The existing knowledge of perinatal HIV-1 infection on developing immunity is limited, and a need exists to define the unique characteristics of immunity in infants that influence pediatric disease progression. The long- term goal of this project is to develop a pathway to achieve durable remission for infants in the absence of prolonged drug treatment. The central hypothesis is that understanding the quality and magnitude of the innate and adaptive immune systems of newborns in response to HIV-1 infection is essential for developing better strategies to achieve durable remission of HIV-1. The project will first address pathogenesis of perinatal HIV infection, with and without ART, using a proven pre-clinical model of SHIV infection in newborn macaques. For human infants, the incidence of infection is greatest between late stages of gestation and early weeks of postpartum. Infection in utero or peripartum without early ART intervention leads to high mortality in the first year of life. The risk of death is about half as great if infection occurs postnatally during breastfeeding. To mirror peripartum infection, newborn macaques will be infected within the first few weeks of life (< 2 weeks old) with SHIV by the oral route. Using serial sacrifices, the macaque experiments will allow for a comprehensive evaluation of B cell and T cell function in blood, and multiple lymphoid and gut tissues at specific timepoints during infection. The effect of an immature immune system at the time of infection on immune dysfunction and disease progression will be assessed and compared between groups of animals that receive daily ART starting within days of infection versus no ART groups. In addition to studying the impact of viremia on immune cell function and viral reservoir kinetics, experiments in Years 2?4 will examine viremia rebound in infants after modulating and potentially protecting adaptive immunity by limiting viral replication during the first week of infection with ART. To mitigate immune dysregulation, further modulation of immune responses will be assessed with the addition of potent neutralizing antibodies to complement the intervention strategy during and just prior to ART cessation. Together, these studies will inform current clinical practices that are poised to advance very early ART in circumstances of in utero or intrapatrum infection, but are challenged by incomplete pre-clincal data to guide future practices at or near delivery. The proposed approaches and methodologies that can be used in a nonhuman primate model but are not feasible in human infants will provide mechanistic evidence of when and how active viral reservoirs can be prevented, reduced, or eliminated. Innovative technologies, including the use of a new Primate Multimodal Imaging Core at the Oregon National Primate Research Center, will provide access to state-of-the-art reagents and expertise for imaging viral latency, reactivation, and treatment in macaques in real time using PET scans. The questions addressed and answered in these studies will provide a strong foundation for future expansion of optimal approaches to decrease the morbidity and mortality associated with perinatal HIV-1 infection.