While current ART has prevented AIDS and reduced HIV-related morbidities and mortality for the majority of infected individuals, a therapeutic regimen able to eradicate or functionally cure HIV infection does not exist. Persistence of HIV in a small pool of latently infected cells remains the major obstacle for HIV eradication largely because the mechanisms that underlie viral persistence are still unknown. Our group has generated significant and convincing results in cART treated HIV infected humans and SIV infected rhesus macaques (RMs) suggesting that Interleukin(IL)-10 plays an important role in the establishment and maintenance of the HIV reservoir by (i) impeding the early antiviral innate and the HIV/SIV specific adaptive immune response and (ii) promoting the differentiation of Tfh and Tr1 cells that are major HIV/SIV reservoirs. The importance of IL-10 in the establishment and maintenance of HIV has prompted Merck to successfully develop a Rhesus form of an anti-human IL-10 Ab that is currently being tested in clinic; administration of this Ab in a proof of concept study to SIV infected RMs was safe and well tolerated; it also recapitulated several of the biological activities of the human Ab as it showed a negative impact on Tfh frequencies which could translate in a smaller reservoir. In this proposal, we will test the hypothesis that neutralization of IL-10 activity systemically and in lymphoid tissues will lead to restoration of cellular immune responses, decreased Tfh and Tr1 numbers, and a decay in HIV reservoir. Biomarkers that predict successful clinical interventions involving anti-IL-10 and leading to HIV eradication are not available. In Aim 1, we will perform an unbiased OMICs integrated approach to identify cell subsets, soluble effector molecules, metabolites and molecular pathways, which underlie the modulation of HIV reservoirs by IL-10 in cell subsets isolated from PBMCs and tissues from cART treated HIV infected subjects. We will identify markers that are associated to low levels of IL-10 and conversely to lower HIV reservoir in Tfh and Tr1 cells and efficient innate antiviral and cell mediated immunity. These markers will be used to monitor the impact of the anti-IL-10 intervention that aims at restoring innate antiviral immunity and cell mediated immunity for HIV eradication. Direct demonstration that IL-10 regulates HIV persistence will be provided by examining the impact of IL-10 blockade on virus persistence in a large study of ART-treated, SIV-infected RMs. Preclinical trial of Aim 2 will allow us to determine the restoration of innate immunity by early IL-10 blockade as this intervention should inhibit the upregulation of NLRX-1, a molecule we have shown to play a critical role in the early HIV/SIV dissemination and conversely in the seeding of the HIV/SIV reservoir. Pre-clinical trial of Aim 3 should allow the restoration of the adaptive immune response by preventing the development of IL-10 producing Tr1 cells; IL-10 blockade will also trigger the HIV/SIV reservoir decay in Tfh cells which depend on IL-10 for their survival and differentiation. Achievement of these goals will lead to the development of a much-needed strategy aimed at eradicating HIV. RELEVANCE (See instructions): HIV eradication have become a realistic possibility as was shown by the Berlin patient who was cured of HIV by bone marrow transplantation of cells that cannot be infected by HIV. Therapeutic interventions which are less invasive must be explored and tested. We present here a novel strategy that targets IL-10, a cytokine that enhances the number of cells that can become reservoirs for HIV and inhibits antiviral immune responses. We expect that our approach will restore immune responses and decrease the reservoir size, thus promoting HIV remission.