The pursuit of a cure for HIV-1 infection is founded on the hypothesis that reservoirs that support viral persistence are amenable to elimination. As such, most of the research on HIV-1 cure and remission has centered on identifying the dynamics of CD4+ T cell reservoirs as well as on approaches to eliminate them. We recently presented evidence that following analytic treatment interruption (ATI), rebounding viremia comprised virions that were highly macrophage tropic. Through the use of a novel immunoaffinity enrichment method, we further demonstrated that macrophage-tropic viruses in post-ATI plasma have a myeloid cell origin [1]. These observations define myeloid cells as a reservoir under suppressive ART and that these reservoirs require consideration in the design of viral remission and cure strategies The myeloid compartments that house HIV-1 reservoirs under ART are unkown. However, the approaches we developed have the capacity to yield this information. Those approaches hinge upon our demonstration that virion membranes are derived from the host cell plasma membrane and as such, virions harbor ligands that inform on their host cell of origin. We will adopt these approaches to address the long-standing issue of whether Kupffer Cells in the liver, which is the largest myeloid compartment of the immune system, serve as viral reservoirs in the face of suppressive ART. Our objectives are: Aim1: Identify host cell ligands on virions derived from primary Kupffer cells that enable immunoaffinity isolation of virions with a Kupffer cell origin in post ATI-plasma. Aim 2: Derive libraries of full length viral envelopes from liver tissue of HIV-1-infected individuals and assess their cellular tropism and dynamics by high-throughput viral phenotyping and Molecular Clock analysis, respectively. Aim 3: Employ liganded virion capture and high discrimation Taq (HiDi Taq) polymerase-directed allele amplification to assess whether virions in tissue-matched plasma originate from Kupffer cells and whether immunocaptured virions from plasma and proviruses from liver tissue exhibit related virological characteristics and phylogenetic structures. This proposal leverages important clinical resources that will be used to define whether Kupffer cells serve as viral reservoirs of HIV-1. The information derived from this proposal will provide the rationale for the identification of tailored approaches to eliminate myeloid reservoirs within the liver and other myeloid compartments.