Patients with an AA KIR genotype receiving a transplant from a donor with a Bx genotype have poorer clinical outcome following HLA-matched sibling transplantation for myeloid disease. A. Kaplan-Meier analysis of disease-free survival in myeloablative AML/MDS patients (n=59) with the KIR genotypes (i) donor-AA/recipient-AA (n=2/12), (ii) donor-AA/recipient-Bx (n=0/5), (iii) donor-Bx/recipient-AA (n=4/8) and (iv) donor-Bx/recipient-Bx (n=5/34). The equality of all four curves was tested (d.f.=3, p=0.02). B. Kaplan-Meier analysis of acute GVHD grade II-IV in myeloid patients (n=112) with different KIR genotype combinations. The equality of all four curves was tested (d.f.=3, p=0.13). Pairwise comparisons of the curves was then performed by Cox proportional hazard modeling, where the overall type I error rate was controlled by the initial test. Comparison of aGVHD between (i) donor-AA/recipient-AA (n=2/20) patients and: (ii) donor-AA/recipient-Bx (n=2/10, p=0.5); (iii) donor-Bx/recipient-AA (n=5/11, p=0.04; hazard ratio=5.8, 95% CI=1.1-30.3); and (iv) donor-Bx/recipient-Bx (n=21/71, p=0.14). ‘Bx’ and ‘(n=)’ are defined in Figure 2.