ART effectively suppresses HIV-1 viremia but in most patients, virus rebounds within 2-3 weeks of stopping ART. ART is unable to cure HIV due to the persistence of virus as long-lived latently infected cells, residual virus replication and anatomical reservoirs. Understanding the contribution of residual virus replication to virus persistence on ART is important because first, no interventions aimed at eliminating latency will be effective in the presence of residual virus replication; second, residual virus replication may contribute to persisting immune activation which has been associated with all-cause mortality.