Heterologous prime-boost vaccination with DNA and MVA vaccines, expressing HIV-1 subtype C mosaic Gag virus-like particles, is highly immunogenic in mice.

In an effort to make affordable vaccines suitable for the regions most affected by HIV-1, we have constructed stable vaccines that express an HIV-1 subtype C mosaic Gag immunogen (BCG-Gag^M, MVA-Gag^M and DNA-Gag^M). Mosaic immunogens have been designed to address the tremendous diversity of this virus. Here we have shown that Gag^M buds from cells infected and transfected with MVA-Gag^M and DNA-Gag^M respectively and forms virus-like particles. Previously we showed that a BCG-Gag^M prime MVA-Gag^M boost generated strong cellular immune responses in mice. In this study immune responses to the DNA-Gag^M and MVA-Gag^M vaccines were evaluated in homologous and heterologous prime-boost vaccinations. The DNA homologous prime boost vaccination elicited predominantly CD8+ T cells while the homologous MVA vaccination induced predominantly CD4+ T cells. A heterologous DNA-Gag^M prime MVA-Gag^M boost induced strong, more balanced Gag CD8+ and CD4+ T cell responses and that were predominantly of an effector memory phenotype. The immunogenicity of the mosaic Gag (Gag^M) was compared to a naturally occurring subtype C Gag (Gag^N) using a DNA homologous vaccination regimen. DNA-Gag^N expresses a natural Gag with a sequence that was closest to the consensus sequence of subtype C viruses sampled in South Africa. DNA-Gag^M homologous vaccination induced cumulative HIV-1 Gag-specific IFN-γ ELISPOT responses that were 6.5-fold higher than those induced by the DNA-Gag^N vaccination. Similarly, DNA-Gag^M vaccination generated 7-fold higher levels of cytokine-positive CD8+ T cells than DNA-Gag^N, indicating that this subtype C mosaic Gag elicits far more potent immune responses than a consensus-type Gag. Cells transfected and infected with DNA-Gag^M and MVA-Gag^M respectively, expressed high levels of Gag^M and produced budding virus-like particles. Our data indicates that a heterologous prime boost regimen using DNA and MVA vaccines expressing HIV-1 subtype C mosaic Gag is highly immunogenic in mice and warrants further investigation in non-human primates. [ABSTRACT FROM AUTHOR]