Control and primed NK cells were assessed for the expression of 33 markers using mass cytometry following stimulation with K562 tumor targets in a functional assay. (A) Density plots from a representative donor of control and primed NK cells in the tSNE1/2 fields demonstrating the proportion of NK cells that are CD56^bright (B), immature CD56^dim (Imm), or mature CD56^dim (Mat). Percentages of NK cells belonging to the different groups are indicated in parentheses. Cell maturity state was determined according to expression of CD56, NKG2A, KIR, and CD57. Immature CD56^dim NK cells were primarily NKG2A⁺KIR^–CD57^–, whereas mature CD56^dim NK cells were primarily NKG2A⁺KIR⁺CD57⁺ or NKG2A^–KIR⁺CD57⁺. (B) Median expression of the indicated markers (CD56, NKG2A, KIR2DL2/3, CD57) is shown for the same representative donor, demonstrating that maturity marker expression is unchanged by priming. (C) Summary data show mean ± SEM percentage of CD107a⁺, IFN-γ⁺, and TNF⁺ control or primed CD56^bright, CD56^dim (immature + mature), immature CD56^dim, and mature CD56^dim NK cells from n = 8 normal donors, 3 independent experiments. (D) Summary data show mean ± SEM fold change of primed relative to control percentage CD107a⁺, IFN-γ⁺, and TNF⁺ CD56^bright, CD56^dim (immature + mature), immature CD56^dim, and mature CD56^dim NK cells from n = 8 normal donors, 3 independent experiments. Data were compared using a 1-way repeated-measures ANOVA with (C) Bonferroni’s multiple-comparisons testing of indicated groups or (D) Tukey’s multiple-comparisons testing. *P < 0.05, ***P < 0.001.