Immune profile and mitochondrial alterations driven by age and HIV infection: Associations with T-cell senescence in people with HIV receiving suppressive antiretroviral therapy.

Antiretroviral therapy (ART) has significantly extended the life expectancy of people with HIV (PWH), rendering population ageing and immunosenescence prominent clinical priorities. T-cell senescence is linked to mitochondrial dysfunction and drives age-related immune remodelling, yet how HIV infection and ageing jointly shape CD4+ and CD8+ T-cell immunophenotypes and mitochondrial remodelling remains unclear. This cross-sectional study included 61 PWH on suppressive ART for ≥ 12 months and 61 age- and sex-matched HIV-negative men who have sex with men, stratified into younger (≤ 35 years) and older (≥ 50 years) groups. Multiparameter flow cytometry was used to profile CD4+ and CD8+ T-cell differentiation, stemness, activation/exhaustion, and metabolic phenotypes, together with mitochondrial mass and membrane potential. We found that ageing and HIV infection were associated with T-cell remodelling, characterized by expanded late-differentiated phenotypes and reduced stem-like, homeostatic and costimulatory CD4+ and CD8+ T-cell subsets, as indicated by upregulated CD57 and CX3CR1 and downregulated CD45RA+CD31+, FOXO1, and CD28. Notably, younger PWH had an ageing-like CD4+ T-cell profile, with higher CD57, CX3CR1 and TIGIT expression than younger HIV-negative individuals. In contrast, HIV-related CD8+ T-cell perturbations (KLRG1, CXCR3, NKG2C and CD95) were more pronounced in older PWH. PWH exhibited increased mitochondrial mass and membrane potential in both total and senescent-like CD4+ and CD8+ T cells, particularly in CD8+ T cells from older PWH. In CD4+ T cells, KLRG1 and CX3CR1 expression correlated positively with age, and inversely with CD4+ T-cell counts and CD4/CD8 ratio. By contrast, FOXO1 expression in CD8+ T cells was inversely associated with age, late-differentiation markers, and ART duration in PWH. Overall, age is a major driver of T-cell immunosenescence, and HIV infection modulates and exacerbates these alterations. Mitochondrial stress, FOXO1 downregulation and immune network remodelling support a multifaceted model of HIV-associated immune ageing that may contribute to heterogeneous immune reconstitution in PWH, highlighting potential targets to mitigate immune ageing.