Regulatory T (Treg) cell activity has been observed in anti-tumor and autoimmunity since the 1970s. Functional and molecular characterization of Treg cells has been made possible by the recent association of cell markers, such as CD25, CTLA-4, GITR, and Foxp3 gene product, with immunoregulatory activity. Here the influence of Treg cells in both anti-tumor immunity and autoimmunity was measured in BALB/c mice. Depletion of CD4(+)CD25(+) Treg cells with CD25 mAb resulted in mammary tumor regression and increased susceptibility to thyroiditis. This in vivo priming to both tumor-associated antigens and self-thyroglobulin attests to the presence of otherwise undetectable immune effectors which are under negative regulation. Modulation of Treg cells is a powerful strategy in cancer therapy, but may potentiate autoimmune complications. Murine models exhibiting breakable tolerance to tumor-associated antigens, such as ErbB-2 (HER-2/neu), and increased susceptibility to autoimmunity following Treg-cell depletion are being established to test new vaccination or therapeutic strategies involving Treg-cell modulation.
