Vaccine strategies for human papillomavirus-associated cancers

HPV pathogenesis, various types of vaccines, safety concern, prophylactic and therapeutic applications to control cervical cancer, and future perspective

Over 98% of cervical cancers (CC) are caused by regular infections with "high risk" genotype of the human papilloma virus (HPV). However, this is not always the causative factor. Therefore, production of HPV vaccinations represents a significant chance to minimize the risk of CC. Phase III studies for a number of preventative HPV vaccines based on L1-virus-like particle (VLPs) have just been completed and the preliminary results are very convincing. However, there are a lot of practical concerns that need to be resolved before the use of these vaccinations. These vaccines were challenged with obvious queries such as protection time, subject receiving vaccines, time of vaccination, and how to include them into ongoing screening programs. Although these vaccines were 90% effective at preventing HPV infection as these offered only modest advantages for the removal of pre-existing infections. New advancements in the creation of therapeutic vaccinations have been explored for further improvement and post-vaccination surveillance. Therapeutic vaccines attempted to boost cell-mediated immunities and these are detrimental to the infected cell as opposed to neutralizing antibodies (different from prophylactic vaccines).

Exploiting the Plant Secretory Pathway to Improve the Anticancer Activity of a Plant-Derived HPV16 E7 Vaccine

The human papillomavirus 16 (HPV16) E7 oncoprotein can be considered a ‘tumor-specific antigen’ and, therefore, it represents a promising target for a therapeutic vaccine against HPV-associated tumors. Efficient production of E7 protein with a plant-based transient expression system has been already described and it was demonstrated that E7-containing crude plant extracts confer partial protection against tumor challenge in a mouse model system. Before adopting the plant-based system as a cost-effective method for the production of an E7-based anti-cancer vaccine, some aspects, such as the oncoprotein yield, need further investigation. In the present study, we report the transient expression, mediated by a potato virus X (PVX)-derived vector, of the E7 protein targeted to the secretory system of Nicotiana benthamiana plants by using a plant-derived signal sequence. Targeting the antigen to the secretory pathway enhanced the E7 protein expression levels about five-fold. Mice immunized by s.c. administration with crude foliar extracts containing E7 showed strong stimulation of cell-mediated immune response after five boosters, as detected by ELISPOT. After challenging with the E7-expressing C3 tumor cells, tumor growth was completely inhibited in 80% of the vaccinated animals and a drastic reduction of tumor burden was observed in the remaining tumor-affected mice. These data demonstrate that, by enhancing E7 yield, it is possible to improve the anti-cancer activity of the plant-based experimental vaccine and open the way for a large-scale production of the E7 protein which could be purified or used as ‘in planta’ formulation, also suitable for oral therapeutic vaccination.

Human papillomavirus and cervical cancer

Cervical cancer is caused by human papillomavirus infection. Most human papillomavirus infection is harmless and clears spontaneously but persistent infection with high-risk human papillomavirus (especially type 16) can cause cancer of the cervix, vulva, vagina, anus, penis, and oropharynx. The virus exclusively infects epithelium and produces new viral particles only in fully mature epithelial cells. Human papillomavirus disrupts normal cell-cycle control, promoting uncontrolled cell division and the accumulation of genetic damage. Two effective prophylactic vaccines composed of human papillomavirus type 16 and 18, and human papillomavirus type 16, 18, 6, and 11 virus-like particles have been introduced in many developed countries as a primary prevention strategy. Human papillomavirus testing is clinically valuable for secondary prevention in triaging low-grade cytology and as a test of cure after treatment. More sensitive than cytology, primary screening by human papillomavirus testing could enable screening intervals to be extended. If these prevention strategies can be implemented in developing countries, many thousands of lives could be saved.

Cell-mediated immune response to human papillomavirus 16 E7 peptide pools in patients with cervical neoplasia

OBJECTIVE

To identify characteristics of the cell-mediated immune (CMI) response to human papillomavirus-16 (HPV) E7 viral peptide pools to help the formulation of therapeutic vaccines.

DESIGN

Prospective study. Population. Korean women.

SETTING

University hospital.

METHODS

From December 2008 to August 2010, 33 HPV-16-positive patients, seven patients exhibiting a high-risk HPV infection other than HPV-16 with grade 2/3 cervical intraepithelial neoplasm (CIN2/3), and nine healthy control donors were enrolled.

MAIN OUTCOME MEASURES

CMI response to synthetic HPV-16 E7 overlapping peptide pools using the IFN-γ ELISPOT assay.

RESULTS

The E7 sequence comprising amino acids 16-55 was a major immunogenic region. The CMI response to HPV-16 E7 is highly type-specific. The follow-up CMI response may last longer than expected after the lesion is resected.

CONCLUSIONS

We found that the E7 sequence comprising amino acids 16-55 is a major immunogenic region that is critical for the T-cell-mediated immune response with CIN2/3 or cervical cancer. The identification of CMI responses to HPV-16 E7 peptide pools may provide insight into therapeutic vaccine trials for the control of HPV-associated diseases.

Advances in human papilloma virus vaccines: a patent review

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Radioimmunotherapy with an antibody to the HPV16 E6 oncoprotein is effective in an experimental cervical tumor expressing low levels of E6

PURPOSE

HPV16 is associated with ~50% of all cervical cancers worldwide. The E6 and E7 genes of oncogenic HPV types, such as HPV16, are necessary for the HPV transforming function and tumorogenesis making them ideal targets for novel treatments. Radioimmunotherapy employs systemically administered radiolabeled monoclonal antibodies (mAbs) that bind to tumor-associated antigens. Previously we demonstrated in mice that radioimmunotherapy targeting viral antigens with mAb to HPV16 E6 suppressed CasKi cervical tumors expressing high levels of E6 (~600 copies of HPV per cell). However, that study opened the question whether radioimmunotherapy can suppress the growth of cervical tumors with low E6 and E7 expression, such as may be seen in patients.

EXPERIMENTAL DESIGN

We evaluated the expression of E6 in patients' tumors and in the SiHa cell line expressing low levels of E6 and E7 (1-2 copies of HPV per cell) and found them comparable. We initiated SiHa tumors in nude mice, radiolabeled C1P5 mAb to E6 with a beta-emitter 188-Rhenium (¹⁸⁸Re) and treated tumor-bearing mice with: (1) 200 μCi ¹⁸⁸Re-C1P5 alone; (2) proteasome inhibitor MG132 alone; (3) MG132 followed by 200 μCi ¹⁸⁸Re-C1P5; (4) unlabeled C1P5; (5) 200 μCi ¹⁸⁸Re-18B7 (isotype-matching control mAb); (6) no treatment. ¹⁸⁸Re-C1P5 alone and in combination with MG-132 significantly retarded tumor growth compared to all control groups.

CONCLUSIONS

Our data demonstrate the possibility to suppress tumor growth by targeting viral antigens even in cervical tumors with low E6 expression and provide additional evidence for the potential usefulness of radioimmunotherapy targeting HPV-related antigens in the clinic.

Serological response to an HPV16 E7 based therapeutic vaccine in women with high-grade cervical dysplasia

PURPOSE

Infection with oncogenic human papillomaviruses has been linked to the development of cervical neoplasia and cancer. The exclusive expression of E7, a viral oncogene, in infected cells makes this protein an ideal target for immunotherapy. We recently reported on the results of a trial in women with cervical carcinoma-in-situ using HspE7, a protein vaccine consisting of full length HPV16 E7 linked to a heat shock protein from M. bovis. The stimulating effects of HspE7 on specific cytotoxic T lymphocytes have been demonstrated in vitro and in (pre-)clinical trials. The induction of a B-cell response by HspE7 and its association with clinical outcome is unknown, and is the purpose of this study.

EXPERIMENTAL DESIGN

We measured the serum IgG levels against HPV16 E7 and HPV16 and -18 VLPs using a multiplexed Luminex based assay in 57 women with CIS who received the HspE7 vaccine.

RESULTS

Vaccination with HspE7 results in a modest, yet maintained increase in HPV16 E7 specific IgG levels. While not significant, increased HPV16 E7 IgG levels appear to be correlated with a positive therapeutic effect. Women who were previously treated for recurrent disease (by LEEP) had significantly higher HPV16 E7 IgG levels compared with subjects without recurrent disease (p=0.01). In women with recurrent disease, higher IgG levels correlated with complete pathological response.

CONCLUSIONS

This study suggests that IgG levels could potentially be used as a marker for response to a therapeutic vaccine. Further translational investigations of the 'priming' of local immune responses using extirpative procedures should be explored.

Human endogenous retrovirus K triggers an antigen-specific immune response in breast cancer patients

Recent evidence indicates that human cancer cells reactivate the expression of latent human endogenous retroviral (HERV) proteins. However, the extent to which cancer patients mount de novo immune responses against expressed HERV elements is unclear. In this study, we determined the extent of HERV-K env expression in human breast cancer (BC) and whether both humoral and cell-mediated immunity against HERV-K can be found in BC patients. We found HERV-K env protein expression in 88% of BC (n = 119) but not in normal breast (n = 76) tissues. ELISA screening assays detected significant titers of anti-HERV-K env IgG in a large proportion of BC patients. T-cell responses against HERV-K were also detected in peripheral blood mononuclear cells (PBMC) from BC patients stimulated with autologous dendritic cells pulsed with HERV-K env SU antigens. These responses included induction of T-cell proliferation (P = 0.0043), IFN-gamma production measured by enzyme-linked immunospot (P < 0.0001), and multiplex cytokine secretion (P = 0.0033). Multiplex cytokine analysis found a T-helper 1 cytokine response, including interleukin (IL)-2 (P = 0.0109), IL-6 (P = 0.0396), IL-8 (P = 0.0169), and IP-10 (P = 0.0045) secretion during in vitro stimulation of BC PBMC with HERV-K antigen. We also found HERV-K-specific CTLs that were capable of lysing target cells expressing HERV-K env protein in BC patients but not in normal female controls without cancer. These findings suggest that retroviral gene products are capable of acting as tumor-associated antigens activating both T-cell and B-cell responses in BC patients.

Therapeutic dendritic cell vaccination with Ag coupled to cholera toxin in combination with intratumoural CpG injection leads to complete tumour eradication in mice bearing HPV 16 expressing tumours

We have evaluated whether cholera toxin (CT) can enhance the efficiency of therapeutic dendritic cell (DC) vaccination in mice bearing a human papilloma virus (HPV) 16 antigen (Ag) expressing tumour. Mice were therefore injected with the TC-1 cancer cell line expressing E6 and E7, which are the major oncogenic proteins produced in HPV-induced cervical cancer, and they were then vaccinated with Ag pulsed DCs. While vaccination with E7 pulsed DCs had no impact on tumour growth, DCs pulsed with CT conjugated E7 (CT-E7) significantly reduced tumour size. However, this treatment was only able to eradicate the tumour in 11% of the affected animals. For complete tumour eradication, combinational therapy with CT-E7 pulsed DCs and local treatment of the tumour with CpG oligodeoxynucleotides (CpG) was required. Combinational therapy was associated with increased expression of MHC I and MHC II and increased levels of chemokine production in the tumour. These results suggest that combined treatment with CT-Ag pulsed DCs and local CpG administration offers an efficient strategy to eradicate an already existing HPV-E7 expressing tumour in mice.

Pediatrician knowledge and attitudes regarding human papillomavirus disease and its prevention

Between 1 September and 8 October 2006, we used a self-administered, anonymous questionnaire in order to evaluate knowledge and attitudes regarding HPV disease and its prevention in a nationally representative sample of Italian pediatricians. Three hundred and eleven of the 400 enrolled physicians (175 primary care pediatricians, 160 hospital pediatricians and 65 residents in pediatrics) returned completed surveys (227 females; mean age+/-standard deviation, 45.3+/-11.61 years). The results showed a lack of knowledge concerning HPV disease and its prevention, with marginal differences between the subgroups, even though the majority would recommend HPV vaccination. These findings highlight an urgent need to improve pediatrician information in order to ensure the optimal implementation of HPV vaccination, and the adequate acceptability of HPV vaccines to adolescents and their parents.

Heat shock fusion protein-based immunotherapy for treatment of cervical intraepithelial neoplasia III

OBJECTIVES

SGN-00101 (HspE7, Nventa, San Diego, CA) is a novel therapeutic vaccine consisting of a fusion protein containing an M. bovis BCG heat shock protein (Hsp65) covalently linked to the entire sequence of HPV 16 E7. This trial was designed to evaluate the efficacy and toxicities of HspE7 in women with CIN III.

METHODS

HIV (-) women with biopsy-proven CIN III were eligible. Two cohorts were accrued; one cohort to establish efficacy and a second cohort with a longer follow-up period to improve the precision of the trial to estimate response rates. Each patient underwent 3 monthly subcutaneous vaccinations with 500 microg of HspE7 followed by monthly colposcopic follow-up for 1 month in cohort 1 and an extended observation period (2 months) in cohort 2. All patients then underwent a LEEP or cone biopsy of the cervix. A complete pathologic response (pCR) was defined as no evidence of CIN or CIN I (only HPV changes). A partial response (PR) was defined as colposcopic lesion regression of >50% in size. Cervicovaginal lavage samples were obtained at each visit for HPV typing using MY09/ MY11 HPV PCR.

RESULTS

Seventy-two patients were registered and screened, of whom 64 were eligible. Fifty-eight patients completed the trial and were evaluable (31 in cohort 1, 27 in cohort 2). There were no significant epidemiologic or HPV type differences between the 2 cohorts so responses were combined for analysis. Of the 58 evaluable patients, 13 (22.5%) had a pCR; 32 (55%) had a PR and 11 (19%) had stable disease. Two (3.5%) patients in cohort 2 had microinvasive disease and were defined as progressive disease. Thirty-three of 58 (57%) of the patients were infected with HPV 16 prior to vaccination or in subsequent visits. There was no significant difference in regression in women infected with HPV 16 compared to those without HPV 16 infection (88% vs. 70%; p=0.12). Women who had a previous LEEP or ablation for CIN were 2.7 times more likely to have a complete response compared to patients without previous treatment, although the difference was not statistically significant (95% CI for rate ratio: 0.95-6.19, p=0.10). At a cellular level, there was a significant association between local inflammation and response; lower grade of lesional inflammation correlated with a response to HspE7 (p=0.04 using Wilcoxon rank sum test).

CONCLUSIONS

HspE7 appeared to demonstrate activity in women with CIN III and met a priori assumptions for efficacy; however, it is unclear whether this response was due to natural regression rather than treatment effect. HspE7, which targets the HPV 16 E7 oncoprotein, had efficacy in patients infected with HPV types other than 16, suggesting cross-reactivity. A larger randomized, controlled trial is needed to better define efficacy and to identify subsets of women most likely to benefit from immunotherapy.

A truncated Bacillus subtilis dal gene with a 3' ssrA gene tag regulates the growth and virulence of racemase-deficient Listeria monocytogenes

Listeria monocytogenes (Lm) is a Gram-positive intracellular pathogen that can elicit strong cellular immunity. An attenuated strain (Lmdd) with deletions in two genes (dal and dat) required for d-alanine synthesis and viability has been shown to induce long-lived protective systemic and mucosal immune responses in mice when administered in the presence of the required amino acid. To bypass the necessity for exogenous d-alanine without compromising the safety of the original strain, the defect of Lmdd was complemented with a heterologous Bacillus subtilis dal gene, and the effects of truncating the upstream region of the gene on its transcription efficiency and of modifying its protein product with an ssrA tag at the 3'-terminus were examined. The strains with 551 bp and 80 bp upstream regions showed high levels of transcription and grew without d-alanine. The strains with the shortest upstream regions, 48 bp and 18 bp, showed greatly decreased levels of transcription and failed to grow in the absence of d-alanine. Addition of an ssrA tag to the longer genes resulted in a somewhat altered growth pattern in media and a reduced plaque size on L2 fibroblasts. These bacteria contained low levels of racemase protein and reduced free pools of d-alanine. One of the strains tested further, Lmdd/pA80S, was rapidly cleared from the spleens of infected mice but nevertheless induced a strong immune response that protected mice against challenge by wild-type L. monocytogenes. These bacteria can thus induce immune responses in mice comparable to the original Lmdd strain, but without the need for exogenous d-alanine, and may have use as a live vaccine vector against infectious diseases and cancers.

Vacuna frente al virus del papiloma humano: un nuevo reto para el pediatra

Human papillomavirus (HPV) infections are the most common sexually transmitted infections in the world. This infection is a necessary cause of cervical cancer, has been related to other forms of anogenital, airway and digestive cancers, and also causes anogenital warts. The recent advances in HPV prophylactic vaccines and their imminent commercial availability will post a new challenge to pediatricians: the indication and administration of these vaccines for the prevention of HPV infection, and consequently, of cervical cancer and other HPV-related diseases. The present article reviews the essentials of HPV infection, its relationship with cervical cancer, the advances in prophylactic HPV vaccines, and the role of the pediatrician in this context.

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.

Progress in the development of a cervical cancer vaccine

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

Vaccinia virus preferentially infects and controls human and murine ovarian tumors in mice

Vaccinia virus has been shown to efficiently infect tumor cells. Therefore, vaccinia virus represents a potentially safe and effective antitumor agent against ovarian cancer. Here, we assessed the ability of vaccinia virus to preferentially infect and control both human and murine ovarian tumors in vivo. We used the non-invasive luminescence imaging system to monitor the infection and suppression of ovarian tumors by vaccinia in live mice. Our data indicated that vaccinia was able to effectively infect and kill both human and murine ovarian tumors. Vaccinia virus administered to mice intraperitoneally was specifically targeted to the murine or human ovarian tumors and led to antitumor responses. These findings suggest that vaccinia virus is capable of selectively targeting and controlling ovarian tumors. Thus, intraperitoneal injection with vaccinia virus may provide a potentially effective strategy for treating advanced-stage ovarian cancers.