Despite the success of HIV-1 therapies in reducing the concentration of virus in the bloodstream , a long-lived reservoir of infectious virus persists in CD4 T cells [2–6] and perhaps other cell types . Although most of the proviral DNA within CD4 T cells is not able to replicate , replication-competent virus can persist in long-lived resting memory CD4 T cells in a quiescent state [4,5,9–11]. These latently infected cells, which are replenished through proliferation  or new infection can release infectious virus when reactivated . HIV-1 can also be derived from ongoing cycles of replication of CD4 T cells in tissue compartments where antiretroviral drugs have difficulty reaching–the so called drug sanctuaries [13–15]–and viral particles produced from infected CD4 T helper follicular cells that are captured and presented on the follicular dendritic cell network .