HIV infection leads to a phenomenon of inflammaging, in which chronic inflammation induces an immune aged phenotype, even in individuals on combined antiretroviral therapy (cART) with undetectable viremia. In this study, we investigated T cell homeostasis and telomeric DNA damage and repair machineries in cART-controlled HIV patients at risk for inflammaging. We found a significant depletion of CD4 T cells, which was inversely correlated with the cell apoptosis in virus-suppressed HIV subjects compared to age-matched healthy subjects (HS). In addition, HIV CD4 T cells were prone to DNA damage that extended to chromosome ends—telomeres, leading to accelerated telomere erosion—a hallmark of cell senescence. Mechanistically, the DNA double-strand break (DSB) sensors MRE11, RAD50, and NBS1 (MRN complex) remained intact, but both expression and activity of the DNA damage checkpoint kinase ataxia-telangiectasia mutated (ATM) and its downstream checkpoint kinase 2 (CHK2) were significantly suppressed in HIV CD4 T cells. Consistently, ATM/CHK2 activation, DNA repair, and cellular functions were also impaired in healthy CD4 T cells following ATM knockdown or exposure to the ATM inhibitor KU60019 in vitro, recapitulating the biological effects observed in HIV-derived CD4 T cells in vivo. Importantly, ectopic expression of ATM was essential and sufficient to reduce the DNA damage, apoptosis, and cellular dysfunction in HIV-derived CD4 T cells. These results demonstrate that failure of DSB repair due to ATM deficiency leads to increased DNA damage and renders CD4 T cells prone to senescence and apoptotic death, contributing to CD4 T cell depletion or dysfunction in cART-controlled, latent HIV infection.

Hepatitis C virus (HCV) or human immunodeficiency virus (HIV) infection leads to a phenomenon of inflammaging, in which chronic infection or inflammation induces an immune aged phenotype with T cell dysfunction. Thus, HCV or HIV infection has been deemed as a model to study the mechanisms of T cell infammaging and viral persistence in humans. In this dissertation, T cell homeostasis, DNA damage and repair machineries were investigated in patients with chronic HCV or HIV infection at risk for inflammaging. We found a significant depletion in CD4 T cells, which was correlated with their apoptosis in chronically HCV/HIVinfected patients, compared to age-matched healthy subjects. In addition, virus-infected patients’ CD4 T cells were prone to DNA damage that extended to chromosome ends (telomeres), leading to accelerated telomere erosion - a hallmark of senescence. Mechanistically, the DNA doublestrand break (DSB) sensor MRE11, RAD50, and NBS1 (MRN) remained intact, but the DNA damage checkpoint kinase ataxia telangiectasia mutated (ATM) and its downstream checkpoint kinase 2 (CHK2) were significantly suppressed in T cells from HCV/HIV-infected individuals. Consistently, ATM/CHK2 activation, DNA repair, and cellular functions were also impaired in primary CD4 T cells following ATM knockdown, or exposure to the ATM inhibitor (KU60019), as well as in CD4 T cells co-cultured with HCV-infected hepatocytes, or a T cell line infected with HIV-1 in the presence of raltegravir in vitro, which recapitulates the biological effects observed in T cells in the setting of HCV/HIV infection in vivo. Importantly, ectopic expression of ATM was essential and sufficient to reduce the DNA damage, survival deficit, and cellular dysfunction in T cells from both HCV and HIV-infected individuals. These results demonstrate that failure of DSB repair due to ATM deficiency leads to unrepaired DNA damage and renders virally infected patients’ T cells prone to senescence and apoptosis, thus contributing to CD4 T cell loss or dysfunction during chronic HCV or HIV infection. This study reveals a novel mechanism by which ATM deficiency promotes telomeric DNA damage and premature T cell aging, and provides a new therapeutic target for inflammaging-induced immune dysfunction during chronic viral infection.