PROJECT SUMMARY During suppressive antiretroviral therapy (ART), chronic inflammation persists among people with HIV (PWH) and appears to be driven by low levels of HIV replication, monocyte/macrophage activation, and other mechanisms. This persistent inflammation has been linked to adverse neuropsychiatric (e.g., depression, psychological stress, emotion dysfunction), neurocognitive, and medical outcomes. Cannabis, which is used more commonly by PWH than people without HIV, appears to have anti-inflammatory effects and therefore may have therapeutic applications for inflammation and end-organ complications. Cannabinoids exert their effects in part via the endocannabinoid (EC) system (ECS), which includes cannabinoid receptors that are expressed on the surface of cells of the immune and central nervous systems. Cannabinoids have demonstrated clinical benefits for conditions like pain and nausea, but less is known about its effects on inflammation in HIV. Moreover, the range of cannabis exposure (e.g., dose and frequency of use) that may be effective, ineffective, or unsafe for different neuropsychiatric and medical conditions is unknown. In response to RFA-DA-20-022, this application proposes to address key scientific gaps by examining the effects of chronic cannabis use and the role of the ECS in persistent inflammation in PWH who are taking suppressive ART. We propose to assess 120 participants (60 PWH on suppressive ART and 60 HIV- persons) across a spectrum of cannabis use from persons who have never used cannabis to daily users. We will comprehensively evaluate participants with multimodal in vivo and ex vivo assessments of the biological pathways underlying the effects of chronic cannabis use on persistent inflammation in PWH and its corresponding impact on neuropsychiatric and neurocognitive complications. In vivo assessments will include standardized medical, neuropsychiatric, and neurocognitive assessments, including collection of cerebrospinal fluid and blood. Current cannabis users within this sample (n=80) will also be assessed with novel brain imaging of microglial activation with [(18)F]FEPPA translocator protein (TSPO) positron emission tomography. In the collected specimens, we will measure soluble (e.g., pro- and anti- inflammatory cytokines) and cellular (e.g., HLA-DR, CD38) biomarkers of inflammation and immune activation as well as components of the ECS (e.g., anandamide, CB2 receptors). Blood specimens will also serve as the source for primary cell cultures for ex vivo mechanistic experiments that will assess the effects of cannabinoids, HIV, and ART on biological pathways such as the TREM2 and the NLRP3 inflammasome. Data from all assessments and experiments will be integrated and analyzed centrally to identify cross-cutting signals and reduce noise from our multimodal assessments. Knowledge gained from this study will contribute to OAR priorities (e.g., comorbidities, end organ injury) and provide valuable insight into str...