Mismatching at HLA-DPB1 Is Not Associated with Survival in Patients with Acquired Aplastic Anemia Who Receive Unrelated Bone Marrow Transplantation

DNA typing for HLA-A, -B, -C, -DQB1 and -DRB1 determines outcome in patients with severe aplastic anemia (SAA) who receive unrelated bone marrow transplantation (U-BMT). Based on our previous study of 300 subjects, complete matched (10/10) donors are preferable, but 1-allele-mismatched (9/10) donors are also acceptable. Several studies have addressed the additive effects of HLA-DPB1 for patients with hematological malignancies. In recent reports, HLA-DPB1 mismatching decreased the incidence of relapse, but increased the incidence of acute GVHD. However, the impact of matching for HLA-DPB1 remains unknown in SAA patients. To explore the impact of HLA-DPB1 on the outcome, we analyzed outcomes in 169 recipients with SAA who received U-BMT from an HLA complete matched or 1-allele mismatched donor through the Japan Marrow Donor Program. Median patient age was 17 years (range: 1 to 64 years), and 102 males and 67 females were included. Among 169 pairs, 101 were matched for 10/10 alleles and 68 matched for 9/10 alleles. Although the overall survival was comparable between the groups (10/10 matched group; 75.2%, 9/10 matched group; 64.5%, p=0.633), the incidence of acute GVHD (II–IV) was significantly higher in the 9/10 matched group (15.3%) than in 10/10 matched group (32.2%) (p=0.012). Therefore the impact of HLA-DPB1 matching was analyzed independently in each group. In the 10/10 matched group, 30 of 101 pairs (30%) were matched for HLA-DPB1, whereas 71 pairs (70%) were mismatched for HLA-DPB1. In the 9/10 matched group, 21 of 68 pairs (30%) were matched for HLA-DPB1, whereas 47 pairs (70%) were mismatched for HLA-DPB1. In the 10/10 matched transplants, the survival rate was comparable between the HLA-DPB1 matched group (74.4%) and the HLA-DPB1 mismatched group (75.7%) (p=0.894). The incidence of acute GVHD (II-IV) was lower in the HLA-DPB1 matched group (8.0%) than in the HLA-DPB1 mismatched group (18.1%), but this difference was not significant (p=0.193). In 9/10 matched transplants, the survival rate was comparable between the HLA-DPB1 matched group (71.4%) and the HLA-DPB1 mismatched group (61.7%) (p=0.826). The incidence of acute GVHD (II-IV) was also lower in the HLADPB1 matched group (21.0%) than in the HLA-DPB1 mismatched group (37.2%), but this difference was not significant (p=0.169). The incidence of chronic GVHD and rejection rate were not associated with HLA-DPB1 matching. In conclusion, HLA-DPB1 matching is not essential for U-BMT recipients with SAA when 10/10 or 9/10 allele-matched donors are available.