralizing assays, including 12 novel beta PsV types. Chimeric VLP displaying the HPV17 RG1 epitope, but not the HPV5L2 aa53-72 epitope, induced cross-neutralizing humoral immune responses to beta HPV. In vivo cross-protection was evaluated by passive serum transfer in a murine PsV challenge model. Immune sera to HPV16L1-17RG1 VLP (cross-) protected against beta HPV5/20/24/38/96/16 (but not type 76), while antisera to HPV5L1-17RG1 VLP cross-protected against HPV20/24/96 only, and sera to HPV1L1-4RG1 VLP cross-protected against HPV4 challenge. In conclusion, RG1-based VLP are promising next generation vaccine candidates to target cutaneous HPV infections.

Papillomavirus assembly: An overview and perspectives

Papillomavirus life cycle is tightly coupled to epithelial cell differentiation, which has hindered the investigation of many aspects of papillomavirus biology, including virion assembly. The development of in vitro production methods of papillomavirus pseudoviruses, and the production of "native" virus in raft cultures have facilitated the study of some aspects of the assembly process. In this paper we review the current knowledge of papillomavirus assembly, directions for future research, and the implications of these studies on new therapeutic interventions.

The CD63-Syntenin-1 Complex Controls Post-Endocytic Trafficking of Oncogenic Human Papillomaviruses

Human papillomaviruses enter host cells via a clathrin-independent endocytic pathway involving tetraspanin proteins. However, post-endocytic trafficking required for virus capsid disassembly remains unclear. Here we demonstrate that the early trafficking pathway of internalised HPV particles involves tetraspanin CD63, syntenin-1 and ESCRT-associated adaptor protein ALIX. Following internalisation, viral particles are found in CD63-positive endosomes recruiting syntenin-1, a CD63-interacting adaptor protein. Electron microscopy and immunofluorescence experiments indicate that the CD63-syntenin-1 complex controls delivery of internalised viral particles to multivesicular endosomes. Accordingly, infectivity of high-risk HPV types 16, 18 and 31 as well as disassembly and post-uncoating processing of viral particles was markedly suppressed in CD63 or syntenin-1 depleted cells. Our analyses also present the syntenin-1 interacting protein ALIX as critical for HPV infection and CD63-syntenin-1-ALIX complex formation as a prerequisite for intracellular transport enabling viral capsid disassembly. Thus, our results identify the CD63-syntenin-1-ALIX complex as a key regulatory component in post-endocytic HPV trafficking.

Broad Cross-Protection Is Induced in Preclinical Models by a Human Papillomavirus Vaccine Composed of L1/L2 Chimeric Virus-Like Particles

At least 15 high-risk human papillomaviruses (HPVs) are linked to anogenital preneoplastic lesions and cancer. Currently, there are three licensed prophylactic HPV vaccines based on virus-like particles (VLPs) of the L1 major capsid protein from HPV-2, -4, or -9, including the AS04-adjuvanted HPV-16/18 L1 vaccine. The L2 minor capsid protein contains HPV-neutralizing epitopes that are well conserved across numerous high-risk HPVs. Therefore, the objective of our study was to assess the capacity to broaden vaccine-mediated protection using AS04-adjuvanted vaccines based on VLP chimeras of L1 with one or two L2 epitopes. Several chimeric VLPs were constructed by inserting L2 epitopes within the DE loop and/or C terminus of L1. Based on the shape, yield, size, and immunogenicity, one of seven chimeras was selected for further evaluation in mouse and rabbit challenge models. The chimeric VLP consisted of HPV-18 L1 with insertions of HPV-33 L2 (amino acid residues 17 to 36; L1 DE loop) and HPV-58 L2 (amino acid residues 56 to 75; L1 C terminus). This chimeric L1/L2 VLP vaccine induced persistent immune responses and protected against all of the different HPVs evaluated (HPV-6, -11, -16, -31, -35, -39, -45, -58, and -59 as pseudovirions or quasivirions) in both mouse and rabbit challenge models. The degree and breadth of protection in the rabbit were further enhanced when the chimeric L1/L2 VLP was formulated with the L1 VLPs from the HPV-16/18 L1 vaccine. Therefore, the novel HPV-18 L1/L2 chimeric VLP (alone or in combination with HPV-16 and HPV-18 L1 VLPs) formulated with AS04 has the potential to provide broad protective efficacy in human subjects.

IMPORTANCE

From evaluations in human papillomavirus (HPV) protection models in rabbits and mice, our study has identified a prophylactic vaccine with the potential to target a wide range of HPVs linked to anogenital cancer. The three currently licensed vaccines contain virus-like particles (VLPs) of the L1 major capsid protein from two, four, or nine different HPVs. Rather than increasing the diversity of L1 VLPs, this vaccine contains VLPs based on a recombinant chimera of two highly conserved neutralizing epitopes from the L2 capsid protein inserted into L1. Our study demonstrated that the chimeric L1/L2 VLP is an effective vehicle for displaying two different L2 epitopes and can be used in a quantity equivalent to what is used in the licensed vaccines. Hence, using the chimeric L1/L2 VLP may be a more cost-effective approach for vaccine formulation than adding different VLPs for each HPV.

Development of a Triple-Color Pseudovirion-Based Assay to Detect Neutralizing Antibodies against Human Papillomavirus

Pseudovirion-based neutralization assay is considered the gold standard method for evaluating the immune response to human papillomavirus (HPV) vaccines. In this study, we developed a multicolor neutralization assay to simultaneously detect the neutralizing antibodies against different HPV types. FluoroSpot was used to interpret the fluorescent protein expression instead of flow cytometry. The results of FluoroSpot and flow cytometry showed good consistency, with R² > 0.98 for the log-transformed IC₅₀ values. Regardless of the reporter color, the single-, dual-, and triple-color neutralization assays reported identical results for the same samples. In low-titer samples from naturally HPV-infected individuals, there was strong agreement between the single- and triple-color assays, with kappa scores of 0.92, 0.89, and 0.96 for HPV16, HPV18, and HPV58, respectively. Good reproducibility was observed for the triple-color assay, with coefficients of variation of 2.0%–41.5% within the assays and 8.3%–36.2% between the assays. Three triple-color systems, HPV16-18-58, HPV6-33-45, and HPV11-31-52, were developed that could evaluate the immunogenicity of a nonavalent vaccine in three rounds of the assay. With the advantages of an easy-to-use procedure and less sample consumption, the multiple-color assay is more suitable than classical assays for large sero-epidemiological studies and clinical trials and is more amenable to automation.

Protein transduction domain can enhance the humoral immunity and cross-protection of HPV16L2 peptide vaccines

Due to type-specificity, commercially available human papillomavirus (HPV) vaccines are only effective against homologous HPV serotypes, providing limited protection. Recent studies have highlighted the role of HPV minor capsid protein (known as L2) in inducing cross-protection. The N-terminal peptides of L2 contain conserved cross-response epitopes that can induce neutralizing antibodies against heterogeneous HPVs. However, when compared with L1, these peptides have lower immunogenicity, which limits the application of these vaccines. The protein transduction domain (PTD), located in the Tat protein of human immunodeficiency virus, facilitates delivery of DNA, peptides, proteins and virus particles into cells by unknown mechanisms, and has been reported to enhance immunogenicity of several antigens. In the present study, two peptides derived from the N-terminal of HPV16L2 were chosen as model antigens and constructed a series of L2 peptide vaccines by either fusing or mixing with PTD. Subsequently their immunogenicity was evaluated. The results indicated that the L2 peptides fused with PTD show considerably enhanced humoral immunity. In particular, they increased the titer of cross-neutralizing antibodies, while L2 peptides that had only been mixed with PTD induced only small cross-protection responses. Overall, the data suggest that fusion of L2 peptides with PTD significantly enhances their cross-protection and may be a promising strategy for the development of broad-spectrum HPV prophylactic vaccines.

Gardasil-9: A global survey of projected efficacy

Human papillomaviruses (HPVs) are the causative agents of human neoplasias such as warts and cancers. There are ∼19 HPV types associated with cancers, which has made it very challenging for first generation HPV vaccines to offer complete protection against all cancer-causing HPV types. Recently, a second generation HPV vaccine, Gardasil-9, has been approved to protect against more HPV types. Worldwide, Gardasil-9 will protect against HPV types associated with ∼90% of cervical cancer case in women and 80-95% of other HPV-associated anogenital cancers in both men and women. However, due to variation in HPV-type specific prevalence and distribution, the vaccine will offer different percentages of protection in different geographical regions; Gardasil-9 will offer protection against HPV types associated with ∼87.7% of cervical cancers in Asia, 91.7% in Africa, 92% in North America, 90.9% in Europe, 89.5% in Latin America & the Caribbean, and 86.5% in Australia. Because of this, Pap smear screening and testing for HPV types not included in Gardasil-9 will need to continue, especially in HIV/AIDS patients. In order to achieve complete protection against all HPV types that cause cervical cancer, a third-generation HPV vaccine is needed.

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.

Functional assessment and structural basis of antibody binding to human papillomavirus capsid

Persistent high-risk human papillomavirus (HPV) infection is linked to cervical cancer. Two prophylactic virus-like particle (VLP)-based vaccines have been marketed globally for nearly a decade. Here, we review the HPV pseudovirion (PsV)-based assays for the functional assessment of the HPV neutralizing antibodies and the structural basis for these clinically relevant epitopes. The PsV-based neutralization assay was developed to evaluate the efficacy of neutralization antibodies in sera elicited by vaccination or natural infection or to assess the functional characteristics of monoclonal antibodies. Different antibody binding modes were observed when an antibody was complexed with virions, PsVs or VLPs. The neutralizing epitopes are localized on surface loops of the L1 capsid protein, at various locations on the capsomere. Different neutralization antibodies exert their neutralizing function via different mechanisms. Some antibodies neutralize the virions by inducing conformational changes in the viral capsid, which can result in concealing the binding site for a cellular receptor like 1A1D-2 against dengue virus, or inducing premature genome release like E18 against enterovirus 71. Higher-resolution details on the epitope composition of HPV neutralizing antibodies would shed light on the structural basis of the highly efficacious vaccines and aid the design of next generation vaccines. In-depth understanding of epitope composition would ensure the development of function-indicating assays for the comparability exercise to support process improvement or process scale up. Elucidation of the structural elements of the type-specific epitopes would enable rational design of cross-type neutralization via epitope re-engineering or epitope grafting in hybrid VLPs.

Robust In Vitro and In Vivo Neutralization against Multiple High-Risk HPV Types Induced by a Thermostable Thioredoxin-L2 Vaccine

Current prophylactic virus-like particle (VLP) human papillomavirus (HPV) vaccines are based on the L1 major capsid protein and provide robust but virus type-restricted protection. Moreover, VLP vaccines have a high production cost, require cold-chain storage, and are thus not readily implementable in developing countries, which endure 85% of the cervical cancer-related death burden worldwide. In contrast with L1, immunization with minor capsid protein L2 elicits broad cross-neutralization, and we previously showed that insertion of a peptide spanning amino acids 20-38 of L2 into bacterial thioredoxin (Trx) greatly enhances its immunogenicity. Building on this finding, we use, here, four different neutralization assays to demonstrate that low doses of a trivalent Trx-L2 vaccine, incorporating L2(20-38) epitopes from HPV16, HPV31 and HPV51, and formulated in a human-compatible adjuvant, induce broadly protective responses. Specifically, we show that this vaccine, which uses a far-divergent archaebacterial thioredoxin as scaffold and is amenable to an easy one-step thermal purification, induces robust cross-neutralization against 12 of the 13 known oncogenic HPV types. Immune performance measured with two different in vitro neutralization assays was corroborated by the results of mouse cervico-vaginal challenge and passive transfer experiments indicating robust cross-protection also in vivo. Altogether, our results attest to the potential of Trx-L2 as a thermostable second-generation HPV vaccine particularly well suited for low-resource countries.

Capsid display of a conserved human papillomavirus L2 peptide in the adenovirus 5 hexon protein: a candidate prophylactic hpv vaccine approach

Background

Infection by any one of 15 high risk human papillomavirus (hrHPV) types causes most invasive cervical cancers. Their oncogenic genome is encapsidated by L1 (major) and L2 (minor) coat proteins. Current HPV prophylactic vaccines are composed of L1 virus-like particles (VLP) that elicit type restricted immunity. An N-terminal region of L2 protein identified by neutralizing monoclonal antibodies comprises a protective epitope conserved among HPV types, but it is weakly immunogenic compared to L1 VLP. The major antigenic capsid protein of adenovirus type 5 (Ad5) is hexon which contains 9 hypervariable regions (HVRs) that form the immunodominant neutralizing epitopes. Insertion of weakly antigenic foreign B cell epitopes into these HVRs has shown promise in eliciting robust neutralizing antibody responses. Thus here we sought to generate a broadly protective prophylactic HPV vaccine candidate by inserting a conserved protective L2 epitope into the Ad5 hexon protein for VLP-like display.

Methods

Four recombinant adenoviruses were generated without significant compromise of viral replication by introduction of HPV16 amino acids L2 12–41 into Ad5 hexon, either by insertion into, or substitution of, either hexon HVR1 or HVR5.

Results

Vaccination of mice three times with each of these L2-recombinant adenoviruses induced similarly robust adenovirus-specific serum antibody but weak titers against L2. These L2-specific responses were enhanced by vaccination in the presence of alum and monophoryl lipid A adjuvant. Sera obtained after the third immunization exhibited low neutralizing antibody titers against HPV16 and HPV73. L2-recombinant adenovirus vaccination without adjuvant provided partial protection of mice against HPV16 challenge to either the vagina or skin. In contrast, vaccination with each L2-recombinant adenovirus formulated in adjuvant provided robust protection against vaginal challenge with HPV16, but not against HPV56.

Conclusion

We conclude that introduction of HPV16 L2 12–41 epitope into Ad5 hexon HVR1 or HVR5 is a feasible method of generating a protective HPV vaccine, but further optimization is required to strengthen the L2-specific response and broaden protection to the more diverse hrHPV.

Papillomavirus Infectious Pathways: A Comparison of Systems

The HPV viral lifecycle is tightly linked to the host cell differentiation, causing difficulty in growing virions in culture. A system that bypasses the need for differentiating epithelium has allowed for generation of recombinant particles, such as virus-like particles (VLPs), pseudovirions (PsV), and quasivirions (QV). Much of the research looking at the HPV life cycle, infectivity, and structure has been generated utilizing recombinant particles. While recombinant particles have proven to be invaluable, allowing for a rapid progression of the HPV field, there are some significant differences between recombinant particles and native virions and very few comparative studies using native virions to confirm results are done. This review serves to address the conflicting data in the HPV field regarding native virions and recombinant particles.

Preclinical refinements of a broadly protective VLP-based HPV vaccine targeting the minor capsid protein, L2

An ideal prophylactic human papillomavirus (HPV) vaccine would provide broadly protective and long-lasting immune responses against all high-risk HPV types, would be effective after a single dose, and would be formulated in such a manner to allow for long-term storage without the necessity for refrigeration. We have developed candidate HPV vaccines consisting of bacteriophage virus-like particles (VLPs) that display a broadly neutralizing epitope derived from the HPV16 minor capsid protein, L2. Immunization with 16L2 VLPs elicited high titer and broadly cross-reactive and cross-neutralizing antibodies against diverse HPV types. In this study we introduce two refinements for our candidate vaccines, with an eye towards enhancing efficacy and clinical applicability in the developing world. First, we assessed the role of antigen dose and boosting on immunogenicity. Mice immunized with 16L2-MS2 VLPs at doses ranging from 2 to 25 μg with or without alum were highly immunogenic at all doses; alum appeared to have an adjuvant effect at the lowest dose. Although boosting enhanced antibody titers, even a single immunization could elicit strong and long-lasting antibody responses. We also developed a method to enhance vaccine stability. Using a spray dry apparatus and a combination of sugars & an amino acid as protein stabilizers, we generated dry powder vaccine formulations of our L2 VLPs. Spray drying of our L2 VLPs did not affect the integrity or immunogenicity of VLPs upon reconstitution. Spray dried VLPs were stable at room temperature and at 37 °C for over one month and the VLPs were highly immunogenic. Taken together, these enhancements are designed to facilitate implementation of a next-generation VLP-based HPV vaccine which addresses U.S. and global disparities in vaccine affordability and access in rural/remote populations.

Identification of Broad-Genotype HPV L2 Neutralization Site for Pan-HPV Vaccine Development by a Cross-Neutralizing Antibody

Human Papillomavirus (HPV), a non-enveloped, double-stranded DNA virus, is responsible for 5% of human cancers. The HPV capsid consists of major and minor structural proteins, L1 and L2. L1 proteins form an icosahedral shell with building blocks of the pentameric capsomere, and one L2 molecule extends outward from the central hole of the capsid. Thus, L2 is concealed within L1 and only becomes exposed when the capsid interacts with host cells. The low antigenic variation of L2 means that this protein could offer a target for the development of a pan-HPV vaccine. Toward this goal, here we describe an anti-L2 monoclonal antibody, 14H6, which broadly neutralizes at least 11 types of HPV, covering types 6, 11, 16, 18, 31, 33, 35, 45, 52, 58 and 59, in pseudovirion--based cell neutralization assay. The mAb 14H6 recognizes a minimal linear epitope located on amino acids 21 to 30 of the L2 protein. Alanine scanning mutagenesis and sequence alignment identified several conserved residues (Cys22, Lys23, Thr27, Cys28 and Pro29) that are involved in the 14H6 binding with L2. The epitope was grafted to several scaffolding proteins, including HPV16 L1 virus-like particles, HBV 149 core antigen and CRM197. The resultant chimeric constructs were expressed in Escherichia coli and purified with high efficiency. Immunization with these pan-HPV vaccine candidates elicited high titers of the L2-specific antibody in mice and conferred robust (3-log) titers of cross-genotype neutralization, including against HPV11, 16, 18, 45, 52, 58 and 59. These findings will help in the development of an L2-based, pan-HPV vaccine.

Replication of human papillomavirus in culture

Human papillomaviruses (HPV) are the major factor in causing cervical cancer as well as being implicated in causing oral and anal cancers. The life cycle of HPV is tied to the epithelial differentiation system, as only native virus can be produced in stratified human skin. Initially, HPV research was only possible utilizing recombinant systems in monolayer culture. With new cell culture technology, systems using differentiated skin have allowed HPV to be studied in its native environment. Here, we describe current research studying native virions in differentiated skin including viral assembly, maturation, capsid protein interactions, and L2 cross-neutralizing epitopes. In doing so, we hope to show how differentiating skin systems have increased our knowledge of HPV biology and identify gaps in our knowledge about this important virus.

Prophylactic papillomavirus vaccines

Human papillomaviruses (HPV) are the causative agents of cervical cancer, the third most common cancer in women. The development of prophylactic HPV vaccines Gardasil® and Cervarix® targeting the major oncogenic HPV types is now the frontline of cervical cancer prevention. Both vaccines have been proven to be highly effective and safe although there are still open questions about their target population, cross-protection, and long-term efficacy. The main limitation for a worldwide implementation of Gardasil® and Cervarix® is their high cost. To develop more affordable vaccines research groups are concentrated in new formulations with different antigens including capsomeres, the minor capsid protein L2 and DNA. In this article we describe the vaccines' impact on HPV-associated disease, the main open questions about the marketed vaccines, and current efforts for the development of second-generation vaccines.

Coat as a dagger: the use of capsid proteins to perforate membranes during non-enveloped DNA viruses trafficking

To get access to the replication site, small non-enveloped DNA viruses have to cross the cell membrane using a limited number of capsid proteins, which also protect the viral genome in the extracellular environment. Most of DNA viruses have to reach the nucleus to replicate. The capsid proteins involved in transmembrane penetration are exposed or released during endosomal trafficking of the virus. Subsequently, the conserved domains of capsid proteins interact with cellular membranes and ensure their efficient permeabilization. This review summarizes our current knowledge concerning the role of capsid proteins of small non-enveloped DNA viruses in intracellular membrane perturbation in the early stages of infection.

Measurement of neutralizing serum antibodies of patients vaccinated with human papillomavirus L1 or L2-based immunogens using furin-cleaved HPV Pseudovirions

Antibodies specific for neutralizing epitopes in either Human papillomavirus (HPV) capsid protein L1 or L2 can mediate protection from viral challenge and thus their accurate and sensitive measurement at high throughput is likely informative for monitoring response to prophylactic vaccination. Here we compare measurement of L1 and L2-specific neutralizing antibodies in human sera using the standard Pseudovirion-Based Neutralization Assay (L1-PBNA) with the newer Furin-Cleaved Pseudovirion-Based Neutralization Assay (FC-PBNA), a modification of the L1-PBNA intended to improve sensitivity towards L2-specific neutralizing antibodies without compromising assay of L1-specific responses. For detection of L1-specific neutralizing antibodies in human sera, the FC- PBNA and L1-PBNA assays showed similar sensitivity and a high level of correlation using WHO standard sera (n = 2), and sera from patients vaccinated with Gardasil (n = 30) or an experimental human papillomavirus type 16 (HPV16) L1 VLP vaccine (n = 70). The detection of L1-specific cross-neutralizing antibodies in these sera using pseudovirions of types phylogenetically-related to those targeted by the L1 virus-like particle (VLP) vaccines was also consistent between the two assays. However, for sera from patients (n = 17) vaccinated with an L2-based immunogen (TA-CIN), the FC-PBNA was more sensitive than the L1-PBNA in detecting L2-specific neutralizing antibodies. Further, the neutralizing antibody titers measured with the FC-PBNA correlated with those determined with the L2-PBNA, another modification of the L1-PBNA that spacio-temporally separates primary and secondary receptor engagement, as well as the protective titers measured using passive transfer studies in the murine genital-challenge model. In sum, the FC-PBNA provided sensitive measurement for both L1 VLP and L2-specific neutralizing antibody in human sera. Vaccination with TA-CIN elicits weak cross-protective antibody in a subset of patients, suggesting the need for an adjuvant.