Project Summary/Abstract The main obstacle to curing HIV-1 infection is a reservoir that consists of resting memory CD4 T cells whose genomes contain inducible and replication-competent HIV-1 proviruses. Decay of the reservoir is slow and requires lifelong antiretroviral therapy (ART). It has become increasingly clear that the predominant mechanism sustaining HIV-1 persistence during ART is the physiologic proliferation of latent-infected memory CD4 T cells. Infected CD4 T cells can proliferate without producing virus, the result of which will lead to daughter cells harboring expanded HIV-1 proviral clones that share identical sequence and host integration sites. The rate of expansion among distinct proviral clones in this setting however is not equal. In some individuals, upwards of 30% of proviruses sampled can belong to populations that are highly clonally expanded, a mechanism consistent with clonal proliferation by antigen encounter. Establishing a link between particular antigens and the degree to which they independently contribute to HIV persistence, however, is an unresolved question. Cytomegalovirus (CMV) is a latent betaherpesvirus that while asymptomatic in immunocompetent hosts, persistently stimulates the memory T cell pool. Persons living with HIV are near universally coinfected with CMV. In this project, we have assembled a multidisciplinary team of investigators to directly assess the degree to which chronic antigenic stimulation by CMV (i) promotes proliferation of the memory CD4 T cell pool (ii) contributes to clonal diversity and size of the HIV- 1 reservoir during ART and (iii) impacts the time to viral recrudescence when ART is interrupted. Specifically, we will utilize the well-established model of ART-treated SIV-infected rhesus macaques to examine these questions by a dual approach. The first will exploit availability of pathogen-free, rhesus CMV (RhCMV)-naïve rhesus macaques (RMs) to compare SIV reservoir dynamics in the presence or absence of CMV. The second will assess measures of SIV persistence when CMV replication is blocked pharmacologically with antiviral Cidofovir. Critical to our aims are that we will interrogate SIV proviral DNA at multiple longitudinal timepoints, in multiple tissues, and with several assays that inform both quantitative and qualitative aspects of the SIV reservoir. We believe that the comprehensive, highly synergistic, and rigorously controlled studies we propose will (i) identify an immunodominant target that promotes turnover of memory CD4 T cells during ART and by extension, persistence of the HIV-1 reservoir and (ii) provide a rationale to employ recent well-tolerated FDA-approved CMV antivirals as a means to accelerate HIV-1 clearance.