Aging and HIV are characterized by systemic chronic inflammation (inflammaging) and chronic immune activation (IA), both associated with cell senescence, functional impairment of immune cells and reduced immunity to infections and vaccines. Aging and HIV are also associated with metabolic changes such as decreased insulin sensitivity, dysregulated nutrient uptake and dysfunctional mitochondria. As a consequence of these changes, metabolites involved in glucose and fatty acid metabolism are released in blood. Some of these metabolites have been shown to be positively associated with inflammaging and therefore expected to be also associated with dysfunctional immunity. In people living with HIV (PWH) metabolic abnormalities have been related to virus-induced irreversible tissue damage in viremic individuals, as well as to anti-retroviral therapy (ART)-induced effects in virally suppressed individuals. Immune cells need to undergo metabolic reprogramming to meet the demands associated with immune responses, and rely on anaerobic glycolysis and oxidative phosphorylation to do so. The effects of aging in PWH on these pathways and on the metabolic mechanisms involved in the regulation of immune cell function are largely unknown and are the primary objectives of this proposal. Our hypothesis, supported by strong preliminary results, is that aging exacerbates immune defects through a dysregulated metabolic reprogramming and this effect is even more pronounced in PWH. Our studies have demonstrated that a higher metabolic status of immune cells is associated with higher intrinsic IA and lower capacity to generate protective immunity. This proposal will use data and samples from the MACS/WIHS Combined Cohort Study (MWCCS) of PWH and age- gender- and sociodemographically matched people without HIV (PWoH). We plan to evaluate how aging influences the serum metabolic profile of PWH and how this impacts the function, phenotype and transcriptional profiles of B cells, T cells and monocytes, the major cell types participating in immune responses to infections and vaccines. The role played by gut microbial metabolism on metabolic status will also be evaluated (Aim 1); we will investigate the metabolic mechanisms as well as metabolic requirements of the immune cells (Aim 2); and we will perform experiments using senolytics and metabolic modifiers to block senescent and metabolic pathways and improve, at least in vitro, immune cell function (Aim 3). Because obesity is a condition associated with altered metabolism, experiments will use samples from lean and obese PWH of different ages, as evaluated by body composition measures such as weight, waist/hip/thigh circumference, and bioelectrical impedance analysis to assess body fat amounts and depots. Younger (<50 years) and older (>60 years) lean and obese PWoH will also be included as controls. Results obtained will allow the identification of senescent and metabolic pathways to be targeted to improve the immune fun...