Optimization of heterologous DNA-prime, protein boost regimens and site of vaccination to enhance therapeutic immunity against human papillomavirus-associated disease

Molecular targets and strategies in the development of nucleic acid cancer vaccines: from shared to personalized antigens

Recent breakthroughs in cancer immunotherapies have emphasized the importance of harnessing the immune system for treating cancer. Vaccines, which have traditionally been used to promote protective immunity against pathogens, are now being explored as a method to target cancer neoantigens. Over the past few years, extensive preclinical research and more than a hundred clinical trials have been dedicated to investigating various approaches to neoantigen discovery and vaccine formulations, encouraging development of personalized medicine. Nucleic acids (DNA and mRNA) have become particularly promising platform for the development of these cancer immunotherapies. This shift towards nucleic acid-based personalized vaccines has been facilitated by advancements in molecular techniques for identifying neoantigens, antigen prediction methodologies, and the development of new vaccine platforms. Generating these personalized vaccines involves a comprehensive pipeline that includes sequencing of patient tumor samples, data analysis for antigen prediction, and tailored vaccine manufacturing. In this review, we will discuss the various shared and personalized antigens used for cancer vaccine development and introduce strategies for identifying neoantigens through the characterization of gene mutation, transcription, translation and post translational modifications associated with oncogenesis. In addition, we will focus on the most up-to-date nucleic acid vaccine platforms, discuss the limitations of cancer vaccines as well as provide potential solutions, and raise key clinical and technical considerations in vaccine development.

Evaluation of immunogenicity-induced DNA vaccines against different SARS-CoV-2 variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 and caused the coronavirus disease 2019 (COVID-19) pandemic worldwide. As of September 2023, the number of confirmed coronavirus cases has reached over 770 million and caused nearly 7 million deaths. The World Health Organization assigned and informed the characterization of variants of concern (VOCs) to help control the COVID-19 pandemic through global monitoring of circulating viruses. Although many vaccines have been proposed, developing an effective vaccine against variants is still essential to reach the endemic stage of COVID-19. We designed five DNA vaccine candidates composed of the first isolated genotype and major SARS-CoV-2 strains from isolated Korean patients classified as VOCs, such as Alpha, Beta, Gamma, and Delta. To evaluate the immunogenicity of each genotype via homologous and heterologous vaccination, mice were immunized twice within a 3-week interval, and the blood and spleen were collected 1 week after the final vaccination to analyze the immune responses. The group vaccinated with DNA vaccine candidates based on the S genotype and the Alpha and Beta variants elicited both humoral and cellular immune responses, with higher total IgG levels and neutralizing antibody responses than the other groups. In particular, the vaccine candidate based on the Alpha variant induced a highly diverse cytokine response. Additionally, we found that the group subjected to homologous vaccination with the S genotype and heterologous vaccination with S/Alpha induced high total IgG levels and a neutralization antibody response. Homologous vaccination with the S genotype and heterologous vaccination with S/Alpha and S/Beta significantly induced IFN-γ immune responses. The immunogenicity after homologous vaccination with S and Alpha and heterologous vaccination with the S/Alpha candidate was better than that of the other groups, indicating the potential for developing novel DNA vaccines against different SARS-CoV-2 variants.

Albumin and interferon-β fusion protein serves as an effective vaccine adjuvant to enhance antigen-specific CD8+ T cell-mediated antitumor immunity

BACKGROUND

Type I interferons (IFN) promote dendritic cells maturation and subsequently enhance generation of antigen-specific CD8 +T cell for the control of tumor. Using type I interferons as an adjuvant to vaccination could prove to be a potent strategy. However, type I interferons have a short half-life. Albumin linked to a protein will prolong the half-life of the linked protein.

METHODS

In this study, we explored the fusion of albumin to IFNβ (Alb-IFNβ) for its functional activity both in vitro and in vivo. We determined the half-life of Alb-IFNβ following treatment in the serum, tumor, and tumor draining lymph nodes in both wild type and FcRn knockout mice. We characterized the ability of Alb-IFNβ to enhance antigen-specific CD8+ T cells using ovalbumin (OVA) or human papillomavirus (HPV) E7 long peptides. Next, we evaluated the therapeutic antitumor effect of coadministration of AlbIFNβ with antigenic peptides against HPVE7 expressing tumor and the treatment's ability to generate HPVE7 antigen specific CD8+ T cells. The contribution of the antitumor effect by lymphocytes was also examined by an antibody depletion experiment. The ability of Alb-IFNβ to serve as an adjuvant was tested using clinical grade therapeutic protein-based HPV vaccine, TACIN.

RESULTS

Alb-IFNβ retains biological function and does not alter the biological activity of IFNβ. In addition, Alb-IFNβ extends half-life of IFNβ in serum, lymph nodes and tumor. The coadministration of Alb-IFNβ with OVA or HPVE7 antigenic peptides enhances antigen-specific CD8 +T cell immunity, and in a TC-1 tumor model results in a significant therapeutic antitumor effect. We found that CD8 +T cells and dendritic cells, but not CD4 +T cells, are important for the observed antitumor therapeutic effect mediated by Alb-IFNβ. Finally, Alb-IFNβ served as a potent adjuvant for TA-CIN for the treatment of HPV antigen expressing tumors.

CONCLUSIONS

Overall, Alb-IFNβ serves as a potent adjuvant for enhancement of strong antigen-specific CD8 +T cell antitumor immunity, reduction of tumor burden, and increase in overall survival. Alb-IFNβ potentially can serve as an innovative adjuvant for the development of vaccines for the control of infectious disease and cancer.

Cervical Cancer Immunotherapy: Facts and Hopes

It is a sad fact that despite being almost completely preventable through human papillomavirus (HPV) vaccination and screening, cervical cancer remains the fourth most common cancer to affect women worldwide. Persistent high-risk HPV (hrHPV) infection is the primary etiologic factor for cervical cancer. Upward of 70% of cases are driven by HPV types 16 and 18, with a dozen other hrHPVs associated with the remainder of cases. Current standard-of-care treatments include radiotherapy, chemotherapy, and/or surgical resection. However, they have significant side effects and limited efficacy against advanced disease. There are a few treatment options for recurrent or metastatic cases. Immunotherapy offers new hope, as demonstrated by the recent approval of programmed cell death protein 1-blocking antibody for recurrent or metastatic disease. This might be augmented by combination with antigen-specific immunotherapy approaches, such as vaccines or adoptive cell transfer, to enhance the host cellular immune response targeting HPV-positive cancer cells. As cervical cancer progresses, it can foster an immunosuppressive microenvironment and counteract host anticancer immunity. Thus, approaches to reverse suppressive immune environments and bolster effector T-cell functioning are likely to enhance the success of such cervical cancer immunotherapy. The success of nonspecific immunostimulants like imiquimod against genital warts also suggest the possibility of utilizing these immunotherapeutic strategies in cervical cancer prevention to treat precursor lesions (cervical intraepithelial neoplasia) and persistent hrHPV infections against which the licensed prophylactic HPV vaccines have no efficacy. Here, we review the progress and challenges in the development of immunotherapeutic approaches for the prevention and treatment of cervical cancer.

Development of DNA Vaccine Targeting E6 and E7 Proteins of Human Papillomavirus 16 (HPV16) and HPV18 for Immunotherapy in Combination with Recombinant Vaccinia Boost and PD-1 Antibody

Immunotherapy for cervical cancer should target high-risk human papillomavirus types 16 and 18, which cause 50% and 20% of cervical cancers, respectively. Here, we describe the construction and characterization of the pBI-11 DNA vaccine via the addition of codon-optimized human papillomavirus 18 (HPV18) E7 and HPV16 and 18 E6 genes to the HPV16 E7-targeted DNA vaccine pNGVL4a-SigE7(detox)HSP70 (DNA vaccine pBI-1). Codon optimization of the HPV16/18 E6/E7 genes in pBI-11 improved fusion protein expression compared to that in DNA vaccine pBI-10.1 that utilized the native viral sequences fused 3' to a signal sequence and 5' to the HSP70 gene of Mycobacterium tuberculosis Intramuscular vaccination of mice with pBI-11 DNA better induced HPV antigen-specific CD8+ T cell immune responses than pBI-10.1 DNA. Furthermore, intramuscular vaccination with pBI-11 DNA generated stronger therapeutic responses for C57BL/6 mice bearing HPV16 E6/E7-expressing TC-1 tumors. The HPV16/18 antigen-specific T cell-mediated immune responses generated by pBI-11 DNA vaccination were further enhanced by boosting with tissue-antigen HPV vaccine (TA-HPV). Combination of the pBI-11 DNA and TA-HPV boost vaccination with PD-1 antibody blockade significantly improved the control of TC-1 tumors and extended the survival of the mice. Finally, repeat vaccination with clinical-grade pBI-11 with or without clinical-grade TA-HPV was well tolerated in vaccinated mice. These preclinical studies suggest that the pBI-11 DNA vaccine may be used with TA-HPV in a heterologous prime-boost strategy to enhance HPV 16/18 E6/E7-specific CD8+ T cell responses, either alone or in combination with immune checkpoint blockade, to control HPV16/18-associated tumors. Our data serve as an important foundation for future clinical translation.IMPORTANCE Persistent expression of high-risk human papillomavirus (HPV) E6 and E7 is an obligate driver for several human malignancies, including cervical cancer, wherein HPV16 and HPV18 are the most common types. PD-1 antibody immunotherapy helps a subset of cervical cancer patients, and its efficacy might be improved by combination with active vaccination against E6 and/or E7. For patients with HPV16+ cervical intraepithelial neoplasia grade 2/3 (CIN2/3), the precursor of cervical cancer, intramuscular vaccination with a DNA vaccine targeting HPV16 E7 and then a recombinant vaccinia virus expressing HPV16/18 E6-E7 fusion proteins (TA-HPV) was safe, and half of the patients cleared their lesions in a small study (NCT00788164). Here, we sought to improve upon this therapeutic approach by developing a new DNA vaccine that targets E6 and E7 of HPV16 and HPV18 for administration prior to a TA-HPV booster vaccination and for application against cervical cancer in combination with a PD-1-blocking antibody.

Vaccination Strategies for the Control and Treatment of HPV Infection and HPV-Associated Cancer

Human papillomavirus (HPV) is the most common sexually transmitted infection, currently affecting close to 80 million Americans. Importantly, HPV infection is recognized as the etiologic factor for numerous cancers, including cervical, vulval, vaginal, penile, anal, and a subset of oropharyngeal cancers. The prevalence of HPV infection and its associated diseases are a significant problem, affecting millions of individuals worldwide. Likewise, the incidence of HPV infection poses a significant burden on individuals and the broader healthcare system. Between 2011 and 2015, there were an estimated 42,700 new cases of HPV-associated cancers each year in the United States alone. Similarly, the global burden of HPV is high, with around 630,000 new cases of HPV-associated cancer occurring each year. In the last decade, a total of three preventive major capsid protein (L1) virus-like particle-based HPV vaccines have been licensed and brought to market as a means to prevent the spread of HPV infection. These prophylactic vaccines have been demonstrated to be safe and efficacious in preventing HPV infection. The most recent iteration of the preventive HPV vaccine, a nanovalent, L1-VLP vaccine, protects against a total of nine HPV types (seven high-risk and two low-risk HPV types), including the high-risk types HPV16 and HPV18, which are responsible for causing the majority of HPV-associated cancers. Although current prophylactic HPV vaccines have demonstrated huge success in preventing infection, existing barriers to vaccine acquisition have limited their widespread use, especially in low- and middle-income countries, where the burden of HPV-associated diseases is highest. Prophylactic vaccines are unable to provide protection to individuals with existing HPV infections or HPV-associated diseases. Instead, therapeutic HPV vaccines capable of generating T cell-mediated immunity against HPV infection and associated diseases are needed to ameliorate the burden of disease in individuals with existing HPV infection. To generate a cell-mediated immune response against HPV, most therapeutic vaccines target HPV oncoproteins E6 and E7. Several types of therapeutic HPV vaccine candidates have been developed including live-vector, protein, peptide, dendritic cell, and DNA-based vaccines. This chapter will review the commercially available prophylactic HPV vaccines and discuss the recent progress in the development of therapeutic HPV vaccines.

Complete protection for mice conferred by a DNA vaccine based on the Japanese encephalitis virus P3 strain used to prepare the inactivated vaccine in China

BACKGROUND

The incidence of Japanese encephalitis (JE) has been dramatically reduced in China after sufficient vaccine coverage. The live-attenuated Japanese encephalitis virus (JEV) vaccine SA14-14-2 is believed to have strongly contribute to this decrease. Another vaccine that seems to have decreased in importance is an inactivated vaccine based on the JEV P3 strain, which is considered to be modifiable, such as being transformed into a DNA vaccine to improve its immunogenicity.

METHODS

In this study, the protective efficacy induced by the Japanese encephalitis DNA vaccine candidate pV-JP3ME encoding the premembrane (prM) and envelope (E) proteins of the P3 strain was assessed in BALB/c mice. The prM/E genes of the JEV P3 strain were subcloned into the vector pVAX1 (pV) to construct pV-JP3ME.

RESULTS

The plasmid DNA was immunized into BALB/c mice, and high titers of IgG antibody and neutralizing antibody (nAb) against JEV were detected. The key cytokines in splenocytes were secreted upon stimulation with JEV antigens. Finally, complete protective efficacy was generated after challenge with the JEV P3 strain in the mice.

CONCLUSIONS

The DNA vaccine pV-JP3ME based on the JEV P3 strain in this study can induce specific humoral immune and cytokine responses and provide complete protection against JEV in mice.

Dysregulation of Stemness Pathways in HPV Mediated Cervical Malignant Transformation Identifies Potential Oncotherapy Targets

Human papillomavirus (HPV) infection is associated with a range of malignancies that affect anogenital and oropharyngeal sites. α-HPVs dominantly infect basal epithelial cells of mucosal tissues, where they dysregulate cell division and local immunity. The cervix is one of the mucosal sites most susceptible to HPV infections. It consists of anatomically diverse regions, and the majority of cervical intraepithelial neoplasia and cancers arise within the cervical squamo-columnar junction where undifferentiated basal progenitor cells with stem cell properties are found. The cancer stem cell theory particularly associates tumorigenesis, invasion, dissemination, and metastasis with cancer cells exhibiting stem cell properties. In this perspective, we discuss evidence of a cervical cancer stem cell niche and explore the association of stemness related genes with 5-year survival using a publicly available transcriptomic dataset of a cervical cancer cohort. We report that poor prognosis in this cohort correlates with overexpression of a subset of stemness pathway genes, a majority of which regulate the central Focal Adhesion pathway, and are also found to be enriched in the HPV infection pathway. These observations support therapeutic targeting of stemness genes overexpressed by mucosal cells infected with high-risk HPVs.

Therapeutic Vaccines Against Human Papilloma Viruses: Achievements and Prospects

Human papillomaviruses of high carcinogenic risk (HR HPVs) are major etiological agents of malignant diseases of the cervix, vulva, penis, anal canal, larynx, head, and neck. Prophylactic vaccination against HPV, which mainly covers girls and women under 25, does not prevent vertical and horizontal HPV transmission in infants and children and does not have a therapeutic effect. As a result, a significant proportion of the population is not protected from the HPV infection and development of HPV-associated neoplastic transformation and cancer, which indicates the need for development and introduction of therapeutic HPV vaccines. Unlike prophylactic vaccines aimed at the formation of virus-neutralizing antibodies, therapeutic vaccines elicit cellular immune response leading to the elimination of infected and malignant cells expressing viral proteins. The ideal targets for vaccine immunotherapy are highly conserved HR HPV oncoproteins E6 and E7 expressed in precancerous and tumor tissues. Here, we describe expression of these proteins during different stages of HPV infection, their antigenic and immunogenic properties, and T-cell epitopes, the response to which correlates with natural regression of HPV-induced neoplastic changes. The review describes patterns of E6 and E7 oncoproteins presentation to the immune system as components of candidate vaccines along with the results of the most promising preclinical trials and animal models used in these trials. Special attention is paid to vaccine candidates which have shown efficacy in clinical trials in patients with HPV-associated neoplastic changes.

Construction of a novel tetravalent dengue vaccine with a Salmonella Typhimurium bacterial ghost and evaluation of its immunogenicity and protective efficacy using a murine model

Efforts to develop a safe, effective, and affordable dengue vaccine have focused on providing simultaneous immunity against all four serotypes of the dengue virus (DENV). In the current study, Salmonella Typhimurium (ST) lysed by gene E activation was genetically constructed to deliver the envelope protein domain III (EDIII) of all four serotypes of DENV using a foreign antigen delivery and expression vector, pJHL184. Each DENV-EDIII protein expressed in the constructed strain was validated by immunoblot analysis. To assess the immunogenicity and protective efficacy of the constructs against dengue infection, BALB/c mice were injected once orally with either the individual ST-EDIII constructs or a mix of all four ST-EDIII constructs followed by intramuscular administration of the purified EDIII protein. Significantly elevated titers of EDIII-specific IgG, IgG1, and IgG2a were observed in the immunized mice (P < 0.01). Furthermore, lymphocyte proliferative activity and CD3⁺CD4⁺ T-cell subpopulations increased significantly in vitro in re-pulsed splenic T cells compared with those from non-immunized mice. In addition, a lower viral load was detected in the BG-EDIII vaccinated group after challenge with DENV-infected K562 cells. Collectively, the results demonstrate that DENV-EDIII expressed in the inactivated ST strain could induce robust humoral and cell-mediated immunity specific to the target antigen and could provide significant protective potential.

Immunogenicity of RNA Replicons Encoding HIV Env Immunogens Designed for Self-Assembly into Nanoparticles

RNA replicons are a promising platform technology for vaccines. To evaluate the potential of lipid nanoparticle-formulated replicons for delivery of HIV immunogens, we designed and tested an alphavirus replicon expressing a self-assembling protein nanoparticle immunogen, the glycoprotein 120 (gp120) germline-targeting engineered outer domain (eOD-GT8) 60-mer. The eOD-GT8 immunogen is a germline-targeting antigen designed to prime human B cells capable of evolving toward VRC01-class broadly neutralizing antibodies. Replicon RNA was encapsulated with high efficiency in 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)-based lipid nanoparticles, which provided effective delivery in the muscle and expression of luciferase lasting ∼30 days in normal mice, contrasting with very brief and low levels of expression obtained by delivery of equivalent modified mRNA (modRNA). eOD-GT8 60-mer-encoding replicons elicited high titers of gp120-specific antibodies following a single injection in mice, and increased levels of antigen-specific germinal center B cells compared with protein immunization. Immunization of transgenic mice expressing human inferred-germline VRC01 heavy chain B cell receptors that are the targets of the eOD antigen led to priming of B cells and somatic hypermutation consistent with VRC01-class antibody development. Altogether, these data suggest replicon delivery of Env immunogens may be a promising avenue for HIV vaccine development.

Demarcated thresholds of tumor-specific CD8 T cells elicited by MCMV-based vaccine vectors provide robust correlates of protection

BACKGROUND

The capacity of cytomegalovirus (CMV) to elicit long-lasting strong T cell responses, and the ability to engineer the genome of this DNA virus positions CMV-based vaccine vectors highly suitable as a cancer vaccine platform. Defined immune thresholds for tumor protection and the factors affecting such thresholds have not well been investigated in cancer immunotherapy. We here determined using CMV as a vaccine platform whether critical thresholds of vaccine-specific T cell responses can be established that relate to tumor protection, and which factors control such thresholds.

METHODS

We generated CMV-based vaccine vectors expressing the E7 epitope and tested these in preclinical models of HPV16-induced cancer. Vaccination was applied via different doses and routes (intraperitoneal (IP), subcutaneous (SC) and intranasal (IN)). The magnitude, kinetics and phenotype of the circulating tumor-specific CD8⁺ T cell response were determined. Mice were subsequently challenged with tumor cells, and the tumor protection was monitored.

RESULTS

Immunization with CMV-based vaccines via the IP or SC route eliciting vaccine-induced CD8⁺ T cell responses of > 0.3% of the total circulating CD8 T cell population fully protects mice against lethal tumor challenge. However, low dose inoculations via the IP or SC route or IN vaccination elicited vaccine-induced CD8⁺ T cell responses that did not reach protective thresholds for tumor protection. In addition, whereas weak pre-existing immunity did not alter the protective thresholds of the vaccine-specific T cell response following subsequent immunization with CMV-based vaccine vectors, strong pre-existing immunity inhibited the development of vaccine-induced T cells and their control on tumor progression.

CONCLUSIONS

This study highlight the effectiveness of CMV-based vaccine vectors, and shows that demarcated thresholds of vaccine-specific T cells could be defined that correlate to tumor protection. Together, these results may hold importance for cancer vaccine development to achieve high efficacy in vaccine recipients.

Bioproduction of a Therapeutic Vaccine Against Human Papillomavirus in Tomato Hairy Root Cultures

Human papillomavirus (HPV) tumor disease is a critical public health problem worldwide, especially in the developing countries. The recognized pathogenic function of E5, E6, and E7 oncoproteins offers the opportunity to devise therapeutic vaccines based on engineered recombinant proteins. The potential of plants to manufacture engineered compounds for pharmaceutical purposes, from small to complex protein molecules, allows the expression of HPV antigens and, possibly, the regulation of immune functions to develop very specific therapies as a reinforcement to available nonspecific therapies and preventive vaccination also in developed countries. Among plant-based expression formats, hairy root cultures are a robust platform combining the benefits of eukaryotic plant-based bioreactors, with those typical of cell cultures. In this work, to devise an experimental therapeutic vaccine against HPV, hairy root cultures were used to express a harmless form of the HPV type 16 E7 protein (E7*) fused to SAPKQ, a noncytotoxic form of the saporin protein from Saponaria officinalis, that we had shown to improve E7-specific cell-mediated responses as a fusion E7*-SAPKQ DNA vaccine. Hairy root clones expressing the E7*-SAPKQ candidate vaccine were obtained upon infection of leaf explants of Solanum lycopersicum using a recombinant plant expression vector. Yield was approximately 35.5 μg/g of fresh weight. Mouse immunization with vaccine-containing crude extracts was performed together with immunological and biological tests to investigate immune responses and anticancer activity, respectively. Animals were primed with either E7*-SAPKQ DNA-based vaccine or E7*-SAPKQ root extract-based vaccine and boosted with the same (homologous schedule) or with the other vaccine preparation (heterologous schedule) in the context of TC-1 experimental mouse model of HPV-associated tumor. All the formulations exhibited an immunological response associated to anticancer activity. In particular, DNA as prime and hairy root extract as boost demonstrated the highest efficacy. This work, based on the development of low-cost technologies, highlights the suitability of hairy root cultures as possible biofactories of therapeutic HPV vaccines and underlines the importance of the synergic combination of treatment modalities for future developments in this field.

DNA Vaccine Encoding HPV16 Oncogenes E6 and E7 Induces Potent Cell-mediated and Humoral Immunity Which Protects in Tumor Challenge and Drives E7-expressing Skin Graft Rejection

We have previously shown that a novel DNA vaccine technology of codon optimization and the addition of ubiquitin sequences enhanced immunogenicity of a herpes simplex virus 2 polynucleotide vaccine in mice, and induced cell-mediated immunity when administered in humans at relatively low doses of naked DNA. We here show that a new polynucleotide vaccine using the same technology and encoding a fusion protein of the E6 and E7 oncogenes of high-risk human papillomavirus type 16 (HPV16) is immunogenic in mice. This vaccine induces long-lasting humoral and cell-mediated immunity and protects mice from establishment of HPV16-E7-expressing tumors. In addition, it suppresses growth of readily established tumors and shows enhanced efficacy when combined with immune checkpoint blockade targeted at PD-L1. This vaccine also facilitates rejection of HPV16-E7-expressing skin grafts that demonstrate epidermal hyperplasia with characteristics of cervical and vulvar intraepithelial neoplasia. Clinical studies evaluating the efficacy of this vaccine in patients with HPV16 premalignancies are planned.

Spontaneous and Vaccine-Induced Clearance of Mus Musculus Papillomavirus 1 Infection

Mus musculus papillomavirus 1 (MmuPV1/MusPV1) induces persistent papillomas in immunodeficient mice but not in common laboratory strains. To facilitate the study of immune control, we sought an outbred and immunocompetent laboratory mouse strain in which persistent papillomas could be established. We found that challenge of SKH1 mice (Crl:SKH1-Hrhr) with MmuPV1 by scarification on their tail resulted in three clinical outcomes: (i) persistent (>2-month) papillomas (∼20%); (ii) transient papillomas that spontaneously regress, typically within 2 months (∼15%); and (iii) no visible papillomas and viral clearance (∼65%). SKH1 mice with persistent papillomas were treated by using a candidate preventive/therapeutic naked-DNA vaccine that expresses human calreticulin (hCRT) fused in frame to MmuPV1 E6 (mE6) and mE7 early proteins and residues 11 to 200 of the late protein L2 (hCRTmE6/mE7/mL2). Three intramuscular DNA vaccinations were delivered biweekly via in vivo electroporation, and both humoral and CD8 T cell responses were mapped and measured. Previously persistent papillomas disappeared within 2 months after the final vaccination. Coincident virologic clearance was confirmed by in situ hybridization and a failure of disease to recur after CD3 T cell depletion. Vaccination induced strong mE6 and mE7 CD8⁺ T cell responses in all mice, although they were significantly weaker in mice that initially presented with persistent warts than in those that spontaneously cleared their infection. A human papillomavirus 16 (HPV16)-targeted version of the DNA vaccine also induced L2 antibodies and protected mice from vaginal challenge with an HPV16 pseudovirus. Thus, MmuPV1 challenge of SKH1 mice is a promising model of spontaneous and immunotherapy-directed clearances of HPV-related disease.IMPORTANCE High-risk-type human papillomaviruses (hrHPVs) cause 5% of all cancer cases worldwide, notably cervical, anogenital, and oropharyngeal cancers. Since preventative HPV vaccines have not been widely used in many countries and do not impact existing infections, there is considerable interest in the development of therapeutic vaccines to address existing disease and infections. The strict tropism of HPV requires the use of animal papillomavirus models for therapeutic vaccine development. However, MmuPV1 failed to grow in common laboratory strains of mice with an intact immune system. We show that MmuPV1 challenge of the outbred immunocompetent SKH1 strain produces both transient and persistent papillomas and that vaccination of the mice with a DNA expressing an MmuPV1 E6E7L2 fusion with calreticulin can rapidly clear persistent papillomas. Furthermore, an HPV16-targeted version of the DNA can protect against vaginal challenge with HPV16, suggesting the promise of this approach to both prevent and treat papillomavirus-related disease.

A prime/boost vaccination with HA DNA and Pichia-produced HA protein elicits a strong humoral response in chickens against H5N1

Highly pathogenic avian influenza viruses cause severe disease and huge economic losses in domestic poultry and might pose a serious threat to people because of the high mortality rates in case of an accidental transmission to humans. The main goal of this work was to evaluate the immune responses and hemagglutination inhibition potential elicited by a combined DNA/recombinant protein prime/boost vaccination compared to DNA/DNA and protein/protein regimens in chickens. A plasmid encoding hemagglutinin (HA) from the A/swan/Poland/305-135V08/2006 (H5N1) virus, or the recombinant HA protein produced in Pichia pastoris system, both induced H5 HA-specific humoral immune responses in chickens. In two independent experiments, anti-HA antibodies were detected in sera collected two weeks after the first dose and the response was enhanced by the second dose of a vaccine, regardless of the type of subunit vaccine (DNA or recombinant protein) administered. The serum collected from chickens two weeks after the second dose was characterized by three types of assays: indirect ELISA, hemagglutination inhibition (HI) and a diagnostic test based on H5 antibody competition. Although the indirect ELISA failed to detect superiority of any of the three vaccine regimens, the other two tests clearly indicated that priming of chickens with the DNA vaccine significantly enhanced the protective potential of the recombinant protein vaccine produced in P. pastoris.

Recent advances in preclinical model systems for papillomaviruses

Preclinical model systems to study multiple features of the papillomavirus life cycle have greatly aided our understanding of Human Papillomavirus (HPV) biology, disease progression and treatments. The challenge to studying HPV in hosts is that HPV along with most PVs are both species and tissue restricted. Thus, fundamental properties of HPV viral proteins can be assessed in specialized cell culture systems but host responses that involve innate immunity and host restriction factors requires preclinical surrogate models. Fortunately, there are several well-characterized and new animal models of papillomavirus infections that are available to the PV research community. Old models that continue to have value include canine, bovine and rabbit PV models and new rodent models are in place to better assess host-virus interactions. Questions arise as to the strengths and weaknesses of animal PV models for HPV disease and how accurately these preclinical models predict malignant progression, vaccine efficacy and therapeutic control of HPV-associated disease. In this review, we examine current preclinical models and highlight the strengths and weaknesses of the various models as well as provide an update on new opportunities to study the numerous unknowns that persist in the HPV research field.