Impact of donor KIR2DS1 in C1-positive patients. This figure shows the cumulative incidences of relapse (left panels) and overall survival (right panels) of patients grouped according to their donors’ KIR2DS1-status (absence vs presence) and according to the patients’ C1/C2-ligand status. The upper panels show outcomes of C1-positive patients (ie, C1/C2 or C1/C1 patients). The lower panels show outcomes of C1/C2-positive patients only. This subgroup of patients whose leukemia cells express C2, the activating ligand for KIR2DS1, should have the greatest benefit of KIR2DS1-positive donors. Patients were classified according to the algorithm published by Venstrom et al¹⁸  in 2012. The HRs were calculated in multivariable Cox regression models adjusted for patient age, donor age, disease risk index, Karnofsky performance status, sex match, cytomegalovirus match, HLA match, conditioning intensity, T-cell depletion, and stem cell source. The P values represent the Wald tests.