Consideration of noninherited maternal Ags as permissible HLA mismatches in cord blood donor selection

In cord blood (CB) transplantation, virtual 6/6 HLA matches, whereby the donor–recipient mismatch is identical to the CB noninherited maternal Ag (NIMA), have similar outcomes to inherited 6/6 matches. In the UK-British Bone Marrow Registry (BBMR), 4707 of the total 21 020 CB donors have the NIMA defined. Retrospective searches of these donors, for 1–3 NIMA matches, identified a virtual 6/6 match for 31.4% of 274 European Caucasoid (EC) and 25.4% of 67 other ethnicity (OE) patients. Patients weighing ⩽50 kg were also evaluated for a single graft with adequate cell dose. In 125 EC patients, 6/6 HLA matches were identified for 24.0% and virtual 6/6 matches were identified for a further 21.6%. The remaining EC patients had a 5/6 (30.4%) or a 4/6 (22.4%) match. In OE patients, 6/6 HLA matches were identified for 9.3% and virtual 6/6 matches were identified for a further 18.7%. The remaining OE patients had a 5/6 (30.2%) or a 4/6 (37.2%) match. Searches were also performed using the 26 735 Bone Marrow Donors Worldwide CB with defined NIMA and yielded comparable increases. Considering NIMA as permissible mismatches in donor selection therefore increased the availability of a 6/6 match in this cohort.