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Reduced thymopoiesis and continuous mobilization of naive T cells into the effector-memory pool can lead to severe alterations of the naive T cell compartment. However, maintenance of the naive T cell population is essential to mount effective immune responses. Evidence of homeostatic regulation of naive T cells is currently debated in animal models. In humans, the situation remains unresolved, in particular with advanced age. In this study, we analyzed the CD4+ and CD8+ naive T cell compartments from elderly, young adults thymectomized during early childhood, and HIV-l-infected patients, which are characterized by T lymphocytopenia. We show a direct association between increased turnover and decreased frequency of naive T cells. Moreover, the IL-7-induced pathway was fully functional in naive T cells from elderly and young adults thymectomized during early childhood, who are characterized by elevated IL-7 plasma levels. Our findings support the establishment of homeostatic regulation of naive T cell proliferation in humans. This regulation is particularly active in lymphopenic hosts, such as elderly and thymec-tomized patients. [ABSTRACT FROM AUTHOR]

Compared with HTV-1, HIV-2 infection is characterized by a larger proportion of slow or nonprogressors. A better understanding of HIV-2 pathogenesis should open new therapeutic avenues to establish control of HIV-1 replication in infected patients. In this study, we studied the production of CD8+ T cells and their capacity for viral control in HIV-2 controllers from the French ANRS C05 HIV-2 cohort. HIV-2 controllers display a robust capacity to support long-term renewal of the CD8+ T cell compartment by preserving immune resources, including hematopoietic progenitors and thymic activity, which could contribute to the long-term maintenance of the CD8+ T cell response and the avoidance of premature immune aging. Our data support the presence of HTV-2 Gag-specific CD8+ T cells that display an early memory differentiation phenotype and robust effector potential in HTV-2 controllers. Accordingly, to our knowledge, we show for the first time that HIV-2 controllers possess CD8+ T cells that show an unusually strong capacity to suppress HIV-2 infection in autologous CD4+ T cells ex vivo, an ability that likely depends on the preservation of host immune resources. This effective and durable antiviral response probably participates in a virtuous circle, during which controlled viral replication permits the preservation of potent immune functions, thus preventing HIV-2 disease progression. [ABSTRACT FROM AUTHOR]