Unlicensed KIR⁺NKG2A⁻ NK cells after HSCT demonstrate functional competence. IFN-γ response to class I–negative 721.221 target cells was calculated relative to baseline for each inhibitory KIR in each of 3 TCD-HSCT donor-recipient pairs (nos. 10, 12, and 14) by the formula (NKG2A⁻KIR⁺IFN-γ⁺/NKG2A⁻KIR⁺)/(NKG2A⁻KIR⁻IFN-γ⁺/NKG2A⁻KIR⁻). The relative response of NK cells exclusively expressing specific inhibitory KIR was compared between the allograft donor and the patient at days +100 to +200 after HSCT. (A) CD94/NKG2A-negative NK cells exclusively expressing inhibitory KIR to self-HLA from patients at days +100 to +200 are slightly hyporesponsive compared with their donors (P = .02). (B) CD94/NKG2A-negative NK cells exclusively expressing inhibitory KIR to non-self HLA from patients demonstrate higher response compared with the donor (P < .01). The paired Student t test was performed to compute the P value for these comparisons.