Preactivation doseresponse of IL-12 and IL-18 for memory-like NK cell induction. Purified (≥ 95% CD56⁺CD3⁻) NK cells were preactivated for 16 hours with the indicated concentrations of IL-12 + IL-18 or control conditions (C; 1 ng/mL of IL-15 only). After preactivation, cells were washed as in Figure 1A and then rested for 7 days in 1 ng/mL of IL-15 before restimulation with IL-12 + IL-15 for 6 hours to assess IFN-γ production (n = 4; 2 independent experiments). Summary data are shown as means ± SEM percentage of IFN-γ⁺ CD56^bright (A) and CD56^dim (B) NK cells. Statistical comparisons are made between the indicated dose of IL-12 and IL-18 and the control cells. *P < .05; **P < .01