Modulation of the immune response induced by gene electrotransfer of a hepatitis C virus DNA vaccine in nonhuman primates

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.

Strong HCV NS3- and NS4A-specific cellular immune responses induced in mice and Rhesus macaques by a novel HCV genotype 1a/1b consensus DNA vaccine

Hepatitis C virus (HCV) represents a major health burden with more than 170 million individuals currently infected worldwide, equaling roughly 3% of the world's population. HCV preferentially infects hepatocytes and is able to persist in up to 70% of infected individuals. It is estimated that up to 30% of chronically infected individuals will go on to develop progressive liver disease as a result of HCV infection, making the virus the leading cause of liver transplantation in the world. Currently there is no vaccine for HCV. In this study, we have taken a multi-step approach to develop a novel genotype 1a/1b consensus HCV NS3/NS4A DNA vaccine able to induce strong cellular immunity. We show that this construct is able to induce strong anti-NS3/NS4A T cell responses in C57BL/6 mice, as well as, in Rhesus macaques. Our data suggest that DNA vaccines encoding HCV proteins NS3/NS4A merit further study in the context of future prophylactic and therapeutic HCV T cell based vaccines.

Macaque models of human infectious disease

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents—bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease.

Immunogenicity in mice and rabbits of DNA vaccines expressing woodchuck hepatitis virus antigens

The licensed vaccine against hepatitis B virus (HBV) is an effective means to prevent infection, but is not an effective therapeutic strategy to treat established chronic infections when used alone. In an animal model of chronic HBV infection (the woodchuck experimentally infected with woodchuck hepatitis virus (WHV)), the combination of conventional vaccine and potent antiviral drugs has shown promise as a potential therapeutic intervention. This approach might be improved further through the application of newer vaccine technologies. In the present study, we evaluated electroporation (EP)-based intramuscular (i.m.) delivery of a codon-optimized DNA vaccine for the WHV surface antigen (WHsAg) in mice and rabbits. In mice, this immunization procedure compared favorably to vaccination by i.m. injection of the DNA vaccine or i.m. administration of a recombinant WHsAg-alum vaccine, exhibiting characteristics expected to be beneficial for a therapeutic vaccine strategy. These included dose efficiency, consistency, vigorous induction of antibody responses to WHsAg, as well as a Th1 bias. Following scale-up to rabbits, a species that approximates the size of the woodchuck, the EP dosing regimen was markedly more effective than conventional i.m. injection of the DNA vaccine. Taken together, these results provide the foundation for studies of EP-based DNA immunization in the woodchuck in order to further assess its potential as an immunotherapeutic approach for treatment of chronic HBV infection in humans.

A vector-based minigene vaccine approach results in strong induction of T-cell responses specific of hepatitis C virus

Multiepitope-based vaccines against hepatitis C virus (HCV) were designed in the form of three minigenes encompassing four domains of the NS3, NS4 and NS5B proteins that contain multiple class I/II restricted epitopes. The polyEp-WT minigene encodes all four domains in fusion, the polyEp-C minigene encodes the same fusion but optimised for mammalian translation and the polyEp-E3 minigene has an additional endoplasmic reticulum targeting sequence. Whereas the minigenes vectorised by DNA were poorly immunogenic, adenovirus vectorisation induced strong and broader IFNgamma-ELISpot and CTL responses in HLA-A2 transgenic mice. In addition, polyEp-WT and polyEp-E3 responses were found cross-reactive in a recombinant Listeria-NS3-based surrogate challenge. This study illustrates the potency of vectorised minigenes in the field of HCV vaccine development.

Combined effects of IL-12 and electroporation enhances the potency of DNA vaccination in macaques

DNA vaccines are a promising technology. Historically, however, the ability of DNA vaccines to induce high response rates and strong immune responses, especially antibody responses, in non-human primates and human clinical trials has proven suboptimal. Here, we performed a pilot study in rhesus macaques to evaluate whether we could improve the immunogenicity of DNA vaccines through the use of adjuvant technology and improved delivery systems. The study consisted of four groups of animals that received: DNA by intramuscular (IM) injection, DNA with plasmid-encoded IL-12 by IM injection, DNA by IM injection with in vivo electroporation (EP), and DNA with IL-12 by IM EP. Each group was immunized three times with optimized HIV gag and env constructs. Vaccine immunogenicity was assessed by IFNgamma ELISpot, CFSE proliferation, polyfunctional flow cytometry, and antibody ELISA. Similar to previous studies, use of IL-12 as an adjuvant increased the gag and env-specific cellular responses. The use of EP to enhance plasmid delivery resulted in dramatically higher cellular as well as humoral responses. Interestingly, the use of EP to administer the DNA and IL-12 adjuvant combination resulted in the induction of higher, more efficient responses such that a 10-fold increase in antigen-specific IFNgamma(+) cells compared to IM DNA immunization was observed after a single immunization. In addition to increases in the magnitude of IFNgamma production in the initial and memory responses, the combined approach resulted in enhancements in the proliferative capacity of antigen-specific CD8(+) T cells and the amount of polyfunctional cells capable of producing IL-2 and TNFalpha in addition to IFNgamma. These data suggest that adjuvant and improved delivery methods may be able to overcome previous immunogenicity limitations in DNA vaccine technology.

New pre-pandemic influenza vaccines: an egg- and adjuvant-independent human adenoviral vector strategy induces long-lasting protective immune responses in mice

Highly pathogenic avian H5N1 influenza viruses that are currently circulating in southeast Asia may acquire the potential to cause the next influenza pandemic. A number of alternate approaches are being pursued to generate cross-protective, dose-sparing, safe, and effective vaccines, as traditional vaccine approaches, i.e., embryonated egg-grown, are not immunogenic. We developed a replication-incompetent adenoviral vector-based, adjuvant- and egg-independent pandemic influenza vaccine strategy as a potential alternative to conventional egg-derived vaccines. In this paper, we address suboptimal dose and longevity of vaccine-induced protective immunity and demonstrate that a vaccine dose as little as 1 x 10(6) plaque-forming unit (PFU) is sufficient to induce protective immune responses against a highly pathogenic H5N1 virus. Furthermore, the vaccine-induced humoral and cellular immune responses and protective immunity persisted at least for a year.

In Vivo Electroporation Enhances the Immunogenicity of Hepatitis C Virus Nonstructural 3/4A DNA by Increased Local DNA Uptake, Protein Expression, Inflammation, and Infiltration of CD3+ T Cells

The mechanisms by which in vivo electroporation (EP) improves the potency of i.m. DNA vaccination were characterized by using the hepatitis C virus nonstructural (NS) 3/4A gene. Following a standard i.m. injection of DNA with or without in vivo EP, plasmid levels peaked immediately at the site of injection and decreased by 4 logs the first week. In vivo EP did not promote plasmid persistence and, depending on the dose, the plasmid was cleared or almost cleared after 60 days. In vivo imaging and immunohistochemistry revealed that protein expression was restricted to the injection site despite the detection of significant levels of plasmid in adjacent muscle groups. In vivo EP increased and prolonged NS3/4A protein expression levels as well as an increased infiltration of CD3+ T cells at the injection site. These factors most likely additively contributed to the enhanced and broadened priming of NS3/4A-specific Abs, CD4+ T cells, CD8+ T cells, and gamma-IFN production. The primed CD8+ responses were functional in vivo, resulting in elimination of hepatitis C virus NS3/4A-expressing liver cells in transiently transgenic mice. Collectively, the enhanced protein expression and inflammation at the injection site following in vivo EP contributed to the priming of in vivo functional immune responses. These localized effects most likely help to insure that the strength and duration of the responses are maintained when the vaccine is tested in larger animals, including rabbits and humans. Thus, the combined effects mediated by in vivo EP serves as a potent adjuvant for the NS3/4A-based DNA vaccine.