Induction of Human Immunodeficiency Virus Type-1-Specific Immunity with a Novel Gene Transport Unit (GTU)-MultiHIV DNA Vaccine

A multiHIV fusion gene expressing an antigenic fusion protein composed of regulatory HIV-1 proteins Rev, Nef, and Tat, as well as Gag p17/p24 and a stretch of 11 cytotoxic T lymphocyte (CTL) epitope clusters from Pol and Env, was cloned into a novel DNA vector named the Gene Transport Unit (GTU). A mouse H-2^d-restricted HIV-1 gp120 epitope (RGPGRAFVTI) was cloned into the fusion gene as well. In addition to the HIV- 1 genes the GTU codes for a nuclear anchoring protein (bovine papilloma virus E2), ensuring the long maintenance of the vector and a high expression level of the selected immunogens. BALB/c mice were immunized with the GTU-MultiHIV DNA construct by different routes and regimens of immunization to assess the immunogenicity of the DNA vaccine in vivo. Mice developed strong CD8⁺ CTL responses to HIV-1 Env and Gag measured by an ELISPOT-IFN-γ assay and chromium release assay. In addition, T cell responses to regulatory proteins Rev, Nef, and Tat were induced. Antibody responses were detected to each of the HIV antigens encoded by the DNA construct. Minimal doses of the GTU-MultiHIV DNA delivered by gene gun were potent in inducing significant HIV-specific CTL responses. The equivalent doses of the conventional plasmid expressing MultiHIV DNA delivered by gene gun failed to do so. An ideal DNA vaccine should yield high expression of the viral antigens for a prolonged period of time, and expression of the multiple viral antigens is probably required for the induction of a broad and protective immune response. The GTU-MultiHIV DNA vaccine described is a good vaccine candidate that meets the above criteria.