A series of seminal studies have shown that in hemi-compatible HSCT, those recipients whose HLA molecules are mismatched to the donor KIR have a lower rate of post-transplant relapse, suggesting a strong NK-mediated graft-versus-leukemia (GvL) effect, whereas KIR mismatch did not lead to GVHD (40). This evidence concerns the gene KIR3DL1 and graft versus host disease.