PROJECT SUMMARY HIV infection of humans and SIV/SHIV infection of rhesus macaques (RMs) persist despite long-term ART. Numerous observations indicate that CD8+ T cells inhibit HIV and SIV replication. More recently, two studies conducted as part of R01-AI-125064 have shown that: (i) CD8+ lymphocytes are required to maintain virus suppression under ART (Cartwright, Immunity 2016); and (ii) CD8 depletion reveals a powerful latency-reversal effect by the interleukin-15 super-agonist N-803 (McBrien, Nature 2020). Collectively, these studies revealed a previously unrecognized function of CD8+ lymphocytes that, while antiviral in its nature, in the setting of ART may paradoxically favor the long-term persistence of CD4+ T cells harboring integrated, replication-competent virus. If further confirmed, this hypothesis would have profound implications in terms of designing HIV “shock and kill” cure strategies based on modulating the latency promoting activity of CD8+ T cells in combination with agents that would promote the demise of the CD4+ T cells that have reactivated virus production. The overarching aim of this proposal is to better understand the ultimate potential of interventions based on the removal of CD8+ lymphocytes to disrupt SIV/SHIV persistence and reduce or even eliminate the virus reservoir under ART. We will build upon our previously published data and use the highly relevant, well validated model of SIV/SHIV infection of rhesus macaques (RM), to answer three important questions: (i) what are the cellular and anatomic sources of the robust and persistent virus reactivation observed in ART-treated SIV-infected RMs after combined treatment with CD8α depletion and N-803? (Aim #1); (ii) can we clear the CD4+ T cells that have reactivated virus production following CD8α or CD8β depletion + N-803 administration in ART- treated SHIV-infected RMs by treating the animals with a cocktail of Env-specific broadly neutralizing antibodies (bnAbs)? (Aim #2); and (iii) can we induce apoptosis of the CD4+ T cells that have reactivated virus production following CD8α depletion + N-803 administration in ART-treated SHIV-infected RMs by treating the animals with an inhibitor of the anti-apoptotic molecule Bcl-2? (Aim #3). We are uniquely poised to conduct the proposed experimental work, with an accomplished team of investigators and key resources at the Yerkes National Primate Research Center of Emory University. We therefore believe that we will be able to provide novel, critical information on how the latency promoting activity of CD8+ lymphocytes can be manipulated in vivo to reduce the persistent virus reservoir under ART.