ABSTRACT – Project 1 The overall objective of this Program project application is to generate a comprehensive understanding of the complex host-pathogen interactions critical for HIV reservoir seeding and persistence such that novel cure strategies truly targeted for the unique immune environment of children living with HIV (CLWH) can be created. The knowledge gap we address in Project 1 is how the establishment and maintenance of HIV reservoirs are regulated by the neonatal and childhood immune system, with specific focus on the role of IL-10 and TGF-β on innate and adaptive immune function, thymic output, survival of infected cells, and virus rebound. Multiple features of the early life immune environment differ from that of adults, including the active thymus and the tolerogenic/regulatory bias, with prominent T helper 2 and regulatory CD4+ T cells. The anti-inflammatory cytokines IL-10 and TGF-β are increased in infants and IL-10 is known to suppress antigen presentation, T cell effector function, and cell proliferation, while promoting survival of central memory CD4+ T cells. We have shown that lymph node CD4+ T cells from a subset of SHIV-infected infant rhesus macaques (RMs) that controlled viremia after analytical treatment interruption (ATI) were notable for an anti-IL-10 gene signature. The hypothesis to be tested in Project 1 is that IL-10 and TGF-β influence the magnitude of the HIV reservoir in infants and viral rebound post-ATI, while targeted modulation of IL-10/TGF-β signaling pathways will impair reservoir persistence and boost the immune responses that lead to post-ATI viral control. In Aim 1, we will evaluate how the cytokine milieu in infants impacts intact reservoir size, viral rebound, and antiviral immunity. In Aim 2, we will perform IL-10 blockade using an anti-IL-10 monoclonal antibody in vivo in SIV- infected infant RMs at the time of ART initiation to define the role of the IL-10 signaling pathway on reservoir establishment. In Aim 3, we will perform IL-10 blockade in vivo in SIV-infected infant RMs on long-term ART to determine the impact of IL-10 signaling on reservoir maintenance. Bulk and single-cell multiomic approaches will be applied in all Aims to identify and validate major immune pathways associated with HIV/SIV reservoirs and/or viral rebound and to advance our understanding of host-pathogen interactions that dictate virus persistence in early life. A better understanding of the vulnerability of HIV reservoirs to innate and adaptive immune pressure will drive informed approaches to a cure for CLWH. The research proposed builds on our expertise with infant RM models and cutting-edge systems immunology approaches to deeply interrogate pediatric HIV/SIV. With multidisciplinary approaches, synergies across Projects and Cores, and our highly collaborative group of established and early-stage investigators, we are confident that Project 1 will lead to important discoveries regarding immune regulation of the pediatr...