Project Summary: Although the resting memory CD4+ T cells are the best-recognized long-lived reservoirs of latent HIV provirus, it is now well accepted that the myeloid cells, especially of the central nervous system (CNS)- -including perivascular macrophages and microglial cells--can also contribute to viral reservoirs. The molecular mechanisms relevant to HIV latency are primarily defined by analyzing HIV latency in latently infected CD4+ lymphoid cells. However, very little is known about HIV latency/persistence in myeloid cells. Notably, the presence of HIV-harboring myeloid cells in the CNS are documented to be the key factor contributing to CNS inflammation and promoting HIV-associated neurocognitive disorder (HAND) in HIV patients. Microglial cells are the main HIV reservoir in the CNS, yet a gap in the knowledge regarding our understanding of the molecular mechanisms that maintains HIV reservoirs in those cells. Our long term goal is identifying and characterizing the underlying molecular mechanisms that regulate HIV latency in microglial cells. The important role of CBF-1-mediated transcriptional inhibition during HIV latency is well established in lymphoid cells. The objective of this grant is to characterize the role of CBF-1 during HIV latency in microglial cells. Based on our published and preliminary findings, we have hypothesized that, similar to lymphocytes, in microglial cells CBF- 1 promotes HIV latency/slowdown by inducing the generation of transcriptionally-repressive heterochromatin structures at HIV LTR. Our rationale is that since HIV latency is primarily regulated at the transcriptional level, defining the precise mechanism(s) that regulate HIV transcription in microglial cells will offer new therapeutic opportunities to target HIV reservoirs in the CNS. In Aim 1, we will examine the role of CBF-1-induced epigenetic changes in restricting HIV transcription and their eventual impact on the establishment and the maintenance phases of HIV latency. In Aim 2, we will characterize the corepressor complexes that CBF-1 recruits at HIV LTR and their functional significance in promoting HIV reservoir in microglial cells. Upon conclusion, we will be able to define the CBF-1-mediated mechanisms that facilitate the establishment and maintenance of HIV latency in microglial cells. These studies will also provide a well-defined therapeutic target in the form of CBF-1 and its corepressor complexes in order to relieve multiple repressive epigenetic modifications simultaneously. Proposed research is innovative because it uses human primary microglial cells, and a novel ex vivo model system for HIV latency in microglial cells that, for the first time, allows the studies of the molecular correlates for HIV entry and exit into latency in microglial cells, which is otherwise an impossible task due to insufficient availability of brain autopsy specimens. This contribution is significant since the identified mechanisms, which regulate HIV transcr...