DNA-MVA Vaccine Protection after X4 SHIV Challenge in Macaques Correlates with Day-of-Challenge Antiviral CD4 + Cell-Mediated Immunity Levels and Postchallenge Preservation of CD4 + T Cell Memory

The ability of vaccines to induce immunity both in mucosal and systemic compartments may be required for prevention of HIV infection and AIDS. We compared DNA-MVA vaccination regimens adjuvanted by IL-12 DNA, administered intramuscularly and nasally or only nasally. Most of the vaccinated Rhesus macaques developed mucosal and systemic humoral and cell-mediated SHIV-specific immune responses. Stimulation of mucosal anti-Env IgA responses was limited. After rectal challenge with SHIV 89.6P, all vaccinated and naive animals became infected. However, most of the vaccinated animals showed significant control of viremia and protection from CD4⁺ T cell loss and AIDS progression compared to the control animals. The levels of CD4⁺ and CD8⁺ T cell virus-specific responses measured on the day of challenge correlated with the level of viremia control observed later during the chronic infection. Postchallenge viremia levels inversely correlated with the preservation of SHIV-specific CD4⁺/IL-2⁺ and CD8⁺/TNF-α ⁺ T cells but not with CD4⁺/IFN-γ ⁺ T cells measured over time after challenge. We also found that during the early chronic infection SHIV vaccination permitted a more significant preservation of both naive and memory CD4⁺ T cells compared to controls. In addition, we observed a more significant and prolonged preservation of memory CD4⁺ T cells after SHIV vaccination and challenge than that observed after SIV vaccination and challenge. As the antiviral immunity stimulated by vaccination is present in the memory CD4⁺ T cell subpopulations, its more limited targeting by SHIV compared to SIV may explain the better control of X4 tropic SHIV than R5 tropic SIVs by vaccination.