Simulation of non-inherited maternal antigens acceptable HLA mismatches to increase the chance of matched cord blood units: Hong Kong's experience

In Cord blood transplantation (CBT), the non-inherited maternal antigen (NIMA) virtual six HLA matched CB is found to have similar outcomes to six HLA inherited matched CB. Such virtual HLA matched CB units can be generated by substituting the inherited alleles with one to three NIMAs. In Hong Kong Cord Blood Bank, CB units have no NIMA defined. 100 CB samples were collected with NIMA defined. Retrospective searches of Hong Kong patients (n = 520) were matched against the inherited and virtual HLA phenotypes of NIMA CB file. One to three NIMA matches was analyzed, virtual six HLA matches were identified for 31.7% patients, 29.4% from CB units with 5/6 HLA match with 1 NIMA match and 1.7% CB units with a 4/6 HLA match and 2 NIMA matches. However, searches in the 167,201 Bone Marrow Donors Worldwide CB units with defined NIMA did not yield similar increases, possibly due to the ethnicity differences between populations. The match performance rises from 26% to 60% after including the NIMA match. Comparing the match performance of 32% in a previous Dutch study, we calculated with 60% matching in this smaller size study. This provides a solid ground to considering NIMA in stem cell donor selection which was adopted in some centers, to be extended to Asian and local CB registries to increase the chance for matches and also to improve patient outcomes, increase the utilization of CB units, enhance clinical flexibility and signify economic intelligence.