This notice of funding opportunity (NOFO) will support high risk high impact studies that 1) develop or apply novel tools or technologies or 2) test novel hypotheses to investigate mechanistic questions in HIV infection, replication, latency, and/or pathogenesis (including neuroHIV) in the context of Substance Use Disorders (SUDs). This initiative focuses on exploration and characterization of signaling pathways that are involved in CNS HIV establishment and expansion. The NOFO aims to promote milestone-driven research to investigate the underlying molecular mechanisms by which HIV infection is initiated, established, and maintained in the CNS and to determine how addictive substances modulate HIV infection, latency and the size and persistence of CNS HIV reservoirs.