Enhanced induction of hepatitis C virus-specific cytotoxic T lymphocytes and protective efficacy in mice by DNA vaccination followed by adenovirus boosting in combination with the interleukin-12 expression plasmid

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.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

IL-12 DNA Displays Efficient Adjuvant Effects Improving Immunogenicity of Ag85A in DNA Prime/MVA Boost Immunizations

Mycobacterium tuberculosis (Mtb) infection is one of the leading causes of death worldwide. The Modified Vaccinia Ankara (MVA) vaccine vector expressing the mycobacterial antigen 85A (MVA85A) was demonstrated to be safe, although it did not improve BCG efficacy, denoting the need to search for improved tuberculosis vaccines. In this work, we investigated the effect of IL-12 DNA -as an adjuvant- on an Ag85A DNA prime/MVA85A boost vaccination regimen. We evaluated the immune response profile elicited in mice and the protection conferred against intratracheal Mtb H37Rv challenge. We observed that the immunization scheme including DNA-A85A+DNA-IL-12/MVA85A induced a strong IFN-γ production to Ag85A in vitro, with a significant expansion of IFN-γ⁺CD4⁺ and IFN-γ⁺CD8⁺ anti-Ag85A lymphocytes. Furthermore, we also detected a significant increase in the proportion of specific CD8⁺CD107⁺ T cells against Ag85A. Additionally, inclusion of IL-12 DNA in the DNA-A85A/MVA85A vaccine scheme induced a marked augment in anti-Ag85A IgG levels. Interestingly, after 30 days of infection with Mtb H37Rv, DNA-A85A+DNA-IL-12/MVA85A vaccinated mice displayed a significant reduction in lung bacterial burden. Together, our findings suggest that IL-12 DNA might be useful as a molecular adjuvant in an Ag85A DNA/MVA prime-boost vaccine against Mtb infection.

Priming with two DNA vaccines expressing hepatitis C virus NS3 protein targeting dendritic cells elicits superior heterologous protective potential in mice

Development an effective vaccine may offer an alternative preventive and therapeutic strategy against HCV infection. DNA vaccination has been shown to induce robust humoral and cellular immunity and overcome many problems associated with conventional vaccines. In this study, mice were primed with either conventional pVRC-based or suicidal pSC-based DNA vaccines carrying DEC-205-targeted NS3 antigen (DEC-NS3) and boosted with type 5 adenoviral vectors encoding the partial NS3 and core antigens (C44P). The prime boost regimen induced a marked increase in antigen-specific humoral and T-cell responses in comparison with either rAd5-based vaccines or DEC-205-targeted DNA immunization in isolation. The protective effect against heterogeneous challenge was correlated with high levels of anti-NS3 IgG and T-cell-mediated immunity against NS3 peptides. Moreover, priming with a suicidal DNA vaccine (pSC-DEC-NS3), which elicited increased TNF-α-producing CD4+ and CD8+ T-cells against NS3-2 peptides (aa 1245-1461), after boosting, showed increased heterogeneous protective potential compared with priming with a conventional DNA vaccine (pVRC-DEC-NS3). In conclusion, a suicidal DNA vector (pSC-DEC-NS3) expressing DEC-205-targeted NS3 combined with boosting using an rAd5-based HCV vaccine (rAd5-C44P) is a good candidate for a safe and effective vaccine against HCV infection.

Construction and preparation of three recombinant adenoviruses expressing truncated NS3 and core genes of hepatitis C virus for vaccine purposes

BACKGROUND

In spite of dozens of clinical trials to establish effective therapeutic and/or preventive vaccine to resolve HCV infection, no real vaccine has been proved to date. Genetic vaccines based on replication-defective adenoviruses have proved to elicit strong and long lasting T-cell responses against a number of viral antigens and are even currently being used for vaccine trials in humans. According to the controversy in the immune modulatory effects of both core and NS3 full length genes, it seemed more practical to employ some parts of these HCV proteins for vaccine design.

OBJECTIVES

To generate recombinant Adenoviral vectors containing new overlapping-truncated region of NS3 gene or both the N- and C-terminal deleted parts of core gene, as well as a fusion fragment derived from both of them.

MATERIALS AND METHODS

The corresponding transfer vectors expressing truncated fragments of core, NS3 or a fusion fragment of both genes were prepared. The integrity and sequence of the transfer vectors were confirmed, and followed by experiments involving homologous recombination between them and the adenovirus backbone plasmid in the bacterial host. Recombinant Ad-pNS3, Ad-pCore and Ad-pNS3pCore viruses were prepared by transfection of these new recombined constructs into 293 packaging cell lines. The virus titer was then calculated by an immunohistochemistry based method. The RT-PCR, Real-Time PCR and western blotting were used to evaluate gene expression by all recombinant constructs. The production of complete virion particles was evaluated by detailed electron microscopy in addition to the appearance of typical cytopathic effects (CPE) and GFP expression patterns in 293 cells. The RT-PCR and GFP detection were employed to monitor the integrity as well as infectivity potency of the viral particles in Hep-G2 cells.

RESULTS

RT-PCR, Real-Time PCR or western blotting confirmed expression of truncated fragment of NS3, core or a fusion fragment of theirs by newly constructed Ad-pNS3, Ad-pCore, Ad- pNS3pCore particles. Electron microscopy, which revealed many adenovirus-like particles and characteristics of CPE in infected cells in addition to GFP detection, confirmed the infectivity, potency and integrity of recombinant adenoviral particles.

CONCLUSIONS

These adenoviruses expressing novel fragments of NS3 and core genes may be suitable tools to overcome shortcomings associated with full gene expression in the setting of HCV vaccine therapy.

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.

An assessment of the use of chimpanzees in hepatitis C research past, present and future: 1. Validity of the chimpanzee model

The USA is the only significant user of chimpanzees in biomedical research in the world, since many countries have banned or limited the practice due to substantial ethical, economic and scientific concerns. Advocates of chimpanzee use cite hepatitis C research as a major reason for its necessity and continuation, in spite of supporting evidence that is scant and often anecdotal. This paper examines the scientific and ethical issues surrounding chimpanzee hepatitis C research, and concludes that claims of the necessity of chimpanzees in historical and future hepatitis C research are exaggerated and unjustifiable, respectively. The chimpanzee model has several major scientific, ethical, economic and practical caveats. It has made a relatively negligible contribution to knowledge of, and tangible progress against, the hepatitis C virus compared to non-chimpanzee research, and must be considered scientifically redundant, given the array of alternative methods of inquiry now available. The continuation of chimpanzee use in hepatitis C research adversely affects scientific progress, as well as chimpanzees and humans in need of treatment. Unfounded claims of its necessity should not discourage changes in public policy regarding the use of chimpanzees in US laboratories.

Synthetic peptides coupled to the surface of liposomes effectively induce SARS coronavirus-specific cytotoxic T lymphocytes and viral clearance in HLA-A*0201 transgenic mice

We investigated whether the surface-linked liposomal peptide was applicable to a vaccine based on cytotoxic T lymphocytes (CTLs) against severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV). We first identified four HLA-A*0201-restricted CTL epitopes derived from SARS-CoV using HLA-A*0201 transgenic mice and recombinant adenovirus expressing predicted epitopes. These peptides were coupled to the surface of liposomes, and inoculated into mice. Two of the liposomal peptides were effective for peptide-specific CTL induction, and one of them was efficient for the clearance of vaccinia virus expressing epitopes of SARS-CoV, suggesting that the surface-linked liposomal peptide might offer an effective CTL-based vaccine against SARS.

Evidence for protection against chronic hepatitis C virus infection in chimpanzees by immunization with replicating recombinant vaccinia virus

Given the failures of nonreplicating vaccines against chronic hepatitis C virus (HCV) infection, we hypothesized that a replicating viral vector may provide protective immunity. Four chimpanzees were immunized transdermally twice with recombinant vaccinia viruses (rVV) expressing HCV genes. After challenge with 24 50% chimpanzee infective doses of homologous HCV, the two control animals that had received only the parental VV developed chronic HCV infection. All four immunized animals resolved HCV infection. The difference in the rate of chronicity between the immunized and the control animals was close to statistical significance (P = 0.067). Immunized animals developed vigorous gamma interferon enzyme-linked immunospot responses and moderate proliferative responses. To investigate cross-genotype protection, the immunized recovered chimpanzees were challenged with a pool of six major HCV genotypes. During the acute phase after the multigenotype challenge, all animals had high-titer viremia in which genotype 4 dominated (87%), followed by genotype 5 (13%). However, after fluctuating low-level viremia, the viremia finally turned negative or persisted at very low levels. This study suggests the potential efficacy of replicating recombinant vaccinia virus-based immunization against chronic HCV infection.

Immune response induced by a different combined immunization of HBsAg vaccine

AIMS

To evaluate the immune responses induced by different combined immunizations of HBsAg protein vaccine (P), recombinant vaccinia virus vaccine (V) and DNA vaccine (D).

METHODS

Balb/c mice were primed by one of the three HBsAg vaccines P, V or D and boosted by the same or another, thus nine immune combinations were constructed. Titers of anti-HBsAg IgG and their sub-isotypes were determined by ELISA. Specific cellular immune responses were determined by calcein-release assay.

RESULTS

V could induce the quickest humoral immune response with the geometrical mean titer of 1:10(1.6) at week 2 after prime immunization. The antibody titer primed by P (including PP, PV, PD) mounted up to the highest after the first boost. Antibody induced by PP was more polarized to Th2 while the other groups induced balanced Th1/Th2 response. Among all the groups, VD and DV induced the strongest CTL response. After the fourth boost, the specific lysis ratio was 64 and 71% separately at an E:T ratio of 1:1.

CONCLUSIONS

P was the most potent for inducing humoral immune response while the weakest for CTL response. D was a poor immunogen to induce specific antibody production. Among all the immune combinations, DV and VD induced the strongest CTL response in Balb/c mice.

Enhancing Th2 immune responses against amyloid protein by a DNA prime-adenovirus boost regimen for Alzheimer's disease

Accumulation of aggregated amyloid beta-protein (Abeta) in the brain is thought to be the initiating event leading to neurodegeneration and dementia in Alzheimer's disease (AD). Therefore, therapeutic strategies that clear accumulated Abeta and/or prevent Abeta production and its aggregation are predicted to be effective against AD. Immunization of AD mouse models with synthetic Abeta prevented or reduced Abeta load in the brain and ameliorated their memory and learning deficits. The clinical trials of Abeta immunization elicited immune responses in only 20% of AD patients and caused T-lymphocyte meningoencephalitis in 6% of AD patients. In attempting to develop safer vaccines, we previously demonstrated that an adenovirus vector, AdPEDI-(Abeta1-6)11, which encodes 11 tandem repeats of Abeta1-6 can induce anti-inflammatory Th2 immune responses in mice. Here, we investigated whether a DNA prime-adenovirus boost regimen could elicit a more robust Th2 response using AdPEDI-(Abeta1-6)11 and a DNA plasmid encoding the same antigen. All mice (n=7) subjected to the DNA prime-adenovirus boost regimen were positive for anti-Abeta antibody, while, out of 7 mice immunized with only AdPEDI-(Abeta1-6)11, four mice developed anti-Abeta antibody. Anti-Abeta titers were indiscernible in mice (n=7) vaccinated with only DNA plasmid. The mean anti-Abeta titer induced by the DNA prime-adenovirus boost regimen was approximately 7-fold greater than that by AdPEDI-(Abeta1-6)11 alone. Furthermore, anti-Abeta antibodies induced by the DNA prime-adenovirus boost regimen were predominantly of the IgG1 isotype. These results indicate that the DNA prime-adenovirus boost regimen can enhance Th2-biased responses with AdPEDI-(Abeta1-6)11 in mice and suggest that heterologous prime-boost strategies may make AD immunotherapy more effective in reducing accumulated Abeta.

An OriP/EBNA-1-based baculovirus vector with prolonged and enhanced transgene expression

BACKGROUND

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been explored as a gene delivery vehicle for a variety of mammalian cell lines. However, the transient expression nature due to its incapability to replicate in mammalian cells and insufficient transduction efficiency limit its application.

METHODS

Recombinant baculovirus vectors containing genetic elements from Epstein-Barr virus (EBV), OriP and EBNA-1, which are essential for the episomal maintenance of the EBV genome in latently infected cells, were constructed and tested for their ability to sustain and express transgene (enhanced green fluorescence protein (egfp)) in mammalian cells.

RESULTS

The recombinant baculovirus containing OriP and EBNA-1 genes driven by the cytomegalovirus (CMV) promoter was capable of persisting in a significant proportion of infected mammalian cells, HEK293, Vero, Cos-7, and Hone-1, without any selective pressure. In HEK293, the expression of EGFP lasted for 60 days with markedly enhanced expression level. The persistence of baculovirus genome correlated with the expression of EBNA-1.

CONCLUSIONS

The improved baculovirus vector could mediate prolonged and enhanced foreign gene expression in some mammalian cells. Furthermore, an adequate level of the EBNA-1 protein was essential for the maintenance of the OriP-containing baculovirus genome. The new vector has potential for use in gene therapy.

Adenovirus vaccination against neu oncogene exerts long-term protection from tumorigenesis in BALB/neuT transgenic mice

The transforming rat HER2/neu oncogene (neu), when embedded in the genome of transgenic BALB/c (neuT) mice, provokes the development of an invasive carcinoma in each of their 10 mammary glands. We used the neuT mice model system to evaluate the immunization efficiency and the protective effect of intramuscular injection of adenovirus (Ad) and/or of DNA with electrostimulation (DNA+ES), both expressing the rat p185(neu) protein. A neu cDNA sequence, which exclusively contains codons preferred by highly expressed mammalian genes, was used in this study. This "optimized" cDNA displayed higher expression in cultured cells and greater cell-mediated response than the original gene when injected as DNA+ES. Ad expressing the optimized sequence (Ad5-neu.opt) induced a higher immune response, as measured by the frequency of IFN-gamma-secreting spleen cells and antibody titers. Different Ad/DNA combinations and immunization schedules confirmed the superiority of Ad5-neu.opt in inducing a strong Th1-skewed humoral and CD8(+) cell-mediated response. Two Ad5-neu.opt injections of 10(9) viral particles at week 10 and 12 were sufficient to induce the highest response, which persisted at detectable levels up to 33 weeks of age. Anti-Ad5 antibodies elicited by previous injections neutralized the effect of an additional Ad5-neu.opt immunization at week 19. A group, which received 3 injections of DNA+ES at week 23, 27 and 31, in addition to the 3 Ad injections at week 10, 12 and 19 showed an increased frequency of IFN-gamma(+), CD8(+) PBMC at week 25, which persisted at detectable levels till week 38. Ad5-neu.opt administration at 10 and 12 weeks of age had a significant impact on tumor progression. At 44 weeks, 40% of the mice were completely protected from tumors with a mean tumor of 3.8. In contrast, control mice developed 10 tumors and died by week 27. Vaccination blocked the tumor development at the atypical hyperplasia stage present at the time of treatment. Tumors developing at later times express reduced levels of rat p185(neu) protein.

Effective Induction of Type 1 Cytotoxic T Cell Responses in Mice with DNA Vaccine Encoding Two Hepatitis C Virus Cytotoxic T Lymphocyte Epitopes

The aims of this study were to explain whether a multiple cytotoxic T lymphocyte (CTL) epitope-based anti-hepatitis C virus (HCV) DNA vaccine can induce specific CTL responses to each HCV CTL epitope independently and long-term CD8(+) T cell memory responses, and to determine the cytokine secretion pattern and subtype of epitope-specific cytotoxic T cells. A multi-CTL epitope gene, which consists of two epitopes of HCV (H-2(d)-restricted HCV core(133142) and E1(315322)), was cloned into the eukaryotic expression vector pcDNA3.1. BALB/c mice (H-2(d) restricted) were vaccinated intramuscularly with this multi-CTL epitope-based DNA vaccine. The epitope-specific CTLs against target cells (P815,H-2(d) restricted) pulsed with various CTL epitope peptides were detected by lactate dehydrogenase release assay, and the precursor frequency of epitope-specific CTLs was determined by limiting dilution analysis. Cytokines (interleukin [IL]-2, IL-4, and interferon-) in culture supernatants were determined by enzyme-linked immunosorbent assay. The multi-CTL epitope-based DNA vaccine directed against two HCV CTL epitopes could induce specific CTL responses to each of the two CTL epitopes independently and long-term CD8(+) T cell memory responses. The epitope-specific cytotoxic T cells produced helper T cell type 1 cytokines. This work demonstrated that multiepitope DNA vaccination is a potential strategy to control HCV infection.

Protective immunity against respiratory tract challenge with Yersinia pestis in mice immunized with an adenovirus-based vaccine vector expressing V antigen

The aerosol form of the bacterium Yersinia pestis causes the pneumonic plague, a rapidly fatal disease. At present, no plague vaccines are available for use in the United States. One candidate for the development of a subunit vaccine is the Y. pestis virulence (V) antigen, a protein that mediates the function of the Yersinia outer protein virulence factors and suppresses inflammatory responses in the host. On the basis of the knowledge that adenovirus (Ad) gene-transfer vectors act as adjuvants in eliciting host immunity against the transgene they carry, we tested the hypothesis that a single administration of a replication-defective Ad gene-transfer vector encoding the Y. pestis V antigen (AdsecV) could stimulate strong protective immune responses without a requirement for repeat administration. AdsecV elicited specific T cell responses and high IgG titers in serum within 2 weeks after a single intramuscular immunization. Importantly, the mice were protected from a lethal intranasal challenge of Y. pestis CO92 from 4 weeks up to 6 months after immunization with a single intramuscular dose of AdsecV. These observations suggest that an Ad gene-transfer vector expressing V antigen is a candidate for development of an effective anti-plague vaccine

Enhanced immunogenicity and antitumour effects with heterologous prime-boost regime using vaccines based on MG7-Ag mimotope of gastric cancer

MG7-Ag, gastric cancer-associated antigen, has been shown to be immunogenic and has been used as marker molecule for prognosis. In a previous study, we developed an oral DNA vaccine based on MG7-Ag mimotope. However, we failed to detect cellular immune response using the oral MG7-Ag mimotope DNA vaccine. To induce significant T cell response, we developed a recombinant adenovirus vaccine based on MG7-Ag mimotope and evaluated the efficacy and protective effects of heterologous prime-boost immunization protocol with an oral DNA vaccine previously developed. We found that both vaccines were able to elicit a significant humoral response against MG7-Ag, while the highest serum titre MG7 antibody was detected in mice immunized with the heterologous prime-boost immunization protocol. Enzyme-linked immunospot (ELISPOT) assay demonstrated that the heterologous prime-boost immunization strategy was more efficient in inducing T cell response than the homologous prime-boost strategy. In the tumour challenge assay, 2 of 5 mice immunized with the heterologous prime-boost protocol were tumour free, while none of the mice in homologous prime-boost groups or control groups was tumour free. Those tumour-bearing mice in the heterologous prime-boost regime had smaller tumour masses than their counterparts in the homologous prime-boost groups or control groups. Therefore, our study suggests that vaccines against MG7-Ag induce significant immune response against gastric cancer, and that the heterologous prime-boost protocol using different types of vaccines could achieve better protective effect than the homologous prime-boost protocol.

Enhanced induction of SARS-CoV nucleocapsid protein-specific immune response using DNA vaccination followed by adenovirus boosting in BALB/c mice

Objective

To investigate immunogenicity in the induction of humoral and cellular immune responses to genetic vaccines of the recombinant severe acute respiratory syndrome-associated coronavirus (SARS-CoV)-N gene expressing the same protein plasmid, pcDNA3.1-N, and replication-defective adenoviral vector, rAd-N, in a pcDNA3.1-N prime-rAd-N boost regimen and the reverse sequence in a rAd-N prime-pcDNA3.1-N boost regimen.

Method

After the mice had been immunized intramuscularly and/or intraperitoneally with pcDNA3.1-N and rAd-N in prime-triple boost immunization, humoral and cellular immune responses were detected.

Results

After detection, different levels of anti-N humoral and cellular responses are shown compared to controls. The humoral immune response was induced more effectively by the DNA priming and recombinant adenovirus boosting regimen and the reverse sequence of heterogeneous combinations. There is a significant difference between heterogeneous and homologous vaccinations. However, the cytotoxic T lymphocyte (CTL) response was not significantly altered by the different prime-boost immunizations or the recombinant adenovirus of pcDNA3.1-N prime-rAd-N boost regimen alone, but lymphoproliferation and interferon-γ (IFN-γ) secretion were all enhanced by heterologous combination immunizations compared to homologous combinations. For the reverse sequence immunization regimen, lymphoproliferation, IFN-γ and CTL responses were all significantly weaker compared with pcDNA3.1-N prime-rAd-N boost regimen.

Conclusion

Taken together, of all the combinations, the prime-triple boost immunization of pcDNA3.1-N/pcDNA3.1-N/pcDNA3.1-N/rAd-N can effectively induce SARS-CoV-N-specific and strong humoral and cellular immune responses in mice. The present results suggest that DNA immunization followed by recombinant adenovirus boosting could be used as a potential SARS-CoV vaccine in the induction of an enhanced humoral and cellular immune response.

The cell-mediated immune response induced by plasmid encoding bovine herpesvirus 1 glycoprotein B is enhanced by plasmid encoding IL-12 when delivered intramuscularly or by gene gun, but not after intradermal injection

Bovine herpesvirus 1 (BHV-1) causes respiratory and genital infections in cattle. Previously we demonstrated that a DNA vaccine encoding a truncated, secreted form of BHV-1 glycoprotein B (tgB) induces cytotoxic T lymphocyte (CTL) responses in C3H mice. In this study we investigated the potential of interleukin 12 (IL-12) to further enhance the CTL response. C3H mice were immunized with a plasmid encoding tgB or with plasmids encoding tgB and murine IL-12. When the plasmid encoding tgB was delivered intramuscularly or epidermally by a gene gun, co-administration with IL-12 plasmid stimulated the synthesis of more IgG2a, the production of higher levels of IFN-gamma, and more effective killing by CTLs. In contrast, after intradermal delivery no effect of co-administration of IL-12 encoding plasmid was observed. Further investigation suggested that antigen and IL-12 need to be expressed in the draining lymph nodes, where IL-12 can have a direct effect on T cells.

Adenovirus as vehicle for anticancer genetic immunotherapy

Adenoviruses (Ads) are in the forefront of genetic immunization methods being developed against cancer. Their ability to elicit an effective immune response against tumor-associated antigens has been demonstrated in many model systems. Several clinical trials, which use Ad as vehicle for immunization, are already in progress. Preclinical studies have also demonstrated the efficacy of combining Ad-mediated immunization with adjuvants such as chemotherapeutic agents and cytokines. Issues related to sero-prevalence and safety of Ads, however, continue to pose a challenge and need to be addressed.

Plasmid interleukin-23 (IL-23), but not plasmid IL-27, enhances the protective efficacy of a DNA vaccine against Mycobacterium tuberculosis infection

Protection against intracellular pathogens such as Mycobacterium tuberculosis requires the development of Th1-like T-cell responses. This in turn is dependent on the pattern of cytokine produced from dendritic cells (DCs) after infection. Three heterodimeric cytokines, interleukin-12 (IL-12), IL-23, and IL-27, as well as IL-18, contribute to the differentiation and expansion of naive CD4(+) T cells. In this study we compared the effects of plasmids expressing both chains of IL-12, IL-23, or IL-27 as adjuvants for DNA immunization against M. tuberculosis infection. The genes encoding p19 and p40 chains of IL-23 or EBI3 and p28 chains of IL-27 were cloned on either side of a self-cleaving peptide from the FMDV2A protein. The secretion of functional cytokines from transfected cells was detected with bioassays. Supernatant from p2AIL-23-transfected cells induced the release of IL-17 from activated lymphocytes, confirming the presence of bioactive IL-23. Further, supernatant from p2AIL-27-transfected cells stimulated a significant increase in the proliferation of peptide-stimulated transgenic CD4(+) T cells. In initial experiments, M. tuberculosis infection of DCs was more potent at inducing IL-12 and IL-23 secretion than infection with the vaccine strain Mycobacterium bovis bacille Calmette-Guérin (BCG), and no significant upregulation of IL-27 was observed. Coimmunization of C57BL/6 mice with DNA expressing M. tuberculosis antigen 85B (Ag85B; DNA85B) and plasmids expressing IL-23 or IL-12 stimulated stronger Ag85B-specific T-cell proliferative and IFN-gamma responses than DNA85B alone, whereas the addition of p2AIL-27 had no effect. Interestingly, DNA85B codelivered with p2AIL-12, but not p2AIL-23, reduced the immunoglobulin G antibody response. Both p2AIL-23 and p2AIL-12, but not p2AIL-27, enhanced the protective efficacy of DNA85B against aerosol M. tuberculosis challenge. Therefore, both p2AIL-23 and p2AIL-12 are valuable as cytokine adjuvants for increasing the protective antituberculosis immunity induced by DNA vaccines.

A novel adenovirus type 6 (Ad6)-based hepatitis C virus vector that overcomes preexisting anti-ad5 immunity and induces potent and broad cellular immune responses in rhesus macaques

Success in resolving hepatitis C virus (HCV) infection has been correlated to vigorous, multispecific, and sustained CD8(+) T-cell response in humans and chimpanzees. The efficacy of inducing T-cell-mediated immunity by recombinant serotype 5 adenovirus vector has been proven in many animal models of infectious diseases, but its immunogenicity can be negatively influenced by preexisting immunity against the vector itself. To evaluate the less prevalent adenovirus serotype 6 (Ad6) as an alternative vector for and HCV vaccine development, we have generated serotype 5 and 6 adenoviral vectors directing expression of the nonstructural region of HCV (MRKAd5-NSmut and MRKAd6-NSmut). Immunogenicity studies in mice showed that the two vectors induced comparable T-cell responses but that only MRKAd6-NSmut was not suppressed in the presence of anti-Ad5 immunity. In contrast, preexisting anti-Ad5 immunity dramatically blunted the immunogenicity of the serotype 5-based HCV vector. Furthermore, MRKAd6-NSmut showed equivalent potency, breadth, and longevity of HCV-specific T-cell responses in rhesus macaques as the corresponding Ad5-based vector over a wide range of doses and was capable of boosting DNA-primed animals even if administered at low doses. These data support the use of the MRKAd6-NSmut for anti-HCV immunotherapy and, more generally, for the Ad6 serotype as a better genetic vaccine vehicle than Ad5.

T-bet is required for protection against vaccinia virus infection

The transcription factor T-bet regulates the differentiation of CD4(+) T-helper type 1 (Th1) cells and represses Th2 lineage commitment. Since Th1 cells are crucial in the defense against pathogens, several studies addressed the role of T-bet in immunity to infection using T-bet knockout (T-bet(-/-)) mice. Nevertheless, it is still unclear whether T-bet is required for defense. Although vaccinia virus (VV) has extensively been used as an expression vector and the smallpox vaccine, there is only limited knowledge about immunity to VV infection. The urgency to understand the immune responses has been increased because of concerns about bioterrorism. Here, we show that T-bet is critical in the defense against VV infection as follows: (i) the survival rate of T-bet(-/-) mice was lower than that of control littermates postinfection; (ii) T-bet(-/-) mice lost more weight postinfection; and (iii) control mice cleared VV faster than T-bet(-/-) mice. As expected, a significant Th2 shift was observed in CD4(+) T cells of T-bet(-/-) mice. Furthermore, absence of T-bet impaired VV-specific CD8(+) cytotoxic T-lymphocyte (CTL) function, including cytolytic activity, antiviral cytokine production, and proliferation. Cytolytic capacity of natural killer (NK) cells was also diminished in T-bet(-/-) mice, whereas anti-VV antibody production was not impaired. These data reveal that the enhanced susceptibility to VV infection in T-bet(-/-) mice was at least partially due to the Th2 shift of CD4(+) T cells and the diminished function of VV-specific CTLs and NK cells but not due to downregulation of antibody production.

Combined prime-boost vaccination against tick-borne encephalitis (TBE) using a recombinant vaccinia virus and a bacterial plasmid both expressing TBE virus non-structural NS1 protein

BACKGROUND

Heterologous prime-boost immunization protocols using different gene expression systems have proven to be successful tools in protecting against various diseases in experimental animal models. The main reason for using this approach is to exploit the ability of expression cassettes to prime or boost the immune system in different ways during vaccination procedures. The purpose of the project was to study the ability of recombinant vaccinia virus (VV) and bacterial plasmid, both carrying the NS1 gene from tick-borne encephalitis (TBE) virus under the control of different promoters, to protect mice against lethal challenge using a heterologous prime-boost vaccination protocol.

RESULTS

The heterologous prime-boost vaccination protocol, using a VV recombinant and bacterial plasmid, both containing the NS1 TBE virus protein gene under the control of different promoters, achieved a high level of protection in mice against lethal challenge with a highly pathogenic TBE virus strain. No signs of pronounced TBE infection were detected in the surviving animals.

CONCLUSION

Heterologous prime-boost vaccination protocols using recombinant VV and bacterial plasmids could be used for the development of flavivirus vaccines.

Adenoviruses as vaccine vectors

Adenoviruses have transitioned from tools for gene replacement therapy to bona fide vaccine delivery vehicles. They are attractive vaccine vectors as they induce both innate and adaptive immune responses in mammalian hosts. Currently, adenovirus vectors are being tested as subunit vaccine systems for numerous infectious agents ranging from malaria to HIV-1. Additionally, they are being explored as vaccines against a multitude of tumor-associated antigens. In this review we describe the molecular biology of adenoviruses as well as ways the adenovirus vectors can be manipulated to enhance their efficacy as vaccine carriers. We describe methods of evaluating immune responses to transgene products expressed by adenoviral vectors and discuss data on adenoviral vaccines to a selected number of pathogens. Last, we comment on the limitations of using human adenoviral vectors and provide alternatives to circumvent these problems. This field is growing at an exciting and rapid pace, thus we have limited our scope to the use of adenoviral vectors as vaccines against viral pathogens.

Xenogeneic immunization in mice using HER2 DNA delivered by an adenoviral vector

The protective efficacy of xenogeneic vaccination with DNA encoding the HER2 oncogene was evaluated in BALB/c mice transgenic for the transforming form of the neu oncogene, which spontaneously develops carcinomas in all mammary glands. Intramuscular injection of either plasmid DNA followed by electrical stimulation (pVIJ-HER2 with ES) or an adenoviral vector (Ad5-HER2), both expressing the HER2 oncogene, was tested. Immunization using pVIJ-HER2 with ES elicited a cell-mediated response that was much lower than that elicited by the immunization with Ad5-HER2, as measured by the frequency of IFN-gamma-secreting spleen cells. The dominant T-cell epitope of the HER2 protein product (p185) in the BALB/c (H-2(d)) genetic background was identified. While the T-cell response elicited was only partially crossreactive with the corresponding rat epitopes because of sequence variations (89% similarity), a cytotoxic T-lymphocyte activity against the rat immunodominant epitope was also evident. The Ad5-HER2 vaccination induced also antibodies against p185, which crossreacted with the rat protein homolog. Both T- and B-cell responses slowly declined with time. Vaccination with Ad5-HER2 at 6 and 9 weeks of age delayed incidence and reduced multiplicity of tumors in neu transgenic mice.

Chronic Hepatitis C and Genotyping: The Clinical Significance of Determining HCV Genotypes

Chronic hepatitis C, attributed to infection with hepatitis C virus (HCV), is a global health problem. The overall prevalence of viral hepatitis worldwide is estimated to be 3–5% with over 175 million people infected with HCV. Clinically, HCV can establish a persistent, chronic infection contributing to progressive liver disease, including cirrhosis and hepatocellular carcinoma (HCC), requiring intensive treatment regimens, possible liver transplantation and long-term care. Due to the chronic nature of HCV infection and the tremendous burden on healthcare resources, clinicians and laboratorians have looked for key epidemiological, pathological and viral characteristics that may provide insight into disease progression, severity and response to therapy to permit the administration of effective therapeutic regimens as well as long-term management of infected individuals. Determination of viral genotype has been identified as one parameter that could provide direction in the clinical management of patients with chronic HCV infections. The following review provides background on determination of HCV genotypes and the relevance of viral genome characterization in the current clinical setting.

DNA immunization followed by a viral vector booster in a Chlamydia pneumoniae mouse model

Vaccination against Chlamydia pneumoniae would be a beneficial strategy for either preventing or controlling infection by this human respiratory pathogen that also causes persistent infections. In the present study, we used recombinant Semliki Forest virus (rSFV) particles for delivering C. pneumoniae antigens major outer membrane protein (MOMP) or outer membrane protein 2 (Omp2) to the mice or applied the prime-boost technique, where mice were first primed with naked DNA and then boosted with the viral vector coding for the same proteins. Partial protection suggested by the reduced number of cultivable bacteria from the lungs of the challenged mice was seen in mice immunized by either method with MOMP expressing constructs. A significant protection was also achieved after DNA/rSFV immunization with Omp2. DNA priming followed by rSFV boosting induced a more prominent IFN-gamma production after challenge at the site of the infection in pulmonary and mediastinal cells.

Adjuvant activities of novel cytokines, interleukin-23 (IL-23) and IL-27, for induction of hepatitis C virus-specific cytotoxic T lymphocytes in HLA-A*0201 transgenic mice

Searching the sequence databases has revealed two novel cytokines: interleukin-23 (IL-23) and IL-27. These cytokines are quite similar to, but clearly distinct from IL-12 in their structures and T-cell stimulatory fashions. In contrast to IL-12, however, little is known about the roles of IL-23 and IL-27 in the immune regulation. Previously, we evaluated the prime-boost immunization consisting of priming and the first boosting with the hepatitis C virus (HCV)-core expression plasmid, followed by a second boosting with recombinant adenovirus expressing HCV core for induction of HCV core-specific cytotoxic T lymphocytes (CTLs) in BALB/c mice. The present study demonstrates that HCV-specific CTL induction was greatly enhanced by coinoculation of an IL-12 expression plasmid in the prime-boost immunization, indicating the potent adjuvant activity of IL-12. We investigated whether similar adjuvant effects could be exerted by either IL-23 or IL-27 in a prime-boost immunization with HLA-A*0201 transgenic mice. Coadministration of either an IL-23 or an IL-27 expression plasmid, as well as an IL-12 expression plasmid, in a prime-boost immunization enhanced induction of HCV-specific CTLs and led to dramatic increases in the numbers of gamma interferon (IFN-gamma)-producing, HCV-specific CD8+ cells. Further, preinjections of IL-12, IL-23, or IL-27 expression plasmids before immunization resulted in great increases in the number of IFN-gamma-producing, HCV-specific CD8+ cells in response to immunization with recombinant adenovirus. These data revealed that both IL-23 and IL-27, as well as IL-12, are potent adjuvants for epitope-specific CTL induction. The two novel cytokines might offer new prophylactic and therapeutic strategies against infectious pathogens such as HCV.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Baculovirus vectors elicit antigen-specific immune responses in mice

To characterize the induction of antigen-specific immune response mediated by baculovirus, vectors expressing the E2 glycoprotein of hepatitis C virus or the carcinoembryonic antigen (CEA) under the control of the cytomegalovirus immediate-early promoter-enhancer were constructed. Additionally, a baculovirus vector encoding the E2 glycoprotein (Bac-G-E2) and expressing vesicular stomatitis virus glycoprotein (VSV-G) in the viral envelope was generated by inserting the VSV-G coding sequence downstream of the polyhedrin promoter. Mice were subjected to intramuscular, intranasal, or subcutaneous inoculations with Bac-E2 and the cellular immune response was monitored by ELISPOT and intracellular staining. Additionally, humoral response was monitored by titrating anti-E2 antibodies. Induction of a measurable anti-E2 T-cell response was observed only after intramuscular injection and was predominantly CD8(+) specific. The immunogenic properties of baculovirus as vaccine vector were not restricted to E2 because a CEA-specific CD4(+) T-cell response was observed upon intramuscular injection of Bac-CEA. Interestingly, the Bac-G-E2 vector was shown to be a more efficient immunogen than Bac-E2, in view of the 10-fold difference in the minimal dose required to elicit a measurable T-cell response upon intramuscular injection. Induction of inflammatory cytokines such as gamma interferon, tumor necrosis factor alpha, and interleukin-6 was detected as early as 6 h postinjection of Bac-G-E2. Most importantly, both vectors elicited CD8(+) T cells with effector function capable of lysing target cells loaded with a hepatitis C virus-specific epitope. Additionally, enhanced NK cytolytic activity was detected in immunized mice. Thus, these results further demonstrate that baculovirus may be considered a useful vector for gene therapy.

Immunization with hepatitis C virus core gene triggers potent T-cell response, but affects CD4+ T-cells

Numerous attempts to induce immunity against HCV core (HCV-C) by DNA immunization met serious difficulties in optimizing T-helper cell and antibody responses. Immunomodulatory properties of HCV-C could be blamed that seem to be dependent on the genotype of HCV source. Here, we characterized HCV-C gene from HCV 1b isolate 274933RU. Eukaryotic expression of HCV-C was effectively driven by CMVIE, while human elongation factor 1 alpha promoter directed low levels of HCV-C expression. C57BL/6 mice were immunized with CMVIE-driven HCV-C gene, and assessed for specific antibody production, T-cell proliferation and cytokine secretion. The number and proportion of CD19+, CD3+, CD3+/CD4+, and CD3+/CD8+ splenocytes in HCV-C gene recipients was evaluated by flow cytometry. A significant mounting drop in CD3+/CD4+ T-cell counts occurred in HCV-C gene-recipients as compared to the controls. Despite that, 75% of mice exhibited core-specific cellular reactivity revealed as high proliferative responses to HCV-C and HCV-C peptides. Stimulated T-cells secreted predominantly IFN-gamma and IL-2. A shift of epitope specificity was observed with the early response being broad, and the late limited to the HCV-C C-terminus. Thus, we demonstrate both T-cell immunogenicity and T-cell modulation by core of HCV 1b. Immune modulation by HCV core may affect host ability to mount long-lasting cellular and antibody response and should be dealt with in designing core-based HCV vaccines.

Jump-starting the immune system: prime-boosting comes of age

A major challenge for immunologists has been the development of vaccines designed to emphasize cellular immune responses. One particularly promising approach is the prime-boost strategy, which has been shown to generate high levels of T-cell memory in animal models. Recently, several papers have highlighted the power of prime-boost strategies in eliciting protective cellular immunity to a variety of pathogens and have demonstrated efficacy in humans. Coupled with recent advances in our understanding of the mechanisms underlying the generation, maintenance and recall of T-cell memory, the field is poised to make tremendous progress. This Review discusses the impact of these recent developments on the future of prime-boost vaccine strategies.