Lymph node T cell responses predict the efficacy of live attenuated SIV vaccines.

Live attenuated SIV vaccines protect nonhuman primates from infection with pathogenic wild-type SIV, but the crucial mechanisms have not been clear. In this issue, Louis Picker and colleagues show that protection by live attenuated vaccines against intravenous SIV challenge in rhesus macaques is associated with SIV-specific T cell response in the lymph nodes, and not the blood, and persistent SIV replication in lymph node follicular T helper cells.