A Multiantigenic DNA Vaccine That Induces Broad Hepatitis C Virus-Specific T-Cell Responses in Mice

Hepatitis C virus DNA vaccines: a systematic review

BACKGROUND

Vaccination against HCV is an effective measure in reduction of virus-related public health burden and mortality. However, no prophylactic vaccine is available as of yet. DNA-based immunization is a promising modality to generate cellular and humoral immune responses. The objective of this study is to provide a systematic review of HCV DNA vaccines and investigate and discuss the strategies employed to optimize their efficacies.

METHODS

MEDLINE (PubMed), Web of Science, Scopus, ScienceDirect, and databases in persian language including the Regional Information Centre for Science & Technology (RICeST), the Scientific Information Database and the Iranian Research Institute for Information Science and Technology (IranDoc) were examined to identify studies pertaining to HCV nucleic acid vaccine development from 2000 to 2020.

RESULTS

Twenty-seven articles were included. Studies related to HCV RNA vaccines were yet to be published. A variety of strategies were identified with the potential to optimize HCV DNA vaccines such as incorporating multiple viral proteins and molecular tags such as HBsAg and Immunoglobulin Fc, multi-epitope expression, co-expression plasmid utilization, recombinant subunit immunogens, heterologous prime-boosting, incorporating NS3 mutants in DNA vaccines, utilization of adjuvants, employment of less explored methods such as Gene Electro Transfer, construction of multi- CTL epitopes, utilizing co/post translational modifications and polycistronic genes, among others. The effectiveness of the aforementioned strategies in boosting immune response and improving vaccine potency was assessed.

CONCLUSIONS

The recent progress on HCV vaccine development was examined in this systematic review to identify candidates with most promising prophylactic and therapeutic potential.

Reciprocal Inhibition of Immunogenic Performance in Mice of Two Potent DNA Immunogens Targeting HCV-Related Liver Cancer

Chronic HCV infection and associated liver cancer impose a heavy burden on the healthcare system. Direct acting antivirals eliminate HCV, unless it is drug resistant, and partially reverse liver disease, but they cannot cure HCV-related cancer. A possible remedy could be a multi-component immunotherapeutic vaccine targeting both HCV-infected and malignant cells, but also those not infected with HCV. To meet this need we developed a two-component DNA vaccine based on the highly conserved core protein of HCV to target HCV-infected cells, and a renowned tumor-associated antigen telomerase reverse transcriptase (TERT) based on the rat TERT, to target malignant cells. Their synthetic genes were expression-optimized, and HCV core was truncated after aa 152 (Core152opt) to delete the domain interfering with immunogenicity. Core152opt and TERT DNA were highly immunogenic in BALB/c mice, inducing IFN-γ/IL-2/TNF-α response of CD4+ and CD8+ T cells. Additionally, DNA-immunization with TERT enhanced cellular immune response against luciferase encoded by a co-delivered plasmid (Luc DNA). However, DNA-immunization with Core152opt and TERT mix resulted in abrogation of immune response against both components. A loss of bioluminescence signal after co-delivery of TERT and Luc DNA into mice indicated that TERT affects the in vivo expression of luciferase directed by the immediate early cytomegalovirus and interferon-β promoters. Panel of mutant TERT variants was created and tested for their expression effects. TERT with deleted N-terminal nucleoli localization signal and mutations abrogating telomerase activity still suppressed the IFN-β driven Luc expression, while the inactivated reverse transcriptase domain of TERT and its analogue, enzymatically active HIV-1 reverse transcriptase, exerted only weak suppressive effects, implying that suppression relied on the presence of the full-length/nearly full-length TERT, but not its enzymatic activity. The effect(s) could be due to interference of the ectopically expressed xenogeneic rat TERT with biogenesis of mRNA, ribosomes and protein translation in murine cells, affecting the expression of immunogens. HCV core can aggravate this effect, leading to early apoptosis of co-expressing cells, preventing the induction of immune response.

Structure-Based and Rational Design of a Hepatitis C Virus Vaccine

A hepatitis C virus (HCV) vaccine is a critical yet unfulfilled step in addressing the global disease burden of HCV. While decades of research have led to numerous clinical and pre-clinical vaccine candidates, these efforts have been hindered by factors including HCV antigenic variability and immune evasion. Structure-based and rational vaccine design approaches have capitalized on insights regarding the immune response to HCV and the structures of antibody-bound envelope glycoproteins. Despite successes with other viruses, designing an immunogen based on HCV glycoproteins that can elicit broadly protective immunity against HCV infection is an ongoing challenge. Here, we describe HCV vaccine design approaches where immunogens were selected and optimized through analysis of available structures, identification of conserved epitopes targeted by neutralizing antibodies, or both. Several designs have elicited immune responses against HCV in vivo, revealing correlates of HCV antigen immunogenicity and breadth of induced responses. Recent studies have elucidated the functional, dynamic and immunological features of key regions of the viral envelope glycoproteins, which can inform next-generation immunogen design efforts. These insights and design strategies represent promising pathways to HCV vaccine development, which can be further informed by successful immunogen designs generated for other viruses.

Enhanced T Cell Responses Induced by a Necrotic Dendritic Cell Vaccine, Expressing HCV NS3

A vaccine that induces potent, broad and sustained cell-mediated immunity, resulting in effective memory has the potential to restrict hepatitis C (HCV) virus infection. Early, multi-functional CD4⁺ and CD8⁺ T cell responses against non-structural protein 3 (NS3) have been associated with HCV clearance. Necrotic cells generate strong immune responses and represent a major antigenic source used by dendritic cells (DC) for processing and presentation, but there is conflicting evidence as to their immunogenicity in vaccination. Immunization with DC loaded with viral antigens has been done in the past, but to date the immunogenicity of live vs. necrotic DC vaccines has not been investigated. We developed a DC2.4 cell line stably expressing HCV NS3, and compared the NS3-specific responses of live vs. necrotic NS3 DC. Vaccination of mice with necrotic NS3 DC increased the breadth of T-cell responses and enhanced the production of IL-2, TNF-α, and IFN-γ by effector memory CD4⁺ and CD8⁺T cells, compared to mice vaccinated with live NS3 DC. A single dose of necrotic NS3 DC vaccine induced a greater influx and activation of cross-presenting CD11c⁺ CD8α⁺ DC and necrosis-sensing Clec9A⁺ DC in the draining lymph nodes. Furthermore, using a hydrodynamic challenge model necrotic NS3 DC vaccination resulted in enhanced clearance of NS3-positive hepatocytes from the livers of vaccinated mice. Taken together, the data demonstrate that necrotic DC represent a novel and exciting vaccination strategy capable of inducing broad and multifunctional T cell memory.

Safety Profile of a Multi-Antigenic DNA Vaccine Against Hepatitis C Virus

Despite direct acting antivirals (DAAs) curing >95% of individuals infected with hepatitis C (HCV), in order to achieve the World Health Organization HCV Global Elimination Goals by 2030 there are still major challenges that need to be overcome. DAAs alone are unlikely to eliminate HCV in the absence of a vaccine that can limit viral transmission. Consequently, a prophylactic HCV vaccine is necessary to relieve the worldwide burden of HCV disease. DNA vaccines are a promising vaccine platform due to their commercial viability and ability to elicit robust T-cell-mediated immunity (CMI). We have developed a novel cytolytic DNA vaccine that encodes non-structural HCV proteins and a truncated mouse perforin (PRF), which is more immunogenic than the respective canonical DNA vaccine lacking PRF. Initially we assessed the ability of the HCV pNS3-PRF and pNS4/5-PRF DNA vaccines to elicit robust long-term CMI without any adverse side-effects in mice. Interferon-γ (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay was used to evaluate CMI against NS3, NS4 and NS5B in a dose-dependent manner. This analysis showed a dose-dependent bell-curve of HCV-specific responses in vaccinated animals. We then thoroughly examined the effects associated with reactogenicity of cytolytic DNA vaccination with the multi-antigenic HCV DNA vaccine (pNS3/4/5B). Hematological, biochemical and histological studies were performed in male Sprague Dawley rats with a relative vaccine dose 10–20-fold higher than the proposed dose in Phase I clinical studies. The vaccine was well tolerated, and no toxicity was observed. Thus, the cytolytic multi-antigenic DNA vaccine is safe and elicits broad memory CMI.

NS1 DNA vaccination protects against Zika infection through T cell-mediated immunity in immunocompetent mice

The causal association of Zika virus (ZIKV) with microcephaly, congenital malformations in infants, and Guillain-Barré syndrome in adults highlights the need for effective vaccines. Thus far, efforts to develop ZIKV vaccines have focused on the viral envelope. ZIKV NS1 as a vaccine immunogen has not been fully explored, although it can circumvent the risk of antibody-dependent enhancement of ZIKV infection, associated with envelope antibodies. Here, we describe a novel DNA vaccine encoding a secreted ZIKV NS1, that confers rapid protection from systemic ZIKV infection in immunocompetent mice. We identify novel NS1 T cell epitopes in vivo and show that functional NS1-specific T cell responses are critical for protection against ZIKV infection. We demonstrate that vaccine-induced anti-NS1 antibodies fail to confer protection in the absence of a functional T cell response. This highlights the importance of using NS1 as a target for T cell-based ZIKV vaccines.

Single-Dose Vaccination with a Hepatotropic Adeno-associated Virus Efficiently Localizes T Cell Immunity in the Liver with the Potential To Confer Rapid Protection against Hepatitis C Virus

Hepatitis C virus (HCV) is a significant contributor to the global disease burden, and development of an effective vaccine is required to eliminate HCV infections worldwide. CD4⁺ and CD8⁺ T cell immunity correlates with viral clearance in primary HCV infection, and intrahepatic CD8⁺ tissue-resident memory T (T_RM) cells provide lifelong and rapid protection against hepatotropic pathogens. Consequently, we aimed to develop a vaccine to elicit HCV-specific CD4⁺ and CD8⁺ T cells, including CD8⁺ T_RM cells, in the liver, given that HCV primarily infects hepatocytes. To achieve this, we vaccinated wild-type BALB/c mice with a highly immunogenic cytolytic DNA vaccine encoding a model HCV (genotype 3a) nonstructural protein (NS5B) and a mutant perforin (pVAX-NS5B-PRF), as well as a recombinant adeno-associated virus (AAV) encoding NS5B (rAAV-NS5B). A novel fluorescent target array (FTA) was used to map immunodominant CD4⁺ T helper (T_H) cell and cytotoxic CD8⁺ T cell epitopes of NS5B in vivo, which were subsequently used to design a K^dNS5B_451-459 tetramer and analyze NS5B-specific T cell responses in vaccinated mice in vivo The data showed that intradermal prime/boost vaccination with pVAX-NS5B-PRF was effective in eliciting T_H and cytotoxic CD8⁺ T cell responses and intrahepatic CD8⁺ T_RM cells, but a single intravenous dose of hepatotropic rAAV-NS5B was significantly more effective. As a T-cell-based vaccine against HCV should ideally result in localized T cell responses in the liver, this study describes primary observations in the context of HCV vaccination that can be used to achieve this goal.IMPORTANCE There are currently at least 71 million individuals with chronic HCV worldwide and almost two million new infections annually. Although the advent of direct-acting antivirals (DAAs) offers highly effective therapy, considerable remaining challenges argue against reliance on DAAs for HCV elimination, including high drug cost, poorly developed health infrastructure, low screening rates, and significant reinfection rates. Accordingly, development of an effective vaccine is crucial to HCV elimination. An HCV vaccine that elicits T cell immunity in the liver will be highly protective for the following reasons: (i) T cell responses against nonstructural proteins of the virus are associated with clearance of primary infection, and (ii) long-lived liver-resident T cells alone can protect against malaria infection of hepatocytes. Thus, in this study we exploit promising vaccination platforms to highlight strategies that can be used to evoke highly functional and long-lived T cell responses in the liver for protection against HCV.

Simultaneous use of natural adjuvants and cell penetrating peptides improves HCV NS3 antigen-specific immune responses

To improve an effective hepatitis C virus (HCV) therapeutic vaccine, induction of a strong and long term HCV antigen-specific immune response is an important parameter. HCV non-structural protein 3 (NS3) has antigenic properties and plays a major role in viral clearance. In this study, DNA constructs encoding HCV NS3 and heat shock protein 27 (Hsp27)-NS3 genes, and the recombinant (r) NS3 and rHsp27-NS3 proteins complexed with HR9 and Cady-2 cell penetrating peptides (CPPs) were utilized to evaluate antibody, cytokine and Granzyme B secretion in mice. Herein, the formation of NS3 and Hsp27-NS3 DNA/ HR9 CPP complexes were revealed by gel retardation assay and protection against DNase and protease. Cady-2 peptide was used to form the nanoparticles with rNS3 and rHsp27-NS3 proteins. The size and charge of the nanoparticles were confirmed by SEM and Zetasizer instruments. Next, in vitro transfection of the nanoparticles was assessed by flow cytometry and western blotting. Finally, humoral and cellular immune responses were evaluated using different modalities in mice. Our data showed that HR9 and Cady-2 could form stable nanoparticles with DNA and proteins, respectively and enhance their delivery into HEK-293 T cells in a non-covalent approach. Furthermore, the heterologous Hsp27-NS3 DNA + HR9 prime/rHsp27-NS3+Cady-2 protein boost elicited a higher Th1 cellular immune response with a predominant IgG2a, IgG2b, IFN-γ profile and strong Granzyme B secretion than those induced by other groups. Briefly, the combination of a natural adjuvant (Hsp27) and CPPs (HR9 and Cady-2) could significantly stimulate effective immune responses as a promising approach for development of HCV therapeutic vaccines.

A Hepatitis C Virus DNA Vaccine Encoding a Secreted, Oligomerized Form of Envelope Proteins Is Highly Immunogenic and Elicits Neutralizing Antibodies in Vaccinated Mice

Hepatitis C virus (HCV) persistently infects approximately 71 million people globally. To prevent infection a vaccine which elicits neutralizing antibodies against the virus envelope proteins (E1/E2) which are required for entry into host cells is desirable. DNA vaccines are cost-effective to manufacture globally and despite recent landmark studies highlighting the therapeutic efficacy of DNA vaccines in humans against cervical cancer, DNA vaccines encoding E1/E2 developed thus far are poorly immunogenic. We now report a novel and highly immunogenic DNA vaccination strategy that incorporates secreted E1 and E2 (sE1 and sE2) into oligomers by fusion with the oligomerization domain of the C4b-binding protein, IMX313P. The FDA approved plasmid, pVax, was used to encode sE1, sE2, or sE1E2 with or without IMX313P, and intradermal prime-boost vaccination studies in BALB/c mice showed that vaccines encoding IMX313P were the most effective in eliciting humoral and cell-mediated immunity against the envelope proteins. Further boosting with recombinant E1E2 proteins but not DNA nor virus-like particles (VLPs) expressing E1E2 increased the immunogenicity of the DNA prime-boost regimen. Nevertheless, the antibodies generated by the homologous DNA prime-boost vaccinations more effectively inhibited the binding of VLPs to target cells and neutralized transduction with HCV pseudoparticles (HCVpp) derived from different genotypes including genotypes 1, 2, 3, 4, 5, and 6. This report provides the first evidence that IMX313P can be used as an adjuvant for E1/E2-based DNA vaccines and represents a translatable approach for the development of a HCV DNA vaccine.

Cytolytic Perforin as an Adjuvant to Enhance the Immunogenicity of DNA Vaccines

DNA vaccines present one of the most cost-effective platforms to develop global vaccines, which have been tested for nearly three decades in preclinical and clinical settings with some success in the clinic. However, one of the major challenges for the development of DNA vaccines is their poor immunogenicity in humans, which has led to refinements in DNA delivery, dosage in prime/boost regimens and the inclusion of adjuvants to enhance their immunogenicity. In this review, we focus on adjuvants that can enhance the immunogenicity of DNA encoded antigens and highlight the development of a novel cytolytic DNA platform encoding a truncated mouse perforin. The application of this innovative DNA technology has considerable potential in the development of effective vaccines.

Toward DNA-Based T-Cell Mediated Vaccines to Target HIV-1 and Hepatitis C Virus: Approaches to Elicit Localized Immunity for Protection

Human immunodeficiency virus (HIV)-1 and hepatitis C virus (HCV) are major contributors to the global disease burden with many experts recognizing the requirement of an effective vaccine to bring a durable end to these viral epidemics. The most promising vaccine candidates that have advanced into pre-clinical models and the clinic to eliminate or provide protection against these chronic viruses are viral vectors [e.g., recombinant cytomegalovirus, Adenovirus, and modified vaccinia Ankara (MVA)]. This raises the question, is there a need to develop DNA vaccines against HIV-1 and HCV? Since the initial study from Wolff and colleagues which showed that DNA represents a vector that can be used to express transgenes durably in vivo, DNA has been regularly evaluated as a vaccine vector albeit with limited success in large animal models and humans. However, several recent studies in Phase I-IIb trials showed that vaccination of patients with recombinant DNA represents a feasible therapeutic intervention to even cure cervical cancer, highlighting the potential of using DNA for human vaccinations. In this review, we will discuss the limitations and the strategies of using DNA as a vector to develop prophylactic T cell-mediated vaccines against HIV-1 and HCV. In particular, we focus on potential strategies exploiting DNA vectors to elicit protective localized CD8⁺ T cell immunity in the liver for HCV and in the cervicovaginal mucosa for HIV-1 as localized immunity will be an important, if not critical component, of an efficacious vaccine against these viral infections.

Induction of Genotype Cross-Reactive, Hepatitis C Virus-Specific, Cell-Mediated Immunity in DNA-Vaccinated Mice

A universal hepatitis C virus (HCV) vaccine should elicit multiantigenic, multigenotypic responses, which are more likely to protect against challenge with the range of genotypes and subtypes circulating in the community. A vaccine cocktail and vaccines encoding consensus HCV sequences are attractive approaches to achieve this goal. Consequently, in a series of mouse vaccination studies, we compared the immunogenicity of a DNA vaccine encoding a consensus HCV nonstructural 5B (NS5B) protein to that of a cocktail of DNA plasmids encoding the genotype 1b (Gt1b) and Gt3a NS5B proteins. To complement this study, we assessed responses to a multiantigenic cocktail regimen by comparing a DNA vaccine cocktail encoding Gt1b and Gt3a NS3, NS4, and NS5B proteins to a single-genotype NS3/4/5B DNA vaccine. To thoroughly evaluate in vivo cytotoxic T lymphocyte (CTL) and T helper (Th) cell responses against Gt1b and Gt3a HCV peptide-pulsed target cells, we exploited a novel fluorescent-target array (FTA). FTA and enzyme-linked immunosorbent spot (ELISpot) analyses collectively indicated that the cocktail regimens elicited higher responses to Gt1b and Gt3a NS5B proteins than those with the consensus vaccine, while the multiantigenic DNA cocktail significantly increased the responses to NS3 and NS5B compared to those elicited by the single-genotype vaccines. Thus, a DNA cocktail vaccination regimen is more effective than a consensus vaccine or a monovalent vaccine at increasing the breadth of multigenotypic T cell responses, which has implications for the development of vaccines for communities where multiple HCV genotypes circulate.IMPORTANCE Despite the development of highly effective direct-acting antivirals (DAA), infections with hepatitis C virus (HCV) continue, particularly in countries where the supply of DAA is limited. Furthermore, patients who eliminate the virus as a result of DAA therapy can still be reinfected. Thus, a vaccine for HCV is urgently required, but the heterogeneity of HCV strains makes the development of a universal vaccine difficult. To address this, we developed a novel cytolytic DNA vaccine which elicits robust cell-mediated immunity (CMI) to the nonstructural (NS) proteins in vaccinated animals. We compared the immune responses against genotypes 1 and 3 that were elicited by a consensus DNA vaccine or a DNA vaccine cocktail and showed that the cocktail induced higher levels of CMI to the NS proteins of both genotypes. This study suggests that a universal HCV vaccine can most readily be achieved by use of a DNA vaccine cocktail.

Cytolytic DNA vaccine encoding lytic perforin augments the maturation of- and antigen presentation by- dendritic cells in a time-dependent manner

The use of cost-effective vaccines capable of inducing robust CD8⁺ T cell immunity will contribute significantly towards the elimination of persistent viral infections and cancers worldwide. We have previously reported that a cytolytic DNA vaccine encoding an immunogen and a truncated mouse perforin (PRF) protein significantly augments anti-viral T cell (including CD8⁺ T cell) immunity. Thus, the current study investigated whether this vaccine enhances activation of dendritic cells (DCs) resulting in greater priming of CD8⁺ T cell immunity. In vitro data showed that transfection of HEK293T cells with the cytolytic DNA resulted in the release of lactate dehydrogenase, indicative of necrotic/lytic cell death. In vitro exposure of this lytic cell debris to purified DCs from naïve C57BL/6 mice resulted in maturation of DCs as determined by up-regulation of CD80/CD86. Using activation/proliferation of adoptively transferred OT-I CD8⁺ T cells to measure antigen presentation by DCs in vivo, it was determined that cytolytic DNA immunisation resulted in a time-dependent increase in the proliferation of OT-I CD8⁺ T cells compared to canonical DNA immunisation. Overall, the data suggest that the cytolytic DNA vaccine increases the activity of DCs which has important implications for the design of DNA vaccines to improve their translational prospects.

Delivery methods to increase cellular uptake and immunogenicity of DNA vaccines

DNA vaccines are ideal candidates for global vaccination purposes because they are inexpensive and easy to manufacture on a large scale such that even people living in low-income countries can benefit from vaccination. However, the potential of DNA vaccines has not been realized owing mainly to the poor cellular uptake of DNA in vivo resulting in the poor immunogenicity of DNA vaccines. In this review, we discuss the benefits and shortcomings of several promising and innovative non-biological methods of DNA delivery that can be used to increase cellular delivery and efficacy of DNA vaccines.

Effect of adefovir dipivoxil on T cell immune function in the treatment of chronic hepatitis B and hepatocirrhosis

The aim of the present study was to investigate the T cell immune function in chronic hepatitis B hepatocirrhosis patients at the compensated and decompensated stage following treatment with adefovir dipivoxil. A total of 104 patients diagnosed with hepatitis B hepatocirrhosis during the period from October 2013 to October 2014 were enrolled in the study. Among the cases, there were 56 cases at compensated stage, and another 48 at decompensated stage. Adefovir dipivoxil was administered for antiviral therapy (10 mg/time, 1 time/day, for a total of 24 weeks), and we compared the virus disappearance rate, liver function improvement and T cell immune function between the two groups before and after treatment. The difference between the virus disappearance rate in the two groups was not statistically significant (P>0.05). The decreased level of ALT decrease in the compensated group was significantly higher than that in the decompensated group, while the increased level of albumin in the compensated group was significantly higher as well. The differences showed statistical significance (P<0.05). After treatment, the level of CD4⁺ and CD4⁺/CD8⁺ ratio were higher than before treatment, while the level of CD8⁺ was lower after treatment than before treatment in the two groups. The differences all showed statistical significance (P<0.05). The CD4⁺CXCR5⁺ T follicular helper (TFH) cell level in the two groups was higher after treatment, as was interleukin-2 and interferon-γ. The differences all showed statistical significance (P<0.05). As for comparison between groups, the difference had no statistical significance (P>0.05). Adefovir dipivoxil treatment can improve T cell immune function at the compensated and decompensated stages in chronic hepatitis B hepatocirrhosis patients. This may be associated with virus disappearance and liver function improvement.

Large scale production of a mammalian cell derived quadrivalent hepatitis C virus like particle vaccine

A method for the large-scale production of a quadrivalent mammalian cell derived hepatitis C virus-like particles (HCV VLPs) is described. The HCV core E1 and E2 coding sequences of genotype 1a, 1b, 2a or 3a were co-expressed in Huh7 cell factories using a recombinant adenoviral expression system. The structural proteins self-assembled into VLPs that were purified from Huh7 cell lysates by iodixanol ultracentrifugation and Stirred cell ultrafiltration. Electron microscopy, revealed VLPs of the different genotypes that are morphologically similar. Our results show that it is possible to produce large quantities of individual HCV genotype VLPs with relative ease thus making this approach an alternative for the manufacture of a quadrivalent mammalian cell derived HCV VLP vaccine.

The structural HCV genes delivered by MPG cell penetrating peptide are directed to enhance immune responses in mice model

One of the significant problems in vaccination projects is the lack of an effective vaccine against hepatitis C virus (HCV). The goal of the current study is to evaluate and compare two DNA constructs encoding HCV core and coreE1E2 genes alone or complexed with MPG peptide as a delivery system for stimulation of antibody responses and IFN-γ secretion in Balb/c mice model. Indeed, MPG cell penetrating peptide was used to improve DNA immunization in mice. Our results demonstrated that MPG forms stable non-covalent nanoparticles with pcDNA-core and pcDNA-coreE1E2 at an N/P ratio of 10:1. The in vitro transfection efficiency of core or coreE1E2 DNA using MPG and TurboFect delivery systems was confirmed by western blot analysis. The results indicated the expression of the full-length core (∼21 kDa), and coreE1E2 (∼83 kDa) proteins using an anti-His monoclonal antibody. In addition, the expression of HCV core and coreE1E2 proteins was performed in bacteria and the purified recombinant proteins were injected to mice with Montanide 720 adjuvant. Our data showed that the immunized mice with HCV core and coreE1E2 proteins generated the mixture of sera IgG1 and IgG2a isotypes considerably higher than other groups. Furthermore, DNA constructs encoding core and coreE1E2 complexed with MPG could significantly induce IFN-γ secretion in lower concentrations than the naked core and coreE1E2 DNAs. Taken together, the DNA formulations as well as protein regimens used in this study triggered high-level IFN-γ production in mice, an important feature for the development of Th1 immune responses.

Intradermal delivery of DNA encoding HCV NS3 and perforin elicits robust cell-mediated immunity in mice and pigs

Currently, no vaccine is available against hepatitis C virus (HCV), and although DNA vaccines have considerable potential, this has not been realised. Previously, the efficacy of DNA vaccines for human immunodeficiency virus (HIV) and HCV was shown to be enhanced by including the gene for a cytolytic protein, viz. perforin. In this study, we examined the mechanism of cell death by this bicistronic DNA vaccine, which encoded the HCV non-structural protein 3 (NS3) under the control of the CMV promoter and perforin is controlled by the SV40 promoter. Compared with a canonical DNA vaccine and a bicistronic DNA vaccine encoding NS3 and the proapoptotic gene NSP4, the perforin-containing vaccine elicited enhanced cell-mediated immune responses against the NS3 protein in vaccinated mice and pigs, as determined by ELISpot and intracellular cytokine staining, whereas a mouse challenge model suggested that the immunity was CD8(+) T-cell-dependent. The results of the study showed that the inclusion of perforin in the DNA vaccine altered the fate of NS3-positive cells from apoptosis to necrosis, and this resulted in more robust immune responses in mice and pigs, the latter of which represents an accepted large animal model in which to test vaccine efficacy.