Human papillomavirus vaccines

Virus-like particle (VLP) subunit vaccines composed of the major capsid protein L1 of the genital human papillomaviruses (HPVs) are under test in phase I and II clinical trials. The vaccines are immunogenic and safe but no data on efficacy are yet available. 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. Recombinant virus, peptide, protein, polynucleotide and dendritic cell 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. Immunogenicity, but no efficacy, has been demonstrated in small clinical trials with some of these approaches.     

Recombinant DNA vaccines protect against tumors that are resistant to recombinant vaccinia vaccines containing the same gene

Antigen-specific cancer immunotherapy involves the delivery of tumor-associated antigen to the host for the generation of tumor-specific immune responses and antitumor effects. We hypothesized that different delivery systems may influence the pattern of antigen-specific immune response and the outcome of antitumor effect. We therefore evaluated recombinant vaccinia virus and naked DNA for the generation of antigen-specific immune responses and antitumor effects. We previously found that recombinant vaccinia and naked DNA vaccines containing the chimeric Sig/E7/LAMP-1 gene were capable of controlling the growth of HPV-16 E7-expressing tumor cells (TC-1). In this study, we performed a head-to-head comparison of optimized delivery of Sig/E7/LAMP-1 vaccinia and DNA vaccines using dose-escalating tumor challenge. At a dose of 1 x 10(6) TC-1 cells per mouse, Sig/E7/LAMP-1 DNA provided 100% protection against subcutaneous growth of tumors, while Vac-Sig/E7/LAMP-1 protected only 40% of the mice. Furthermore, Sig/E7/LAMP-1 DNA vaccines are capable of protecting against challenge with a more stringent subclone of TC-1 (TC-1 P2) established from TC-1 tumors that survived initial Sig/E7/LAMP-1 vaccinia vaccination. Immunological assays revealed that both vaccines induced comparable levels of CD8(+) T cell precursors and anti-E7 antibody titers. Interestingly, Sig/E7/LAMP-1 vaccinia induced both E7-specific IFN-gamma- and IL4-secreting CD4(+) T cell precursors while Sig/E7/LAMP-1 DNA induced only E7-specific IFN-gamma-secreting CD4(+) T cell precursors. We also found that IL-4 knockout C57BL/6 mice vaccinated with Sig/E7/LAMP-1 vaccinia exhibited a more potent antitumor effect than vaccinated wild-type C57BL/6 mice in our tumor protection experiments. These results suggest that IL-4 may play a detrimental role in the antitumor effect mediated by vaccinia vaccines. Our findings suggested that DNA vaccines may provide better tumor protection than vaccinia vaccines employing the same gene, which may have implications in the future design of antigen-specific cancer immunotherapy.     

Comparison of human papillomavirus type 16 L1 chimeric virus-like particles versus L1/L2 chimeric virus-like particles in tumor prevention

Chimeric human papillomavirus (HPV) virus-like particles (cVLPs) with the HPV16 E7 antigen fused to either the major capsid protein, L1, or the minor capsid protein, L2, have been used independently to protect against the formation of HPV-induced tumors in animal models. However, the advantages and disadvantages of both types of particles with respect to production and vaccine efficacy have never been analyzed. Therefore, in this study, we compared cVLPs with the HPV16 E7 antigen fused to L1 versus cVLPs with E7 fused to L2 with respect to their ability to protect mice from tumor challenge. The first 57 amino acids of E7 were used to overcome the size limitation and limited VLP production imposed by inserting polypeptides into L1 cVLPs. C57BL/6 mice were immunized with the above cVLPs at various doses. Tumor challenge was then performed with HPV16 E7-positive TC-1 cells. HPV16 L1-E7((1-57)) was superior to HPV16 L1/L2-E7((1-57)) in eliciting tumor protection at equivalent doses, although both types of particles were able to protect mice. Both cVLPs induced a specific cytotoxic T lymphocyte (CTL) response to the H2-D(b)-restricted E7 peptide (E7(49-57)) as determined by an ELISPOT assay and tetramer staining; however, immunization with the L1-E7((1-57)) cVLPs resulted in twofold higher CTL precursor frequencies. Our results demonstrate that cVLPs with the antigen fused to L1 are a more efficient vaccine with respect to tumor prevention than cVLPs with the antigen fused to L2. At the same time, however, L1 cVLPs are limited by the size of the antigen that can be incorporated and in the amount of cVLP that can be obtained from cultures when compared to L1/L2 cVLPs. This balances out their superior ability to induce protective immunity.     

Genetic immunization against cervical carcinoma: induction of cytotoxic T lymphocyte activity with a recombinant alphavirus vector expressing human papillomavirus type 16 E6 and E7

Infection of genital epithelial cells with human papillomavirus (HPV) types 16 and 18 is closely associated with the development of cervical carcinoma. The transforming potential of these high-risk HPVs depends on the expression of the E6 and E7 early viral gene products. Since the expression of E6 and E7 is selectively maintained in premalignant and malignant cervical lesions these proteins are attractive candidates for immunotherapeutic and prophylactic strategies. This report describes the construction, characterization and the in vivo immunotherapeutic potential of recombinant Semliki Forest virus (SFV) expressing the HPV16 E6 and E7 proteins (SFV-E6E7). Western blot analysis and immunofluorescence staining demonstrated expression of E6 and E7 in BHK cells infected with SFV-E6E7. Immunization of mice with SFV-E6E7 resulted in an efficient in vivo priming of HPV-specific CTL activity. The induced CTL lysed murine tumor cells transformed with the HPV16 genome and EL4 cells loaded with an immunodominant class I-binding HPV E7 peptide. CTLs could reproducibly be induced by immunization with three injections of as few as 10(5) infectious units of SFV-E6E7. Protection from tumor challenge was studied using the tumor cell line TC-1. Immunization with 5 x 10(6) SFV-E6E7 particles protected 40% of the mice from tumor challenge. These results indicate that E6E7 expression by the efficient and safe recombinant SFV system represents a promising strategy for immunotherapy or immunoprophylaxis of cervical carcinoma.     

Therapeutic human papillomavirus vaccines: current clinical trials and future directions

Background: Cervical cancer is the second largest cause of cancer deaths in women worldwide. It is now evident that persistent infection with high-risk human papillomavirus (HPV) is necessary for the development and maintenance of cervical cancer. Thus, effective vaccination against HPV represents an opportunity to restrain cervical cancer and other important cancers. The FDA recently approved the HPV vaccine Gardasil for the preventive control of HPV, using HPV virus-like particles (VLP) to generate neutralizing antibodies against major capsid protein, L1. However, prophylactic HPV vaccines do not have therapeutic effects against pre-existing HPV infections and HPV-associated lesions. Furthermore, due to the considerable burden of HPV infections worldwide, it would take decades for preventive vaccines to affect the prevalence of cervical cancer. Thus, in order to speed up the control of cervical cancer and treat current infections, the continued development of therapeutic vaccines against HPV is critical. Therapeutic HPV vaccines can potentially eliminate pre-existing lesions and malignant tumors by generating cellular immunity against HPV-infected cells that express early viral proteins such as E6 and E7. Objective: This review discusses the future directions of therapeutic HPV vaccine approaches for the treatment of established HPV-associated malignancies, with emphasis on current progress of HPV vaccine clinical trials. Methods: Relevant literature is discussed. Results/conclusion: Though their development has been challenging, many therapeutic HPV vaccines have been shown to induce HPV-specific antitumor immune responses in preclinical animal models and several promising strategies have been applied in clinical trials. With continued progress in the field of vaccine development, HPV therapeutic vaccines may provide a potentially promising approach for the control of lethal HPV-associated malignancies.     

Antigen-specific CD8+ T lymphocytes generated from a DNA vaccine control tumors through the Fas-FasL pathway.

Human papillomavirus, particularly type 16, and its oncogenic proteins, E6 and E7, are consistently expressed in most cervical cancers. One of the major issues facing cancer immunotherapy is that many human cancers evade the immune system by downregulating the expression of Fas molecules. An E7-expressing murine tumor model with a downregulated Fas expression--TC-1 P3(A15) tumors--was created. A DNA vaccine encoding calreticulin linked to E7 (CRT/E7) was able to generate protective and therapeutic antitumor effects against TC-1 P3(A15) tumors. In vitro Ab depletion and in vivo adoptive experiments showed that the antitumor effect of E7-specific CD8+ T lymphocytes against the TC-1 P3(A15) tumor cells was through the Fas-FasL-dependent CTL effector mechanism, and the TC-1 P3(A15) tumor cells needed higher numbers of antigen-specific CD8+ T lymphocytes for in vivo elimination. Our results demonstrated that chimeric CRT/E7 DNA vaccine resulted in control of tumors with downregulated Fas expression, highlighting the importance of the Fas-FasL pathway in the potent antitumor effect of antigen-specific CD8+ cytotoxic T lymphocytes and the role of Fas as part of in vivo tumor evasion.     

Secretory heat-shock protein as a dendritic cell-targeting molecule: a new strategy to enhance the potency of genetic vaccines

DNA vaccines are an appealing strategy for inducing cytotoxic T-lymphocyte and antibody responses against tumor cells as well as infectious agents. Dendritic cells (DCs) play a critical role in inducing immune responses, but their potential is not fully utilized in the DNA vaccine setting since they take up only a minor fraction of the injected DNA. Here we describe a novel DNA vaccination strategy based on the targeting of a modified tumor-associated antigen, the human papilloma virus (HPV) type 16 E7 protein, to DCs by a heat-shock protein (HSP) to enhance antigen presentation and immune responses. Specifically, a chimerical HPV-E7 and HSP70 fusion gene preceded with a leader sequence was constructed. When mice were immunized with this construct, the DNA is taken up by various types of cells, which then produce and secrete an HPV-E7-HSP70 fusion protein that is targeted to DCs by the HSP70 portion of the chimerical molecule for antigen presentation. In studies to test the efficacy of this strategy, we demonstrated that DNA vaccination with this secretory HPV-E7-HSP70 construct strongly enhanced an antigen-specific CD8+ T-cell response as well as a specific B-cell response in mice. Furthermore, this immunization approach not only protected mice against lethal challenge with an HPV E7-expressing tumor line (TC-1), but also showed a therapeutic effect against established tumors. The results of this study indicate that secretory HSPs can be broadly used to target tumor-associated antigens to DCs to enhance antigen-specific immune responses.     

Immunization strategy against cervical cancer involving an alphavirus vector expressing high levels of a stable fusion protein of human papillomavirus 16 E6 and E7

We are developing immunization strategies against cervical carcinoma and premalignant disease, based on the use of recombinant Semliki Forest virus (SFV) encoding the oncoproteins E6 and E7 from high-risk human papilloma viruses (HPV). Thus far, protein-based, as well as genetic immunization studies have demonstrated low to moderate cellular immune responses against E6 and E7. To improve these responses, we modified the structure and expression level of the E6 and E7 proteins produced by the SFV vector. Specifically, a construct was generated encoding a fusion protein of E6 and E7, while furthermore a translational enhancer was included (enhE6,7). Infection of cells with recombinant SFV-enhE6,7 resulted in the production of large amounts of the E6,7 fusion protein. The fusion protein was more stable than either one of the separate proteins. Immunization of mice with SFV-enhE6,7 resulted in strong, long-lasting HPV-specific cytotoxic T lymphocyte responses. Tumor challenge experiments in mice demonstrated that immunization with SFV-enhE6,7 resulted in prevention of tumor outgrowth and subsequent protection against tumor re-challenge.     

Human papillomavirus vaccines for cervical cancer.

Cervical cancer is one of the most common causes of cancer-related death in women. As a result of several recent advances in molecular biology, the association between human papillomavirus (HPV) infection and cervical cancer has been firmly established, and the oncogenic potential of certain HPV types has been clearly demonstrated. Several lines of evidence suggest the importance of the host's immune response, especially cellular immune response, in the pathogenesis of HPV-associated cervical lesions. These observations form a compelling rationale for the development of vaccine therapy to combat HPV infection. Both prophylactic and therapeutic HPV vaccine strategies are being developed. Prophylactic strategies currently under investigation focus on the induction of effective humoral immune responses against subsequent HPV infection. In this respect, impressive immunoprophylactic effects have been demonstrated in animals using papillomavirus-like particles (VLPs). VLPs are antigenic and protective, but are devoid of any viral DNA that may be carcinogenic to the host. For treatment of existing HPV infection, techniques to improve cellular immunity by enhancing viral antigen recognition are being studied. For this purpose, the oncogenic proteins E6 and E7 of HPV-16 and -18 are the focus of current clinical trials for cervical cancer patients. The development of successful HPV-specific vaccines may offer an attractive alternative to existing screening and treatment programs for cervical cancer.     

Control of cervicovaginal HPV-16 E7-expressing tumors by the combination of therapeutic HPV vaccination and vascular disrupting agents

Abstract Antigen-specific immunotherapy and vascular disrupting agents, such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA), have emerged as attractive approaches for the treatment of cancers. In the current study, we tested the combination of DMXAA treatment with therapeutic human papillomavirus type 16 (HPV-16) E7 peptide-based vaccination for their ability to generate E7-specific CD8+ T-cell immune responses, as well as their ability to control E7-expressing tumors in a subcutaneous and a cervicovaginal tumor model. We found that the combination of DMXAA treatment with E7 long peptide (amino acids 43-62) vaccination mixed with polyriboinosinic:polyribocytidylic generated significantly stronger E7-specific CD8+ T-cell immune responses and antitumor effects compared with treatment with DMXAA alone or HPV peptide vaccination alone in the subcutaneous model. Additionally, we found that the DMXAA-mediated enhancement of E7-specific CD8+ T-cell immune responses generated by the therapeutic HPV peptide-based vaccine was dependent on the timing of administration of DMXAA. Treatment with DMXAA in tumor-bearing mice was also shown to lead to increased dendritic cell maturation and increased production of inflammatory cytokines in the tumor. Furthermore, we observed that the combination of DMXAA with HPV-16 E7 peptide vaccination generated a significant enhancement in the antitumor effects in the cervicovaginal TC-1 tumor growth model, which closely resembles the tumor microenvironment of cervical cancer. Taken together, our data demonstrated that administration of the vascular disrupting agent, DMXAA, enhances therapeutic HPV vaccine-induced cytotoxic T-lymphocyte responses and antitumor effects against E7-expressing tumors in two different locations. Our study has significant implications for future clinical translation.     

Targeting human papillomavirus type 16 E7 to the endosomal/lysosomal compartment enhances the antitumor immunity of DNA vaccines against murine human papillomavirus type 16 E7-expressing tumors

DNA vaccination is an attractive approach for tumor immunotherapy because of its stability and simplicity of delivery. Advances demonstrate that helper T cell responses play a critical role in initiating immune responses. The aim of the current study is to test whether targeting HPV-16 E7 to the endosomal/lysosomal compartment can enhance the potency of DNA vaccines. We linked the lysosome-associated membrane protein 1 (LAMP-1) to HPV-E7 to construct a chimeric DNA, Sig/E7/LAMP-1 DNA. For in vivo tumor prevention experiments, mice were vaccinated with E7 DNA or Sig/E7/LAMP-1 DNA via gene gun, followed by tumor challenge. For in vivo tumor regression experiments, mice were first challenged with tumor cells and then vaccinated with E7-DNA or Sig/E7/LAMP-1 DNA. Intracellular cytokine staining with flow cytometry analysis, cytotoxic T lymphocyte (CTL) assays, enzyme-linked immunoabsorbent assay (ELISA), and enzyme-linked immunospot (ELISPOT) assays were used for in vitro E7-specific immunological studies. In both tumor prevention and tumor regression assays, Sig/E7/LAMP-1 DNA generated greater antitumor immunity than did wild-type E7 DNA. In addition, mice vaccinated with Sig/E7/LAMP-1 DNA had greater numbers of E7-specific CD4+ helper T cells, higher E7-specific CTL activity, and greater numbers of CD8+ T cell precursors than did mice vaccinated with Sig/E7 or wild-type E7 DNA. Sig/E7 generated a stronger E7-specific antibody response than did Sig/E7/LAMP-1 or wild-type E7 DNA. Our results indicate that linkage of the antigen gene to an endosomal/lysosomal targeting signal may greatly enhance the potency of DNA vaccines.     

Innovative DNA vaccine for human papillomavirus (HPV)-associated head and neck cancer

Human papillomavirus (HPV), particularly type 16, has been associated with a subset of head and neck cancers. The viral-encoded oncogenic proteins E6 and E7 represent ideal targets for immunotherapy against HPV-associated head and neck cancers. DNA vaccines have emerged as attractive approaches for immunotherapy due to its simplicity, safety and ease of preparation. Intradermal administration of DNA vaccine by means of gene gun represents an efficient method to deliver DNA directly into dendritic cells for priming antigen-specific T cells. We have previously shown that a DNA vaccine encoding an invariant chain (Ii), in which the class II-associated Ii peptide (CLIP) region has been replaced by a Pan-DR-epitope (PADRE) sequence to form Ii-PADRE, is capable of generating PADRE-specific CD4+ T cells in vaccinated mice. In the current study, we hypothesize that a DNA vaccine encoding Ii-PADRE linked to E6 (Ii-PADRE-E6) will further enhance E6-specific CD8+ T cell immune responses through PADRE-specific CD4+ T-helper cells. We found that mice vaccinated with Ii-PADRE-E6 DNA generated comparable levels of PADRE-specific CD4+ T-cell immune responses, as well as significantly stronger E6-specific CD8+ T-cell immune responses and antitumor effects against the lethal challenge of E6-expressing tumor compared with mice vaccinated with Ii-E6 DNA. Taken together, our data indicate that vaccination with Ii-E6 DNA with PADRE replacing the CLIP region is capable of enhancing the E6-specific CD8+ T-cell immune response generated by the Ii-E6 DNA. Thus, Ii-PADRE-E6 represents a novel DNA vaccine for the treatment of HPV-associated head and neck cancer and other HPV-associated malignancies.     

Activation of dendritic cells and induction of T cell responses by HPV 16 L1/E7 chimeric virus-like particles are enhanced by CpG ODN or sorbitol

Chimeric human papillomavirus-like particles, consisting of human papillomavirus (HPV) 16 L1-E7 fusion proteins [HPV 16 L1/E7 chimeric virus-like particles (CVLP)], are a vaccine candidate for treatment and prevention of cervical cancer. Although in preclinical studies CVLPs were shown to induce neutralizing antibodies and L1- and E7-specific T cell responses, the results of a recent clinical trial emphasized the need of improved immunogenicity of CVLPs. Here we studied the interaction of HPV 16 L1/E7 CVLPs with mouse bone marrow-derived dendritic cells (BMDCs) activated with different immune adjuvants. We found that lipopolysaccharides (LPS), unmethylated CpG motifs (CpG ODN) and sorbitol enhanced CVLP-induced stimulation of C57BL/6 mouse BMDCs as revealed by increased levels of CD40, CD80, MHC II and CD54 at the cell surface. CpG ODN and sorbitol also enhanced the presentation of Db-restricted cytotoxic T lymphocyte epitopes to HPV 16 L1- or E7-specific T lymphocytes after loading of CVLPs onto BMDCs. Treatment of BMDCs with CpG ODN in combination with CVLPs improved in vitro priming of naive T lymphocytes by CVLP-loaded BMDCs. In vivo, CVLP-loaded BMDCs were more immunogenic as compared with injection of CVLPs alone. CpG ODN and sorbitol further enhanced priming of antigen-specific T cell responses. Our data demonstrate that CpG ODN- or sorbitol-activated BMDCs substantially increase the immunogenicity of CVLPs. Implementing our results in clinical trial protocols may lead to improved activity of therapeutic HPV vaccines for the treatment of HPV-induced cancer.     

Comparison of HPV DNA vaccines employing intracellular targeting strategies

Intradermal vaccination via gene gun efficiently delivers DNA vaccines into dendritic cells (DCs) of the skin, resulting in the activation and priming of antigen-specific T cells in vivo. In the context of DNA vaccines, we previously used the gene gun approach to test several intracellular targeting strategies that are able to route a model antigen, such as the human papillomavirus type-16 (HPV-16) E7, to desired subcellular compartments in order to enhance antigen processing and presentation to T cells. These strategies include the use of the sorting signal of lysosome-associated membrane protein (LAMP-1), Mycobacterium tuberculosis heat-shock protein 70 (HSP70), calreticulin (CRT) and the translocation domain (dII) of Pseudomonas aeruginosa exotoxin A (ETA). Vaccination with DNA vaccines encoding E7 antigen linked to any of these molecules all led to a significant enhancement of E7-specific CD8(+) T-cell immune responses and strong antitumor effects against an E7-expressing tumor, TC-1. However, we were interested in identifying the most potent DNA vaccine for our future clinical trials. Thus, we performed a series of experiments to directly compare the potency of the various DNA vaccines. Among the DNA vaccines we tested, we found that vaccination with pcDNA3-CRT/E7 generated the highest number of E7-specific CD8(+) T cells and potent long-term protection and treatment effects against E7-expressing tumors in mice. Interestingly, we observed that pcDNA3-CRT/E7 is also capable of protecting against an E7-expressing tumor with downregulated MHC class I expression, a common feature associated with most HPV-associated cervical cancers. Our data suggest that the DNA vaccine linking CRT to E7 (CRT/E7) may be a suitable candidate for human trials for the control of HPV infections and HPV-associated lesions.     

A combination of DNA vaccines targeting human papillomavirus type 16 E6 and E7 generates potent antitumor effects

Human papillomavirus (HPV) infects large numbers of women worldwide and is present in more than 99% of all cervical cancers. HPV E6 and E7 are two viral oncoproteins that are consistently expressed in HPV infections and HPV-associated malignancies. We have previously developed DNA vaccines encoding calreticulin (CRT) linked either to HPV type 16 (HPV-16) E6 or to HPV-16 E7, both of which generated significant antitumor effects against E6- and E7-expressing tumors. In this study, we demonstrate that simultaneous vaccination of C57BL/6 mice or HLA-A2 transgenic mice with both CRT/E6 and CRT/E7 DNA vaccines generates significant E6- and E7-specific T-cell immune responses in vaccinated mice. Furthermore, combined vaccination with both CRT/E6 and CRT/E7 DNA generates significantly better therapeutic antitumor effects against HPV E6- and E7-expressing tumors than vaccination with either CRT/E6 DNA or CRT/E7 DNA alone. Our data suggest that it may be desirable to combine DNA vaccines targeting E6 with DNA vaccines targeting E7 to develop effective immunotherapeutic strategies for control of HPV infection and HPV-associated lesions in a clinical setting.     

Novel methods to treat and prevent human papillomavirus infection

The human papillomavirus (HPV), a ubiquitous sexually transmitted virus, is the causative agent for cervical dysplasia and carcinoma worldwide. Current treatment methods primarily utilize ablative and excisional procedures to remove dysplastic, HPV-infected cervical tissue. However, these procedures require intensive cytopathological surveillance and carry inherent risks of bleeding, infection and possible future pregnancy complications. Development of an effective vaccine against HPV would dramatically reduce the need for costly cytological and histological surveillance. HPV represents an ideal candidate for vaccine development, and current research efforts in the realm of prophylactic and therapeutic vaccine design show great promise. A host of various vaccine techniques are currently being developed and tested and, if effective, will have a significant impact on the incidence of cervical dysplasia and carcinoma.     

Immune responses against human papillomavirus (HPV) infection and evasion of host defense in cervical cancer

Human papillomavirus (HPV) is the most important etiological factor for cervical cancer. A recent study demonstrated that more than 20 HPV types were thought to be oncogenic for uterine cervical cancer. Notably, more than one-half of women show cervical HPV infections soon after their sexual debut, and about 90 % of such infections are cleared within 3 years. Immunity against HPV might be important for elimination of the virus. The innate immune responses involving macrophages, natural killer cells, and natural killer T cells may play a role in the first line of defense against HPV infection. In the second line of defense, adaptive immunity via cytotoxic T lymphocytes (CTLs) targeting HPV16 E2 and E6 proteins appears to eliminate cells infected with HPV16. However, HPV can evade host immune responses. First, HPV does not kill host cells during viral replication and therefore neither presents viral antigen nor induces inflammation. HPV16 E6 and E7 proteins downregulate the expression of type-1 interferons (IFNs) in host cells. The lack of co-stimulatory signals by inflammatory cytokines including IFNs during antigen recognition may induce immune tolerance rather than the appropriate responses. Moreover, HPV16 E5 protein downregulates the expression of HLA-class 1, and it facilitates evasion of CTL attack. These mechanisms of immune evasion may eventually support the establishment of persistent HPV infection, leading to the induction of cervical cancer. Considering such immunological events, prophylactic HPV16 and 18 vaccine appears to be the best way to prevent cervical cancer in women who are immunized in adolescence.     

Evaluation of HBs, HBc, and frCP virus-like particles for expression of human papillomavirus 16 E7 oncoprotein epitopes

OBJECTIVES: In an attempt to develop virus-like particles (VLPs) as experimental vaccine against human papilloma virus (HPV)-induced tumours, the HPV16 E7 oncoprotein epitopes spanning amino acid (aa) residues 35-98 were expressed on three proteins capable of VLP formation: hepatitis B virus (HBV) surface (HBs) and core (HBc) antigens, and RNA phage fr coats (frCP). METHODS: The profile of immunoglobulin isotypes induced in Balb/C mice after immunization with purified chimeric proteins was studied. RESULTS: The HBs*-E7(35-54) protein expressing E7 residues 35-54 between residues 139 and 142 of the HBs carrier formed HBs-like particles in Saccharomyces cerevisiae. The HBc Delta-E7(35-98), but not the frCP-E7(35-98), ensured VLP formation in Escherichia coli. In Balb/C mice, the HBs*-E7(35-54) VLPs predominantly induced an anti-E7 antibody, but not anti-HBs carrier response, whereas the HBc Delta-E7(35-98) VLPs induced a lower anti-E7 compared to anti-HBc carrier response. The frCP-E7(35-98) protein elicited equally high antibody responses to both E7 and frCP carrier. Analysis of the immunoglobulin G isotype profile of the antibodies induced by the E7-carrying chimeras showed that the HBs and frCP derivatives were capable of eliciting the Th1 and Th2 subsets of T helper cells, whereas the HBc-derived chimeras elicited only the Th2 subset. CONCLUSIONS: The HBs and HBc, but not frCP carriers support an efficient outcome for VLPs carrying the HPV16 E7 epitopes. All chimeric proteins may be regarded as potential vaccine candidates.     

Introducing human papillomavirus vaccines - questions remain

Genital human papillomavirus (HPV) infection and HPV-associated cervical and other anogenital cancers are significant public health problems. HPV 16 and HPV 18 are responsible for approximately 70% of all invasive cervical cancers worldwide. The first prophylactic HPV virus-like particle (VLP) vaccine against HPV types 6/11/16/18 was licensed in 2006 for girls and women aged 9-26 years. The second prophylactic HPV vaccine against HPV types 16 and 18 has been licensed this year. These vaccines are almost 100% effective in preventing infection and high-grade precancer associated with the HPV types included in the vaccine. The vaccines are well tolerated, safe, and highly immunogenic when given in three doses within 6 months. Efficacy of the vaccine against external vulvar and HPV-related vaginal lesions is also high. Even though the vaccine is highly effective against high-grade cervical, vaginal, or vulvar precancers, this only applies to women unexposed to these HPV types and only to high-grade intraepithelial lesions caused by these HPV types. Therefore, it is important to understand that the population impact of the vaccines will be much lower than vaccinating naive populations. Implementing HPV vaccine is a great opportunity but also a great challenge. However, mandatory HPV vaccination may raise many questions, and more answers are needed.     

Systemic administration of naked DNA encoding interleukin 12 for the treatment of human papillomavirus DNA-positive tumor.

Interleukin 12 (IL-12) is one of the most effective and promising cytokines for cancer therapy. Its therapeutic effects have been demonstrated in a variety of tumors in animal models when it is administrated locally or systemically. We describe here a systemic delivery of naked murine IL-12 (mIL-12) gene in vivo. Dose-dependent systemic production of mIL-12, with a serum level up to approximately 20 microg/ml, was observed 24 hr after systemic gene delivery. The apparent half-life in the circulation was about 5 hr. The result of a bioactivity assay (in vitro interferon gamma [IFN-gamma] release) indicated that the gene product in mice was as active as the purified recombinant murine IL-12 protein (rmIL-12). The circulating mIL-12 activated natural killer cells and stimulated IFN-gamma production in vivo. A single administration of mIL-12 gene resulted in prominent regression of established subcutaneous tumor in a human papillomavirus (HPV) DNA-positive tumor model (TC-1) in C57BL/6J mice. The antitumor effect of the single gene dose was comparable to repeated intraperitoneal administration of rmIL-12 (0.5 microg/day for consecutive 5 days). This systemic gene delivery is simple, economical, and highly efficient for the production of large amounts of cytokine in vivo. With this gene delivery method, we have demonstrated the therapeutic potential of IL-12 for the treatment of HPV DNA-positive tumor and the usefulness of the systemic gene delivery for assessing the therapeutic effect of a candidate gene.