The increase of the global donor inventory is of limited benefit to patients of non-Northwestern European descent.

Between 2001 and 2012, the number of unrelated donors registered worldwide increased from 7 to 21 million, and the number of public cord blood units increased to over 500,000. We addressed the question of whether this expansion resulted in higher percentages of patients reaching transplantation. Unrelated donor searches were evaluated for 3,124 eligible patients in the Netherlands in two cohorts (2001-2006, n=995; 2007-2012, n=2129), comparing results for patients of Northwestern European and non-Northwestern European origin. Endpoints were 'donor found' and 'transplantation reached'. The substantial growth of the donor inventory over the period studied did not increase the median number of potential unrelated donors (n=7) for non-Northwestern European patients, but almost doubled the number for Northwestern European patients from 42 to 71. Before and after 2007, an unrelated donor or cord blood was identified for 91% and 95%, respectively, of Northwestern European patients and for 65% and 82% of non-Northwestern European patients (P<0.0001). Non-Northwestern European patients more often needed a cord blood transplant. The degree of HLA matching was significantly lower for non-Northwestern European patients (P<0.0006). The time needed to identify a donor decreased for both populations. The percentage of Northwestern European patients reaching transplantation increased from 77% to 83% and for non-Northwestern European patients from 57% to 72% (P=0.0003). The increase of the global inventory resulted in more transplants for patients lacking a family donor, although the quality and quantity of (potential) haematopoietic cell grafts for patients of a non-Northwestern European descent remained inferior, indicating the need for adaptation of recruitment.

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.