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Construction and Evaluation of BCG and Modified Vaccinia Ankara Vaccines Expressing HIV-1 Subtype C Mosaic Gag

Background: Over 90% of people with HIV-1 in sub-Saharan Africa are infected with the clade C virus. High mutagenesis rates and diversity, even within clades, make it difficult to develop effective vaccines. Mosaic immunogens have been computationally designed to maximize inclusion of common T-cell epitopes. Compared to consensus immunogens, polyvalent mosaic immunogens of HIV-1 group M have increased breadth and depth of antigen-specific T-cell responses.  Here, we determined the immunogenicity of vaccines expressing HIV-1 subtype C Gag mosaic in mice.

Methods: BCG (BCG-GagM) and MVA (MVA-GagM) vaccines expressing the HIV subtype C mosaic gag gene were constructed. p24 ELISA and electron microscopy (EM) of MVA-GagM -infected cells was used to determine the ability of the mosaic Gag to bud and form virus-like particles (VLPs). Shuttle vector integrity in BCG-GagM was determined by PCR.  Mice were primed intraperitoneally with 2x107-cfu BCG-GagM and boosted intramuscularly with 104-pfu MVA-GagM at week 10. Mice were sacrificed 12 days later and T-cell responses analysed by IFN-γ ELISPOT, CBA, and ICS assays.

Results: Gag VLP production was confirmed by EM and p24 ELISA in the media of infected cells. A Th1 response was induced by the BCG-GagM/MVA-GagM vaccination regimen, and both CD4+ and CD8+ IFN-γ responses were detected. A potent effector memory phenotype was detected from both CD4+ and CD8+ cells. Overall, the BCG-GagM prime MVA-GagM boost induced robust HIV-specific CD4+ and CD8+ T cell responses that were 3 fold higher than responses induced by a control BCG prime MVA-GagM boost. Genetic integrity of the BCG-GagM vaccine was confirmed 10 weeks post vaccination in mice.

Conclusion: These vaccines are immunogenic in Balb/c mice in a prime-boost vaccination regimen. Either vaccine alone had a dominant CD4 response while the combination of vaccines induced a greater CD8 response.   The vaccines induce strong effector memory functions and will be further evaluated in non-human primates.