Loss of long term protection with the inclusion of HIV pol to a DNA vaccine encoding gag

•Lower induction of gag-specific IFN-γ secreting T cells with the inclusion of pol.•T cell functionality lower with the inclusion of pol in a DNA vaccine encoding gag.•Long term protection is lost with the inclusion of the pol gene.

Traditional vaccine strategies that induce antibody responses have failed to protect against HIV infection in clinical trials, and thus cell-mediated immunity is now an additional criterion. Recent clinical trials that aimed to induce strong T cell responses failed to do so. Therefore, to enhance induction of protective T cell responses, it is crucial that the optimum antigen combination is chosen. Limited research has been performed into the number of antigens selected for an HIV vaccine. This study aimed to compare DNA vaccines encoding either a single HIV antigen or a combination of two antigens, using intradermal vaccination of C57BL/6 mice. Immune assays were performed on splenocytes, and in vivo protection was examined by challenge with a chimeric virus, EcoHIV, able to infect mouse but not human leukocytes, at 10 days (short term) and 60 days (long term) post final vaccination. At 60 days there was significantly lower frequency of induced antigen-specific CD8+ T cells in the spleens of pCMVgag–pol-vaccinated mice compared with mice which received pCMVgag only. Most importantly, short term viral control of EcoHIV was similar for pCMVgag and pCMVgag–pol-vaccinated mice at day 10, but only the pCMVgag-vaccinated significantly controlled EcoHIV at day 60 compared with pCMV-vaccinated mice, showing that control was reduced with the inclusion of the HIV pol gene.