In the univariate analysis, performed using demographic factors and transplantation variables such as sex, age (>14 years or ≤14 years), diagnosis (AML or ALL), status at transplant (first CR vs. >first CR), type of conditioning (myeloablative vs. reduced-intensity), KIR-ligand absence, and number of HLA disparities (6/6, 5/6 match vs. 4/6 match), the unique factor significantly associated with PR was KIR-ligand absence. This evidence concerns the gene KIR3DL1 and acute lymphoblastic leukemia.