Abstract: Indexation of regulatory T cells (Treg) to the number of activated T cells constitutes a homeostatic mechanism ensuring that T-cell expansion remains under control. However, immune hyperactivation observed in HIV-infected patients suggests a possible dysfunction of this mechanism. Here we show that the Treg/IL-2–producing cells' balance is deeply disturbed in viremic HIV-infected patients. We found a lower expression of IL-2 receptor alpha on Treg from viremic patients. We confirmed in vitro that HIV infection of Treg downregulates IL-2 receptor alpha and phosphorylated STAT5. Our results argue for an impaired capacity of Treg to sense the expansion of activated T cells in HIV-infected patients that could contribute to the immune deregulation.