HIV/AIDS annually kills millions of people worldwide. Those claimed by the disease are quickly replaced by those newly infected. Three times as many new infections occur globally, as patients who are likely to have access to antiretroviral therapy. We need a HIV vaccine. However, the better HIV protein to target for this vaccine in unknown. Structural proteins such as Group specific antigen (Gag) and Envelope (Env) were thought likely candidates due to viral structural proteins usually being highly conserved and constrained in their ability to mutate to escape T cell attack. To establish if Env-specific T cells could control viraemia, 2 large vaccine trials were conducted with 66 pigtail macaques participating. Also, 2 reversion trials involving 4 pigtail macaques were undertaken. Env-specific T cell epitopes were mapped in both SHIV (simian/human immunodeficiency virus) and SIV (simian immunodeficiency virus)-infected macaques using IFNγ intracellular cytokine staining and flow cytometry.