ABSTRACT
Replacement of damaged, defective, or diseased hematopoietic and immune systems by hematopoietic progenitor cells, through a process of transplantation, has become the treatment of choice for many congenital and acquired diseases. Unfortunately, only 25% of patients who may benefit from hematopoietic stem cell transplantation (HSCT) have a genotypically identical sibling available. When a human leukocyte antigen (HLA)–matched related donor cannot be identified, an alternative donor becomes the only available option. Despite having more than eight million volunteers in the international registries network, and increasing numbers of umbilical cord blood banked units, many patients needing HSCT still cannot identify an appropriate donor within a reasonable period of time. In general, ethnic groups other than Caucasians are poorly represented in the registries. Moreover, in some nonCaucasian ethnic groups, the probability of finding a matched donor is even smaller due to greater degree of HLA polymorphism within these populations (1-4). Unrelated banked cord blood units represent similar ethnic groups as the adult unrelated donors regestrip but can be used with a lesser degree of HLA match. Nevertheless, because of the size of the graft it cannot be used in heavy or older children. Partially mismatched related donor transplantation (PMRD-HSCT) remains the only therapeutic option available to most recipients thus has been the focus of interest for many researchers. In this chapter we will review the challenges of decreasing the risk of graft-versus-host disease (GVHD), relapse, and transplant-related mortality (TRM) while avoiding graft rejection in partially mismatched related donor transplantation.
