The risks after unrelated - donor haemopoietic - cell transplantation with matched HLA - A, HLA - B, HLA - C, HLA - DRB1, HLA - DQB1 alleles between donor and recipient can be decreased by selection of unrelated donors who also match for HLA-DPB1; however, such donors are diffi cult to find. Classfi cation of HLA - DPB1 mismatches based on T-cell-epitope groups could identify mismatches that might be tolerated (permissive) and those that would increase risks (non - permissive) after transplantation. We did a retrospective study to compare outcomes between permissive and non - permissive HLA - DPB1 mismatches in unrelated - donor haemopoietic - cell trans plantation.