CD4 and Autoimmunity: Regulatory T cells include CD4+/CD25+/FoxP3+ Tregs and a subset of CD8+/CD122+ T cells which are critical in maintaining the peripheral self-tolerance (avoiding autoimmunity) by suppression of CD8+ cytotoxic T cells and IFN-γ secretion; however, they also favor tumor immune-escape and progression, leading to poor outcomes: they are increased in peripheral blood and microenvironments of various tumors.