Noninherited maternal antigens identify acceptable HLA mismatches: benefit to patients and cost-effectiveness for cord blood banks.

Cord blood unit (CBU) transplantations to patients mismatched for only 1 HLA antigen, which is identical to the CBU noninherited maternal antigen (NIMA), are designated as having a 6/6 "virtual" NIMA-matched phenotype and have a prognosis similar to 6/6 inherited HLA-matched CBUs. Such virtual HLA phenotypes of CBUs can be created by replacing the inherited alleles with 1 or more NIMAs. Phenotypes of Dutch patients (n = 2020) were matched against the inherited and virtual HLA phenotypes of the National Cord Blood Program CBU file (with known NIMA, n = 6827). Inherited 6/6 matches were found for 11% of the patients. Including virtual phenotypes resulted in, overall, 19-fold more different phenotypes than were inherited, conferring 6/6 virtual matches for an additional 20% of the patients, whereas another 17% might benefit from CBUs with a 4/6 HLA match and 1 NIMA match (4/6 + 1NIMA or 5/6 virtual match). The elucidation of donors' maternal HLA phenotypes can provide significant numbers of 6/6 and 5/6 virtually matched CBUs to patients and is potentially cost effective.