When it comes to HIV infection, CD4 + T cells are usually thought of as the cells that are preferentially infected and killed by the virus. In a new study, Soghoian et al. now show that during the early stages of HIV infection, CD4 + T cells suppress virus replication and delay disease onset. Thus, the robustness of the CD4 + T cell response during early HIV infection could be used as a marker to determine the speed of disease progression. The new findings also have implications for the design of preventive and therapeutic AIDS vaccines.