NK cell educational responses based on HLA-B −21. (A) Frequency of responding NK cells toward K562 cells in terms of CD107a, IFN-γ, and TNF-α positivity in unstimulated and IL-2–stimulated NK cells from donors with an M/x (red, n = 11) or T/T (white, n = 13) genotype. (B) Frequency of responding NK cell subsets in the K562 assay as in (A). (C) Frequency of CD107a⁺ NK cells against HLA-matched CD34⁺ AML blasts using unstimulated and IL-2–stimulated NK cells from M/x (red, n = 11) or T/T (white, n = 10) donors (left panel). Responses in IL-2–stimulated NK cell subsets (right panel). *P < .05, **P < .005.