HLA-DRB1 and acute lymphoblastic leukemia: Further, a highly powered study of children with medically refractory ALL, those being considered for or going to stem cell transplantation, has revealed highly significant associations to both HLA class I (HLA-A and -B) and class II (HLA-DRB1), results which may shed light on the role of HLA in the less severe disease form of pediatric ALL.