Figure 1. IL-15–primed human CD56^bright NK cells have enhanced responses to tumor target cells.

(A) Purified NK cells from normal donors underwent short-term (12–16 hours) culture in media alone (control) or media with 5 ng/ml IL-15 (primed). Cells were then washed and triggered with tumor targets. (B) Control or primed purified NK cells were incubated with K562 AML target cells for 6 hours at a 5:1 E:T ratio. Bivariate flow cytometry plots from a representative normal donor show surface CD107a as well as intracellular IFN-γ and TNF following tumor target triggering. Summary data show mean ± SEM percentage of CD107a⁺, IFN-γ⁺, and TNF⁺ NK cells. n = 14 normal donors, 7 independent experiments. (C) Flow-sorted, control or primed CD56^bright and CD56^dim NK cells were triggered with K562 tumor targets for 6 hours at a 5:1 E:T ratio. Summary data show mean ± SEM percentage of CD107a⁺, IFN-γ⁺, and TNF⁺ NK cells. n = 9 normal donors, 6 independent experiments. Data were compared using a 1-way repeated-measures ANOVA, with Bonferroni’s multiple-comparisons testing of indicated groups. *P < 0.05, **P < 0.01, ***P < 0.001.