SUMMARY Both HIV disease and chronic exposure to opioids are associated with increased microbial translocation contributing to immune activation. The objective of this study is to determine the role of μ-opioid receptor (MOR) engagement as an independent determinant of levels of immune activation and viral persistence in ART- suppressed HIV-infected individuals. We will address this objective by comparing individuals with opioid use disorder (OUD) receiving medication-assisted treatment (MAT) based on μ-opioid receptor agonists (methadone, buprenorphine) or antagonist (long-acting naltrexone). Based on the literature and our pilot studies, our primary hypothesis is that ART suppressed individuals with OUD under MAT treatment with MOR agonists will maintain greater myeloid activation and HIV persistence when compared to persons under MOR antagonist naltrexone (long-acting) due to greater A) microbial translocation; B) immune activation and inflammation; and C) viral reservoir. We will test this hypothesis by studying three groups of 30 HIV-1 infected individuals with OUD receiving suppressive ART (VL < 50 c/ml for > 12 months) and either (1) methadone, (2) suboxone, or (3) long-acting naltrexone. A control group of HIV-infected individuals without OUD will also be included. We will use blood and rectal mucosa specimens derived from out participants to: Specific Aim 1. Assess the clinical, immunological and virological correlates of sustained or blocked MOR engagement on ART. A. Determine clinical parameters of immune recovery and serum markers of chronic inflammation. B. Establish the extent of microbial translocation and mucosal integrity. C. Define immune activation with chronic MOR engagement, with a focus on the myelo-mononocytic compartment, using multiparameter flow cytometry (16-color FACS) on PBMC. D. Establish the effect of MOR engagement on HIV persistence (HIV DNA/RNA, inducible reservoirs). E. Study the interplay between MOR and TLR pathways by assessing the effect of MOR engagement on the response to TLR (2 and 4)-mediated responses in PBMC-derived macrophages in vitro. Specific Aim 2. Determine gut tissue immune cell distribution and myeloid cell transcriptional modulation as a central determinant of systemic activation upon sustained or blocked MOR engagement on ART. We will analyze paired colorectal biopsies and blood monocytes to: A. Define the phenotype and functional state of the GALT (colorectal mucosa biopsies) using CyTOF B. Define single cell myeloid and T-cell transcriptomic and pathway analysis in relation to microbial translocation measures. This study includes established collaboration between the University of Pennsylvania, Jonathan Lax Treatment Center, The Icahn School of Medicine at Mount Sinai, and The Wistar Institute. ! !