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

Characterization of an Escherichia coli-derived triple-type chimeric vaccine against human papillomavirus types 39, 68 and 70

In vaccinology, a potent immunogen has two prerequisite attributes-antigenicity and immunogenicity. We have rational designed a triple-type HPV vaccine against HPV58, -33 and -52 covered in Gardasil 9 based on the sequence homology and similar surface loop structure of L1 protein, which is related to cross-type antigenicity. Here, we design another triple-type vaccine against non-vaccine types HPV39, -68 and -70 by immunogenicity optimization considering type specific immunodominant epitopes located in separate region for different types. First, we optimized the expression of wild-type HPV39, -68 and -70 L1-only virus-like particles (VLPs) in E. coli through N-terminal truncation of HPV L1 proteins and non-fusion soluble expression. Second, based on genetic relationships and an L1 homologous loop-swapping rationale, we constructed several triple-type chimeric VLPs for HPV39, -68 and -70, and obtained the lead candidate named H39-68FG-70DE by the immunogenicity optimization using reactivity profile of a panel type-specific monoclonal antibodies. Through comprehensive characterization using various biochemical, VLP-based analyses and immune assays, we show that H39-68FG-70DE assumes similar particulate properties as that of its parental VLPs, along with comparable neutralization immunogenicity for all three HPV types. Overall, this study shows the promise and translatability of an HPV39/68/70 triple-type vaccine, and the possibility of expanding the type-coverage of current HPV vaccines. Our study further expanded the essential criteria on the rational design of a cross-type vaccine, i.e. separate sites with inter-type similar sequence and structure as well as type-specific immunodominant epitope to be clustered together.

RG2-VLP: a Vaccine Designed to Broadly Protect against Anogenital and Skin Human Papillomaviruses Causing Human Cancer

The family of human papillomaviruses (HPV) includes over 400 genotypes. Genus α genotypes generally infect the anogenital mucosa, and a subset of these HPV are a necessary, but not sufficient, cause of cervical cancer. Of the 13 high-risk (HR) and 11 intermediate-risk (IR) HPV associated with cervical cancer, genotypes 16 and 18 cause 50% and 20% of cases, respectively, whereas HPV16 dominates in other anogenital and oropharyngeal cancers. A plethora of βHPVs are associated with cutaneous squamous cell carcinoma (CSCC), especially in sun-exposed skin sites of epidermodysplasia verruciformis (EV), AIDS, and immunosuppressed patients. Licensed L1 virus-like particle (VLP) vaccines, such as Gardasil 9, target a subset of αHPV but no βHPV. To comprehensively target both α- and βHPVs, we developed a two-component VLP vaccine, RG2-VLP, in which L2 protective epitopes derived from a conserved αHPV epitope (amino acids 17 to 36 of HPV16 L2) and a consensus βHPV sequence in the same region are displayed within the DE loop of HPV16 and HPV18 L1 VLP, respectively. Unlike vaccination with Gardasil 9, vaccination of wild-type and EV model mice (Tmc6Δ/Δ or Tmc8Δ/Δ) with RG2-VLP induced robust L2-specific antibody titers and protected against β-type HPV5. RG2-VLP protected rabbits against 17 αHPV, including those not covered by Gardasil 9. HPV16- and HPV18-specific neutralizing antibody responses were similar between RG2-VLP- and Gardasil 9-vaccinated animals. However, only transfer of RG2-VLP antiserum effectively protected naive mice from challenge with all βHPVs tested. Taken together, these observations suggest RG2-VLP's potential as a broad-spectrum vaccine to prevent αHPV-driven anogenital, oropharyngeal, and βHPV-associated cutaneous cancers. IMPORTANCE Licensed preventive HPV vaccines are composed of VLPs derived by expression of major capsid protein L1. They confer protection generally restricted to infection by the αHPVs targeted by the up-to-9-valent vaccine, and their associated anogenital cancers and genital warts, but do not target βHPV that are associated with CSCC in EV and immunocompromised patients. We describe the development of a two-antigen vaccine protective in animal models against known oncogenic αHPVs as well as diverse βHPVs by incorporation into HPV16 and HPV18 L1 VLP of 20-amino-acid conserved protective epitopes derived from minor capsid protein L2.

Sustainability of neutralising antibodies induced by bivalent or quadrivalent HPV vaccines and correlation with efficacy: a combined follow-up analysis of data from two randomised, double-blind, multicentre, phase 3 trials

BACKGROUND

Quadrivalent and bivalent vaccines against oncogenic human papillomavirus (HPV) are used worldwide with different reported overall efficacies against HPV infections. Although protective concentrations of vaccine-induced antibodies are still not formally defined, we evaluated the sustainability of neutralising antibodies in vaccine trial participants 2-12 years after vaccination and the correlation with reported vaccine efficacy.

METHODS

We did a follow-up analysis of data from the Finnish cohorts of two international, randomised, double-blind, phase 3 trials of HPV vaccines, PATRICIA (bivalent, HPV16 and 18) and FUTURE II (quadrivalent, HPV6, 11, 16, and 18). In 2002 and 2004-05, respectively, Finnish girls aged 16-17 years participated in one of these two trials and consented to health registry follow-up with the Finnish Cancer Registry. The cohorts were also linked with the Finnish Maternity Cohort (FMC) that collects first-trimester serum samples from nearly all pregnant Finnish women, resulting in 2046 post-vaccination serum samples obtained during up to 12 years of follow-up. We obtained serum samples from the FMC-based follow-up of the FUTURE II trial (from the quadrivalent vaccine recipients) and the PATRICIA trial (from corresponding bivalent vaccine recipients who were aligned by follow-up time, and matched by the number of pregnancies). We assessed neutralising antibody concentrations (type-specific seroprevalence) to HPV6, 16, and 18, and cross-neutralising antibody responses to non-vaccine HPV types 31, 33, 45, 52, and 58 from 2 to 12 years after vaccination.

FINDINGS

Up to Dec 31, 2016, we obtained and analysed 577 serum samples from the quadrivalent vaccine recipients and 568 from the bivalent vaccine recipients. In 681 first-pregnancy serum samples, neutralising antibodies to HPV6, 16, and 18 were generally found up to 12 years after vaccination. However, 51 (15%) of 339 quadrivalent vaccine recipients had no detectable HPV18 neutralising antibodies 2-12 years after vaccination, whereas all 342 corresponding bivalent vaccine recipients had HPV18 neutralising antibodies.. In seropositive quadrivalent vaccine recipients, HPV16 geometric mean titres (GMT) halved by years 5-7 (GMT 3679, 95% CI 2377 to 4708) compared with years 2-4 (6642, 2371 to 13 717). Between 5 and 12 years after vaccination, GMT of neutralising antibodies to HPV16 and 18 were 5·7 times and 12·4 times higher, respectively, in seropositive bivalent vaccine recipients than in the quadrivalent vaccine recipients. Cross-neutralising antibodies to HPV31, 33, 45, 52, and 58 were more prevalent in the bivalent vaccine recipients but, when measurable, sustainable up to 12 years after vaccination with similar GMTs in both vaccine cohorts. Seroprevalence for HPV16, 31, 33, 52, and 58 significantly correlated with vaccine efficacy against persistent HPV infections in the bivalent vaccine recipients only (r_s=0·90, 95% CI 0·09 to 0·99, p=0·037, compared with r_s=0·62, 95% CI -0·58 to 0·97, p=0·27 for the quadrivalent vaccine recipients). Correlation of protection with prevalence of neutralising or cross-neutralising HPV antibodies was not significant in the quadrivalent vaccine recipients.

INTERPRETATION

The observed significant differences in the immunogenicity of the two vaccines are in line with the differences in their cross-protective efficacy. Protective HPV vaccine-induced antibody titres can be detected up to 12 years after vaccination.

FUNDING

Academy of Finland and Finnish Cancer Foundation.

Public-private knowledge transfer and access to medicines: a systematic review and qualitative study of perceptions and roles of scientists involved in HPV vaccine research

Background

Public research organizations and their interactions with industry partners play a crucial role for public health and access to medicines. The development and commercialization of the Human Papillomavirus (HPV) vaccines illustrate how licensing practices of public research organizations can contribute to high prices of the resulting product and affect accessibility to vulnerable populations. Efforts by the international community to improve access to medicines have recognised this issue and promote the public health-sensitive management of research conducted by public research organizations. This paper explores: how medical knowledge is exchanged between public and private actors; what role inventor scientists play in this process; and how they view the implementation of public health-sensitive knowledge exchange strategies.

Methods

We conducted a systematic qualitative literature review on medical knowledge exchange and qualitative interviews with a purposive sample of public sector scientists working on HPV vaccines. We explored the strategies by which knowledge is exchanged across institutional boundaries, how these strategies are negotiated, and the views of scientists regarding public health-sensitive knowledge exchange.

Results

We included 13 studies in the systematic review and conducted seven semi-structured interviews with high-ranking scientists. The main avenues of public-private medical knowledge exchange were publications, formal transfer of patented knowledge, problem-specific exchanges such as service agreements, informal exchanges and collaborative research. Scientists played a crucial role in these processes but appeared to be sceptical of public health-sensitive knowledge exchange strategies, as these were believed to deter corporate interest in the development of new medicines and thus risk the translation of the scientists’ research.

Conclusion

Medical scientists at public research institutions play a key role in the exchange of knowledge they generate and are concerned about the accessibility of medicines resulting from their research. Their scepticism towards implementing public health-sensitive knowledge management strategies appears to be based on a biased understanding of the costs and risks involved in drug development and a perceived lack of alternatives to private engagement. Scientists could be encouraged to exchange knowledge in a public health-sensitive manner through not-for-profit drug development mechanisms, education on industry engagement, and stronger institutional and legal backing.

Scalable Production of HPV16 L1 Protein and VLPs from Tobacco Leaves

Cervical cancer is the most common malignancy among women particularly in developing countries, with human papillomavirus (HPV) 16 causing 50% of invasive cervical cancers. A plant-based HPV vaccine is an alternative to the currently available virus-like particle (VLP) vaccines, and would be much less expensive. We optimized methods to express HPV16 L1 protein and purify VLPs from tobacco (Nicotiana benthamiana) leaves transfected with the magnICON deconstructed viral vector expression system. L1 proteins were extracted from agro-infiltrated leaves using a series of pH and salt mediated buffers. Expression levels of L1 proteins and VLPs were verified by immunoblot and ELISA, which confirmed the presence of sequential and conformational epitopes, respectively. Among three constructs tested (16L1d22, TPL1d22, and TPL1F), TPL1F, containing a full-length L1 and chloroplast transit peptide, was best. Extraction of HPV16 L1 from leaf tissue was most efficient (> 2.5% of total soluble protein) with a low-salt phosphate buffer. VLPs were purified using both cesium chloride (CsCl) density gradient and size exclusion chromatography. Electron microscopy studies confirmed the presence of assembled forms of HPV16 L1 VLPs. Collectively; our results indicated that chloroplast-targeted transient expression in tobacco plants is promising for the production of a cheap, efficacious HPV16 L1 VLP vaccine. Studies are underway to develop plant VLPs for the production of a cervical cancer vaccine.

Anti-Infectious Human Vaccination in Historical Perspective

A brief history of vaccination is presented since the Jenner's observation, through the first golden age of vaccinology (from Pasteur's era to 1938), the second golden age (from 1940 to 1970), until the current period. In the first golden age, live, such as Bacille Calmette Guérin (BCG), and yellow fever, inactivated, such as typhoid, cholera, plague, and influenza, and subunit vaccines, such as tetanus and diphtheria toxoids, have been developed. In the second golden age, the cell culture technology enabled polio, measles, mumps, and rubella vaccines be developed. In the era of modern vaccines, in addition to the conjugate polysaccharide, hepatitis A, oral typhoid, and varicella vaccines, the advent of molecular biology enabled to develop hepatitis B, acellular pertussis, papillomavirus, and rotavirus recombinant vaccines. Great successes have been achieved in the fight against infectious diseases, including the smallpox global eradication, the nearly disappearance of polio, the control of tetanus, diphtheria, measles, rubella, yellow fever, and rabies. However, much work should still be done for improving old vaccines, such as BCG, anthrax, smallpox, plague, or for developing effective vaccines against old or emerging infectious threats, such as human-immunodeficiency-virus, malaria, hepatitis C, dengue, respiratory-syncytial-virus, cytomegalovirus, multiresistant bacteria, Clostridium difficile, Ebola virus. In addition to search for innovative and effective vaccines and global infant coverage, even risk categories should adequately be protected. Despite patients under immunosuppressive therapy are globally increasing, their vaccine coverage is lower than recommended, even in developed and affluent countries.

Human papillomavirus vaccination: a case study in translational science

Each year 610,000 cases of anogenital and oropharyngeal cancers caused by human papillomavirus (HPV) occur worldwide. HPV vaccination represents a promising opportunity to prevent cancer on a global scale. The vaccine's story dates back to discoveries in chickens at the beginning of the 20th century with evidence that a cell-free filtrate could transmit the propensity to grow cancers. Later, studies with similarly derived filtrates from mammalian tumors showed that hosts could develop immunity to subsequent exposures. Epidemiologic studies linked cervical cancer to members of a family of viruses that cause papillomatosis and common warts. This led to work with DNA hybridization demonstrating a causal relationship. The formation of virus-like particles from viral capsid proteins led to the development of models for safe and effective vaccines. While much work remains with the acceptance of universal vaccination, the HPV vaccines Gardasil and Cervarix thus represent a century of successful translational research.

Factors influencing the willingness of US women to vaccinate their daughters against the human papillomavirus to prevent cervical cancer

The human papillomavirus (HPV) vaccine helps to prevent cervical cancer. However, research indicates that public acceptance of the vaccine is suboptimal. Our aims were to evaluate the willingness of US women to use the HPV vaccine in their daughters, examine their current understanding of HPV, and determine the impact of HPV knowledge and other socio-demographic factors on their willingness to get their daughters vaccinated. Women aged ≥ 18 years were identified from the US Health Information National Trends Survey. We developed a 6-point composite scoring system based on individual responses to HPV-related questions to characterize personal understanding about HPV. Logistic regression models were constructed to explore the influence of the women's HPV knowledge level and additional socio-demographic factors on the willingness to use HPV in their daughters. There were 804 female respondents: mean age was 44.9 (SD = 2.53) years and 73 % were White. In total, 75 % of women indicated they would vaccinate their daughters against HPV. Mean knowledge score was 4.6 (SD = 0.80). While White race was associated with higher willingness to use the vaccine in their daughters (OR = 1.86, p = 0.04), HPV knowledge level was not (OR = 0.47, p = 0.22). Among US women, HPV knowledge level was high, but it was not associated with the willingness to vaccinate their daughters against HPV. Interventions focused on alleviating racial disparities might better modify the use of the HPV vaccine.

Prophylactic human papillomavirus vaccines: past, present and future

Human papillomavirus (HPV) is a highly transmissible infection responsible for a range of diseases in women including cervical carcinomas, vulval carcinomas, anogenital carcinomas and genital warts. In men it is associated with penile carcinomas, anogenital carcinomas and oropharyngeal carcinomas. The history of the development of HPV vaccines includes a significant Australian input and represents a tremendous advancement in our understanding of HPV virology as well as further elucidating the overall contribution of viruses to carcinogenesis. Prophylactic HPV vaccines were licensed for use in Australia in 2007 in order to protect against development of future cases of cervical carcinoma and early results are promising. The benefit of the vaccine will not be restricted to cervical lesions and cross protection amongst a variety of HPV subtypes is described. The development of the HPV vaccine and its ultimate incorporation into our National Immunisation Schedule is reviewed.

Construction and characterisation of a recombinant fowlpox virus that expresses the human papilloma virus L1 protein

BACKGROUND

Human papilloma virus (HPV)-16 is the most prevalent high-risk mucosal genotype. Virus-like-particle (VLP)-based immunogens developed recently have proven to be successful as prophylactic HPV vaccines, but are still too expensive for developing countries. Although vaccinia viruses expressing the HPV-16 L1 protein (HPV-L1) have been studied, fowlpox-based recombinants represent efficient and safer vectors for immunocompromised hosts due to their ability to elicit a complete immune response and their natural host-range restriction to avian species.

METHODS

A new fowlpox virus recombinant encoding HPV-L1 (FPL1) was engineered and evaluated for the correct expression of HPV-L1 in vitro, using RT-PCR, immunoprecipitation, Western blotting, electron microscopy, immunofluorescence, and real-time PCR assays.

RESULTS

The FPL1 recombinant correctly expresses HPV-L1 in mammalian cells, which are non-permissive for the replication of this vector.

CONCLUSION

This FPL1 recombinant represents an appropriate immunogen for expression of HPV-L1 in human cells. The final aim is to develop a safe, immunogenic, and less expensive prophylactic vaccine against HPV.

Development of a 2-plex luminex-based competitive immunoassay to quantify neutralizing antibodies induced by virus-like particles for human papillomavirus 16 and 18

Human papillomavirus (HPV) L1 virus-like particles (VLPs) were proven an effective vaccine candidate to prevent against HPV-16 and -18 infections. In order to evaluate the potency of our produced HPV-16 and -18 L1 VLPs-based vaccine candidates, also to quantify neutralizing antibodies induced by them, a 2-plex Luminex-based competitive immunoassay was developed. Unlike the published paper, the no-biotin conjugated neutralizing mAbs spiked normal human serum (NHS) was used for standard curve preparation, while phycoerythrin (PE) was not labeled directly to neutralizing mAbs for signaling. After the coupling optimization of VLPs to microspheres and the neutralizing mAbs biotinylation, the 2-plex standard curve was prepared with good fit and high dynamic range. In addition, no cross-reactivity was also confirmed. The 2-plex Luminex-based immunoassay represents good potential not only for vaccine candidate's evaluation but also for its further clinical use.

Advances in human papilloma virus vaccines: a patent review

INTRODUCTION

Human papilloma virus (HPV) infection is the main factor associated with the development of cervical cancer. The currently available HPV vaccines, Gardasil and Cervarix, can prevent infection by certain HPV types, but not all. At present, research efforts are being devoted to developing more broad spectrum preventative vaccines, as well as therapeutic vaccines.

AREAS COVERED

Recent advances in HPV vaccine development are reviewed in this paper, with a focus on worldwide patents and patent applications. In principle, patents that have been granted since 2002 are covered. Exceptions are the patents pending at PCT stage and recent patent applications since 2009. Readers will gain insights into the cutting-edge technologies being used in the development and production of vaccines, as well as adjuvant systems.

EXPERT OPINION

In the future, the use of mosaic virus-like particles (VLPs,) comprising at least one L1 protein of each HPV type, may be able to prevent infection by all HPV types while patented codon-optimization techniques and the use of edible or DNA-based vaccines may be good places to start for reducing costs. Future vaccines should ideally have both preventive and therapeutic efficacies. Enhanced immunogenicity could be achieved by the use of more effective adjuvants, such as nanoparticle-based delivery systems, or new classes of adjuvants.

University contributions to the HPV vaccine and implications for access to vaccines in developing countries: addressing materials and know-how in university technology transfer policy

Human Papillomavirus (HPV) is a major cause of morbidity and mortality worldwide, with most of the disease burden concentrated in developing countries. Over 90 percent of cervical cancer deaths, almost all of which are caused by HPV, occur in low- and middle-income countries where access to goods and services for prevention and treatment pose major barriers to intervention. In resource-poor settings lacking the capacity for routine screening for cervical cancer, the HPV vaccines developed by Merck and GlaxoSmithKline are desperately needed to help prevent these unnecessary deaths. The initial development of currently available HPV vaccines took place at a number of universities and other publicly funded institutions, yet there is little low-cost access to the vaccine in developing countries where access would be most critical. This is the rule rather than the exception with most university-discovered medicines. Universities and other publicly-funded institutions can adopt a number of licensing methods to ensure that vaccines discovered on their campuses are available at low-cost in developing countries. Universities Allied for Essential Medicines has proposed that universities adopt Global Access Licensing policies to implement these changes by enabling generic or low-cost production of the end product in developing countries. Generic competition is a critical market force that has, for instance, driven down the price of HIV/AIDS treatments from more than $10,000 to less than $99 per patient per year today. While the central barrier to creation of small molecule generics is patent-protection, there are multiple additional barriers that need to be addressed in order to ensure the efficient production of cost-effective generic vaccines and other biologics. While certain biologics may require generic producers to perform additional clinical trials, vaccines are in a somewhat unique situation with respect to both safety and efficacy. With access to appropriate patents, materials and knowledge, vaccines have the potential to be evaluated efficiently and cost-effectively via a pathway parallel to establishing bioequivalence for generic small molecule drugs. A new paradigm is needed that addresses the additional barriers that exist, outside of simply patent protection, to the generic production of vaccines and other biologics. One possible framework, which builds upon previous work on prize funds and patent pools, is discussed here: a Patents, Materials, and Know-how Pool (PMK Pool), based on the patent pool model such as those outlined in the Essential Medical Inventions Licensing Agency and proposals recently put forth by the governments of Barbados and Bolivia. University approaches to licensing vaccines and other biologics need to ensure access not only to patents, knowledge, and materials covered by intellectual property, but must also address the problem of access to materials and know-how that are often proprietary trade secrets. Universities should actively participate in the creation of this and other novel mechanisms, and in the meantime use currently available technology transfer mechanisms to ensure low-cost access to medicines in developing countries.

The history of tumor virology

In the century since its inception, the field of tumor virology has provided groundbreaking insights into the causes of human cancer. Peyton Rous founded this scientific field in 1911 by discovering an avian virus that induced tumors in chickens; however, it took 40 years for the scientific community to comprehend the effect of this seminal finding. Later identification of mammalian tumor viruses in the 1930s by Richard Shope and John Bittner, and in the 1950s by Ludwik Gross, sparked the first intense interest in tumor virology by suggesting the possibility of a similar causal role for viruses in human cancers. This change in attitude opened the door in the 1960s and 1970s for the discovery of the first human tumor viruses--EBV, hepatitis B virus, and the papillomaviruses. Such knowledge proved instrumental to the development of the first cancer vaccines against cancers having an infectious etiology. Tumor virologists additionally recognized that viruses could serve as powerful discovery tools, leading to revolutionary breakthroughs in the 1970s and 1980s that included the concept of the oncogene, the identification of the p53 tumor suppressor, and the function of the retinoblastoma tumor suppressor. The subsequent availability of more advanced molecular technologies paved the way in the 1980s and 1990s for the identification of additional human tumor viruses--human T-cell leukemia virus type 1, hepatitis C virus, and Kaposi's sarcoma virus. In fact, current estimates suggest that viruses are involved in 15% to 20% of human cancers worldwide. Thus, viruses not only have been shown to represent etiologic agents for many human cancers but have also served as tools to reveal mechanisms that are involved in all human malignancies. This rich history promises that tumor virology will continue to contribute to our understanding of cancer and to the development of new therapeutic and preventive measures for this disease in the 21st century.

Prevention of cancer through immunization: Prospects and challenges for the 21st century

Persistent infection by several microbial agents is responsible for at least 15% of cancer globally, including most cancers of the liver, stomach, and cervix. The recent development of vaccines that can prevent infection and premalignant disease caused by human papillomaviruses (HPV), which cause virtually all cases of cervical cancer as well as some other cancers, has focused renewed attention on infection control as a means of reducing the global cancer burden. For vaccines to prevent cancer-causing infection with hepatitis C virus, Helicobacter pylori, or Epstein Barr virus, new vaccine technologies to induce more effective protective responses are required. For the two available cancer control vaccines, designed to prevent infection with HPV and hepatitis B virus, the major challenge is to promote effective vaccine deployment through education programs and increased affordability/accessibility for underserved populations, particularly in the developing world, where the cancer burden attributable to infection by these two viruses is greatest.

HPV16 L1 capsid protein expressed from viable adenovirus recombinants elicits neutralizing antibody in mice

Immunization against human papillomavirus (HPV) infection promises to reduce the worldwide burden of cervical cancer. To evaluate the potential of live recombinant adenoviruses for induction of HPV infection-blocking immunity, we prepared viable adenovirus recombinants that express the HPV16 L1 gene from the adenovirus major late transcriptional unit. Adenovirus-produced HPV16 L1 assembles into virus-like particles (VLPs) in infected cells in culture. Purified HPV16 VLPs are recognized by HPV16 neutralizing antibodies and induce high neutralizing titers when injected intraperitoneally into mice. Canine oral papillomavirus VLPs derived from previously described recombinants also induce strong antibody responses in mice. These data support our suggestion that viable adenovirus recombinants will be able to induce protective immunity to papillomavirus infection during replication in human vaccinees.

How will HPV vaccines affect cervical cancer?

Cancer of the uterine cervix is the second largest cause of cancer deaths in women, and its toll is greatest in populations that lack screening programmes to detect precursor lesions. Persistent infection with 'high risk' genotypes of human papillomavirus (HPV) is necessary, although not sufficient, to cause cervical carcinoma. Therefore, HPV vaccination provides an opportunity to profoundly affect cervical cancer incidence worldwide. A recently licensed HPV subunit vaccine protects women from a high proportion of precursor lesions of cervical carcinoma and most genital warts. Here we examine the ramifications and remaining questions that surround preventive HPV vaccines.

Progress in the development of a cervical cancer vaccine

Persistent infection by 'high risk' genotypes of human papilloma virus (HPV) is necessary but not sufficient for the development of over 98% of cervical cancers. Thus the development of vaccines that prevent HPV transmission represent an important opportunity to prevent cervical cancer. There are several prophylactic HPV vaccine formulations based upon L1 virus-like particles (VLPs) currently in phase III trials and recently released data are extremely promising. However, many practical issues surrounding implementation of these vaccines need to be addressed including, who and when to vaccinate, duration of protection, and integration with current screening programs. The vaccines currently being evaluated target the two most prevalent high risk HPV types which are responsible for approximately 70% of cervical cancers. To increase the breadth of protection, it is likely that L1 VLPs of other viral subtypes must be included, although vaccines targeting the conserved regions of the L2 minor capsid protein warrant further exploration in this regard. In addition the vaccines nearing licensing will not combat established HPV-related disease and a therapeutic vaccine, of which there are several candidates in early stages of development, would be desirable. This review discusses the background to and progress in vaccine development and the issues surrounding the introduction of HPV vaccines.

Viable adenovirus vaccine prototypes: high-level production of a papillomavirus capsid antigen from the major late transcriptional unit

Safe, effective, orally delivered, live adenovirus vaccines have been in use for three decades. Recombinant derivatives of the live adenovirus vaccines may prove an economical alternative to current vaccines for a variety of diseases. To explore that possibility, we constructed a series of recombinants that express the major capsid protein (L1) of canine oral papillomavirus (COPV), a model for mucosal human papillomavirus (HPV) infection. Vaccination with virus-like particles (VLPs) composed of recombinant HPV L1 completely prevents persistent HPV infection [Koutsky, L. A., Ault, K. A., Wheeler, C. M., Brown, D. R., Barr, E., Alvarez, F. B., Chiacchierini, L. M. & Jansen, K. U. (2002) N. Engl. J. Med. 347, 1645-1651], suggesting that L1 expressed from recombinant adenoviruses might provide protective immunity. In our recombinants, COPV L1 is incorporated into adenovirus late region 5 (Ad L5) and is expressed as a member of the adenoviral major late transcriptional unit (MLTU). COPV L1 production by the most prolific recombinant is comparable to that of the most abundant adenoviral protein, hexon. COPV L1 production by recombinants is influenced by Ad L5 gene order, the specific mRNA processing signals associated with COPV L1, and the state of a putative splicing inhibitor in the COPV L1 gene. Recombinant COPV L1 protein assembles into VLPs that react with an antibody specific for conformational epitopes on native COPV L1 protein that correlate with protection in vivo. The designs of these recombinants can be applied directly to the production of recombinants appropriate for assessing immunogenicity and protective efficacy in animal models and in human trials.

Codon optimization of the human papillomavirus 11 (HPV 11) L1 gene leads to increased gene expression and formation of virus-like particles in mammalian epithelial cells

The 505 amino acid L1 protein of the human papillomavirus type 11 (HPV 11) is the major capsid polypeptide that has been shown to self-assemble into virus-like particles (VLPs) in vivo and in vitro. While L1 is essential for viral infection, expression studies in mammalian cells have been hampered by different codon preference between the virus and its host. To optimize L1 gene expression in mammalian cells, we converted wild-type HPV 11 L1 (11 L1wt) codons to those more common in human genes. The modified HPV 11 L1 gene (11 L1h) generated protein levels that were at least 100-fold higher than those of wild-type HPV 11 L1, while no obvious differences were seen in the level of mRNA. HPV 11 L1 protein was detected in mammalian epithelial and fibroblast cells, by immunoblotting and indirect immunofluorescence (IIF) techniques. Unlike the situation in situ, IIF revealed the presence of L1 mainly at perinuclear sites. Virus-like particles assembled intranuclearly only to a low extent, as indicated by transmission electron microscopy. DNA vaccination using the HPV 11 L1h gene yielded a drastic increase in L1-specific antibody production in mice as compared to immunization with the wild-type gene.

Vaccines for cervical cancer

Human papillomaviruses (HPVs) are responsible for the nearly 450,000 cervical cancers that occur each year throughout the world. In the United States, the cancer rate is low (13,500 cases per year); nevertheless, HPVs affect millions of men and women annually in the form of genital warts and preinvasive diseases of the cervix and anogenital region. The expense of cancer prevention via precancer and cancer management is high, yet most HPV infections resolve spontaneously as a result of a successful host immune response. Recently, the discovery of methods to reproduce HPV virions (viral-like particles) in vitro has resulted in a successful clinical trial of preventing HPV infection and its associated precursor lesions. Although prevention is type-specific and duration of immunity is unknown, these results validate a vaccine strategy targeting prepubertal children that could prevent a significant proportion of genital warts and cervical precancers and cancers from occurring during reproductive life. Reversing advanced preinvasive and invasive cervical neoplasia with immunotherapeutics is a more difficult challenge, inasmuch as little or no evidence for natural immune-mediated regression of these diseases exists. Nonetheless, recent controlled trials have shown some success in inducing precursor regression with vaccines targeting viral oncoproteins. Anecdotal reports of therapies that augmentcellular immunity raise hopesthattherapeutics targeting multiple pathways of anti-viral or anti-tumor immunity will be beneficial to women with established cervical cancer. However, success will require identifying and circumventing the mechanisms by which tumor cells evade the immune system.

Human papillomavirus and skin cancer

Human papillomavirus (HPV) appears to be the most ubiquitous of the human viruses. Over 100 HPV types have been identified. A minority of HPV cause cutaneous warts and mucosal condylomata. The HPV that cause mucosal condylomata put the patient at various degrees of risk for developing cancers, particularly cervical cancer. The majority of HPV infect the skin of normal and immunocompromised individuals. In normal people, most of these HPV appear to establish a latent infection of the skin, most likely as normal flora residing in hair follicles; however, in patients with various systemic and localized depressions of cell-mediated immunity, some HPV infections appear to be involved in the development of nonmelanotic skin cancer and its precursor lesions in skin, usually in sunlight-exposed areas. Circumstantial evidence suggests that these HPV may have a role in promoting proliferative lesions of the skin, although their sites of active infection and mode of transmission to susceptible individuals remain unknown.

Systemic immunization with papillomavirus L1 protein completely prevents the development of viral mucosal papillomas

Infection of mucosal epithelium by papillomaviruses is responsible for the induction of genital and oral warts and plays a critical role in the development of human cervical and oropharyngeal cancer. We have employed a canine model to develop a systemic vaccine that completely protects against experimentally induced oral mucosal papillomas. The major capsid protein, L1, of canine oral papillomavirus (COPV) was expressed in Sf9 insect cells in native conformation. L1 protein, which self-assembled into virus-like particles, was purified on CsCl gradients and injected intradermally into the foot pad of beagles. Vaccinated animals developed circulating antibodies against COPV and became completely resistant to experimental challenge with COPV. Successful immunization was strictly dependent upon native L1 protein conformation and L1 type. Partial protection was achieved with as little as 0.125 ng of L1 protein, and adjuvants appeared useful for prolonging the host immune response. Serum immunoglobulins passively transferred from COPV L1-immunized beagles to naive beagles conferred protection from experimental infection with COPV. Our results indicate the feasibility of developing a human vaccine to prevent mucosal papillomas, which can progress to malignancy.

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

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

A two-site enzyme immunoassay for quantitation of human papillomavirus type 16 particles

A group of human papillomaviruses (HPV), in particular HPV type 16, are the major cause of anogenital dysplasias, which are precursors of anogenital cancer. The mode of transmission, extent of infectivity and natural history of infection are incompletely understood because methods to quantify shedding of viral particles have not been available. A two-site ELISA was developed to detect and quantify HPV-16 particles. Rabbits and guinea pigs were immunized with a series of peptides from the L1 and L2 capsid proteins of HPV-16. Among rabbit antipeptide sera tested for use as capture antibodies, only sera against one peptide bound detectable amounts of virus. Guinea pig antisera against several peptides were used as reporter antibodies to detect bound virus particles. If antisera against the same peptide were used both as capture antibody and reporter antibody, only intact particles were detected. Disrupted particles were quantified using antibodies against one L1 peptide as capture antibody and antibodies against other L1 peptides as reporter antibody. The lowest detectable amount of virus was 3 ng (0.06 micrograms/ml). There was no detectable cross-reaction with HPV type 6 or 11. The assay could be used both with cervical swabs in several common sample collection buffers and with surgical material solubilized in NP40-containing extraction buffers. Among 15 surgically removed condyloma acuminata, only 1 specimen was found to contain HPV-16 particles, at a concentration of 375 ng/ml (1.1 micrograms/specimen). Among 29 cervical swab samples from patients with koilocytotic atypia, 9 samples were found to contain virus. The results indicate that this assay is useful for large-scale studies on shedding of HPV particles.