Immune suppression by tumor-specific CD4+ regulatory T-cells in cancer.

Regulatory T-cells play essential roles in inducing self-tolerance by suppressing immune responses against self such as autoantigens or non-self-antigens such as tumor and pathogenic antigens. Recent studies demonstrate the existence of CD4+ regulatory T-cells at tumor sites, implying that these Treg cells may induce antigen-specific and local immune tolerance. This review will discuss the natural ligands and their potential roles of tumor-specific CD4+ regulatory T-cells in cancer therapy.