Oral vaccination of mice with human papillomavirus virus-like particles induces systemic virus-neutralizing antibodies

Demystifying particle-based oral vaccines

Introduction: The oral route of vaccination is pain- and needle-free and can induce systemic and mucosal immunity. However, gastrointestinal barriers and antigen degradation impose significant hurdles in the development of oral vaccines. Live attenuated viruses and bacteria can overcome these barriers but at the risk of introducing safety concerns. As an alternative, particles have been investigated for antigen protection and delivery, yet there are no FDA-approved oral vaccines based on particle-based delivery systems. Our objective was to discover underlying determinants that can explain the current inadequacies and identify paradigms that can be implemented in future for successful development of oral vaccines relying on particle-based delivery systems.Areas covered: We reviewed literature related to the use of particles for oral vaccination and placed special emphasis on formulation characteristics and administration schedules to gain an insight into how these parameters impact production of antigen-specific antibodies in systemic and mucosal compartments.Expert opinion: Despite the long history of vaccines, particle-based oral vaccination is a relative new field with the first study published in 1989. Substantial variability exists between different studies with respect to dosing schedules, number of doses, and the amount of vaccine per dose. Most studies have not used adjuvants in the formulations. Better standardization in vaccination parameters is required to improve comparison between experiments, and adjuvants should be used to enhance the systemic and mucosal immune responses and to reduce the number of doses, which will make oral vaccines more attractive.

Vaccination strategies for the prevention of cervical cancer

Infection with high-risk human papillomaviruses (HPVs) is an essential step in the multistep process leading to cervical cancer. There are approximately 120 different types of HPV identified: of these, 18 are high-risk types associated with cervical cancer, with HPV-16 being the dominant type in most parts of the world. The major capsid protein of papillomavirus, produced in a number of expression systems, self assembles to form virus-like particles. Virus-like particles are the basis of the first generation of HPV vaccines presently being tested in clinical trials. Virus-like particles are highly immunogenic and afford protection from infection both in animal models and in Phase IIb clinical trials. A number of Phase III trials are in progress to determine if the vaccine will protect against cervical disease and, in some cases, genital warts. However, it is predicted that these vaccines will be too expensive for the developing world, where they are desperately needed. Another problem is that they will be type specific. Novel approaches to the production of virus-like particles in plants, second-generation vaccine approaches including viral and bacterial vaccine vectors and DNA vaccines, as well as different routes of immunization, are also reviewed.

Discussing the diagnosis of HPV-OSCC: common questions and answers

Human papillomavirus (HPV) is responsible for a rising proportion of oropharyngeal squamous cell cancers (OSCCs). HPV-positive OSCCs (HPV-OSCCs) are associated with oral HPV infection and sexual behavior. Patient questions regarding risk factors, prognosis and implications for past, present and future relationships often arise. This manuscript addresses frequently asked questions by patients with HPV-OSCC and their families. A framework for clinicians to address these conversations and the limitations of our present knowledge base is also presented.

Plant-made vaccines for humans and animals

The concept of using plants to produce high-value pharmaceuticals such as vaccines is 20 years old this year and is only now on the brink of realisation as an established technology. The original reliance on transgenic plants has largely given way to transient expression; proofs of concept for human and animal vaccines and of efficacy for animal vaccines have been established; several plant-produced vaccines have been through Phase I clinical trials in humans and more are scheduled; regulatory requirements are more clear than ever, and more facilities exist for manufacture of clinic-grade materials. The original concept of cheap edible vaccines has given way to a realisation that formulated products are required, which may well be injectable. The technology has proven its worth as a means of cheap, easily scalable production of materials: it now needs to find its niche in competition with established technologies. The realised achievements in the field as well as promising new developments will be reviewed, such as rapid-response vaccines for emerging viruses with pandemic potential and bioterror agents.

Listeria monocytogenes delivery of HPV-16 major capsid protein L1 induces systemic and mucosal cell-mediated CD4+ and CD8+ T-cell responses after oral immunization

Neutralizing antibodies are thought to be required at mucosal surfaces to prevent human papillomavirus (HPV) transmission. However, the potential for cell-mediated immunity in mediating protection against HPV infection has not been well explored. We generated recombinant Listeria monocytogenes (Lm) constructs that secrete listeriolysin O (LLO) fused with overlapping N-terminal (LLO-L1(1-258)) or C-terminal (LLO-L1(238-474)) fragments of HPV type 16 major capsid protein L1 (HPV-16-L1). Oral immunization of mice with either construct induced IFN-gamma-producing CD8+ and CD4+ T cells in the spleen and in the Peyer's patches with the C-terminal construct. Oral immunization with both constructs resulted in diminished viral titers in the cervix and uterus of mice after intravaginal challenge with vaccinia virus expressing HPV-16-L1.

Plant-produced vaccines: promise and reality

Plant-produced vaccines are a much-hyped development of the past two decades, whose time to embrace reality may have finally come. Vaccines have been developed against viral, bacterial, parasite and allergenic antigens, for humans and for animals; a wide variety of plants have been used for stable transgenic expression as well as for transient expression via Agrobacterium tumefaciens and plant viral vectors. A great many products have shown significant immunogenicity; several have shown efficacy in target animals or in animal models. The realised potential of plant-produced vaccines is discussed, together with future prospects for production and registration.

A direct comparison of human papillomavirus type 16 L1 particles reveals a lower immunogenicity of capsomeres than viruslike particles with respect to the induced antibody response

Capsomeres are considered to be an alternative to viruslike particle (VLP)-based vaccines as they can be produced in prokaryotic expression systems. So far, no detailed side-by-side comparison of VLPs and capsomeres has been performed. In the present study, we immunized mice with insect cell-derived human papillomavirus type 16 VLPs and capsomeres. VLPs induced consistently higher antibody titers than capsomeres but the two forms induced similar CD8 T-cell responses after subcutaneous, intranasal, and oral immunization, and at least 20 to 40 times more L1 in the form of capsomeres than in the form of VLPs was needed to achieve comparable antibody responses. These results were confirmed by DNA immunization. The lower immunogenicity of capsomeres was independent of the isotype switch, as it was also observed for the early immunoglobulin M responses. Although there were differences in the display of surface epitopes between the L1 particles, these did not contribute significantly to the differences in the immune responses. capsomeres were less immunogenic than VLPs in Toll-like receptor 4 (TLR4)-deficient mice, suggesting that the lower immunogenicity is not due to a failure of capsomeres to trigger TLR4. We observed better correlation between antibody results from enzyme-linked immunosorbent assays and neutralization assays for sera from VLP-immunized mice than for sera from capsomere-immunized mice, suggesting qualitative differences between VLPs and capsomeres. We also showed that the lower immunogenicity of capsomeres could be compensated by the use of an adjuvant system containing MPL. Taken together, these results suggest that, presumably because of the lower degree of complexity of the antigen organization, capsomeres are significantly less immunogenic than VLPs with respect to the humoral immune response and that this characteristic should be considered in the design of putative capsomere-based prophylactic vaccines.

Comparison of serum humoral responses induced by oral immunization with the hepatitis B virus core antigen and the cholera toxin B subunit

The hepatitis B virus core (HBc) virus-like particle (VLP) is known as one of the most immunogenic antigens and carrier vehicles in different immunization strategies. Recent findings are suggesting the potential of the HBc VLPs as an oral immunogen. Here, we focus on the induction of serum humoral responses by oral administration of HBc VLPs in preparations substantially free of lipopolysaccharide and immunomodulating encapsidated RNA. The full-length HBc antigen was used, because the C-terminal arginine-rich tail may contribute to the immunogenicity of the antigen as the region is involved in cell surface heparan sulfate binding and internalization of the protein. Serum antibody levels and isotypes were determined following oral administration of the HBc VLPs with the perspective of using the HBc VLP as an immunostimulatory and carrier molecule for epitopes of blood-borne diseases in oral immunization vaccination strategies. Following oral administration of the HBc VLP preparations to mice, a strong serum humoral response was induced with mainly immunoglobulin G2a (IgG2a) antibodies, pointing toward a Th1 response which is essential in the control of intracellular pathogens. Intraperitoneal immunization with the HBc VLP induced a stronger, mixed Th1/Th2 response. Finally, a comparison was made with the induced serum humoral response following oral administration of the recombinant cholera toxin B pentamer, a commonly used oral immunogen. These immunizations, in contrast, induced predominantly antibodies of the IgG1 isotype, indicative of a Th2 response. These data suggest that the HBc VLP can be an interesting carrier molecule in oral vaccine development.

Oral immunization with different assembly forms of the HPV 16 major capsid protein L1 induces neutralizing antibodies and cytotoxic T-lymphocytes

Human papillomaviruses have been recognized as the causative agent of anogenital cancer. In 2006, a commercial vaccine based on virus-like particles composed of the L1 major capsid protein of the papillomaviruses has been available. This vaccine induces virus-neutralizing antibody responses upon parenteral injection. Here we investigated the oral immunogenicity of different assembly forms of HPV 16 L1, that is: T7-VLPs, T1 particles and capsomeres. Our results show that all three assembly forms induce humoral and cellular immune responses after oral vaccination of mice. The anti-L1 antibodies were conformation-specific and showed neutralizing activity in a pseudovirion-based assay. We also investigated if adjuvants have an influence on the oral immunogenicity of the different L1 forms. For saponins we observed a significant toxicity if applied orally. Co-administration of either CpG DNA or Escherichia coli heat-labile enterotoxin LT(R192G) had no apparent enhancing effect on the production of anti-L1 antibodies. More pronounced was the effect of CpG administration on the long-term immunity as we observed a significantly stronger recall response 244 days after the first vaccination. Compared to capsomeres, VLPs induced stronger humoral immune responses while the CTL responses were induced at comparable levels. Finally, we were also able to induce neutralizing antibodies and L1-specific cytotoxic T-lymphocytes after oral administration of crude extracts of L1-expressing insect cells. In conclusion, all three assembly forms of the L1 protein are immunogenic when administered orally.

Transient expression of Human papillomavirus type 16 L1 protein in Nicotiana benthamiana using an infectious tobamovirus vector

A Tobacco mosaic virus (TMV)-derived vector was used to express a native Human papillomavirus type 16 (HPV-16) L1 gene in Nicotiana benthamiana by means of infectious in vitro RNA transcripts inoculated onto N. benthamiana plants. HPV-16 L1 protein expression was quantitated by enzyme-linked immunosorbent assays (ELISA) after concentration of the plant extract. We estimated that the L1 product yield was 20-37 microg/kg of fresh leaf material. The L1 protein in the concentrated extract was antigenically characterised using the neutralising and conformation-specific Mabs H16:V5 and H16:E70, which bound to the plant-produced protein. Particles observed by transmission electron microscopy were mainly capsomers but virus-like particles (VLPs) similar to those produced in other systems were also present. Immunisation of rabbits with the concentrated plant extract induced a weak immune response. This is the first report of the successful expression of an HPV L1 gene in plants using a plant virus vector.

HPV vaccines

The ability to generate human papillomavirus virus (HPV)-like particles by the synthesis and self-assembly in vitro of the major virus capsid protein L1 has transformed our prospects for preventing cervical carcinoma in women. These particles provide vaccines that are immunogenic and safe, and data from proof-of-principle efficacy trials strongly suggest that they will protect against persistent HPV infection and cervical intraepithelial neoplasia. However, the duration of protection provided by these vaccines is not known, the antibody responses induced are HPV-type-specific and immunisation must occur pre-exposure to the virus. Second-generation vaccines could include an early antigen for protection post exposure and alternative delivery systems might be needed for the developing world. Therapeutic vaccines for low-grade intraepithelial disease are realistic but high-grade disease presents major hurdles for immunotherapies.

Strategies for the prevention of cervical cancer by human papillomavirus vaccination

As cervical cancer is causally associated with 14 high-risk types of human papillomavirus (HPV), a successful HPV vaccine will have a major impact on this disease. Although some persistent HPV infections progress to cervical cancer, host immunity is generally able to clear most HPV infections. Both cell-mediated and antibody responses have been implicated in influencing the susceptibility, persistence or clearance of genital HPV infection. There have been two clinical trials that show that vaccines based on virus-like particles (VLPs) made from the major capsid protein, L1, are able to type specifically protect against cervical intra-epithelial neoplasia and infection. However, there is no evidence that even a mixed VLP vaccine will protect against types not included in the vaccine, and a major challenge that remains is how to engineer protection across a broader spectrum of viruses. Strategies for production of HPV vaccines using different vaccine vectors and different production systems are also reviewed.

Vaccins anti-papillomavirus et prévention du cancer du col de l’utérus

Human papillomaviruses (HPV) cause the development of various cutaneous and mucosal lesions. Some genotypes play a role in the genesis of cervical cancer, which is the second most common cancer in women. HPV types 16 and 18 account for 60 to 72% of all HPV-associated cervical cancers, while types 6 and 11 cause genital warts. Despite the various escape strategies viruses use to fight the natural immune system, more than 90% of the infections clear spontaneously. It should therefore be possible to prepare prophylactic vaccines. The HPV major capsid protein L1 self-assembles into virus-like particles (VLP). Immunization after parenteral vaccination with it provided very good protection against experimental infection in different animal models. The first clinical trials revealed the satisfactory tolerance and excellent immunogenicity of these vaccines. Two vaccine approaches were selected: one based on protection against cervical cancer from 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. Initial results with these vaccines show an efficacy of more than 90% against infection and 100% against the onset of dysplastic lesions. Despite these hopeful results, a vaccined strategy sould still be defined. Meanwhile, the cytology screening program should be carried on until the beginning of the vaccination.

A virus-based vaccine may prevent cervical cancer

High-risk human papillomaviruses (HPVs) are now recognized as the etiologic agents of invasive cervical cancer, a major cancer in women. A single HPV type (type 16) is responsible for about 50% of the cancers. The major capsid protein of papillomaviruses, L1, when expressed by recombinant DNA technology, has the intrinsic ability to assemble into virus-like particles (VLPs). In a recent study, a vaccine based on HPV 16 VLPs was tested in a placebo-controlled proof-of-principle trial in young women in the United States. The vaccine was found to prevent 100% of incident persistent HPV 16 infections and HPV 16-associated cervical intraepithelial neoplasia. These results offer promise that cervical cancer will be preventable by an HPV-based vaccine. Studies planned or in progress are examining the efficacy of the vaccine in men, in HIV-infected individuals, and in other parts of the world. Attempts are being made to prepare vaccines that can be administered more easily to large populations.

Prophylactic human papillomavirus vaccines: the beginning of the end of cervical cancer

Persistent infection with one of the oncogenic human papillomavirus (HPV) types is a necessity for the development of cervical cancer. By HPV vaccination, cervical cancer could become a very rare disease. Two types of HPV vaccines can be distinguished: (i) therapeutic vaccines which induce cellular immunity targeted against epithelial cells infected with HPV and (ii) prophylactic vaccines inducing virus-neutralizing antibodies protecting against new but not against established infections. At present, several vaccines have been developed and tested in clinical trials. The vaccines are generally well tolerated and highly immunogenic. The current clinical data indicate that prophylactic vaccines are very effective against new persistent infections and the development of cervical intraepithelial lesions. The protection is type specific. However, the follow-up of the vaccination trials is still short. The effect of HPV vaccines on future cancer incidence will only be known after decades of follow-up. This article will address the status of recently terminated phase II and currently running phase III trials with prophylactic HPV vaccines.

Preventative and therapeutic vaccines for cervical cancer

"High-risk" genotypes of the human papillomavirus (HPV), most commonly HPV genotype 16, are the primary etiologic agents of cervical cancer. Indeed HPV DNA is detected in 99% of cervical carcinomas. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by the induction of the appropriate viral-antigen-specific immune responses. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. HPV L1 virus-like particles (VLPs) show great promise as prophylactic HPV vaccines in ongoing clinical trials but L2-based preventative vaccines have yet to be tested in patients. Since the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target the nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Although other early viral antigens show promise for vaccination against papillomas, therapeutic vaccines targeting E6 and E7 may provide the best opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or proteins, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should this new generation of HPV preventative and therapeutic vaccines function in patients as demonstrated in animal models, oncogenic HPV infection and its associated malignancies could be controlled by vaccination. Importantly, recent advances in HPV detection and continued improvements in screening further enhance our opportunities to systematically eradicate HPV-associated malignancy.

Hepatitis E: An overview and recent advances in vaccine research

Hepatitis E virus (HEV) is an unclassified, small, non-enveloped RNA virus, as a causative agent of acute hepatitis E that is transmitted principally via the fecal-oral route. The virus can cause large water-born epidemics of the disease and sporadic cases as well. Hepatitis E occurs predominantly in developing countries, usually affecting young adults, with a high fatality rate up to 15%-20% in pregnant women. However, no effective treatment currently exists for hepatitis E, and the only cure is prevention. But so far there are no commercial vaccines for hepatitis E available in the world. Although at least four major genotypes of HEV have been identified to date, only one serotype of HEV is recognized. So there is a possibility to produce a broadly protective vaccine. Several studies for the development of an effective vaccine against hepatitis E are in progress and the best candidate at present for a hepatitis E vaccine is a recombinant HEV capsid antigen expressed in insect cells from a baculovirus vector. In this article, the recent advances of hepatitis E and the development of vaccine research for HEV including recombinant protein vaccine, DNA vaccine and the recombinant hepatitis E virus like particles (rHEV VLPs) are briefly reviewed.

Vaccination to prevent and treat cervical cancer

Human papillomaviruses (HPVs) are the primary etiologic agents of cervical cancer. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by HPV vaccines. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. However, because the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Thus, therapeutic vaccines targeting E6 and E7 may provide the best option for controlling HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or protein, in nucleic acid form, as components of chimeric virus-like particles, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. If these preventive and therapeutic HPV vaccines prove successful in patients, as they have in animal models, then oncogenic HPV infection and its associated malignancies may be controllable by vaccination.

Effect of dose and long-term storage on the immunogenicity of murine polyomavirus VP1 virus-like particles

We have analysed the stability and immunogenicity of murine polyomavirus virus-like particles (VLPs) following intranasal administration without adjuvant. No morphological or immunological changes were observed in a preparation of these VLPs stored for 9 weeks at room temperature. Strong humoral and cellular (Th1) responses were obtained after a single 5.55 microg dose immunisation, which are efficiently boosted after a second dose. However, at dose concentrations above 0.22 microg/microl, these VLPs appear to aggregate and, when used for immunisations, they fail to induce a strong cellular response, even though the humoral response is unaffected. These results may reflect the differential processing of VLP aggregates by the immune system or, alternatively, VLP neutralisation by antibodies induced after a primary immunisation.

New approaches for the management of cervical cancer

Since the introduction of the Pap test by George Papanicolaou, the incidence of cervical cancer has fallen and mortality has decreased, in parallel with effective treatment of the precancerous and in situ stages of the disease. However, women who are not diagnosed through screening usually present with advanced disease. Early invasive disease can be treated successfully with radical abdominal hysterectomy and pelvic lymphadenectomy or with radiotherapy. A surgical alternative is radical trachelectomy, which can preserve fertility in young women. Advances in the techniques of laparoscopy facilitate procedures, such as radical vaginal hysterectomy with laparoscopic lymphadenectomy, that decrease intra-abdominal scarring and length of hospital stays. The presence of lymph node metastases alters the type of therapy. A range of methods is available to assess lymph nodes, including positron emission tomography, a new approach that may be of value. Radiotherapy alone may not be successful in women with locally advanced disease and adding chemotherapy may eradicate systemic micrometastases that are not affected by radiation. Single-agent cisplatin is the current agent of choice for adding to radiotherapy but new agents are being evaluated. Persistent infection with human papillomavirus (HPV) is associated with the development of cervical cancer. Vaccines against HPV are being developed and clinically tested and hopefully in the future it may be possible to eradicate cervical cancer.

Production of human papillomavirus type 16 virus-like particles in transgenic plants

Cervical cancer is linked to infection with human papillomaviruses (HPV) and is the third most common cancer among women worldwide. There is a strong demand for the development of an HPV preventive vaccine. Transgenic plants expressing the HPV major capsid protein L1 could be a system to produce virus-like particles for prophylactic vaccination or could even be used as edible vaccines to induce an L1-specific prophylactic immune response. Here, we describe the generation of transgenic tobacco and potato plants carrying the HPV type 16 major structural gene L1 under the control of the cauliflower mosaic virus 35S promoter. All attempts to express either the original, unmodified L1 gene or an L1 gene with a codon usage optimized for expression in plants failed. Surprisingly, small amounts of the protein were detected using an L1 gene optimized for expression in human cells. However, Northern blot analysis revealed that most of the L1 transcripts were degraded. Introduction of the translational enhancer Omega derived from the tobacco mosaic virus strongly increased transcript stability and resulted in accumulation of L1 protein to approximately 0.5 to 0.2% of total soluble protein in transgenic tobacco and potato plants, respectively. The plant-derived L1 protein displayed conformation-specific epitopes and assembled into virus-like particles. Furthermore, we did not find any indications of protein modification of the L1 protein produced in plants. Plant-derived L1 was as immunogenic as L1 expressed in baculovirus-infected insect cells. Feeding of tubers from transgenic potatoes to mice induced an anti-L1 antibody response in 3 out of 24 mice, although this response was only transient in two of the mice. Our data, however, indicate that an anti-L1 response was primed in about half of the 24 animals.

Oral immunogenicity of human papillomavirus-like particles expressed in potato

Human papillomavirus-like particles (HPV VLPs) have shown considerable promise as a parenteral vaccine for the prevention of cervical cancer and its precursor lesions. Parenteral vaccines are expensive to produce and deliver, however, and therefore are not optimal for use in resource-poor settings, where most cervical HPV disease occurs. Transgenic plants expressing recombinant vaccine immunogens offer an attractive and potentially inexpensive alternative to vaccination by injection. For example, edible plants can be grown locally and can be distributed easily without special training or equipment. To assess the feasibility of an HPV VLP-based edible vaccine, in this study we synthesized a plant codon-optimized version of the HPV type 11 (HPV11) L1 major capsid protein coding sequence and introduced it into tobacco and potato. We show that full-length L1 protein is expressed and localized in plant cell nuclei and that expression of L1 in plants is enhanced by removal of the carboxy-terminal nuclear localization signal sequence. We also show that plant-expressed L1 self-assembles into VLPs with immunological properties comparable to those of native HPV virions. Importantly, ingestion of transgenic L1 potato was associated with activation of an anti-VLP immune response in mice that was qualitatively similar to that induced by VLP parenteral administration, and this response was enhanced significantly by subsequent oral boosting with purified insect cell-derived VLPs. Thus, papillomavirus L1 protein can be expressed in transgenic plants to form immunologically functional VLPs, and ingestion of such material can activate potentially protective humoral immune responses.

Progress in prophylactic and therapeutic vaccines for human papillomavirus infection

Virus-like particle (VLP) subunit vaccines composed of the major capsid protein L1 of the genital human papillomaviruses (HPVs) are now in Phase III clinical trials. The vaccines are immunogenic and safe and early results indicate efficacy. VLPs induce strong cell-mediated as well as humoral immune responses and chimeric VLPs including an HPV early protein may have therapeutic potential. Polynucleotide and recombinant viral vaccines encoding nonstructural viral proteins show therapeutic and prophylactic efficacy in animal models and are candidate immunotherapies for established low-grade benign genital infections. Vaccines designed to elicit cytotoxic T-lymphocytes specific for the HPV oncoproteins E6 and E7 show immunogenicity and efficacy in transplantable tumor models in rodents. In Phase I and II trials these vaccines are immunogenic and safe but show limited efficacy.

Vaccines for viral diseases with dermatologic manifestations

Vaccines against infectious diseases have been available since the 1800s, when an immunization strategy against smallpox developed by Jenner gained wide acceptance. Until recently, the only vaccination strategies available involved the use of protein-based, whole killed, and attenuated live virus vaccines. These strategies have led to the development of effective vaccines against a variety of diseases with primary or prominent cutaneous manifestations. Effective and safe vaccines now used worldwide include those directed against measles and rubella (now commonly used together with a mumps vaccine as the trivalent MMR), chickenpox, and hepatitis B. The eradication of naturally occurring smallpox remains one of the greatest successes in the history of modern medicine, but stockpiles of live smallpox exist in the United States and Russia. Renewed interest in the smallpox vaccine reflects concerns about a possible bioterrorist threat using this virus. Yellow fever is a hemorrhagic virus endemic to tropical areas of South America and Africa. An effective vaccine for this virus has existed since 1937, and it is used widely in endemic areas of South America, and to a lesser extent in Africa. This vaccine is recommended once every 10 years for people who are traveling to endemic areas. Advances in immunology have led to a greater understanding of immune system function in viral diseases. Progress in genetics and molecular biology has allowed researchers to design vaccines with novel mechanisms of action (eg, DNA, vector, and VLP vaccines). Vaccines have also been designed to specifically target particular viral components, allowing for stimulation of various arms of the immune system as desired. Ongoing research shows promise in prophylactic and therapeutic vaccination for viral infections with cutaneous manifestations. Further studies are necessary before vaccines for HSV, HPV, and HIV become commercially available.

Oral vaccination with recombinant Listeria monocytogenes expressing human papillomavirus type 16 E7 can cause tumor growth in mice to regress

Listeria monocytogenes is a Gram-positive, facultative intracellular bacterium with the ability to present secreted proteins to the major histocompatibility complex class I pathway to stimulate cell-mediated immune response. In our study, we constructed the recombinant L. monocytogenes encoding human papillomavirus type 16 E7 gene (rLM-E7). When orally administered to syngeneic mice, rLM-E7 could induce a cytotoxic T-lymphocyte (CTL) response. Furthermore, in vitro flow cytometric assay and in vivo immune deficiency assays showed that rLM-E7 could prevent and eradicate tumor growth via CD8+-dependent CTLs. Hence, the potency of rLM-E7 as a therapeutic vaccine for cervical cancer is the result of the induction E7-specific cell-mediated immunity by L. monocytogenes. In addition to potency, this vaccine also offers ease of administration and reduced cost of production compared with other vaccines formulated for injection. Thus, L. monocytogenes encoding HPV-16 E7 may be a useful oral vaccine for cervical cancer treatment.

Trachea, lung, and tracheobronchial lymph nodes are the major sites where antigen-presenting cells are detected after nasal vaccination of mice with human papillomavirus type 16 virus-like particles

Vaccination by the nasal route has been successfully used for the induction of immune responses. Either the nasal-associated lymphoid tissue (NALT), the bronchus-associated lymphoid tissue, or lung dendritic cells have been mainly involved. Following nasal vaccination of mice with human papillomavirus type 16 (HPV16) virus-like-particles (VLPs), we have previously shown that interaction of the antigen with the lower respiratory tract was necessary to induce high titers of neutralizing antibodies in genital secretions. However, following a parenteral priming, nasal vaccination with HPV16 VLPs did not require interaction with the lung to induce a mucosal immune response. To evaluate the contribution of the upper and lower respiratory tissues and associated lymph nodes (LN) in the induction of humoral responses against HPV16 VLPs after nasal vaccination, we localized the immune inductive sites and identified the antigen-presenting cells involved using a specific CD4(+) T-cell hybridoma. Our results show that the trachea, the lung, and the tracheobronchial LN were the major sites responsible for the induction of the immune response against HPV16 VLP, while the NALT only played a minor role. Altogether, our data suggest that vaccination strategies aiming to induce efficient immune responses against HPV16 VLP in the female genital tract should target the lower respiratory tract.

The use of vaccines in the prevention and treatment of cervical cancer

The close association between high risk HPV infection and cervical carcinoma has provided the impetus for the development of prophylactic and therapeutic vaccination schedules. An effective prophylactic vaccine would obviate the need for population-based cervical screening programmes, while therapeutic vaccination might provide an effective adjunct to or replacement for conventional treatment for benign and malignant cervical disease. While the challenges associated with the design and implemention of immunotherapies are numerous, optimism remains high and it is expected that the next few decades will witness a revolutionary change in the way we treat cervical cancer and its premalignant lesions. A papillomavirus vaccine that prevented HPV infection on the one hand and acted against established disease on the other, would have a profound impact on one of the major cancers affecting women globally.

Route of administration of chimeric BPV1 VLP determines the character of the induced immune responses

To examine the mucosal immune response to papillomavirus virus-like particles (PV-VLP), mice were immunized with VLP intrarectally (i.r.), intravaginally (i.va.) or intramuscularly (i.m.) without adjuvant. PV-VLP were assembled with chimeric BPV-1 L1 proteins incorporating sequence from HIV-1 gp120, either the V3 loop or a shorter peptide incorporating a known CTL epitope (HIVP18I10). Antibody specific for BPV-1 VLP and P18 peptide was detected in serum following i.m., but not i.r. or i.va. immunization. Denatured VLP induced a much reduced immune response when compared with native VLP. Immune responses following mucosal administration of VLP were generally weaker than following systemic administration. VLP specific IgA was higher in intestine washes following i.r. than i.va. immunization, and higher in vaginal washes following i.m. than i.r. or i.va. immunization. No differences in specific antibody responses were seen between animals immunized with BPV-1 P18 VLP or with BPV-1 V3 VLP. Cytotoxic T lymphocyte precursors specific for the P18 CTL epitope were recovered from the spleen following i.m., i.va. or i.r. immunization with P18 VLP, and were similarly detected in Peyer's patches following i.m. or i.r. immunization. Thus, mucosal or systemic immunization with PV VLP induces mucosal CTL responses and this may be important for vaccines for mucosal infection with human papillomaviruses and for other viruses.

Parenteral and oral immunization with a plasmid DNA expressing the human papillomavirus 16-L1 gene induces systemic and mucosal antibodies and cytotoxic T lymphocyte responses

The association of human papillomavirus (HPV) infection and cervical cancer has been demonstrated. The development of a prophylactic vaccine to protect against primary HPV infection may therefore be an efficient means to reduce the incidence of this cancer worldwide. To assess the capacity of a plasmid DNA that expresses the L1 gene of HPV type 16 to induce a protective immune response, mice were immunized by parenteral and oral routes. Animals that received the DNA vaccine intramuscularly, subcutaneously and orally, developed systemic anti-L1 IgG antibodies. Antibodies developed in mice vaccinated subcutaneously were detectable twelve months post-immunization. Specific IgA antibodies were also found in vaginal washes from immunized mice. Both systemic and local antibodies proved effective in a surrogate neutralization assay. Splenic T cells extracted from experimental mice showed cytotoxic T lymphocytes (CTL) activity mediated by CD8 + cells. Mice were challenged with a syngeneic melanoma cell line, engineered to express the HPV16-L1 protein, tumours in vaccinated animals showed slower growth rate, correlated directly with a longer survival of mice. The results suggest that the L1-based DNA vaccine may be useful for the prevention of primary infections by HPV16.

Effect of preexisting neutralizing antibodies on the anti-tumor immune response induced by chimeric human papillomavirus virus-like particle vaccines

Chimeric human papillomavirus virus-like particles (HPV cVLPs) carrying HPV16 E7 protein are potent vaccines for inducing cell-mediated immunity (CMI) against HPV-induced tumors in animal models. We tested the hypothesis that virion-neutralizing antibodies generated during an initial vaccination might prevent effective boosting of CMI to the cVLPs. Mice with circulating HPV16-neutralizing antibodies, generated by direct immunization with wild-type VLPs or by passive transfer of hyperimmune anti-HPV16 VLP mouse sera, were subsequently vaccinated with HPV16 E7-containing cVLPs. Mice with preexisting neutralizing antibodies were not protected from HPV16 E7-positive TC-1 tumor challenge, compared to the protection seen in mice lacking these antibodies. Antibody-coated VLPs bound very inefficiently to receptor-positive cell lines, suggesting that one of the mechanisms of antibody interference is blocking of VLP binding to its receptor and thereby uptake of VLPs by antigen-presenting cells. Our results suggest that repetitive vaccination with a cVLP for induction of cellular immune responses to an incorporated antigen may be of limited effectiveness due to the presence of neutralizing antibodies against the capsid proteins induced after the first application. This limitation could potentially be overcome by boosting with cVLPs containing the same target antigen incorporated into other papillomavirus-type VLPs.

Oral administration of hepatitis E virus-like particles induces a systemic and mucosal immune response in mice

We evaluated the potential of recombinant hepatitis E virus (rHEV) virus-like particles (VLPs) as an oral immunogen by analyzing the response of serum IgM, IgG, and IgA and fecal IgA in mice after oral administration. The capsid proteins of HEV with its N-terminal 111 amino acids truncated were expressed with a recombinant baculovirus in insect cells, where the capsid proteins self-assembled into VLPs. Mice were orally inoculated four times with purified rHEV VLPs in concentrations ranging from 10 to 100 microg without adjuvant. Serum IgM response was obtained with as little as 10 microg of the VLPs, and the level reached its maximum in all mice groups within 2 weeks after the first administration. Serum IgG was detected by 4 weeks post-immunization (p.i.) in the majority of mice given doses of 50 and 100 microg and continuously increased at least until the 10 week mark. Serum IgA was also detected by 4 weeks p.i. in the majority of mice given doses of 50 and 100 microg, and the level reached the maximum at 8 weeks p.i. Furthermore, the maximum level of intestinal IgA responses was detected in the groups of mice receiving 50 and 100 microg rHEV VLPs at 8 weeks p.i. All these antibody responses were obtained without a mucosal adjuvant. We therefore concluded that oral immunization of rHEV VLPs is capable of inducing systemic as well as intestinal antibody responses. Furthermore, serum IgG and fecal IgA thus induced were reactive to the native HEV antigen, as determined by Western blot assays and antigen-capture ELISA.

Papillomavirus-like particle based vaccines: cervical cancer and beyond

Non-infectious human papillomavirus-like particles (VLP), composed of the L1 major capsid protein, are under active development as vaccines to prevent cervical cancer. They would presumably function primarily by generating virion-neutralising antibodies against the genital human papillomavirus (HPV) types that are the principal cause of most cervical cancers. Early phase clinical studies indicate that the VLP vaccines are well tolerated and able to consistently induce high titres of virus type-specific neutralising antibodies. Two types of second-generation VLP-based subunit vaccines with therapeutic implications, both related and unrelated to papillomavirus infection, are in preclinical development. One type seeks to induce cell-mediated immune responses, especially cytotoxic lymphocytes (CTL), against non-structural papillomavirus proteins, proteins of other viruses, or tumour associated antigens. The target antigen is incorporated into the VLPs as a fusion protein of L1 or the L2 minor capsid protein. In mouse models, this approach has generated potent CTL responses after low dose vaccination in the absence adjuvant. The second type of therapeutic VLP-based vaccine seeks to generate autoantibodies to self-antigens. The display of self polypeptides in the context of the highly ordered array of repetitive elements on the papillomavirus VLP surface abrogates the ability of the humoral immune system to functionally distinguish between foreign and self. High titre and high avidity auto-reactive IgG antibodies have been induced to both soluble (TNF-alpha) and cell surface (CCR5) central self-antigens. Vaccines based on this approach could potentially be effective alternatives to monoclonal antibody (mAb)-based therapies for a variety of disease targets.

Human papillomavirus virus-like particles are efficient oral immunogens when coadministered with Escherichia coli heat-labile enterotoxin mutant R192G or CpG DNA

Certain human papillomaviruses (HPVs) cause most cervical cancer, which remains a significant source of morbidity and mortality among women worldwide. HPV recombinant virus-like particles (VLPs) are promising vaccine candidates for controlling anogenital HPV disease and are now being evaluated as a parenteral vaccine modality in human subjects. Vaccines formulated for injection generally are more costly, more difficult to administer, and less acceptable to recipients than are mucosally administered vaccines. Since oral delivery represents an attractive alternative to parenteral injection for large-scale human vaccination, the oral immunogenicity of HPV type 11 (HPV-11) VLPs in mice was previously investigated; it was found that a modest systemic neutralizing antibody response was induced (R. C. Rose, C. Lane, S. Wilson, J. A. Suzich, E. Rybicki, and A. L. Williamson, Vaccine 17:2129-2135, 1999). Here we examine whether VLPs of other genotypes may also be immunogenic when administered orally and whether mucosal adjuvants can be used to enhance VLP oral immunogenicity. We show that HPV-16 and HPV-18 VLPs are immunogenic when administered orally and that oral coadministration of these antigens with Escherichia coli heat-labile enterotoxin (LT) mutant R192G (LT R192G) or CpG DNA can significantly improve anti-VLP humoral responses in peripheral blood and in genital mucosal secretions. Our results also suggest that LT R192G may be superior to CpG DNA in this ability. These findings support the concept of oral immunization against anogenital HPV disease and suggest that clinical studies involving this approach may be warranted.

Developing HPV virus-like particle vaccines to prevent cervical cancer: a progress report

BACKGROUND

the knowledge that sexually transmitted infection with one of a limited number of human papillomaviruses (HPVs) is a central cause of almost all cervical cancers affords the opportunity to prevent this common cancer through anti-viral vaccination.

OBJECTIVE

the spectacular success of vaccines in preventing several other viral diseases offers hope that immunoprophylaxis against the relevant HPVs could lead to a major reduction in cervical cancer incidence.

RESULTS AND CONCLUSION

the results of preclinical studies and early phase clinical trials of virus-like particle (VLP) based subunit vaccines have been very encouraging. However, unique aspects of papillomavirus biology and genital tract infections, and the lack of sexual a transmission model for papillomavirus, make it far from certain that effective prophylactic vaccination against genital HPV infection will be easily achieved. Future clinical efficacy trials will likely test the hypothesis that parenteral injection of VLPs can induce antibody mediated and type specific protection against genital tract HPV infection and subsequent development of premalignant neoplastic disease.

Preventive and therapeutic vaccines for human papillomavirus-associated cervical cancers

'High risk' genotypes of the human papillomavirus (HPV), particularly HPV type 16, are the primary etiologic agent of cervical cancer. Thus, HPV-associated cervical malignancies might be prevented or treated by induction of the appropriate virus-specific immune responses in patients. Sexual transmission of HPV may be prevented by the generation of neutralizing antibodies that are specific for the virus capsid. In ongoing clinical trials, HPV virus-like particles (VLPs) show great promise as prophylactic HPV vaccines. Since the capsid proteins are not expressed at detectable levels by basal keratinocytes, therapeutic vaccines generally target other nonstructural viral antigens. Two HPV oncogenic proteins, E6 and E7, are important in the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Therefore, therapeutic vaccines targeting these proteins may provide an opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, in peptides or protein, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should they fulfill their promise, these vaccines may prevent HPV infection or control its potentially life-threatening consequences in humans.

The nine C-terminal amino acids of the major capsid protein of the human papillomavirus type 16 are essential for DNA binding and gene transfer capacity

Four C-terminal deletion mutants of the human papillomavirus 16 L1 protein were expressed in the baculovirus expression system. They consist of the deletion of amino acids 497-505, 477-505, 403-505 and 302-505 (delta C9, delta C31, delta C103 and delta C204 respectively). Only two of the C-terminally deleted proteins, delta C9 and delta C31, retained the ability to form virus-like particles (VLPs) resembling those obtained with the full length L1 protein. Analysis of deleted L1 proteins and corresponding VLPs indicated that the C-terminus was necessary both for DNA binding and DNA packaging. These results were corroborated by the loss of the gene transfer capacities of C-terminal deleted VLPs.

The immunology of animal papillomaviruses

Papillomaviruses are species- and tissue-specific double-stranded DNA viruses. These viruses cause epithelial tumours in many animals, including man. Typically, the benign warts undergo spontaneous, immune-mediated regression, most likely effected by T-cells (especially CD4, but also CD8 subsets), whereas humoral immunity can prevent new infections. Some papillomavirus infections fail to regress spontaneously and others progress to malignant epithelial tumours. Additionally, the impact of these lesions is greater in immunosuppressed individuals. Many therapies are ineffective, and there is much interest in the potential for immunological intervention in papillomavirus infections of man and animals. Vaccination can be achieved with 'live' virus, formalin-inactivated virus, synthetic virus-like particles, and DNA vaccination. There has been much recent progress in the development of such vaccines for papillomavirus infections in the rabbit, ox and dog. Success in these animal models suggests that similar approaches may prove useful for prophylactic or therapeutic vaccination against the important human papillomaviruses involved in the development of cutaneous and anogenital warts, laryngeal papillomatosis, and cervical cancer.

Human papillomavirus vaccines

Genital human papillomavirus (HPV) infections are the viral sexually transmitted diseases most frequently diagnosed that include anogenital condylomas and squamous intra-$bepithelial lesions, among which the precursors of invasive carcinomas of the uterine cervix. In animal PV models, vaccination against L1 and/or L2 viral capsid proteins provides an efficient protection against infection, involving virus type-specific neutralizing antibodies. Vaccination against non-structural E1, E2, E6 or E7 viral proteins does not prevent infection, unless administered altogether, but tends to stimulate regression, warranting the design of therapeutic vaccines. Prophylactic vaccines based on the use of virus-like particles (VLPs) obtained by auto-assembly of L1 or L1 and L2 proteins produced by recombinant DNA technology are under phase I/II clinical trials for HPV6/11 associated with condylomas and for HPV16, the most frequent oncogenic genotype. Second generation vaccines are chimeric proteins or VLPs incorporating one of the structural proteins (L1 or L2) fused to a non-structural protein (E6, E7 or E2), which should induce both humoral and cellular immunity. Vaccine valency (number of genotypes), route of administration (humoral versus local immunity), vaccinees (children, young adults, gender) and forms of vaccines (recombinant $LSalmonella typhimurium*I$L, edible plants expressing L1 and L2 proteins, DNA vaccines, synthetic antigenic peptides) are under study. End points to evaluate vaccine efficacy in phase III trials should include viral DNA detection and typing, and screening for low or high grade intraepithelial lesions. Therapeutic vaccines based on recombinant HPV E6 and/or E7 vaccinia virus, L2-E7 fusion proteins or E7 peptides corresponding to cytotoxic T cell epitopes are currently tested (phase I/II trials) in patients with cervical carcinomas of advanced clinical stages or high grade intraepithelial lesions. Animal studies, phase I/II clinical trials and implementation of the community support that HPV vaccines will constitute an efficient means to prevent carcinoma of the uterine cervix.