Despite effective antiretroviral therapy (ART), persons with HIV (PWH) are at increased risk for developing several cancers and (ii) HIV persists in multiple tissues and continues to cause inflammation and cellular damage. Mounting evidence suggests that immunotherapeutic approaches have revolutionized the treatment of multiple malignancies by manipulating immune pathways, such as the programmed cell death protein-1 (PD- 1)/programmed death-ligand-1 (PD-L1) axis. In solid tumors, an important step for immune escape of cancer is the development of an immunosuppressive tumor microenvironment (TME). Further, the heterogeneity of TME shapes anti-tumor immunity and influences therapeutic wart the efficacy of immunotherapies, such as immune checkpoint blockers (ICB). Our project’s rationale is that by applying new technologies (i.e. single cell [sc]RNA-Seq and cytometry by time of the flight [CyTOF]), we will uncover signals in immunological composition and gene expression pathways activated in the TME in relation to ICB use. Our long-term goal is to tease out connections between TME and HIV and to expand our understanding of how the immunological composition of the TME and specific gene expression pathways and local HIV persistence are influenced by ICB PD-1 inhibitors. Our central hypothesis is that among PWH and cancer, ICB PD-1 inhibitor use will reshape the composition of immune milieus in TME and will be associated with increased immune infiltration and HIV transcriptional activity. The research proposed in this application is innovative because it will allow for the first time to characterize the TME of PWH with and without treatment with ICB PD-1 inhibitor (i.e. pembrolizumab) by leveraging blood and tumor tissue samples from PWH diagnosed with cancer and enrolled in the novel Last Gift cohort (PI D.M. Smith). We propose to determine: (i) the immune profiles and gene expression networks of TME in relation to ICB use (AIM 1) and (ii) the HIV reservoirs size and activity in TME in relation to ICB use (AIM 2). It is also a unique opportunity to explore the interplay between HIV and the local immune environment in the context of ICB