HLA‐haplotype redundancy and rareness in Canadian Blood Services' Stem Cell Registry and Cord Blood Bank: Novel metrics for optimizing utility.

Background: The utility of unrelated donor registries that support allogeneic hematopoietic cell transplantation could be optimized through greater understanding of redundancy and rareness of HLA phenotypes. Methods: HLA phenotype rareness was determined using known HLA haplotype frequencies. Donor redundancy was determined through pairwise comparison of donor HLA profiles within an inventory. Results: Among 61,730 registrants in the Canadian Blood Services (CBS) Stem Cell Registry (SCR) with high resolution HLA typing at 5 loci, 6.6% of HLA phenotypes were redundant with variation across ethnic groups (8.3% of Caucasian phenotypes; 8% of Native American/First Nations, 4.4% of Asia‐Pacific Islanders (API), 2.1% of Hispanic, 0.7% of African‐American (AFA), and 4.5% of other ethnicities). A total of 18.5% of registrants had redundant HLA phenotypes with variation across ethnic groups. All 3716 cord blood units in the CBS's cord blood bank (CBB) had high resolution HLA typing at 5 loci and 202 units were redundant (5.4%) comprising 78 HLA phenotypes, with varying rareness. Repeated HLA phenotypes were from Caucasian donors (77%), multiple ethnicity (13%), API (9%), and AFA (1%). Registrants and CBUs with AFA ethnicity had the rarest phenotypes while Caucasian ethnicity was associated with the most common HLA phenotypes. Conclusions: Redundancy was greater in the SCR compared to the CBB and was most common with CAU ethnicity. Recruiting non‐Caucasian registrants and continued cord blood banking should reduce redundancy. A sub‐inventory of redundant donors and cord blood units could support new uses for donor‐supported cellular therapies that do not require HLA matching. [ABSTRACT FROM AUTHOR]