IL18 and neoplasm: Two basic findings are the rationale and the major catalyst behind IL-18 engineering aimed for CAR T therapy: (1) IL-18 increases the potency of CAR T cells in tumor immunotherapy via the enhancement of T cell proliferation, IFN-γ production, and cytolytic activity, including cytotoxic T-cell and NK-cell-mediated cell killing; (2) in the tumor microenvironment IL-18’s natural inhibitory decoy protein, IL-18BP, reduces IL-18’s activity.