Heterosubtypic protection against pathogenic human and avian influenza viruses via in vivo electroporation of synthetic consensus DNA antigens

A novel DNA platform designed for vaccine use with high transgene expression and immunogenicity

The development of new, low-cost vaccines and effective gene therapies requires accurate delivery and high-level expression of candidate genes. We developed a plasmid vector, pIDV-II, that allows for both easy manipulation and high expression of exogenous genes in mammalian cells. This plasmid is based upon the pVax1 plasmid and shares a common structure with typical mammalian transcription units. It is composed of a chicken β-actin promoter (CAG), followed by an intron and flanked by two restriction sites, and also includes a post-transcriptional regulatory element, followed by a transcriptional termination signal. While the modification of pVax1 elements either decreased eGFP expression levels or had no effect at all, replacement of the promoter, the poly-A signal, deletion of the T7 and AmpR promoters, and inversion of the ORI-Neo/Kan cassette, significantly increased in vitro eGFP expression with the modified plasmid called pIDV-II. To further evaluate our vector, expression levels of three viral antigens were compared in cell lines transfected either with pVax1 or pCAGGS backbones as controls. Higher transgene expression was consistently observed with pIDV-II. The humoral and cellular responses generated in mice immunized with pIDV-II vs pVax1 expressing each viral antigen individually were superior by 2-fold or more as measured by ELISA and ELISPOT assays. Overall these results indicate that pIDV-II induces robust transgene expression, with concomitant improved cellular and humoral immune responses against the transgene of interest over pVax1. The new vector, pIDV-II, offers an additional alternative for DNA based vaccination and gene therapy for animal and human use.

Intranasal Immunization with the Influenza A Virus Encoding Truncated NS1 Protein Protects Mice from Heterologous Challenge by Restraining the Inflammatory Response in the Lungs

Influenza viruses with an impaired NS1 protein are unable to antagonize the innate immune system and, therefore, are highly immunogenic because of the self-adjuvating effect. Hence, NS1-mutated viruses are considered promising candidates for the development of live-attenuated influenza vaccines and viral vectors for intranasal administration. We investigated whether the immunogenic advantage of the virus expressing only the N-terminal half of the NS1 protein (124 a.a.) can be translated into the induction of protective immunity against a heterologous influenza virus in mice. We found that immunization with either the wild-type A/PR/8/34 (H1N1) influenza strain (A/PR8/NSfull) or its NS1-shortened counterpart (A/PR8/NS124) did not prevent the viral replication in the lungs after the challenge with the A/Aichi/2/68 (H3N2) virus. However, mice immunized with the NS1-shortened virus were better protected from lethality after the challenge with the heterologous virus. Besides showing the enhanced influenza-specific CD8⁺ T-cellular response in the lungs, immunization with the A/PR8/NS124 virus resulted in reduced concentrations of proinflammatory cytokines and the lower extent of leukocyte infiltration in the lungs after the challenge compared to A/PR8/NSfull or the control group. The data show that intranasal immunization with the NS1-truncated virus may better induce not only effector T-cells but also certain immunoregulatory mechanisms, reducing the severity of the innate immune response after the heterologous challenge.

Strategies Targeting Hemagglutinin as a Universal Influenza Vaccine

Influenza virus has significant viral diversity, both through antigenic drift and shift, which makes development of a vaccine challenging. Current influenza vaccines are updated yearly to include strains predicted to circulate in the upcoming influenza season, however this can lead to a mismatch which reduces vaccine efficacy. Several strategies targeting the most abundant and immunogenic surface protein of influenza, the hemagglutinin (HA) protein, have been explored. These strategies include stalk-directed, consensus-based, and computationally derived HA immunogens. In this review, we explore vaccine strategies which utilize novel antigen design of the HA protein to improve cross-reactive immunity for development of a universal influenza vaccine.

Efficacy of recombinant Marek's disease virus vectored vaccines with computationally optimized broadly reactive antigen (COBRA) hemagglutinin insert against genetically diverse H5 high pathogenicity avian influenza viruses

The genetic and antigenic drift associated with the high pathogenicity avian influenza (HPAI) viruses of Goose/Guangdong (Gs/GD) lineage and the emergence of vaccine-resistant field viruses underscores the need for a broadly protective H5 influenza A vaccine. Here, we tested experimental vector herpesvirus of turkey (vHVT)-H5 vaccines containing either wild-type clade 2.3.4.4A-derived H5 inserts or computationally optimized broadly reactive antigen (COBRA) inserts with challenge by homologous and genetically divergent H5 HPAI Gs/GD lineage viruses in chickens. Direct assessment of protection was confirmed for all the tested constructs, which provided clinical protection against the homologous and heterologous H5 HPAI Gs/GD challenge viruses and significantly decreased oropharyngeal shedding titers compared to the sham vaccine. The cross reactivity was assessed by hemagglutinin inhibition (HI) and focus reduction assay against a panel of phylogenetically and antigenically diverse H5 strains. The COBRA-derived H5 inserts elicited antibody responses against antigenically diverse strains, while the wild-type-derived H5 vaccines elicited protection mostly against close antigenically related clades 2.3.4.4A and 2.3.4.4D viruses. In conclusion, the HVT vector, a widely used replicating vaccine platform in poultry, with H5 insert provides clinical protection and significant reduction of viral shedding against homologous and heterologous challenge. In addition, the COBRA-derived inserts have the potential to be used against antigenically distinct co-circulating viruses and future drift variants.

CCR10 expression is required for the adjuvant activity of the mucosal chemokine CCL28 when delivered in the context of an HIV-1 Env DNA vaccine

An effective prophylactic vaccine targeting HIV must induce a robust humoral response and must direct the bulk of this response to the mucosa-the primary site of HIV transmission. The chemokine, CCL28, is secreted by epithelial cells at mucosal surfaces and recruits' cells expressing its receptor CCR10. CCR10 is predominantly expressed by IgA + ASCs. We hypothesized that co-immunization with plasmid DNA encoding consensus envelope antigens with plasmid-encoded CCL28 would enhance anti-HIV IgA responses at mucosal surfaces. Indeed, animals receiving pCCL28 and pEnvA/C had significantly increased HIV-specific IgA in fecal extract. Surprisingly, CCL28 co-immunization induced a significant increase in anti-HIV IgG in the serum in mice compared to those receiving pEnvA/C alone. These robust antibody responses were not associated with changes in the frequency of germinal center B cells but depended upon the expression of CCR10, as these responses we abolished in CCR10-deficient animals. Finally, immunization with CCL28 led to increased frequencies in HIV-specific CCR10 + and CCR10 + IgA + B cells in the small intestine and Peyer's patches of vaccinated animals as compared to those receiving pEnvA/C alone. These data indicate that CCL28 administration can enhance antigen-specific humoral responses systemically and at mucosal surfaces.

Self-destructing Salmonella via temperature induced gene E of phage PhiX174 improves influenza HA DNA vaccine immune protection against H1N1 infection in mice model

The delivery of DNA vaccines is the principle impediment for implementation of DNA vaccination on a mass scale. In this study, we report a temperature induced conditionally expressed phage PhiX174 gene E mediated lysis of Salmonella under in vivo conditions that can increase the immunogenicity of a DNA vaccine delivered via Salmonella carrier system. We electroporated gene E encoding lysis plasmid pJHL187 along with the pcDNA-HA plasmid encoding H1N1 HA into attenuated Salmonella Typhimurium, strain JOL1893. Using C57BL/6 mice as the model, we showed that the mice intragastrically vaccinated with JOL1893 induced significant production of HA-specific humoral and cell mediated immune responses compared to the JOL1837, which carry pcDNA-HA plasmid alone. Furthermore, mice vaccinated with JOL1893 vaccine were fully protected against the lethal H1N1 challenge compared to the JOL1837 strain, which showed 90% protection only. However, none of the animals survived treated with either the PBS or the Salmonella carrying empty vector. Taken together, our results indicate that mucosal immunization with conditional lysis enabled live attenuated S. Typhimurium as a DNA vaccine carrier can induce efficient systemic and mucosal immune responses, and improves immune protection against a highly pathogenic H1N1 infection in mice model.

Novel IFN-γ ELISpot reveals robust T cell responses elicited after influenza nucleoprotein DNA vaccination in New Zealand White rabbits

The New Zealand White rabbit is a highly accessible animal model which is regularly employed in biomedical research. However, the paucity of rabbit-specific reagents available limits its use in certain fields. Specifically, the lack of a reliable T cell assay has limited its employment in immune prophylactic and therapeutic studies. To address this inadequacy, we have developed an ELISpot assay to detect cellular immune responses (IFN-γ production) after antigenic stimulation. We have applied this assay to model the T cell responses elicited by a DNA vaccine. Immunization with an influenza nucleoprotein (NP) DNA vaccine revealed strong antigen-specific T cell responses in the peripheral blood mononuclear cell population. We believe this is the first report of such an assay in rabbit species, and it will become a useful tool to monitor in vivo responses to vaccines and permit the wider adoption of this model to measure immunological responses.

Broad cross-protective anti-hemagglutination responses elicited by influenza microconsensus DNA vaccine

Despite the routine development and distribution of seasonal influenza vaccines, influenza remains an important pathogen contributing to significant human morbidity as well as mortality each year. The seasonal variability of influenza creates a significant issue for vaccine development of seasonal strains that can afford protection from infection or disease based on serotype matching. It is appreciated that the globular head of the HA antigen contained in the vaccines generates antibodies that result in HAI activity that are a major correlates of the protection against a particular strain. Due to seasonal genetic changes in the HA protein, however, new vaccine strains are needed to be developed continually to match the new HA antigen of that seasons virus. A distinct advantage in seasonal vaccine development would be if a small group of antigens could be developed that could span many seasons without needed to be replaced due to this genetic drift. Here we report on a synthetic microconsensus approach that relies on a small collection of 4 synthetic H1HA DNA antigens which together induce broad protective HAI immunity spanning decades of H1 influenza viruses in mice, guinea pigs and non-human primates. The protective HAI titers induced by microconsensus immunogens are fully functional in vivo as immunized ferrets were completely protected from A/Mexico/InDRE4487/2009 virus infection and morbidity associated with lethal challenge. These results are encouraging that a limited easy-to-formulate collection of invariant antigens can be developed which can span seasonal vaccine changes allowing for continued immune protection.

Broadened immunity against influenza by vaccination with computationally designed influenza virus N1 neuraminidase constructs

Split inactivated influenza vaccines remain one of the primary preventative strategies against severe influenza disease in the population. However, current vaccines are only effective against a limited number of matched strains. The need for broadly protective vaccines is acute due to the high mutational rate of influenza viruses and multiple strain variants in circulation at any one time. The neuraminidase (NA) glycoprotein expressed on the influenza virion surface has recently regained recognition as a valuable vaccine candidate. We sought to broaden the protection provided by NA within the N1 subtype by computationally engineering consensus NA sequences. Three NA antigens (NA5200, NA7900, NA9100) were designed based on sequence clusters encompassing three major groupings of NA sequence space; (i) H1N1 2009 pandemic and Swine H1N1, (ii) historical seasonal H1N1 and (iii) H1N1 viruses ranging from 1933 till current times. Recombinant NA proteins were produced as a vaccine and used in a mouse challenge model. The design of the protein dictated the protection provided against the challenge strains. NA5200 protected against H1N1 pdm09, a Swine isolate from 1998 and NIBRG-14 (H5N1). NA7900 protected against all seasonal H1N1 viruses tested, and NA9100 showed the broadest range of protection covering all N1 viruses tested. By passive transfer studies and serological assays, the protection provided by the cluster-based consensus (CBC) designs correlated to antibodies capable of mediating NA inhibition. Importantly, sera raised to the consensus NAs displayed a broader pattern of reactivity and protection than naturally occurring NAs, potentially supporting a predictive approach to antigen design.

The high variability of the influenza virus — arising from its high mutation rate and wide range of strains — limits the effectiveness of influenza vaccines unless they induce a broad immune response, a difficult task when relying on natural viral antigens. Here, Xavier Saelens, Thorsten Vogel, Ray Oomen and colleagues applied a ‘cluster-based’ consensus computational approach to design three consensus sequences of the viral protein neuroaminidase (NA) subtype 1 that induce broadly protective immune responses in vaccinated mice. NA9100, a consensus NA sequence based on H1N1 virus strains collected from 1933 to today, was protective against all N1 viruses tested. By using a computational method to integrate multiple sequences of viral proteins into one consensus protein, the researchers provide a strategy that can be applied to develop broadly protective vaccine formulations for influenza virus.

A Synthetic Micro-Consensus DNA Vaccine Generates Comprehensive Influenza A H3N2 Immunity and Protects Mice Against Lethal Challenge by Multiple H3N2 Viruses

Influenza A H3N2 viruses circulate globally, leading to substantial morbidity and mortality. Commercially available, antigen-matched influenza vaccines must be updated frequently to match dynamic sequence variability in immune epitopes, especially within viral influenza A H3N2 hemagglutinin (H3). In an effort to create comprehensive immune responses against H3N2, four micro-consensus antigens were designed to mimic the sequence and antigenic diversity of H3. Synthetic plasmid DNA constructs were developed to express each micro-consensus immunogen and combined into a multi-antigen DNA vaccine cocktail, pH3HA. Facilitated delivery of pH3HA via intramuscular electroporation in mice induced comprehensive, potent humoral responses against diverse seasonal H3N2 viruses that circulated between 1968 and the present. Vaccination with pH3HA also induced an antigen-specific cellular cytokine response. Mice immunized with pH3HA were protected against lethal challenge using two distinct H3N2 viruses, highlighting the heterologous protection afforded by synthetic micro-consensus immunogens. These findings warrant further study of the DNA vaccine micro-consensus platform for broad protection against influenza viruses.

Delineating the Cellular Mechanisms Associated with Skin Electroporation

The immune responses elicited following delivery of DNA vaccines to the skin has previously been shown to be significantly enhanced by the addition of electroporation (EP) to the treatment protocol. Principally, EP increases the transfection of plasmid DNA (pDNA) into the resident skin cells. In addition to increasing the levels of in vivo transfection, the physical insult induced by EP is associated with activation of innate pathways which are believed to mediate an adjuvant effect, further enhancing DNA vaccine responses. We investigated the possible mechanisms associated with this adjuvant effect, primarily focusing on the cell death pathways associated with the skin EP procedure independent of pDNA delivery. Using the minimally invasive CELLECTRA^®-3P intradermal electroporation device that penetrates the epidermal and dermal layers of the skin, we have investigated apoptotic and necrotic cell death in relation to the vicinity of the electrode needles and electric field generated. Employing the well-established terminal deoxynucleotidyl transferase nick-end labeling assay, we detected apoptosis beginning as early as one hour after EP and peaking at the 4 h time point. The majority of the apoptotic events were detected in the epidermal region directly adjacent to the electrode needle. Using a novel propidium iodide in vivo necrotic cell death assay, we detected necrotic events concentrated in the epidermal region adjacent to the electrode. Furthermore, we detected upregulation of calreticulin expression on skin cells after EP, thus labeling these cells for uptake by dendritic cells and macrophages. These results allow us to delineate the cell death mechanisms occurring in the skin following intradermal EP independently of pDNA delivery. We believe these events contribute to the adjuvant effect observed following electroporation at the skin treatment site.

Avian Influenza A Virus Pandemic Preparedness and Vaccine Development

Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses.

Multigenic DNA vaccine induces protective cross-reactive T cell responses against heterologous influenza virus in nonhuman primates

Recent avian and swine-origin influenza virus outbreaks illustrate the ongoing threat of influenza pandemics. We investigated immunogenicity and protective efficacy of a multi-antigen (MA) universal influenza DNA vaccine consisting of HA, M2, and NP antigens in cynomolgus macaques. Following challenge with a heterologous pandemic H1N1 strain, vaccinated animals exhibited significantly lower viral loads and more rapid viral clearance when compared to unvaccinated controls. The MA DNA vaccine induced robust serum and mucosal antibody responses but these high antibody titers were not broadly neutralizing. In contrast, the vaccine induced broadly-reactive NP specific T cell responses that cross-reacted with the challenge virus and inversely correlated with lower viral loads and inflammation. These results demonstrate that a MA DNA vaccine that induces strong cross-reactive T cell responses can, independent of neutralizing antibody, mediate significant cross-protection in a nonhuman primate model and further supports development as an effective approach to induce broad protection against circulating and emerging influenza strains.

Efficacy of an Adenoviral Vectored Multivalent Centralized Influenza Vaccine

Mice were immunized with Adenovirus expressing the H1-con, H2-con, H3-con and H5-con HA consensus genes in combination (multivalent) and compared to mice immunized with the traditional 2010-2011 FluZone and FluMist seasonal vaccines. Immunized mice were challenged with 10-100 MLD50 of H1N1, H3N1, H3N2 and H5N1 influenza viruses. The traditional vaccines induced robust levels of HA inhibition (HI) titers, but failed to protect against five different heterologous lethal influenza challenges. Conversely, the multivalent consensus vaccine (1 × 1010 virus particles (vp)/mouse) induced protective HI titers of ≥40 against 8 of 10 influenza viruses that represent a wide degree of divergence within the HA subtypes and protected 100% of mice from 8 of 9 lethal heterologous influenza virus challenges. The vaccine protection was dose dependent, in general, and a dose as low as 5 × 107 vp/mouse still provided 100% survival against 7 of 9 lethal heterologous influenza challenges. These data indicate that very low doses of Adenovirus-vectored consensus vaccines induce superior levels of immunity against a wide divergence of influenza subtypes as compared to traditional vaccines. These doses are scalable and translatable to humans and may provide the foundation for complete and long-lasting anti-influenza immunity.

Vaccine approaches conferring cross-protection against influenza viruses

INTRODUCTION

Annual vaccination is one of the most efficient and cost-effective strategies to prevent and control influenza epidemics. Most of the currently available influenza vaccines are strong inducers of antibody responses against viral surface proteins, hemagglutinin (HA) and neuraminidase (NA), but are poor inducers of cell-mediated immune responses against conserved internal proteins. Moreover, due to the high variability of viral surface proteins because of antigenic drift or antigenic shift, many of the currently licensed vaccines confer little or no protection against drift or shift variants. Areas covered: Next generation influenza vaccines that can induce humoral immune responses to receptor-binding epitopes as well as broadly neutralizing conserved epitopes, and cell-mediated immune responses against highly conserved internal proteins would be effective against variant viruses as well as a novel pandemic influenza until circulating strain-specific vaccines become available. Here we discuss vaccine approaches that have the potential to provide broad spectrum protection against influenza viruses. Expert commentary: Based on current progress in defining cross-protective influenza immunity, it seems that the development of a universal influenza vaccine is feasible. It would revolutionize the strategy for influenza pandemic preparedness, and significantly impact the shelf-life and protection efficacy of seasonal influenza vaccines.

Electroporation as a vaccine delivery system and a natural adjuvant to intradermal administration of plasmid DNA in macaques

In vivo electroporation (EP) is used to enhance the uptake of nucleic acids and its association with DNA vaccination greatly stimulates immune responses to vaccine antigens delivered through the skin. However, the effect of EP on cutaneous cell behavior, the dynamics of immune cell recruitment and local inflammatory factors, have not been fully described. Here, we show that intradermal DNA vaccination combined with EP extends antigen expression to the epidermis and the subcutaneous skin muscle in non-human primates. In vivo fibered confocal microscopy and dynamic ex vivo imaging revealed that EP promotes the mobility of Langerhans cells (LC) and their interactions with transfected cells prior to their migration from the epidermis. At the peak of vaccine expression, we detected antigen in damaged keratinocyte areas in the epidermis and we characterized recruited immune cells in the skin, the hypodermis and the subcutaneous muscle. EP alone was sufficient to induce the production of pro-inflammatory cytokines in the skin and significantly increased local concentrations of Transforming Growth Factor (TGF)-alpha and IL-12. Our results show the kinetics of inflammatory processes in response to EP of the skin, and reveal its potential as a vaccine adjuvant.

Development of an intradermal DNA vaccine delivery strategy to achieve single-dose immunity against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a massive medical burden in infants, children and the elderly worldwide, and an effective, safe RSV vaccine remains an unmet need. Here we assess a novel vaccination strategy based on the intradermal delivery of a SynCon® DNA-based vaccine encoding engineered RSV-F antigen using a surface electroporation device (SEP) to target epidermal cells, in clinically relevant experimental models. We demonstrate the ability of this strategy to elicit robust immune responses. Importantly we demonstrate complete resistance to pulmonary infection at a single low dose of vaccine in the cotton rat RSV/A challenge model. In contrast to the formalin-inactivated RSV (FI-RSV) vaccine, there was no enhanced lung inflammation upon virus challenge after DNA vaccination. In summary the data presented outline the pre-clinical development of a highly efficacious, tolerable and safe non-replicating vaccine delivery strategy.

Strategies to induce broadly protective antibody responses to viral glycoproteins

INTRODUCTION

Currently, several universal/broadly protective influenza virus vaccine candidates are under development. Many of these vaccines are based on strategies to induce protective antibody responses against the surface glycoproteins of antigenically and genetically diverse influenza viruses. These strategies might also be applicable to surface glycoproteins of a broad range of other important viral pathogens. Areas covered: Common strategies include sequential vaccination with divergent antigens, multivalent approaches, vaccination with glycan-modified antigens, vaccination with minimal antigens and vaccination with antigens that have centralized/optimized sequences. Here we review these strategies and the underlying concepts. Furthermore, challenges, feasibility and applicability to other viral pathogens are discussed. Expert commentary: Several broadly protective/universal influenza virus vaccine strategies will be tested in humans in the coming years. If successful in terms of safety and immunological readouts, they will move forward into efficacy trials. In the meantime, successful vaccine strategies might also be applied to other antigenically diverse viruses of concern.

Immunogenicity and Protective Efficacy of the DAR-901 Booster Vaccine in a Murine Model of Tuberculosis

Background

The development of a novel tuberculosis vaccine is a leading global health priority. SRL172, an inactivated, whole-cell mycobacterial vaccine, was safe, immunogenic and reduced the incidence of culture-confirmed tuberculosis in a phase III trial in HIV-infected and BCG immunized adults in Tanzania. Here we describe the immunogenicity and protective efficacy of DAR-901, a booster vaccine against tuberculosis manufactured from the same seed strain using a new scalable method.

Methods

We evaluated IFN-γ responses by ELISpot and antibody responses by enzyme linked immunosorbent assay in C57BL/6 and BALB/c mice after three doses of DAR-901. In an aerosol challenge model, we evaluated the protective efficacy of the DAR-901 booster in C57BL/6 mice primed with BCG and boosted with two doses of DAR-901 at 4 dosage levels in comparison with homologous BCG boost.

Results

DAR-901 vaccination elicited IFN-γ responses to mycobacterial antigen preparations derived from both DAR-901 and Mycobacterium tuberculosis. DAR-901 immunization enhanced antibody responses to DAR-901 but not Mycobacterium tuberculosis lysate or purified protein derivative. Among animals primed with BCG, boosting with DAR-901 at 1 mg provided greater protection against aerosol challenge than a homologous BCG boost (lungs P = 0.036, spleen P = 0.028).

Conclusions

DAR-901 induces cellular and humoral immunity and boosts protection from M. tuberculosis compared to a homologous BCG boost.

Advances in novel influenza vaccines: a patent review

The threat of a major human influenza pandemic such as the avian H5N1 or the 2009 new H1N1 has emphasized the need for effective prevention strategies to combat these pathogens. Although egg based influenza vaccines have been well established for a long time, it remains an ongoing public health need to develop alternative production methods that ensures improved safety, efficacy, and ease of administration compared with conventional influenza vaccines. This article is intended to cover some of the recent advances and related patents on the development of influenza vaccines including live attenuated, cell based, genomic and synthetic peptide vaccines.

Novel synthetic plasmid and Doggybone DNA vaccines induce neutralizing antibodies and provide protection from lethal influenza challenge in mice

Nucleic acid-based vaccines (NAVs) are a promising alternative to conventional influenza vaccines with the potential to increase influenza vaccine availability due to their simplicity in design and rapid speed of production. NAVs can also target multiple influenza antigens and control flu variants. Traditionally NAVs have been DNA plasmids however, we are continuing to explore new methods that may enhance vaccine efficacy. Recently new focus has been on RNA cassettes as NAVs. RNA vaccines combine conceptual advantages in that they focus on delivery of only the coding cassette. However, RNA vaccines have a short half-life and cause interferon-induced fevers. Here we describe a new NAV approach where we study delivery of a linear DNA cassette [Doggybone™ linear closed DNA [(dbDNA™)] produced by an enzymatic process that yields an antigen expression cassette comprising a promoter, DNA antigen, poly A tail, and telomeric ends. This focused approach has many of the advantages of plasmid DNA as well as a minimal cassette size similar to RNA strategies. For this study, we characterized the specific CD4⁺ and CD8⁺ T cell responses and determined the hemagglutination inhibition (HI) titers induced by dbDNA™ and compared the responses with those of an optimized plasmid DNA (pDNA) vaccine encoding the same H1N1 influenza A/PR/8/34 HA gene. Immunizations with the constructs resulted in similar humoral and cellular immune responses. Both constructs induced high-titer HI antibodies and fully protected animals from lethal viral challenge. The data obtained from this study provides important validation for further development of novel vector approaches.

Rapid and Long-Term Immunity Elicited by DNA-Encoded Antibody Prophylaxis and DNA Vaccination Against Chikungunya Virus

Background. Vaccination and passive antibody therapies are critical for controlling infectious diseases. Passive antibody administration has limitations, including the necessity for purification and multiple injections for efficacy. Vaccination is associated with a lag phase before generation of immunity. Novel approaches reported here utilize the benefits of both methods for the rapid generation of effective immunity.

Methods. A novel antibody-based prophylaxis/therapy entailing the electroporation-mediated delivery of synthetic DNA plasmids encoding biologically active anti–chikungunya virus (CHIKV) envelope monoclonal antibody (dMAb) was designed and evaluated for antiviral efficacy, as well as for the ability to overcome shortcomings inherent with conventional active vaccination and passive immunotherapy.

Results. One intramuscular injection of dMAb produced antibodies in vivo more rapidly than active vaccination with an anti-CHIKV DNA vaccine. This dMAb neutralized diverse CHIKV clinical isolates and protected mice from viral challenge. Combination of dMAb and the CHIKV DNA vaccine afforded rapid and long-lived protection.

Conclusions. A DNA-based dMAb strategy induced rapid protection against an emerging viral infection. This method can be combined with DNA vaccination as a novel strategy to provide both short- and long-term protection against this emerging infectious disease. These studies have implications for pathogen treatment and control strategies.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This article describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

DNA-based influenza vaccines as immunoprophylactic agents toward universality

Influenza is an illness of global public health concern. Influenza viruses have been responsible for several pandemics affecting humans. Current influenza vaccines have proved satisfactory safety; however, they have limitations and do not provide protection against unexpected emerging influenza virus strains. Therefore, there is an urgent need for alternative approaches to conventional influenza vaccines. The development of universal influenza vaccines will help alleviate the severity of influenza pandemics. Influenza DNA vaccines have been the subject of many studies over the past decades due to their ability to induce broad-based protective immune responses in various animal models. The present review highlights the recent advances in influenza DNA vaccine research and its potential as an affordable universal influenza vaccine.

Centralized Consensus Hemagglutinin Genes Induce Protective Immunity against H1, H3 and H5 Influenza Viruses

With the exception of the live attenuated influenza vaccine there have been no substantial changes in influenza vaccine strategies since the 1940’s. Here we report an alternative vaccine approach that uses Adenovirus-vectored centralized hemagglutinin (HA) genes as vaccine antigens. Consensus H1-Con, H3-Con and H5-Con HA genes were computationally derived. Mice were immunized with Ad vaccines expressing the centralized genes individually. Groups of mice were vaccinated with 1 X 10¹⁰, 5 X 10⁷ and 1 X 10⁷ virus particles per mouse to represent high, intermediate and low doses, respectively. 100% of the mice that were vaccinated with the high dose vaccine were protected from heterologous lethal challenges within each subtype. In addition to 100% survival, there were no signs of weight loss and disease in 7 out of 8 groups of high dose vaccinated mice. Lower doses of vaccine showed a reduction of protection in a dose-dependent manner. However, even the lowest dose of vaccine provided significant levels of protection against the divergent influenza strains, especially considering the stringency of the challenge virus. In addition, we found that all doses of H5-Con vaccine were capable of providing complete protection against mortality when challenged with lethal doses of all 3 H5N1 influenza strains. This data demonstrates that centralized H1-Con, H3-Con and H5-Con genes can be effectively used to completely protect mice against many diverse strains of influenza. Therefore, we believe that these Ad-vectored centralized genes could be easily translated into new human vaccines.

Developing Universal Influenza Vaccines: Hitting the Nail, Not Just on the Head

Influenza viruses have a huge impact on public health. Current influenza vaccines need to be updated annually and protect poorly against antigenic drift variants or novel emerging subtypes. Vaccination against influenza can be improved in two important ways, either by inducing more broadly protective immune responses or by decreasing the time of vaccine production, which is relevant especially during a pandemic outbreak. In this review, we outline the current efforts to develop so-called “universal influenza vaccines”, describing antigens that may induce broadly protective immunity and novel vaccine production platforms that facilitate timely availability of vaccines.

Ferret models of viral pathogenesis

Emerging and well-known viral diseases remain one the most important global public health threats. A better understanding of their pathogenesis and mechanisms of transmission requires animal models that accurately reproduce these aspects of the disease. Here we review the role of ferrets as an animal model for the pathogenesis of different respiratory viruses with an emphasis on influenza and paramyxoviruses. We will describe the anatomic and physiologic characteristics that contribute to the natural susceptibility of ferrets to these viruses, and provide an overview of the approaches available to analyze their immune responses. Recent insights gained using this model will be highlighted, including the development of new prophylactic and therapeutic approaches. To provide decision criteria for the use of this animal model, its strengths and limitations will be discussed.

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Ferrets as models for respiratory virus pathogenesis.

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Ferrets as models for vaccine and drug efficacy assessment.

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Immunological tools for ferrets.

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Housing and handling of ferrets.

The use of nonhuman primates in research on seasonal, pandemic and avian influenza, 1893-2014

Attempts to reproduce the features of human influenza in laboratory animals date from the early 1890s, when Richard Pfeiffer inoculated apes with bacteria recovered from influenza patients and produced a mild respiratory illness. Numerous studies employing nonhuman primates (NHPs) were performed during the 1918 pandemic and the following decade. Most used bacterial preparations to infect animals, but some sought a filterable agent for the disease. Since the viral etiology of influenza was established in the early 1930s, studies in NHPs have been supplemented by a much larger number of experiments in mice, ferrets and human volunteers. However, the emergence of a novel swine-origin H1N1 influenza virus in 1976 and the highly pathogenic H5N1 avian influenza virus in 1997 stimulated an increase in NHP research, because these agents are difficult to study in naturally infected patients and cannot be administered to human volunteers. In this paper, we review the published literature on the use of NHPs in influenza research from 1893 through the end of 2014. The first section summarizes observational studies of naturally occurring influenza-like syndromes in wild and captive primates, including serologic investigations. The second provides a chronological account of experimental infections of NHPs, beginning with Pfeiffer's study and covering all published research on seasonal and pandemic influenza viruses, including vaccine and antiviral drug testing. The third section reviews experimental infections of NHPs with avian influenza viruses that have caused disease in humans since 1997. The paper concludes with suggestions for further studies to more clearly define and optimize the role of NHPs as experimental animals for influenza research.

Tapping the Potential of DNA Delivery with Electroporation for Cancer Immunotherapy

Cancer is a worldwide leading cause of death, and current conventional therapies are limited. The search for alternative preventive or therapeutic solutions is critical if we are going to improve outcomes for patients. The potential for DNA vaccines in the treatment and prevention of cancer has gained great momentum since initial findings almost 2 decades ago that revealed that genetically engineered DNA can elicit an immune response. The combination of adjuvants and an effective delivery method such as electroporation is overcoming past setbacks for naked plasmid DNA (pDNA) as a potential preventive or therapeutic approach to cancer in large animals and humans. In this chapter, we aim to focus on the novel advances in recent years for DNA cancer vaccines, current preclinical data, and the importance of adjuvants and electroporation with emphasis on prostate, melanoma, and cervical cancer.

Activated CD4+CCR5+ T cells in the rectum predict increased SIV acquisition in SIVGag/Tat-vaccinated rhesus macaques

An effective T-cell-based AIDS vaccine should induce strong HIV-specific CD8(+) T cells in mucosal tissues without increasing the availability of target cells for the virus. Here, we evaluated five immunization strategies that include Human adenovirus-5 (AdHu5), Chimpanzee adenovirus-6 (AdC6) or -7 (AdC7), Vaccinia virus (VV), and DNA given by electroporation (DNA/EP), all expressing Simian immunodeficiency virus group specific antigen/transactivator of transcription (SIV(mac239Gag/Tat)). Five groups of six rhesus macaques (RMs) each were vaccinated with DNA/EP-AdC6-AdC7, VV-AdC6-AdC7, DNA/-EP-VV-AdC6, DNA/EP-VV-AdC7, or AdHu5-AdHu5-AdHu5 and were challenged repeatedly with low-dose intrarectal SIVmac239. Upon challenge, there were no significant differences among study groups in terms of virus acquisition or viral load after infection. When taken together, the immunization regimens did not protect against SIV acquisition compared with controls but did result in an ∼ 1.6-log decline in set-point viremia. Although all immunized RMs had detectable SIV-specific CD8(+) T cells in blood and rectal mucosa, we found no correlation between the number or function of these SIV-specific CD8(+) T cells and protection against SIV acquisition. Interestingly, RMs experiencing breakthrough infection showed significantly higher prechallenge levels of CD4(+)C-C chemokine receptor type 5 (CCR5)(+)HLA-DR(+) T cells in the rectal biopsies (RB) than animals that remained uninfected. In addition, among the infected RMs, the percentage of CD4(+)CCR5(+)Ki-67(+) T cells in RBs prechallenge correlated with higher early viremia. Overall, these data suggest that the levels of activated CD4(+)CCR5(+) target T cells in the rectal mucosa may predict the risk of SIV acquisition in RMs vaccinated with vectors that express SIVGag/Tat.

A multi-head intradermal electroporation device allows for tailored and increased dose DNA vaccine delivery to the skin

The identification of an effective and tolerable delivery method is a necessity for the success of DNA vaccines in the clinic. This manuscript describes the development and validation of a multi-headed intradermal electroporation device which would be applicable for delivering multiple DNA vaccine plasmids simultaneously but spatially separated. Reporter gene plasmids expressing green and red fluorescent proteins were used to demonstrate the impact of spatial separation on DNA delivery to increase the number of transfected cells and avoid interference through visible expression patterns. To investigate the impact of plasmid interference on immunogenicity, a disease target was investigated where issues with multi-valent vaccines had been previously described. DNA-based Hantaan and Puumala virus vaccines were delivered separately or as a combination and the effect of multi-valence was determined by appropriate assays. While a negative impact was observed for both antigenic vaccines when delivered together, these effects were mitigated when the vaccine was delivered using the multi-head device. We also demonstrate how the multi-head device facilitates higher dose delivery to the skin resulting in improved immune responses. This new multi-head platform device is an efficient, tolerable and non-invasive method to deliver multiple plasmid DNA constructs simultaneously allowing the tailoring of delivery sites for combination vaccines. Additionally, this device would allow the delivery of multi-plasmid vaccine formulations without risk of impacted immune responses through interference. Such a low-cost, easy to use device platform for the delivery of multi-agent DNA vaccines would have direct applications by the military and healthcare sectors for mass vaccination purposes.

Co-Administration of Molecular Adjuvants Expressing NF-Kappa B Subunit p65/RelA or Type-1 Transactivator T-bet Enhance Antigen Specific DNA Vaccine-Induced Immunity

DNA vaccine-induced immunity can be enhanced by the co-delivery of synthetic gene-encoding molecular adjuvants. Many of these adjuvants have included cytokines, chemokines or co-stimulatory molecules that have been demonstrated to enhance vaccine-induced immunity by increasing the magnitude or type of immune responses and/or protective efficacy. In this way, through the use of adjuvants, immune responses can be highly customizable and functionally tailored for optimal efficacy against pathogen specific (i.e., infectious agent) or non-pathogen (i.e., cancer) antigens. In the novel study presented here, we examined the use of cellular transcription factors as molecular adjuvants. Specifically the co-delivery of (a) RelA, a subunit of the NF-κB transcription complex or (b) T-bet, a T_h1-specific T box transcription factor, along with a prototypical DNA vaccine expressing HIV-1 proteins was evaluated. As well, all of the vaccines and adjuvants were administered to mice using in vivo electroporation (EP), a technology demonstrated to dramatically increase plasmid DNA transfection and subsequent transgene expression with concomitant enhancement of vaccine induced immune responses. As such, this study demonstrated that co-delivery of either adjuvant resulted in enhanced T and B cell responses, specifically characterized by increased T cell numbers, IFN-γ production, as well as enhanced antibody responses. This study demonstrates the use of cellular transcription factors as adjuvants for enhancing DNA vaccine-induced immunity.

A blueprint for DNA vaccine design

Although safety concerns have been overcome, lower immunogenicity profiles of DNA vaccines have hindered their progress in humans. DNA vaccines need to make up for this limitation by altering plasmid construction through vector design innovations intended for enhancement of transgene expression and immunogenicity. The next-generation vectors also address safety issues such as selection markers. This chapter discusses (a) plasmid backbone design, (b) enhancement of antigenic protein expression and immunogenicity, and (c) vector modification to increase innate immunity. Modifications of the basic design, when combined with improved delivery devices and/or prime/boost regimens, may enhance DNA vaccine performance and clinical outcomes.

HIV-1 Env DNA vaccine plus protein boost delivered by EP expands B- and T-cell responses and neutralizing phenotype in vivo

An effective HIV vaccine will most likely require the induction of strong T-cell responses, broadly neutralizing antibodies (bNAbs), and the elicitation of antibody-dependent cellular cytotoxicity (ADCC). Previously, we demonstrated the induction of strong HIV/SIV cellular immune responses in macaques and humans using synthetic consensus DNA immunogens delivered via adaptive electroporation (EP). However, the ability of this improved DNA approach to prime for relevant antibody responses has not been previously studied. Here, we investigate the immunogenicity of consensus DNA constructs encoding gp140 sequences from HIV-1 subtypes A, B, C and D in a DNA prime-protein boost vaccine regimen. Mice and guinea pigs were primed with single- and multi-clade DNA via EP and boosted with recombinant gp120 protein. Sera were analyzed for gp120 binding and induction of neutralizing antibody activity. Immunization with recombinant Env protein alone induced low-titer binding antibodies with limited neutralization breath. In contrast, the synthetic DNA prime-protein boost protocol induced significantly higher antibody binding titers. Furthermore, sera from DNA prime-protein boost groups were able to neutralize a broader range of viruses in a panel of tier 1 clade B viruses as well as multiple tier 1 clade A and clade C viruses. Further investigation of synthetic DNA prime plus adaptive EP plus protein boost appears warranted.

New Orf virus (Parapoxvirus) recombinant expressing H5 hemagglutinin protects mice against H5N1 and H1N1 influenza A virus

Previously we demonstrated the versatile utility of the Parapoxvirus Orf virus (ORFV) as a vector platform for the development of potent recombinant vaccines. In this study we present the generation of new ORFV recombinants expressing the hemagglutinin (HA) or nucleoprotein (NP) of the highly pathogenic avian influenza virus (HPAIV) H5N1. Correct foreign gene expression was examined in vitro by immunofluorescence, Western blotting and flow cytometry. The protective potential of both recombinants was evaluated in the mouse challenge model. Despite adequate expression of NP, the recombinant D1701-V-NPh5 completely failed to protect mice from lethal challenge. However, the H5 HA-expressing recombinant D1701-V-HAh5n mediated solid protection in a dose-dependent manner. Two intramuscular (i.m.) injections of the HA-expressing recombinant protected all animals from lethal HPAIV infection without loss of body weight. Notably, the immunized mice resisted cross-clade H5N1 and heterologous H1N1 (strain PR8) influenza virus challenge. In vivo antibody-mediated depletion of CD4-positive and/or CD8-posititve T-cell subpopulations during immunization and/or challenge infection implicated the relevance of CD4-positive T-cells for induction of protective immunity by D1701-V-HAh5n, whereas the absence of CD8-positive T-cells did not significantly influence protection. In summary, this study validates the potential of the ORFV vectored vaccines also to combat HPAIV.

New vaccines against influenza virus

Vaccination is one of the most effective and cost-benefit interventions that prevent the mortality and reduce morbidity from infectious pathogens. However, the licensed influenza vaccine induces strain-specific immunity and must be updated annually based on predicted strains that will circulate in the upcoming season. Influenza virus still causes significant health problems worldwide due to the low vaccine efficacy from unexpected outbreaks of next epidemic strains or the emergence of pandemic viruses. Current influenza vaccines are based on immunity to the hemagglutinin antigen that is highly variable among different influenza viruses circulating in humans and animals. Several scientific advances have been endeavored to develop universal vaccines that will induce broad protection. Universal vaccines have been focused on regions of viral proteins that are highly conserved across different virus subtypes. The strategies of universal vaccines include the matrix 2 protein, the hemagglutinin HA2 stalk domain, and T cell-based multivalent antigens. Supplemented and/or adjuvanted vaccination in combination with universal target antigenic vaccines would have much promise. This review summarizes encouraging scientific advances in the field with a focus on novel vaccine designs.

DNA vaccine cocktail expressing genotype A and C HBV surface and consensus core antigens generates robust cytotoxic and antibody responses in mice and Rhesus macaques

There are well over a quarter of a billion chronic hepatitis B virus (HBV) carriers across the globe. Most carriers are at high risk for development of liver cirrhosis and subsequent progression to hepatocellular carcinoma. It is therefore imperative to develop new approaches for immunotherapy against this infection. Antibodies and cytotoxic T cells to different HBV antigens are believed to be important for reducing viral load and clearing HBV-infected cells from the liver. Some of the major challenges facing current vaccine candidates have been their inability to induce both humoral and cellular immunity to multiple antigenic targets and the induction of potent immune responses against the major genotypes of HBV. In this study, highly optimized synthetic DNA plasmids against the HBV consensus core (HBc) and surface (HBs) antigens genotypes A and C were developed and evaluated for their immune potential. These plasmids, which encode the most prevalent genotypes of the virus, were observed to individually induce binding antibodies to HBs antigens and drove robust cell-mediated immunity in animal models. Similar responses to both HBc and HBs antigens were observed when mice and non-human primates were inoculated with the HBc-HBs cocktails. In addition to the cytotoxic T lymphocyte activities exhibited by the immunized mice, the vaccine-induced responses were broadly distributed across multiple antigenic epitopes. These elements are believed to be important to develop an effective therapeutic vaccine. These data support further evaluation of multivalent synthetic plasmids as therapeutic HBV vaccines.

H5N1 vaccines in humans

The spread of highly pathogenic avian H5N1 influenza viruses since 1997 and their virulence for poultry and humans has raised concerns about their potential to cause an influenza pandemic. Vaccines offer the most viable means to combat a pandemic threat. However, it will be a challenge to produce, distribute and implement a new vaccine if a pandemic spreads rapidly. Therefore, efforts are being undertaken to develop pandemic vaccines that use less antigen and induce cross-protective and long-lasting responses, that can be administered as soon as a pandemic is declared or possibly even before, in order to prime the population and allow for a rapid and protective antibody response. In the last few years, several vaccine manufacturers have developed candidate pandemic and pre-pandemic vaccines, based on reverse genetics and have improved the immunogenicity by formulating these vaccines with different adjuvants. Some of the important and consistent observations from clinical studies with H5N1 vaccines are as follows: two doses of inactivated vaccine are generally necessary to elicit the level of immunity required to meet licensure criteria, less antigen can be used if an oil-in-water adjuvant is included, in general antibody titers decline rapidly but can be boosted with additional doses of vaccine and if high titers of antibody are elicited, cross-reactivity against other clades is observed. Prime-boost strategies elicit a more robust immune response. In this review, we discuss data from clinical trials with a variety of H5N1 influenza vaccines. We also describe studies conducted in animal models to explore the possibility of reassortment between pandemic live attenuated vaccine candidates and seasonal influenza viruses, since this is an important consideration for the use of live vaccines in a pandemic setting.

Protein engineering strategies for the development of viral vaccines and immunotherapeutics

Vaccines that elicit a protective broadly neutralizing antibody (bNAb) response and monoclonal antibody therapies are critical for the treatment and prevention of viral infections. However, isolation of protective neutralizing antibodies has been challenging for some viruses, notably those with high antigenic diversity or those that do not elicit a bNAb response in the course of natural infection. Here, we discuss recent work that employs protein engineering strategies to design immunogens that elicit bNAbs or engineer novel bNAbs. We highlight the use of rational, computational, and combinatorial strategies and assess the potential of these approaches for the development of new vaccines and immunotherapeutics.

Influenza virus M2e with additional cysteine residues shows enhanced immunogenicity and protection against lethal virus challenge

The amino acid sequence of the extracellular domain of matrix protein 2 (M2e) is conserved among all subtypes of influenza A viruses. Therefore, the M2e peptide can be considered as a target antigen for the development of a universal influenza vaccine. We evaluated the effects of adding cysteine residues to a peptide of amino acids 2-24 of M2e. Mice immunized with some of these peptides containing one, two, three, four, or five extra cysteines displayed enhanced antibody titers to M2e. In addition, immunization with a peptide containing three extra cysteines, along with an aluminum adjuvant, protected mice more effectively against a lethal influenza virus challenge than the original M2e peptide. These results indicated that an M2e peptide containing additional cysteine residues could be a universal influenza vaccine candidate even without the addition of strong adjuvants.

Induction of broad cytotoxic T cells by protective DNA vaccination against Marburg and Ebola

Marburg and Ebola hemorrhagic fevers have been described as the most virulent viral diseases known to man due to associative lethality rates of up to 90%. Death can occur within days to weeks of exposure and there is currently no licensed vaccine or therapeutic. Recent evidence suggests an important role for antiviral T cells in conferring protection, but little detailed analysis of this response as driven by a protective vaccine has been reported. We developed a synthetic polyvalent-filovirus DNA vaccine against Marburg marburgvirus (MARV), Zaire ebolavirus (ZEBOV), and Sudan ebolavirus (SUDV). Preclinical efficacy studies were performed in guinea pigs and mice using rodent-adapted viruses, whereas murine T-cell responses were extensively analyzed using a novel modified assay described herein. Vaccination was highly potent, elicited robust neutralizing antibodies, and completely protected against MARV and ZEBOV challenge. Comprehensive T-cell analysis revealed cytotoxic T lymphocytes (CTLs) of great magnitude, epitopic breadth, and Th1-type marker expression. This model provides an important preclinical tool for studying protective immune correlates that could be applied to existing platforms. Data herein support further evaluation of this enhanced gene-based approach in nonhuman primate studies for in depth analyses of T-cell epitopes in understanding protective efficacy.