Natural killer (NK) cells are innate lymphocytes that have been used in many clinical trials due to they are endowed with potent cytotoxic activity including the direct release of perforin and granzymes, carrying out antibody-dependent cellular cytotoxicity (ADCC) through the CD16 membrane receptor, and utilizing Fas ligand (FasL) or TNF-related apoptosis-inducing ligand (TRAIL) to trigger target cell apoptotic pathways [18], which could target cancer cells in an antigen-independent and non-major histocompatibility complex (MHC)- restricted manner [19]. The gene discussed is FASLG; the disease is cancer.