NKG2A⁺ NK cell responses toward HLA-E–expressing cell lines and AML blasts. (A) Degranulation responses of IL-2–stimulated NKG2A⁺ NK cells (n = 8) toward .221-WT, .221-AEH, T2 cells without HLA peptide (Ctrl), and T2 cells with HLA peptide (T2-E). (B) Comparison of remaining response of NKG2A⁺ NK cells with the presence of HLA-E compared with the response observed in the HLA-E⁻ control cell lines. (C) HLA-E expression in .221-WT and .221-AEH cells and titration curve with HLA peptide of HLA-E expression in T2 cells. (D) Percentage of CD107a⁺ cells among IL-2–activated NKG2A⁺ NK cells after exposure to T2 cells with indicated HLA-E expression. (E) Expression of MHC class I and HLA-E on PBMCs from healthy donors (n = 10) and on CD34⁺ AML blasts (n = 8). (F) Frequency of CD107a⁺ NK cells in indicated NK cell subsets against HLA-matched CD34⁺ AML blasts from 8 patients. (G) Frequency of CD107a⁺ NK cells (unstimulated, n = 10; IL-2 stimulated, n = 12) in indicated NK cell subsets against HLA-matched CD34⁺ AML blasts from 2 patients that triggered substantial degranulation in (F). n.s, not significant. *P < .05, **P < .005, ***P < .0005.