CD4 and neoplasm: Whereas CD4+ T helper cells usually recognize MHC class II antigens and indirectly help clear tumor cells by secreting cytokines such as IL-2 and IFN-γ that enhance phagocytes and other T cells; Tregs prevent overimmunity, inhibit the role of cytotoxic T cells in a variety of tumors, and are generally believed to be associated with tumor immune escape (49).