NK cells derived from myeloid (M-CSFR⁺) precursors show abundant KIR expression and higher cytotoxicity compared with lymphoid (M-CSFR⁻) precursors. (A) Expression of KIR (combination of CD158a, CD158b, and CD158e1) is higher on NK cells derived from myeloid (M-CSFR⁺) precursors (right) compared with M-CSFR⁻–derived NK cells (left). A representative donor is shown (n = 4). (B) Percentages of KIR⁺ NK cells derived from CD56⁻CD117⁺M-CSFR⁺ (▵) and CD56⁻CD117⁺M-CSFR⁻ (●) progenitors for 4 individual donors are shown (mean ± SEM; > 3 replicates for each donor). P < .001, by 2-way analysis of variance. (C) Expression of NKG2A and KIR on CD56-gated NK cells derived from CD56⁻CD117⁺M-CSFR⁻ (left) and CD56⁻CD117⁺M-CSFR⁺ (right) progenitors. Shown is the presence of a potentially alloreactive population of NKG2A-KIR⁺ population in the population derived from the CD56⁻CD117⁺M-CSFR⁺ progenitors. (D) Cytotoxicity of M-CSFR⁺–derived (▵) and M-CSFR⁻–derived (■) NK cells against K562 targets and (E) against 721.221 human leukocyte antigen–negative B-lymphoblastoid cell line. Data points represent average cytotoxicity of triplicates ± SD at the specified effector-to-target (E:T) ratios. A representative donor is shown (n = 3).