Impact of Allele-Level HLA Mismatch on Outcomes in Recipients of Double Umbilical Cord Blood Transplantation

Highlight
• A high degree of allele-level HLA mismatch did not adversely affect transplant outcomes.
• A high degree of HLA mismatch may be associated with reduced relapse of acute leukemia.

The impact of allele-level HLA mismatch is uncertain in recipients of double umbilical cord blood (UCB) transplantation. We report a single-center retrospective study of the clinical effect of using allele-level HLA mismatch HLA-A, -B, -C, -DRB1, and -DQB1 of the 2 UCB units. We studied 342 patients with hematologic malignancy. Donor–recipient pairs were grouped according to the number of matched HLA alleles, with 32 matched at 9-10/10, 202 at 6-8/10, and 108 at 2-5/10 alleles. The incidence of hematopoietic recovery, acute and chronic graft-versus-host disease, and nonrelapse mortality and treatment failure was similar between groups. In an exploratory analysis of 174 patients with acute leukemia, after adjusting for length of first remission and cytogenetic risk group, a 2-5/10 HLA match was associated with lower risk of relapse and treatment failure. These data indicate that a high degree of allele-level HLA mismatch does not adversely affect transplant outcomes and may be associated with reduced relapse risk in patients with acute leukemia.