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.