Bone Marrow Donor Matching for Patients of Mixed Race

Many patients with leukemia and other blood diseases stand a good chance of recovery and a return to normal life if they receive a stem cell transplant from a living donor. In the absence of a transplant, their survival prospects are grim. For a transplant to be successful, the HLA immune systems of the donor and recipient must be a close genetic match. This requires that they have the same set of six alleles located at three genetic loci found on the same chromosome. In sexual diploid species, two alleles are found in each genetic locus. One of these is inherited from each parent. The string of alleles that is passed from parent to child is known as a haplotype. Because the alleles that determine one’s HLA type are located close together on the same chromosome, genetic crossover is rare. Therefore with rare exceptions, HLA haplotypes remain intact from generation to generation, with each parent randomly selecting one of two possible haplotypes to pass to each of its children. Two siblings will be suitable donors for each other only if each received the same haplotype from each parent. This happens with probability one-fourth. About 70% of all patients needing transplants have no matching sibling. Those without a sibling donor must seek a match from the population at large. Finding a non-sibling match is difficult because the distribution of HLA