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Since the early 1990s, DNA immunization has been used as a platform for developing a tetravalent dengue vaccine in response to the high priority need for protecting military personnel deployed to dengue endemic regions of the world. Several approaches have been explored ranging from naked DNA immunization to the use of live virus vectors to deliver the targeted genes for expression. Pre-clinical animal studies were largely successful in generating anti-dengue cellular and humoral immune responses that were protective either completely or partially against challenge with live dengue virus. However, Phase 1 clinical evaluation of a prototype monovalent dengue 1 DNA vaccine expressing prM and E genes revealed anti-dengue T cell IFNγ responses, but poor neutralizing antibody responses. These less than optimal results are thought to be due to poor uptake and expression of the DNA vaccine plasmids. Because DNA immunization as a vaccine platform has the advantages of ease of manufacture, flexible genetic manipulation and enhanced stability, efforts continue to improve the immunogenicity of these vaccines using a variety of methods. [ABSTRACT FROM AUTHOR]

Abstract: A prototype dengue-1 DNA vaccine was shown to be safe and immunogenic in a previous Phase 1 clinical trial. Anti-dengue-1 neutralizing antibody responses were detectable only in the group of volunteers receiving the high dose of nonadjuvanted vaccine and the antibody titers were low. Vaxfectin®, a lipid-based adjuvant, enhances the immunogenicity of DNA vaccines. We conducted a nonhuman primate study to evaluate the effect of Vaxfectin® on the immunogenicity of a tetravalent dengue DNA vaccine. Animals were immunized on days 0, 28 and 84, with each immunization consisting of 3mg of Vaxfectin®-adjuvanted tetravalent dengue DNA vaccine. The use of Vaxfectin® resulted in a significant increase in anti-dengue neutralizing antibody responses against dengue-1, -3 and -4. There was little to no effect on T cell responses as measured by interferon gamma ELISPOT assay. Animals immunized with the Vaxfectin®-formulated tetravalent DNA vaccine showed significant protection against live dengue-2 virus challenge compared to control animals (0.75 mean days of viremia vs 3.3 days). Animals vaccinated with nonadjuvanted DNA had a mean 2.0 days of viremia. These results support further evaluation of the Vaxfectin®-adjuvanted tetravalent dengue DNA vaccine in a Phase 1 clinical trial. [Copyright &y& Elsevier]