Human Papillomavirus Virus-like Particles Research Articles

Intrinsic fluorescence as an analytical probe of virus-like particle assembly and maturation

The assembly and maturation of the human papillomavirus (HPV) virus-like particle (VLP) has been monitored by measuring the intrinsic fluorescence intensity using excitation at 290 nm and emission at 350 nm. The assay was validated to eliminate error due to photo-bleaching, adsorption, and precipitation. Intrinsic fluorescence intensity dropped during both assembly and maturation phases. The decrease during assembly had a second-order dependence on capsomere concentration, as previously observed using light scattering. During post-assembly structural modification the decrease had a first-order dependence on capsomere concentration. Intrinsic fluorescence spectroscopy complements light scattering methodologies for monitoring assembly and enables kinetics of maturation to be observed. The role of environmental factors such as the presence of oxidized glutathione in facilitation of faster and more complete maturation was monitored in real time. Intrinsic fluorescence is a rugged methodology that could be applied to monitoring VLP assembly and maturation unit operations during HPV vaccine manufacturing.

Human Papillomavirus Vaccines versus Cervical Cancer Screening

Prophylactic vaccination with human papillomavirus (HPV) virus-like particle (VLP) vaccines against HPV 16 and HPV 18, which are the cause of 70% or more of cervical cancers in women, has transformed our prospects for reducing the incidence of this disease on a global scale. HPV VLP vaccines are immunogenic, well tolerated and show remarkable efficacy, achieving >98% protection in randomised clinical trials against the obligate precursor lesions cervical intraepithelial neoplasia grade 2/3 (CIN2/3) and adenocarcinoma in situ. The implementation of these vaccines as a public health intervention is, however, complex. Cervical cancer screening can be a highly effective secondary intervention, but in the developing world these programmes are either not available or are ineffective. HPV vaccination represents the most effective intervention in that scenario. In countries with successful well-organised cervical cancer screening programmes, such as the UK, the cost-effectiveness of vaccination as opposed to screening is a major factor. Screening will have to continue, as only two of the 15 oncogenic HPV types are in the vaccines and for two to three decades at least unvaccinated sexually active women will remain at risk for the disease. However, if both vaccination and screening are combined then the virtual elimination of cervical cancer and the other HPV 16 and 18-associated cancers is possible.

Human papillomavirus type 16 L1E7 chimeric capsomeres have prophylactic and therapeutic efficacy against papillomavirus in mice

Genital human papillomavirus (HPV) infection is the primary cause of cervical cancer in women. Although the HPV recombinant L1 protein was recently licensed as an available vaccine, it has numerous shortcomings. New vaccination strategies should be considered. To enable the design of a prophylactic and therapeutic low-cost vaccine candidate, chimeric HPV16 L1DeltaC34E7N1-60 capsomeres were produced in Escherichia coli. The immune characteristics and potential prophylactic and therapeutic effects of these capsomeres were examined in C57BL/6 mice. Following protein purification and renaturation, the majority of the recombinant chimeric proteins (L1DeltaC34E7N1-60) assembled into capsomeres. These capsomeres were able to induce conformational and neutralizing antibodies against HPV virus-like particles and trigger cell-mediated specific immune responses against the L1 and E7 peptides. In vivo tumor challenge assays showed that mice immunized with the capsomeres were protected against a challenge with both C3 and TC-1 tumor cells. Furthermore, in vivo tumor rejection assays showed that capsomeres have therapeutic efficacy in mice following inoculation with C3 and TC-1 tumor cells. Chimeric capsomeres are capable of preventing and eliminating HPV16 infection. Therefore, our study has provided an economical vaccine candidate.

A Microscale Yeast Cell Disruption Technique for Integrated Process Development Strategies

Miniaturizing protein purification processes at the microliter scale (microscale) holds the promise of accelerating process development by enabling multi-parallel experimentation and automation. For intracellular proteins expressed in yeast, small-scale cell breakage methods capable of disrupting the rigid cell wall are needed that can match the protein release and contaminant profile of full-scale methods like homogenization, thereby enabling representative studies of subsequent downstream operations to be performed. In this study, a noncontact method known as adaptive focused acoustics (AFA) was optimized for the disruption of milligram quantities of yeast cells for the subsequent purification of recombinant human papillomavirus (HPV) virus-like particles (VLPs). AFA operates by delivering highly focused, computer-controlled acoustic radiation at frequencies significantly higher than those used in conventional sonication. With this method, the total soluble protein release was equivalent to that of laboratory-scale homogenization, and cell disruption was evident by light microscopy. The recovery of VLPs through a microscale chromatographic purification following AFA treatment was within 10% of that obtained using homogenization, with equivalent product purity. The addition of a yeast lytic enzyme prior to cell disruption reduced processing time by nearly 3-fold and further improved the comparability of the lysate to that of the laboratory-scale homogenate. In addition, unlike conventional sonication methods, sample heating was minimized (< =8 degrees C increase), even using the maximum power settings required for yeast cell disruption. This disruption technique in combination with microscale chromatographic methods for protein purification enables a strategy for the rapid process development of intracellularly expressed proteins.

Evolution of type-specific immunoassays to evaluate the functional immune response to GARDASIL®, a vaccine for Human Papillomavirus types 16, 18, 6, and 11

Epidemiological studies and clinical trials of vaccines depend on the accurate measurement of antibodies within the polyclonal response to infection or vaccination. The assay currently used to measure the antibody response to vaccination with GARDASIL® [Quadrivalent Human Papillomavirus (Types 6, 11, 16, 18) Recombinant Vaccine]―a quadrivalent vaccine used against human papillomavirus (HPV) types 6, 11, 16, and 18―is a competitive Luminex® assay (cLIA) that uses multiplex technology to detect type-specific neutralizing antibodies against all four HPV types in a single serum sample. Here we describe how the cLIA was developed, as well as how the monoclonal antibodies (mAbs), used as competitors in the assay, were characterized. An enzyme-linked immunosorbent assay (ELISA) was used to screen eight previously-identified mAbs for their ability to bind to HPV virus-like particles (VLPs) in a type-specific and conformation-dependent manner. Four of these mAbs, H6.M48, K11.B2, H16.V5, and H18.J4, met our specifications and were shown to have the potential to neutralize HPV infection in hemagglutination inhibition and pseudovirus neutralization assays. The competitive immunoassay format was able to distinguish type-specific antibodies in the sera of nonhuman primates vaccinated with HPV VLPs, whereas a traditional direct-bind ELISA could not. In addition, the serum antibodies measured by the competitive assay are known to be neutralizing, whereas the ELISA does not distinguish neutralizing and non-neutralizing antibodies in a serum sample. By detecting antibodies to neutralizing epitopes, the competitive assay both demonstrates sero-conversion and provides a potential functional link between sero-conversion and protective immunity in response to vaccination with GARDASIL®.

Expression and purification of human papillomavirus 18 L1 virus-like particle from Saccharomyces cerevisiae

Cervical cancer caused by human papillomavirus (HPV) might be successfully prevented by HPV vaccination and screening. HPV vaccination and HPV serology assays have been investigated using HPV virus-like particles (VLPs). In this study we produced HPV18 L1 VLPs in Saccharomyces cerevisiae and purified them. The HPV18 L1 gene was cloned into the yeast expression vector YEGalpha-HIR525, and transformed into Saccharomyces cerevisiae. Expression of HPV18 L1 protein was demonstrated by Western blotting. The HPV18 L1 protein was purified by ultracentrifugation, size-exclusion chromatography and cation-exchange chromatography, and was up to 95% pure. We showed by transmission electron microscopy that the purified protein self-assembled into VLPs. These findings should be useful for establishing vaccine efficacy as well as characterizing vaccine candidates, and may provide an international reference standard for HPV serology assays.

An investigation into the use of human papillomavirus type 16 virus-like particles as a delivery vector system for foreign proteins: N- and C-terminal fusion of GFP to the L1 and L2 capsid proteins

Development of vaccine strategies against human papillomavirus (HPV), which causes cervical cancer, is a priority. We investigated the use of virus-like particles (VLPs) of the most prevalent type, HPV-16, as carriers of foreign proteins. Green fluorescent protein (GFP) was fused to the N or C terminus of both L1 and L2, with L2 chimeras being co-expressed with native L1. Purified chimaeric VLPs were comparable in size ( approximately 55 nm) to native HPV VLPs. Conformation-specific monoclonal antibodies (Mabs) bound to the VLPs, thereby indicating that they possibly retain their antigenicity. In addition, all of the VLPs encapsidated DNA in the range of 6-8 kb.

Safety and immunogenicity of a vaccine targeting human papillomavirus types 6, 11, 16 and 18: a randomized, placebo-controlled trial in 176 Korean subjects

Human papillomavirus (HPV) is a major causative agent of anogenital warts and a necessary cause of cervical cancer. This report will serve to assess the safety and immunogenicity of quadrivalent (types 6, 11, 16, and 18) HPV L1 virus-like particle (VLP) vaccine in the Korean population. We performed a randomized, double-blind, placebo-controlled study in 176 volunteers aged 9-23 years. Using a 2:1 ratio for randomization, 117 women were assigned to quadrivalent HPV (20 mug type 6, 40 mug type 11, 40 mug type 16, and 20 mug type 18) vaccine and 59 women to placebo. Individuals received vaccine at day 1, month 2, and month 6 and provided blood samples for analysis at enrollment at month 7. Analyses were done as specified in the study protocol. Quadrivalent HPV vaccine was generally well tolerated, with no vaccine-related serious adverse experiences. Quadrivalent HPV vaccine induced seroconversion for each vaccine-related HPV type. At month 7, vaccine-induced type-specific antibody titer was high. In conclusion, administration of quadrivalent HPV VLP vaccine to Korean women aged 9-23 years was generally well tolerated and highly immunogenic.

Protection of Rabbits against Challenge with Rabbit Papillomaviruses by Immunization with the N Terminus of Human Papillomavirus Type 16 Minor Capsid Antigen L2

Current L1 virus-like particle (VLP) vaccines provide type-restricted protection against a small subset of the human papillomavirus (HPV) genotypes associated with cervical cancer, necessitating continued cytologic screening of vaccinees. Cervical cancer is most problematic in countries that lack the resources for screening or highly multivalent HPV VLP vaccines, suggesting the need for a low-cost, broadly protective vaccinogen. Here, N-terminal L2 polypeptides comprising residues 1 to 88 or 11 to 200 derived from HPV16, bovine papillomavirus type 1 (BPV1), or cottontail rabbit papillomavirus (CRPV) were produced in bacteria. Rabbits were immunized with these N-terminal L2 polypeptides and concurrently challenged with CRPV and rabbit oral papillomavirus (ROPV). Vaccination with either N-terminal L2 polypeptides of CRPV effectively protected rabbits from CRPV challenge but not from papillomas induced by cutaneous challenge with CRPV genomic DNA. Furthermore, papillomas induced by CRPV genomic DNA deficient for L2 expression grew at the same rate as those induced by wild-type CRPV genomic DNA, further suggesting that the L2 polypeptide vaccines lack therapeutic activity. Neutralizing serum antibody titers of >15 correlated with protection (P < 0.001), a finding consistent with neutralizing antibody-mediated protection. Surprisingly, a remarkable degree of protection against heterologous papillomavirus types was observed after vaccination with N-terminal L2 polypeptides. Notably, vaccination with HPV16 L2 11-200 protected against cutaneous and mucosal challenge with CRPV and ROPV, respectively, papillomaviruses that are evolutionarily divergent from HPV16. Further, vaccination with HPV16 L2 11-200 generates broadly cross-neutralizing serum antibody, suggesting the potential of L2 as a second-generation preventive HPV vaccine antigen.

The seroprevalence of IgG antibodies to human papillomavirus (HPV) types HPV‐16, HPV‐18, and HPV‐11 capsid‐antigens in mothers and their children

Human papillomavirus (HPV) types causing anogenital lesions and cancer are accepted as being sexually transmitted. The methods whereby children acquire these anogenital type HPV infections are unclear. The present study determined the prevalence of anti-HPV-16, HPV-11 and HPV-18 IgG antibodies in mothers and their children in an attempt to identify evidence of HPV transmission from mother to child. HPV virus-like particles (VLP) VLP-16, VLP-11 and VLP-18 were used in enzyme-linked immunosorbent assay to identify IgG antibodies in serum from 100 mothers and their 111 children. Antibodies to VLP-16, VLP-11 and VLP-18 were found in serum from 17%, 21% and 16% of mothers, respectively and seroprevalences were 9%, 11.7% and 9.9%, respectively amongst the children. Of the 111 children, 23 (20.7%) showed antibodies to one or more of the three HPV types tested. Seven of these (30.4%) HPV IgG positive children had the same antibodies to one or more HPV types as their mothers. The prevalence of HPV-11 was similar in children of seropositive compared with seronegative mothers (14% and 11%, respectively). The prevalence of HPV-16 and HPV-18 was higher in children of seropositive mothers compared with seronegative mothers (for HPV-16, 18% and 7%, respectively, P = 0.1, for HPV-18, 19% and 8%, respectively, P = 0.2). None of these differences were statistically significant indicating a lack of correlation between antibodies in mothers and children and no evidence to support vertical or horizontal mother to child transmission of HPV infection. Indications were of multiple sources of HPV infection in the children.

Effect of Alternative Aluminum Adjuvants on the Absorption and Immunogenicity of HPV16 L1 VLPs in Mice

Aluminum adjuvants are commonly used in prophylactic vaccines to enhance antigen immunogenicity through induction of high-titer antibody responses. Three major forms of aluminum adjuvants with substantially different physical and chemical properties have been described: aluminum phosphate (AlPO4), aluminum hydroxide (AlOH) and amorphous aluminum hydroxyphosphate sulfate (AAHS). Here we describe the effect of these different aluminum adjuvants on the formulation and subsequent immunogenicity in mice of virus-like particles (VLPs) consisting of the L1 protein of Human Papillomavirus (HPV) Type 16. Electron microscopy demonstrated that the physical appearance of the phosphate-containing aluminum adjuvants was markedly different from that of aluminum hydroxide. All three aluminum adjuvants were found to display unique surface charge profiles over a range of pH, while AAHS demonstrated the greatest inherent capacity for adsorption of L1 VLPs. These differences were associated with differences in immunogenicity: anti-HPV L1 VLP responses from mice immunized with AAHS-formulated HPV16 vaccine were substantially greater than those produced by mice immunized with the same antigen formulated with aluminum hydroxide. In addition, HPV L1 VLPs formulated on AAHS also induced a substantial interferon-gamma secreting T cell response to L1 peptides indicating the potential for an enhanced memory response to this antigen. These results indicate that the chemical composition of aluminum adjuvants can have a profound influence on the magnitude and quality of the immune response to HPV VLP vaccines.

Uptake of Human Papillomavirus Virus-Like Particles by Dendritic Cells Is Mediated by Fcγ Receptors and Contributes to Acquisition of T Cell Immunity

Chimeric human papillomavirus virus-like particles (HPV cVLP) are immunogens able to elicit potent CTL responses in mice against HPV16-transformed tumors; however, the mechanism of T cell priming has remained elusive. HPV VLP bind to human MHC class II-positive APCs through interaction with FcgammaRIII, and immature dendritic cells (DC) become activated after incubation with HPV VLP; however, it is unclear whether FcgammaR on DC are involved. In mice, FcgammaRII and FcgammaRIII are homologous and bind similar ligands. In this study, we show that binding and uptake of VLP by DC from FcgammaRII, FcgammaRIII, and FcgammaRII/III-deficient mice are reduced by up to 50% compared with wild-type mice. Additionally, maturation of murine DC from FcgammaRII/III-deficient mice by VLP is also reduced, indicating that DC maturation, and thus Ag presentation, is diminished in the absence of expression of FcgammaR. To investigate the in vivo contribution of FcgammaR in the induction of cellular immunity, FcgammaR single- and double-knockout mice were immunized with HPV16 L1/L2-E7 cVLP, and the frequency of E7-specific T cells was analyzed by tetramer binding, IFN-gamma ELISPOT, and cytotoxicity assays. All readouts indicated that the frequency of E7-specific CD4(+) and CD8(+) T cells induced in all FcgammaR-deficient mice after immunization with cVLP was significantly diminished. Based on these results, we propose that the low-affinity FcgammaR contribute to the high immunogenicity of HPV VLP during T cell priming by targeting VLP to DC and inducing a maturation state of the DC that facilitates Ag presentation to and activation of naive T cells.

Modeling the long-term antibody response of a human papillomavirus (HPV) virus-like particle (VLP) type 16 prophylactic vaccine

The duration over which antibody responses persist following HPV vaccination is unknown. To estimate the longevity of responses induced by HPV-16 vaccination, two models were fitted to serum anti-HPV-16 levels measured during a 48-month study period. The first was a conventional model of antibody decay and the second was a modified model that accounts for long-lived immune memory. Using the antibody decay model, it was estimated that following administration of a three-dose regimen of HPV-16 vaccine in women aged 16–23 years, anti-HPV-16 levels will remain above those induced naturally by HPV-16 infection for 12 years, and above detectable levels for 32 years in 50% of vaccinees. With the modified model, which fitted the data better (p<0.001), it was estimated that near life-long persistence of anti-HPV-16 following vaccination is expected at titer levels above those associated with reduction of natural HPV-16 infection in 76% of these subjects, and above detectable levels in 99% of these subjects.

Human papillomavirus-like particles mediate functional delivery of plasmid DNA to antigen presenting cells in vivo

Because recombinant empty viral capsids are potentially attractive vectors for gene therapy, here we examined the ability of human papillomavirus (HPV) virus-like particles (VLPs) to mediate delivery and expression of DNA plasmids in vitro and in vivo. VLP-mediated delivery and expression of a GFP reporter construct in vitro was found to be highly dependent upon the presence of full-length L2 protein within the VLPs. Similarly, expression of GFP and luciferase reporter plasmids in vivo was strongly enhanced by co-administration of L1/L2 VLPs. Interestingly, in these experiments we routinely observed GFP expression in migrating antigen presenting cells (APC) recovered from mice inoculated with GFP plasmid in combination with VLPs, but not in APC recovered from mice inoculated with the plasmid alone. Additional evidence to support this concept was generated in experiments in which co-administration of VLPs with a plasmid designed to express HPV16 E6 oncoprotein was associated with significant enhancement of plasmid-encoded E6-specific cellular immune responses. These findings have implications for the design of vaccines for combined prophylaxis and therapy of HPV-associated diseases, and for other vaccines that rely on the administration of DNA-based immunogens, adjuvants, and/or other factors.

Combined human papillomavirus DNA and human papillomavirus‐like particle serologic assay to identify women at risk for high‐grade cervical intraepithelial neoplasia

The objective of this study was to assess the utility of a second generation human papillomavirus (HPV) virus-like particle (VLP)-based ELISA as an adjunct to HPV DNA testing to identify women at risk for high-grade cervical intraepithelial neoplasia (CIN). Participants provided blood, cervical samples and interviewer-obtained questionnaire information. HPV VLPs for types 16, 18, 33, 45 and 52 were produced using a baculovirus expression system. These highly purified VLPs were used in a polymer-based ELISA test. Cases with biopsy-confirmed CIN (CIN I, n = 237; CIN II, n = 56; CIN III, n = 48) and controls (n = 351) with normal Pap smears were tested for HPV DNA by PCR and serologic response to multiple oncogenic HPV VLPs. 258/341 (76%) of cases and 230/351 (65.5%) of control patients had any type of HPV VLP antibody (OR = 1.63, 95% CI 1.16-2.30). More cases were seropositive than controls for each individual HPV type (p < 0.001 for HPV types 16, 18, 33 and 45; p = 0.06 for HPV 52). Reactivity to an increasing number of different HPV type-specific VLPs are associated with high-grade CIN independent of HPV DNA status. HPV VLP assays may be useful as an adjunct to HPV DNA testing in a subset of patients that needs to be defined by further studies.

Disassembly and reassembly of yeast‐derived recombinant human papillomavirus virus‐like particles (HPV VLPs)

The human papillomavirus (HPV) virus‐like particles (VLPs) produced by recombinant expression systems are promising candidate vaccine antigens for prevention of cervical cancers as well as genital warts. However, expression of HPV type 6, 11, and 16 L1 proteins in Saccharomyces cerevisiae yielded irregularly shaped, broadly distributed VLPs smaller in size (30–50 nm) than expected (60 nm). In this study, we demonstrate that these HPV VLPs can be disassembled into the constituent capsomers (L1 pentamers) by incubation at low ionic strength and elevated pH in the presence of relatively low concentration of reducing agents. Following the removal of reducing agents, lowering of pH and increasing of ionic strength, the capsomers spontaneously reassembled into homogenous, 60‐nm VLPs characterized by significantly enhanced structural stability and improved immunogenicity. In order to achieve quantitative recovery of HPV VLPs, the disassembly/reassembly process was further optimized by use of high ionic strength (>0.5 M sodium chloride) to prevent aggregation of VLPs. The reassembled VLPs possess an architectural structure very similar to that of the natural HPV virus particles. This development illustrates how the natural, in vivo mechanisms facilitating cell entry and virus replication can be utilized to achieve an optimal, in vitro assembly state of yeast‐expressed HPV VLPs.

Preclinical Model To Test Human Papillomavirus Virus (HPV) Capsid Vaccines In Vivo Using Infectious HPV/Cottontail Rabbit Papillomavirus Chimeric Papillomavirus Particles

A human papillomavirus (HPV) vaccine consisting of virus-like particles (VLPs) was recently approved for human use. It is generally assumed that VLP vaccines protect by inducing type-specific neutralizing antibodies. Preclinical animal models cannot be used to test for protection against HPV infections due to species restriction. We developed a model using chimeric HPV capsid/cottontail rabbit papillomavirus (CRPV) genome particles to permit the direct testing of HPV VLP vaccines in rabbits. Animals vaccinated with CRPV, HPV type 16 (HPV-16), or HPV-11 VLPs were challenged with both homologous (CRPV capsid) and chimeric (HPV-16 capsid) particles. Strong type-specific protection was observed, demonstrating the potential application of this approach.

A deletion and point mutation study of the human papillomavirus type 16 major capsid gene

Recombinant human papillomavirus (HPV) virus-like particles (VLPs) made from the major capsid protein L1 are promising vaccine candidates for use as vaccines against genital and other HPV infections, and particularly against HPV-16. However, HPV-16 genotype variants have different binding affinities for neutralising mouse Mabs raised against HPV-16 L1 VLPs. This paper analyses, using a panel of well-characterised Mabs, the effects on the antigenicity of various C- and N-terminal deletants of HPV-16 L1 made in insect cells via recombinant baculovirus, of an A → T mutation at residue 266 (A266T), and of a C → G mutation at conserved position 428 (C428G). The effects of these changes on assembly of the variant L1s were studied by electron microscopy. Binding of Mab H16:E70 to A266T was reduced by almost half in comparison to wild type L1. Retention of the C-terminal region 428–483 was critical for the binding of conformation-specific Mabs (H16:V5, H16:E70, H16:U4 and H16:9A) whereas deletion of the nuclear localisation signal (NLS) or the C428G mutation or an N-terminal deletion (residues 2–9) did not affect the antigenicity. The N-terminal deletion resulted in a mixed population of 30 and 55 nm VLPs, which differs from the same construct expressed in Escherichia coli, whereas pentamer aggregates resulted from deletion of the 428–465 region or the C428G mutation. The results have implications both for considering use of single-genotype HPV vaccines, and for design of novel second-generation vaccines.

Vaccins prophylactiques antipapillomavirus : enjeux et perspectives

Human Papillomavirus (HPV) infection is established as the necessary cause of cervical precancers and cancers. To date, more than 120 genotypes are known, but only high risk oncogen genotypes could induce a cancer. HPV 16 and 18 are implied in nearly 70% of cervical cancer around the world. Although some persistent HPV infections progress to cervical cancer, host immunity is generally able to clear most HPV infections providing an opportunity for cervical cancer prevention through vaccination. Candidate prophylactic vaccines based on papillomavirus L1 virus-like particles (VLPs) are currently on human clinical trials: one targeting cervical cancer with a bivalent VLP L1 vaccine containing the two genotypes most frequently involved in cervical cancer (type 16 and 18) and the other, protecting against warts as well as cervical cancer, with a quadrivalent HPV VLP L1 vaccine containing genotypes 6, 11, 16 and 18. The first clinical trials revealed the satisfactory tolerance and excellent immunogenicity of these vaccines inducing high serum antibody titers with minimal side effects. After more than three years, both clinical trials on women 15 to 25 years old have shown that vaccines are able to type specifically protect against nearly 90% of infection and all cervical intra-epithelial neoplasia. The vaccinal strategy defined to date targets preadolescents and adolescent young females (11-13 years) before the first sexual course but some questions are still not resolved concerning the prescriber, the actors of the vaccination and the duration of the protection. Nevertheless cervical cancer screening should be carried on for many years, even if a large vaccinal strategy is decided. Such a vaccine would save lives and reduce the need for costly medical procedures and the psychological stress induced by this cancer.

Chapter 12: Prophylactic HPV vaccines: Underlying mechanisms

Human papillomavirus virus-like particles (HPV VLP) can be generated by the synthesis and self-assembly in vitro of the major virus capsid protein L1. HPV L1 VLPs are morphologically and antigenically almost identical to native virions, and this technology has been exploited to produce HPV L1 VLP subunit vaccines. The vaccines elicit high titres of anti-L1 VLP antibodies that persist at levels 10 times that of natural infections for at least 48 months. At present the assumption is that the protection achieved by these vaccines against incident HPV infection and HPV-associated ano-genital pathology is mediated via serum neutralising Immunoglobulin G (IgG). However, since there have been very few vaccine failures thus far, immune correlates of protection have not been established. The available evidence is that the immunodominant neutralising antibodies generated by L1 VLPs are type-specific and are not cross-neutralising, although highly homologous HPV pairs share minor cross-neutralisation epitopes. Important issues remaining to be addressed include the duration of protection and genotype replacement.