Loss of Mismatched HLA on the Leukemic Blasts of Patients With Relapsed Lymphoid Malignancies Following Bone Marrow Transplantation From Related Donors With HLA Class II Mismatches in the Graft Versus Host Direction.

Mechanisms of relapse of acute lymphoblastic leukemia (ALL) after human leukocyte antigen (HLA) class II mismatched hematopoietic stem cell transplantation (HSCT) remain unclear. We report two children with relapsed ALL after HSCT from related donors with HLA-DRB1 and -DQB1 mismatches in the graft versus host direction. One lost HLA-DRB1, DQB1, and DPB1 alleles, and the other lost one HLA haplotype of the leukemic blasts at relapse. HLA class II loss may be a triggering event for ALL relapse after partially HLA-mismatched-related HSCT. In addition, HLA typing of relapsed leukemic blasts could be vital in the selection of retransplant donors.