PROJECT SUMMARY Elimination of integrated, replication-competent HIV proviruses from host genomes persisting despite suppressive anti-retroviral therapy (ART) is the major roadblock to a functional cure. Cells harboring these types of proviruses produce marginal levels of viral products thereby becoming refractory to immune surveillance mechanisms. This lack of detection by the immune system, in addition to its increased growth potential, due to homeostatic proliferation and clonal expansion, extend the lifespan of latently infected cells generating a persistent reservoir. There is enormous enthusiasm for the potential of precision therapies targeting the latent reservoir in clinical settings. To achieve this major biomedical goal, we must first discover cell-intrinsic and/or -extrinsic “mediators” of reservoir persistence and latency-reactivation switch before we can leverage this knowledge for clinical intervention. To start filling this gap in knowledge, we implemented a gain- of-function screen in a CD4+ T cell line containing a latent provirus and discovered several novel regulators of the latency-reactivation switch. In this exploratory and developmental R21 grant proposal, we will focus our attention on one of those activators named ADAP1 (Arf-GAP with dual PH domain-containing protein-1). Importantly, ADAP1 has not been previously linked to immune cell biology nor to the control of HIV proviral gene regulation and latency, thus our studies hold conceptual innovation. Given these findings, the major objective of this research proposal is to achieve a better understanding of the molecular mechanisms underlying ADAP1 control of HIV latency and reactivation. To accomplish this, we will leverage the power of primary models of latency in a comprehensive set of CD4+ T cell effector subsets to understand complex and heterogeneous immune cell co-factor–HIV proviral genome interactions during latency and reactivation. The central hypothesis of this proposal is that ADAP1 is required to activate cell signaling-transcription regulatory programs in CD4+ T cell subsets while resting cells are exposed to immune cell stimulation/co-stimulation. Specifically, we will explore if ADAP1 functions to reactivate latent HIV from latency models in various CD4+ T cell subsets (Aim 1), and interrogate the ADAP1-regulated cell signaling- transcriptional programs leading to latent HIV reactivation (Aim 2). These studies could have a revolutionary impact on our understanding of HIV latency biology and have therapeutic implications. By elucidating how CD4+ T cell subsets shape the course of infection and how HIV co-opts host resources (like ADAP1) for the latency-reactivation switch, we will gain insights into basic processes as well as pathways that can be targeted therapeutically to help achieve NIAID mission’s of ending the HIV epidemic.