KIR3DL1 and leukemia: These include (a) testing donor NK KIR expression (genotype or phenotype) and the corresponding HLA [KIR-ligands (KIR-Ls)] in recipient, known as the receptor–ligand model, (b) determining HLA class I typing (KIR-Ls) in both donor and recipient, known as the ligand–ligand model, or (c) performing functional analysis of NK cell alloreactivity, where donor NK cells are tested for their ability to lyse a cell line or the recipient’s leukemia cells, known as the cytotoxicity model (78–81).