To investigate the mechanisms underlying the cytotoxic effects of CD8+NKT-like cells against tumor cells and MDSCs, we examined the expression of cytotoxicity-associated molecules such as granzyme B, perforin, Fas ligand (FasL), tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), IFN-γ, and TNF-α in CD8+NKT-like cells, NK cells and NK1.1−CTLs. The gene discussed is PRF1; the disease is neoplasm.