How to select the donor when there is a choice of several HLA-matched donors?
Allogeneic hematopoietic stem cell transplantation (HSCT) was developed to cure otherwise incurable leukemia.2 Whereas HSCT was initially restricted to patients who had a human leukocyte antigen (HLA)–matched sibling donor, more and more patients with otherwise incurable leukemia benefit from HSCT by the expansion of the donor pool through the recruitment of matched unrelated volunteer donors. HLA matching for HLA class I and II alleles is still the most important criterion for donor selection. Beyond the eradication of leukemic cells by the myeloablative regimen and the replacement of defective bone marrow by the allogeneic graft, the success of HSCT depends to a large extent, on the balance between the donors’ alloreactive T lymphocytes against the recipients’ tissues (graft-versus-host disease [GVHD]) and the favorable reaction of the donors’ T lymphocytes toward the leukemic cells (graft-versus leukemia effect [GVL]).3 More recently, it has also been shown that the recipients’ inna
