Shortened telomeres in the expanded CD28-CD8+ cell subset in HIV disease implicate replicative senescence in HIV pathogenesis

OBJECTIVE: To test the hypothesis that the expanded population of non-proliferative CD28-CD8+ T cells in HIV disease have shortened telomeres, thereby providing evidence that increased rounds of CD8+ cell division occur during HIV disease, possibly leading to replicative senescence and exhaustion of CD8+ T-cell responses. DESIGN: CD8+ cells play a central role in control of HIV infection. In late HIV disease, an expanded population of CD28-CD8+ cells with reduced proliferative potential has been documented. A similar population of CD28-CD8+ cells has been identified in ageing humans, where telomere length measurements have suggested that these cells have reached the irreversible state of replicative senescence. METHODS: CD8+ cells from HIV-infected and control subjects were sorted by flow cytometry into CD28+ and CD28- fractions. Telomere lengths were determined as mean terminal restriction fragment (TRF) lengths by Southern hybridization. RESULTS: The TRF lengths of sorted CD28-CD8+ cells in HIV-infected subjects ranged between 5 and 7 kilobases (kb) and were significantly shorter than TRF lengths of CD28-CD8+ cells in uninfected subjects (P = 0.003). The TRF length in CD28-CD8+ cells from HIV-infected subjects was the same as that observed for centenarian peripheral blood mononuclear cells and is compatible with a state of replicative senescence. CONCLUSIONS: The shortened telomeres in the CD28-CD8+ cells in HIV-infected subjects and the poor proliferative potential of these cells identifies CD8+ cell replicative senescence as a newly described feature of HIV disease. Our results provide a mechanism for the loss of CD8+ cell control of viral replication that accompanies advanced HIV disease. Replicative senescence may contribute to exhaustion of the T-cell response as a result of chronic HIV disease. Whether this phenomenon occurs in other chronic viral infections is unknown.