Cord-blood transplantation (CBT) can cure life-threatening blood disorders. The HLA-B leader affects the success of unrelated donor transplantation but its role in CBT is unknown. We tested the hypothesis that the HLA-B leader influences CBT outcomes in unrelated single-unit cord-blood transplants performed by Eurocord/European Blood and Marrow Transplant (EBMT) centers between 1990 and 2018 with data reported to Eurocord. Among 4822 transplants, 2178 had one HLA-B mismatch of which 1013 were HLA-A and HLA-DRB1-matched. The leader (M or T) was determined for each HLA-B allele in patients and units to define the genotype. Among single HLA-B-mismatched transplants, the patient/unit mismatched alleles were defined as leader-matched if they encoded the same leader, or leader-mismatched if they encoded different leaders; the leader encoded by the matched (shared) allele was determined. The risks of GVHD, relapse, non-relapse mortality and overall mortality were estimated for various leaderdefined groups using multivariable regression models. Among the 1013 HLA-A, -DRB1- matched transplants with one HLA-B mismatch, increasing numbers of cord-blood unit M-leader alleles was associated with increased risk of relapse (hazard ratio [HR] for each increase in one M-leader allele 1.30, 95% confidence interval [CI] 1.05 to 1.60, P 0.02). Furthermore, leader mismatching together with an M-leader of the shared HLA-B allele lowered non-relapse mortality (HR 0.44, 95% CI 0.23 to 0.81; P 0.009) relative to leader-matching and a shared T-leader allele. The HLA-B leader may inform relapse and non-relapse mortality risk after CBT. Future patients might benefit from the appropriate selection of units that consider the leader.
Unrelated Donor Cord Blood Transplantation for Children with Severe Sickle Cell Disease: Results of a Phase II Study from the Blood and Marrow Transplant Clinical Trials Network
