In a seminal study by Ruggeri et al., 57 patients with acute myeloid leukemia (AML) undergoing T cell depleted haploidentical HSCT carrying these alloreactive NK cells had a significantly lower five-year risk of disease relapse (0%) compared to those without KIR ligand incompatibility (75%), suggesting a considerable impact of KIR mismatch on the graft-versus-leukemia effect [2]. This evidence concerns the gene KIR3DL1 and leukemia.