CD25+ regulatory T cells and tumor immunity.

Tumor cells express a range of antigens including self-antigens (those whose expression is shared by normal host tissue) and non-self antigens (such as those that arise as a result of mutations in normal cellular genes or in the case of some tumors, viral antigens). Immune responses to both types of antigen have been identified in human patients with cancer and in murine tumor models. In both cases, these responses are typically weak and generally fail to result in tumor rejection. Accumulating evidence indicates that a population of T cells, namely CD25(+) regulatory cells, is at least partly responsible for the poor immunogenicity of tumor cells. This evidence is discussed in the context of a murine model of melanoma.