CD4 and neoplasm: Tregs regulate the immune response of cells in the tumour microenvironment through the following mechanisms:(a) secreting immunosuppressive factors, such as TGF-β and IL-10, which enhances immunosuppression by decreasing CD8+ T-cell toxicity, suppressing CD4+ T-cell differentiation, promoting Treg transformation, and inhibiting NK-cell proliferation (68).(b) killing effector T cells and antigen-presenting cells by granzymes and perforins (45).