Human CD4+ CD25+ regulatory T cells control T-cell responses to human immunodeficiency virus and cytomegalovirus antigens

Regulatory T (T-R) cells maintain tolerance to self-antigens and control immune responses to alloantigens after organ transplantation. Here, we show that CD4(+) CD25(+) human T-R cells suppress virus-specific T-cell responses. Depletion of T-R cells from peripheral blood mononuclear cells enhances T-cell responses to cytomegalovirus and human immunodeficiency virus antigens. We propose that chronic viral infections lead to induction of suppressive T-R cells that inhibit the antiviral immune response.