Memory-like NK cells proliferate and retain enhanced IFN-γ productionaftercell division. Purified NK cells were labeled with CFSE to track cell division, sorted into CD56^bright and CD56^dim NK subsets (≥ 99% purity), and preactivated and rested as per Figure 1A. After 7 days, cells were restimulated with IL-12 + IL-15 and analyzed simultaneously for IFN-γ and CFSE to track cell divisions. (A) Representative bivariate flow plots of CD56^bright and CD56^dim NK cells demonstrating that preactivation results in both increased cell division (CFSE dilution) and enhanced IFN-γ production. (B) Summary results showing the increased proliferation 7 days after preactivation (p.a.) compared with control (c) in both CD56^bright and CD56^dim NK cell subsets. (C) Summary results are shown as the means ± SEM percentage of IFN-γ⁺ by NK cell generation (n = 4 donors, 2 independent experiments). Similar findings were observed in purified NK cells that were then gated on CD56^bright and CD56^dim NK cells (n = 6 donors; 2 independent experiments; supplemental Figure 5). *P < .05; **P < .01; ***P < .001.