PRF1 and neoplasm: Tregs suppress anti-tumour immune effector responses in the TME, primarily by promoting an immunosuppressive microenvironment by their secretion of cytokines such as IL-10 and transforming growth factor-β (TGFβ) [57–59], and possibly by targeting anti-tumour effector immune cells and antigen-presenting cells for granzyme- and perforin-mediated killing [59–61].