Induction of human papilloma virus E6/E7-specific cytotoxic T-lymphocyte activity in immune-tolerant, E6/E7-transgenic mice

Genetically engineered mouse model of HPV16 E6-E7 with vaginal-cervical intraepithelial neoplasia and decreased immunity

Objective

To construct models of high-risk human papillomavirus (HPV) infection with precancerous lesions or cervical cancer and explore the immune function.

Methods

Using CRISPR/Cas9, the expression vector HPV16-E6-E7-Rosa26 was microinjected into fertilized eggs of C57BL/6 N mice using homologous recombination, and the F0 generation was obtained for reproduction. Then, the formation of precancerous lesions was promoted via intramuscular injection of estradiol. Presence of precancerous cervical-vaginal intraepithelial lesions, Ki67 and p16 expression levels, and CD8+ T cell proportions in the spleen were evaluated.

Results

Two F0 generation mice exhibited correct the homologous recombination. Seven positive mice were identified in the F1 generation. After breeding and mating, 25 homozygous and 11 heterozygous HPV16-E6-E7-engineered mice were obtained from the F2 generation. After estradiol benzoate treatment, the cervical-vaginal epithelium appeared as precancerous lesions with positive Ki67 and p16 expression. The percentage of CD8+ T cells decreased.

Conclusion

HPV16-E6-E7-Rosa26 induced low immune function in mice, and provides a good model for the basic research of the mechanisms of action of HPV infection-associated precancerous lesions or cervical cancer.

Cancer vaccine strategies using self-replicating RNA viral platforms

The development and success of RNA-based vaccines targeting SARS-CoV-2 has awakened new interest in utilizing RNA vaccines against cancer, particularly in the emerging use of self-replicating RNA (srRNA) viral vaccine platforms. These vaccines are based on different single-stranded RNA viruses, which encode RNA for target antigens in addition to replication genes that are capable of massively amplifying RNA messages after infection. The encoded replicase genes also stimulate innate immunity, making srRNA vectors ideal candidates for anti-tumor vaccination. In this review, we summarize different types of srRNA platforms that have emerged and review evidence for their efficacy in provoking anti-tumor immunity to different antigens. These srRNA platforms encompass the use of naked RNA, DNA-launched replicons, viral replicon particles (VRP), and most recently, synthetic srRNA replicon particles. Across these platforms, studies have demonstrated srRNA vaccine platforms to be potent inducers of anti-tumor immunity, which can be enhanced by homologous vaccine boosting and combining with chemotherapies, radiation, and immune checkpoint inhibition. As such, while this remains an active area of research, the past and present trajectory of srRNA vaccine development suggests immense potential for this platform in producing effective cancer vaccines.

Development and Applications of Viral Vectored Vaccines to Combat Zoonotic and Emerging Public Health Threats

Vaccination is arguably the most cost-effective preventative measure against infectious diseases. While vaccines have been successfully developed against certain viruses (e.g., yellow fever virus, polio virus, and human papilloma virus HPV), those against a number of other important public health threats, such as HIV-1, hepatitis C, and respiratory syncytial virus (RSV), have so far had very limited success. The global pandemic of COVID-19, caused by the SARS-CoV-2 virus, highlights the urgency of vaccine development against this and other constant threats of zoonotic infection. While some traditional methods of producing vaccines have proven to be successful, new concepts have emerged in recent years to produce more cost-effective and less time-consuming vaccines that rely on viral vectors to deliver the desired immunogens. This review discusses the advantages and disadvantages of different viral vaccine vectors and their general strategies and applications in both human and veterinary medicines. A careful review of these issues is necessary as they can provide important insights into how some of these viral vaccine vectors can induce robust and long-lasting immune responses in order to provide protective efficacy against a variety of infectious disease threats to humans and animals, including those with zoonotic potential to cause global pandemics.

An alphavirus-based therapeutic cancer vaccine: from design to clinical trial

Cancer immunotherapy has greatly advanced in recent years. Most immunotherapeutic strategies are based on the use of immune checkpoint blockade to unleash antitumor immune responses or on the induction or adoptive transfer of immune effector cells. We aim to develop therapeutic vaccines based on recombinant Semliki Forest virus vectors to induce tumor-specific effector immune cells. In this review, we describe our ongoing work on SFV-based vaccines targeted against human papillomavirus- and hepatitis C virus-related infections and malignancies, focusing on design, delivery, combination strategies, preclinical efficacy and product development for a first-in-man clinical trial with an HPV-specific vaccine.

Therapeutic vaccines for high-risk HPV-associated diseases

Cancer is the second leading cause of death worldwide, and it is estimated that Human papillomavirus (HPV) related cancers account for 5% of all human cancers. Current HPV vaccines are extremely effective at preventing infection and neoplastic disease; however, they are prophylactic and do not clear established infections. Therapeutic vaccines which trigger cell-mediated immune responses for the treatment of established infections and malignancies are therefore required. The E6 and E7 early genes are ideal targets for vaccine therapy due to their role in disruption of the cell cycle and their constitutive expression in premalignant and malignant tissues. Several strategies have been investigated for the development of therapeutic vaccines, including live-vector, nucleic acid, peptide, protein-based and cell-based vaccines as well as combinatorial approaches, with several vaccine candidates progressing to clinical trials. With the current understanding of the HPV life cycle, molecular mechanisms of infection, carcinogenesis, tumour biology, the tumour microenvironment and immune response mechanisms, an approved HPV therapeutic vaccine seems to be a goal not far from being achieved. In this article, the status of therapeutic HPV vaccines in clinical trials are reviewed, and the potential for plant-based vaccine production platforms described.

Targeting Head and Neck Cancer by Vaccination

Head and neck cancer (HNC) is a heterogeneous group of squamous cell cancers that affect the oral cavity, pharynx, and larynx. Worldwide, it is the sixth most common cancer but in parts of Southern and South-East Asia, HNC is one of the most common cancers. A significant proportion of HNC is driven by human papillomavirus (HPV) infection, whereas HPV-independent HNC is associated with alcohol, smoking, and smokeless tobacco consumption. Here, we review the past and present experience of targeting HNC with vaccination focusing on HPV-derived antigens as well as non-viral antigens for HPV-negative HNC. Novel therapeutic approaches for HNC will focus not only on effective vaccine platforms but will also target the stroma-rich immunosuppressive microenvironment found in those tumours.

Targeted immunotherapy of high-grade cervical intra-epithelial neoplasia: Expectations from clinical trials

Targeted immunotherapy of high-grade cervical intra-epithelial neoplasia (CIN) has been developed as an alternative to conization, to preserve future reproductive outcomes and avoid human papillomavirus (HPV) persistence. The objectives of the review are to present drugs according to their process of development and to examine their potential future use. A search for key words associated with CIN and targeted immunotherapy was carried out in the Cochrane library, Pubmed, Embase, and ClinicalTrials.gov from 1990 to 2016. Publications (randomized, prospective and retrospective studies) in any language were eligible for inclusion, as well as ongoing trials registered on the ClinicalTrials.gov website. Targeted immunotherapy includes peptide/protein-based vaccines, nucleic acid-based vaccines (DNA), and live vector-based vaccines (bacterial or viral). A total of 18 vaccines were identified for treatment of CIN at various stages of development, and the majority were well-tolerated. Adverse effects were primarily injection site reactions and flu-like symptoms under grade 2. The efficacy of vaccines defined by regression of CIN2/3 to no CIN or CIN1 ranged from 17 to 59% following a minimum of a 12-week follow-up. In the majority of studies, there was no association demonstrated between histological response and HPV clearance, or between histological or virological response and immune T cell response. Given that the spontaneous regression of CIN2/3 is 20-25% at 6 months, targeted immunotherapy occurs an additional value, which never reaches 50%, with one trial an exception to this. However, research and development on HPV eradication drugs needs to be encouraged, due to HPV-associated disease burden.

Correlation of Circulating CD64+/CD163+ Monocyte Ratio and stroma/peri-tumoral CD163+ Monocyte Density with Human Papillomavirus Infected Cervical Lesion Severity

HPV infected cervical cells secrete mediators that are gradually changed and have influence on infiltrating M2 phenotypic monocytes in cervical lesions. However, profiles of circulating immune cells in women with cervical lesions and M2 phenotypic monocyte activity in HPV infected cervical lesions are limited. This study aimed to investigate circulating monocyte populations correlated with M2 phenotype density and its activity in HPV infected cervical lesions. HPV DNA was investigated in cervical tissues using PCR. High risk HPV E6/E7 mRNA was detected using in situ hybridization. CD163 immunohistochemical staining was performed for M2 macrophage. CD163 and Arg1 mRNA expression were detected using real-time PCR. Circulating monocyte subpopulations were analyzed using flow cytometry. CD163 and Arg1 mRNA expression were increased according to cervical lesion severity and corresponding with density of M2 macrophage in HSIL and SCC in stroma and peri-tumoral areas. Additionally, the relationship between M2 macrophage infiltration and high risk HPV E6/E7 mRNA expression was found and corresponded with cervical lesion severity. Circulating CD14⁺CD16⁺ and CD14⁺CD163⁺ monocytes were elevated in No-SIL and cervical lesions. Interestingly, CD14⁺CD64⁺ monocyte was greatly elevated in HSIL and SCC, whereas intracellular IL-10⁺ monocytes were not significantly different between cervical lesions. The correlation between increasing ratio of circulating CD64⁺/CD163⁺ monocyte and density of infiltrating CD163⁺ monocytes was associated with severity of HPV infected cervical lesions. The elevated circulating CD64⁺/CD163⁺ monocyte ratio correlates to severity of HPV infected cervical lesions and might be a prognostic marker in cervical cancer progression.

Perspectives for therapeutic HPV vaccine development

Background

Human papillomavirus (HPV) infections and associated diseases remain a serious burden worldwide. It is now clear that HPV serves as the etiological factor and biologic carcinogen for HPV-associated lesions and cancers. Although preventative HPV vaccines are available, these vaccines do not induce strong therapeutic effects against established HPV infections and lesions. These concerns create a critical need for the development of therapeutic strategies, such as vaccines, to treat these existing infections and diseases.

Main Body

Unlike preventative vaccines, therapeutic vaccines aim to generate cell-mediated immunity. HPV oncoproteins E6 and E7 are responsible for the malignant progression of HPV-associated diseases and are consistently expressed in HPV-associated diseases and cancer lesions; therefore, they serve as ideal targets for the development of therapeutic HPV vaccines. In this review we revisit therapeutic HPV vaccines that utilize this knowledge to treat HPV-associated lesions and cancers, with a focus on the findings of recent therapeutic HPV vaccine clinical trials.

Conclusion

Great progress has been made to develop and improve novel therapeutic HPV vaccines to treat existing HPV infections and diseases; however, there is still much work to be done. We believe that therapeutic HPV vaccines have the potential to become a widely available and successful therapy to treat HPV and HPV-associated diseases in the near future.

Current state in the development of candidate therapeutic HPV vaccines

The identification of human papillomavirus (HPV) as an etiological factor for HPV-associated malignancies creates the opportunity to control these cancers through vaccination. Currently, available preventive HPV vaccines have not yet demonstrated strong evidences for therapeutic effects against established HPV infections and lesions. Furthermore, HPV infections remain extremely common. Thus, there is urgent need for therapeutic vaccines to treat existing HPV infections and HPV-associated diseases. Therapeutic vaccines differ from preventive vaccines in that they are aimed at generating cell-mediated immunity rather than neutralizing antibodies. The HPV-encoded early proteins, especially oncoproteins E6 and E7, form ideal targets for therapeutic HPV vaccines since they are consistently expressed in HPV-associated malignancies and precancerous lesions, playing crucial roles in the generation and maintenance of HPV-associated disease. Our review will cover various therapeutic vaccines in development for the treatment of HPV-associated lesions and cancers. Furthermore, we review strategies to enhance vaccine efficacy and the latest clinical trials on therapeutic HPV vaccines.

Current therapeutic vaccination and immunotherapy strategies for HPV-related diseases

Carcinomas of the anogenital tract, in particular cervical cancer, remains one of the most common cancers in women, and represent the most frequent gynecological malignancies and the fourth leading cause of cancer death in women worldwide. Human papillomavirus (HPV)-induced lesions are immunologically distinct in that they express viral antigens, which are necessary to maintain the cancerous phenotype. The causal relationship between HPV infection and anogenital cancer has prompted substantial interest in the development of therapeutic vaccines against high-risk HPV types targeting the viral oncoproteins E6 and E7. This review will focus on the most recent clinical trials for immunotherapies for mucosal HPV-induced lesions as well as emerging therapeutic strategies that have been tested in pre-clinical models for HPV-induced diseases. Progress in peptide- and protein-based vaccines, DNA-based vaccines, viral/bacterial vector-based vaccines, immune checkpoint inhibition, immune response modifiers, and adoptive cell therapy for HPV will be discussed.

Antigen design enhances the immunogenicity of Semliki Forest virus-based therapeutic human papillomavirus vaccines

Cellular immunity against cancer can be achieved with viral vector- and DNA-based immunizations. In preclinical studies, cancer vaccines are very potent, but in clinical trials these potencies are not achieved yet. Thus, a rational approach to improve cancer vaccines is warranted. We previously demonstrated that the relatively low intrinsic immunogenicity of DNA vaccines could be enhanced by inclusion of endoplasmic reticulum (ER) targeting and universal helper epitopes within the vaccine. We now evaluated whether an optimal antigen format, as defined in DNA vaccines, can further enhance the effectiveness of recombinant Semliki Forest virus (rSFV) vaccines. To this purpose, we generated, characterized and evaluated the efficacy of rSFV replicon particles expressing human papillomavirus E6 and/or E7 proteins fused to several helper T-cell epitopes and an ER targeting signal. Here, we show that inclusion of a helper cassette and an ER targeting signal enhanced protein stability and markedly augmented the frequencies of human papillomavirus-specific T cells. Even at an immunization dose of as low as 10(5) replicon particles, this novel vaccine achieved tumor regression and protection. Thus, even highly effective viral vector vaccines can benefit from an improved antigen format, based on the inclusion of defined helper epitopes and ER targeting.

Efficacy of DNA vaccines forming e7 recombinant retroviral virus-like particles for the treatment of human papillomavirus-induced cancers

Human papillomavirus (HPV) is involved in the development of anogenital tumors and also in the development of oropharyngeal head and neck carcinomas, where HPV-16, expressing the E6 and E7 oncoproteins, is the most frequent serotype. Although vaccines encoding L1 and L2 capsid HPV proteins are efficient for the prevention of HPV infection, they are inadequate for treating established tumors. Hence, development of innovative vaccine therapies targeting E6/E7 is important for controlling HPV-induced cancers. We have engineered a nononcogenic mutated E7-specific plasmo-retroVLP vaccine (pVLP-E7), consisting of plasmid DNA, that is able to form recombinant retrovirus-based virus-like particles (VLPs) that display E7 antigen into murine leukemia virus Gag proteins pseudotyped with vesicular stomatitis virus envelope glycoprotein (VSV-G). pVLP-E7 vaccinations were studied for their ability to generate specific immune responses and for induction of protective immunity against tumor cell challenge in preventive and therapeutic models. The produced VLPs induce the maturation of human dendritic cells in vitro and mount specific E7 T cell responses. Intradermic vaccinations of mice with pVLP-E7 show their efficacy to generate antigen-specific T cell responses, to prevent and protect animals from early TC-1 tumor development compared with standard DNA or VLP immunizations. The vaccine efficacy was also evaluated for advanced tumors in mice vaccinated at various time after the injection of TC-1 cells. Data show that pVLP-E7 vaccination can cure mice with already established tumors only when combined with Toll-like receptor-7 (TLR7) and TLR9 agonists. Our findings provide evidence that pVLPs, combining the advantages of DNA and VLP vaccines, appear to be a promising strategy for the treatment of HPV-induced cancers.

Biolistic DNA vaccination against cervical cancer

The development of cervical cancer is associated with infection by oncogenic human papillomaviruses (HPVs), of which type 16 (HPV16) is the most prevalent in HPV-induced malignant diseases. The viral oncoproteins E6 and E7 are convenient targets for anti-tumor immunization. To adapt the corresponding genes for DNA vaccination, their oncogenicity needs to be reduced and immunogenicity enhanced. The main modifications for achieving these aims include mutagenesis, rearrangement of gene parts, and fusion with supportive cellular or viral/bacterial genes or their functional parts. As HPVs are strictly human specific, an animal model of HPV infection does not exist. Therefore, immunization against HPV-induced tumors is most frequently tested in mouse models utilizing transplantable syngeneic tumor cells producing the HPV16 E6/E7 oncoproteins. In this chapter, one such cell line designated TC-1 is characterized and the effect of immunization with the modified E7 fusion gene against TC-1-induced subcutaneous tumors is described. As down-regulation of MHC class I molecules is one of the most important escape mechanisms of cervical carcinoma cells, the TC-1/A9 clone with reversibly reduced MHC class I expression has been developed and, herein, its response to DNA vaccination is also shown and compared with that of the TC-1 cells.

Therapeutic vaccination against chronic hepatitis C virus infection

Approximately 170 million people worldwide are chronic carriers of Hepatitis C virus (HCV). To date, there is no prophylactic vaccine available against HCV. The standard-of-care therapy for HCV infection involves a combination of pegylated interferon-α and ribavirin. This therapy, which is commonly associated with side effects, has a curative rate varying from 43% (HCV genotype 1) to 80% (HCV genotype 2). In 2011, two direct-acting antiviral agents, telaprevir and boceprevir, were approved by the US Food and drug Administration and are now being used in combination with standard-of-care therapy in selected patients infected with HCV genotype 1. Although both drugs are promising, resulting in a shortening of therapy, these drugs also induce additional side effects and have reduced efficacy in patients who did not respond to standard-of-care previously. An alternative approach would be to treat HCV by stimulating the immune system with a therapeutic vaccine ideally aimed at (i) the eradication of HCV-infected cells and (ii) neutralization of infectious HCV particles. The challenge is to develop therapeutic vaccination strategies that are either at least as effective as antiviral drugs but with lower side effects, or vaccines that, when combined with antiviral drugs, can circumvent long-term use of these drugs thereby reducing their side effects. In this review, we summarize and discuss recent preclinical developments in the area of therapeutic vaccination against chronic HCV infection. Although neutralizing antibodies have been described to exert protective immunity, clinical studies on the induction of neutralizing antibodies in therapeutic settings are limited. Therefore, we will primarily discuss therapeutic vaccines which aim to induce effective cellular immune response against HCV.

From tumor immunosuppression to eradication: targeting homing and activity of immune effector cells to tumors

Unraveling the mechanisms used by the immune system to fight cancer development is one of the most ambitious undertakings in immunology. Detailed knowledge regarding the mechanisms of induction of tolerance and immunosuppression within the tumor microenvironment will contribute to the development of highly effective tumor eradication strategies. Research within the last few decades has shed more light on the matter. This paper aims to give an overview on the current knowledge of the main tolerance and immunosuppression mechanisms elicited within the tumor microenvironment, with the focus on development of effective immunotherapeutic strategies to improve homing and activity of immune effector cells to tumors.

Role of regulatory T-cells in immunization strategies involving a recombinant alphavirus vector system

BACKGROUND

Regulatory T-cells (Treg) hamper immune responses elicited by cancer vaccines. Therefore, depletion of Treg is being used to improve the outcome of vaccinations.

METHODS

We studied whether an alphavirus vector-based immunotherapeutic vaccine changes the number and/or activity of Treg and if Treg depletion improves the efficacy of this vaccine against tumours. The vaccine is based on a Semliki Forest virus (SFV). The recombinant SFV replicon particles encode a fusion protein of E6 and E7 from human papillomavirus (HPV) type 16 (SFVeE6,7).

RESULTS

We demonstrated that SFVeE6,7 immunization did not change Treg levels and their suppressive activity. Depletion of Treg in mice, using the novel anti-folate receptor 4 antibody, did not enhance the immune response induced by SFVeE6,7 immunization. Both the priming and the proliferation phases of the HPV-specific response elicited with SFVeE6,7 were not affected by the immune-suppressive activity of Treg. Moreover, Treg depletion did not improve the therapeutic antitumour response of SFVeE6,7 in a murine tumour model.

CONCLUSIONS

The efficacy of the SFVeE6,7 vaccine was not hampered by Treg. Therefore, SFVeE6,7 seems a very promising candidate for the treatment of HPV-induced disease, as it may not require additional immune interventions to modulate Treg activity.

Immunotherapy for cervical cancer: Research status and clinical potential

The high-risk types of human papillomavirus (HPV) have been found to be associated with most cervical cancers and play an essential role in the pathogenesis of the disease. Despite recent advances in preventive HPV vaccine development, such preventive vaccines are unlikely to reduce the prevalence of HPV infections within the next few years, due to their cost and limited availability in developing countries. Furthermore, preventive HPV vaccines may not be capable of treating established HPV infections and HPV-associated lesions, which account for high morbidity and mortality worldwide. Thus, it is important to develop therapeutic HPV vaccines for the control of existing HPV infection and associated malignancies. Therapeutic vaccines are quite different from preventive vaccines in that they require the generation of cell-mediated immunity, particularly T cell-mediated immunity, instead of the generation of neutralizing antibodies. The HPV-encoded early proteins, the E6 and E7 oncoproteins, form ideal targets for therapeutic HPV vaccines, since they are consistently expressed in HPV-associated cervical cancer and its precursor lesions and thus play crucial roles in the generation and maintenance of HPV-associated disease. Our review covers the various therapeutic HPV vaccines for cervical cancer, including live vector-based, peptide or protein-based, nucleic acid-based, and cell-based vaccines targeting the HPV E6 and/or E7 antigens. Furthermore, we review the studies using therapeutic HPV vaccines in combination with other therapeutic modalities and review the latest clinical trials on therapeutic HPV vaccines.

Perspectives for preventive and therapeutic HPV vaccines

Human Papillomavirus (HPV) has been associated with several human cancers, including cervical cancer, vulvar cancer, vaginal and anal cancer, and a subset of head and neck cancers. Thus effective vaccination against HPV provides an opportunity to reduce the morbidity and mortality associated with HPV. The Food and Drug Administration of the United States has approved two preventive vaccines to limit the spread of HPV. However, these are unlikely to impact upon HPV prevalence and cervical cancer rates for many years. Furthermore, preventive vaccines do not exert therapeutic effects on pre-existing HPV infections and HPV-associated lesions. In order to further impact upon the burden of HPV infections worldwide, therapeutic vaccines are being developed. These vaccines aim to generate a cell-mediated immune response to infected cells. This review discusses current preventive and therapeutic HPV vaccines and their future directions.

Augmentation of alphavirus vector-induced human papilloma virus-specific immune and anti-tumour responses by co-expression of interleukin-12

To enhance the efficacy of a therapeutic immunisation strategy against human papillomavirus-induced cervical cancer we evaluated the adjuvant effect of interleukin-12 (IL12) expressed by a Semliki Forest virus vector (SFV) in mice. Depending on the dose and schedule, SFV-IL12 stimulated antigen-specific CTL responses elicited upon immunisation with recombinant SFV expressing HPV16-E6E7 (SFVeE6,7). SFVeE6,7-CTL and anti-tumour activity were enhanced by a low dose of SFV-IL12 to the prime immunisation. Using higher dosages these activities were reduced. Addition of SFV-IL12 to the booster immunisation further reduced the efficacy of the SFVeE6,7 immunisation. In transgenic mice, tolerant for HPV16-E6E7, SFV-IL12 also stimulated SFVeE6,7-induced CTL responses. In conclusion, SFV-IL12 can enhance antigen-specific immune responses. Yet, prudence is called for when considering co-administration of SFV-IL12 to a vaccine, as the enhancement of cell-mediated immune responses greatly depends on dosage and schedule.

Induction of antitumor immunity in vivo following delivery of a novel HPV-16 DNA vaccine encoding an E6/E7 fusion antigen

Human papillomavirus type 16 (HPV-16) infection is associated with a majority of cervical cancers and a significant proportion of head and neck cancers. Here, we describe a novel-engineered DNA vaccine that encodes a HPV-16 consensus E6/E7 fusion gene (pConE6E7) with the goal of increasing its antitumor cellular immunity. Compared to an early stage HPV-16 E7 DNA vaccine (pE7), this construct was up to five times more potent in driving E7-specific cellular immune responses. Prophylactic administration of this vaccine resulted in 100% protection against HPV E6 and E7-expressing tumors. Therapeutic studies indicated that vaccination with pConE6E7 prevented or delayed the growth of tumors. Moreover, immunization with pConE6E7 could also partially overcome immune tolerance in E6/E7 transgenic mice. Such DNA immunogens are interesting candidates for further study to investigate mechanisms of tumor immune rejection in vivo.

Therapeutic and prophylactic applications of alphavirus vectors

Alphavirus vectors are high-level, transient expression vectors for therapeutic and prophylactic use. These positive-stranded RNA vectors, derived from Semliki Forest virus, Sindbis virus and Venezuelan equine encephalitis virus, multiply and are expressed in the cytoplasm of most vertebrate cells, including human cells. Part of the genome encoding the structural protein genes, which is amplified during a normal infection, is replaced by a transgene. Three types of vector have been developed: virus-like particles, layered DNA-RNA vectors and replication-competent vectors. Virus-like particles contain replicon RNA that is defective since it contains a cloned gene in place of the structural protein genes, and thus are able to undergo only one cycle of expression. They are produced by transfection of vector RNA, and helper RNAs encoding the structural proteins. Layered DNA-RNA vectors express the Semliki Forest virus replicon from a cDNA copy via a cytomegalovirus promoter. Replication-competent vectors contain a transgene in addition to the structural protein genes. Alphavirus vectors are used for three main applications: vaccine construction, therapy of central nervous system disease, and cancer therapy.

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.

Recent advances in strategies for immunotherapy of human papillomavirus-induced lesions

Human papillomavirus (HPV)-induced lesions are distinct in that they have targetable foreign antigens, the expression of which is necessary to maintain the cancerous phenotype. Hence, they pose as a very attractive target for "proof of concept" studies in the development of therapeutic vaccines. This review will focus on the most recent clinical trials for the immunotherapy of mucosal and cutaneous HPV-induced lesions as well as emerging therapeutic strategies that have been tested in preclinical models for HPV-induced lesions. Progress in peptide-based vaccines, DNA-based vaccines, viral/bacterial vector-based vaccines, immune response modifiers, photodynamic therapy and T cell receptor based therapy for HPV will be discussed.

Frequencies and role of regulatory T cells in patients with (pre)malignant cervical neoplasia

Oncogenic human papillomavirus (HPV)-infection is crucial for developing cervical cancer and its precursor lesions [cervical intraepithelial neoplasia (CIN)]. Regulatory T cells (T(regs)) might be involved in the failure of the immune system to control the development of HPV-induced cancer. We investigated frequencies, phenotype and activity of T(regs) in patients with cervical neoplasia. CIN and cervical cancer patients showed increased CD4(+)/CD25(high) T cell frequencies in peripheral blood and CD4(+) T cell fraction. These CD4(+)/CD25(high) T cells represent T(regs) as demonstrated by their low proliferation rate, low interferon (IFN)-gamma/interleukin (IL)-10 ratio, high expression of CD45RO, GITR, CTLA-4, forkhead box P3 (FoxP3) and low CD45RA expression. Moreover, in HPV16(+) cervical cancer patients, in-vitro depletion of CD25(+) T cells resulted in increased IFN-gamma T cell responses against HPV16 E6- and E7 peptides. Thus, increased frequencies of T(regs) in cervical cancer patients may indeed suppress HPV-specific immunity. Longitudinal analysis of CD4(+)/CD25(high) T cell frequencies in patients showed a modest decline 1 year after curative surgery or chemoradiation. This study demonstrates increased frequencies and suppressive activity of T(regs) in cervical cancer. These results imply that T(regs) may suppress the immune control of cervical neoplasia and furthermore that suppression of immunity by T(regs) will be another hurdle to overcome in therapeutic immunization strategies against cervical neoplasia.

Viral vector-based prime-boost immunization regimens: a possible involvement of T-cell competition

Vaccination with recombinant viral vectors may be impeded by preexisting vector-specific immunity or by vector-specific immunity induced during the priming immunization. It is assumed that virus-neutralizing antibodies represent the principal effector mechanism of vector-specific immunity, while killing of infected cells by vector-specific cytotoxic T lymphocytes (CTLs) has also been suggested. Using recombinant Semliki Forest virus (rSFV) expressing E6E7 antigen from human papillomavirus, we demonstrate that secondary immune responses against E6E7 are neither affected by vector-specific antibodies nor by CTL-mediated killing of infected cells. Instead, the presence of the antigen during the prime immunization appeared to be the main determinant for the boosting efficacy. After priming with rSFVeE6,7, a homologous booster stimulated the primed E6E7-specific CTL response and induced long-lasting memory. Passively transferred SFV-neutralizing antibodies did not inhibit E6E7-specific CTL responses, although transgene expression was strongly reduced under these conditions. Conversely, in mice primed with irrelevant rSFV, induction of E6E7-specific CTLs was inhibited presumably due to vector-specific responses induced by the priming immunization. When during the priming with irrelevant rSFV, E7-protein was co-administered, the inhibitory effect of vector-specific immunity was abolished. These results suggest that, apart from vector-specific antibodies or killing of infected cells, T-cell competition may be involved in determining the efficacy of viral vector-based prime-boost immunization regimens.

In the FVB/N HER-2/neu transgenic mouse both peripheral and central tolerance limit the immune response targeting HER-2/neu induced by Listeria monocytogenes-based vaccines

Listeria monocytogenes-based vaccines for HER-2/neu are capable of breaking tolerance in FVB/N rat HER-2/neu transgenic mice. The growth of implanted NT-2 tumors, derived from a spontaneously occurring tumor in the FVB/N HER-2/neu transgenic mouse, was significantly slower in these mice following vaccination with a series of L. monocytogenes-based vaccines for HER-2/neu. Mechanisms of T cell tolerance that exist in these transgenic mice include the absence of functional high avidity anti-HER-2/neu CD8(+) T cells and the presence of CD4(+)CD25(+) regulatory T cells. The in vivo depletion of these regulatory T cells resulted in the slowing in growth of tumors even without the treatment of mice with an anti-HER-2/neu vaccine. The average avidities of responsive CD8(+) T cells to six of the nine epitopes in HER-2/neu we examined, four of which were identified in this study, are shown here to be of a lower average avidity in the transgenic mice versus wild type FVB/N mice. In contrast, the average avidity of CD8(+) T cells to three epitopes that showed the lowest avidity in the wild-type mice did not differ between wild type and transgenic mice. This study demonstrates the ability of L. monocytogenes-based vaccines to impact upon tolerance to HER-2/neu in FVB/N HER-2/neu transgenic mice and further defines some of the aspects of tolerance in these mice.

Human papillomavirus type 16 E5 protein as a therapeutic target

Cervical cancer is a progressive disease with an onset of one to two decades on average. During the productive replication stage, the Human papillomavirus (HPV) genome is maintained episomally in the infected cervical epithelium and early gene products, including E5, are expressed. Therefore, E5 has a potential to contribute to the HPV-associated carcinogenic process. In invasive malignancies, the HPV genomes are commonly integrated into the host genome, and E6 and E7 genes remain intact. However, the E5 is lost or, if present, under-expressed as compared with the E6 and E7 proteins. This suggests that E5 may play a critical role in the genesis of cervical cancer but less of a role in its persistence or progression. In the initiation of neoplasia and the premalignant stage, there are fewer malignant cells than in the invasive malignancies. Moreover, cells in the invasive malignant stage are found to have a very low level of MHC class I and II, which could hamper the presentation of the antigen and lead to a decreased immune response. Since the E5 protein is likely to play a role during the early tumorigenesis stage, a therapeutic vaccine to target and eliminate the E5-expressing cells may be a good strategy to prevent premalignant lesions from progressing toward invasive cervical cancers. This paper provides an overview of HPV-induced cervical carcinogenesis and strategies for designing prophylactic and therapeutic vaccines to prevent and cure the cervical cancer. In particular, focus will be on the rationale of targeting the E5 protein to develop therapeutic vaccines.

Recombinant alphaviruses as vectors for anti-tumour and anti-microbial immunotherapy

BACKGROUND

Vectors derived from alphaviruses are gaining interest for their high transfection potency and strong immunogenicity.

OBJECTIVES

After a brief introduction on alphaviruses and their vectors, an overview is given on current preclinical immunotherapy studies using vector systems based on alphaviruses. The efficacy of alphavirus vectors in inducing immune responses will be illustrated by a more detailed description of immunization studies using recombinant Semliki Forest virus for the treatment of human papilloma virus-induced cervical cancer.

RESULTS

Immunization with recombinant alphavirus results in the induction of humoral and cellular immune responses against microbes, infected cells and cancer cells. Preclinical studies demonstrate that infectious diseases and cancer can be treated prophylactically as well as therapeutically.

CONCLUSIONS

Alphavirus-based genetic immunization strategies are highly effective in animal model systems, comparing quite favourably with any other approach. Therefore, we hope and expect to see an efficient induction of tumour-or microbial immunity and a positive outcome in future clinical efficacy studies.