PRF1 and neoplasm: The activated T‐cells (ie, effector T‐cells) then can recognize the relevant peptide ligands displayed by MHC molecules on tumor cells and exert tumor killing activities via various mechanisms, including secretion of cytokines such as interferon‐gamma (IFNγ) and tumor necrosis factor‐alpha (TNFα), release of cytotoxic granules such as perforin and granzyme B, and expression of apoptosis‐inducing ligands such as apoptosis antigen‐1 (FAS) and TNF‐related apoptosis‐inducing ligand (TRAIL).30, 31, 32