Cytokine-induced memory-like responses by NK cells. During the pre-activation phase, NK cells are stimulated by distinct combinations of cytokines or via the FcyRIII (anti-CD16 cross-linking) in combination with cytokines. NK cells are washed and maintained in low doses of IL-15 for up to 3 weeks. Thereafter, pre-activated cells, but not those stimulated with low dose IL-15 only, display enhanced proliferative capacity and more pronounced IFN-γ responses after restimulation with IL-12 plus IL-15, IL-12 plus IL18, or cellular targets (K562 cells).