Maximizing optimal hematopoietic stem cell donor selection from registries of unrelated adult volunteers.

Today, more than 50 registries of HLA-typed potential adult hematopoietic stem cell donors have been established in 40 countries and include more than 7.5 million volunteers. HLA testing of new volunteers includes HLA-A, -B and often -DR typing at low to intermediate resolution. Searching patients are tested for these same loci, preferably at a higher level of resolution. Over 95,000 patient searches are received by registries annually resulting in approximately 4660 unrelated transplants. In 2001, nearly one-third of transplants involved a patient in one country receiving stem cells from a donor in another. The diversity of the HLA system complicates the search process, requiring sophisticated registry algorithms for matching, and expertise in allele and haplotype frequencies and associations to design search strategies. Within registries, HLA frequency data have been used to evaluate optimal registry size and composition.