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

Induction of multispecific, functional CD4⁺ and CD8⁺ T cells is the immunological hallmark of acute self-limiting hepatitis C virus (HCV) infection in humans. In the present study, we showed that gene electrotransfer (GET) of a novel candidate DNA vaccine encoding an optimized version of the nonstructural region of HCV (from NS3 to NS5B) induced substantially more potent, broad, and long-lasting CD4⁺ and CD8 ⁺ cellular immunity than naked DNA injection in mice and in rhesus macaques as measured by a combination of assays, including IFN-γ ELISPOT, intracellular cytokine staining, and cytotoxic T cell assays. A protocol based on three injections of DNA with GET induced a substantially higher CD4 ⁺ T cell response than an adenovirus 6-based viral vector encoding the same Ag. To better evaluate the immunological potency and probability of success of this vaccine, we have immunized two chimpanzees and have compared vaccine-induced cell-mediated immunity to that measured in acute self-limiting infection in humans. GET of the candidate HCV vaccine led to vigorous, multispecific IFN-γ⁺CD8⁺ and CD4⁺ T lymphocyte responses in chimpanzees, which were comparable to those measured in five individuals that cleared spontaneously HCV infection. These data support the hypothesis that T cell responses elicited by the present strategy could be beneficial in prophylactic vaccine approaches against HCV.