GRAFT REJECTION

• Graft rejection refers to the immunologic rejection of donor hematopoietic elements by the residual host immune system. Graft rejection occurs more frequently in patients transplanted for aplastic anemia and in patients receiving unrelated or mismatched transplants (because of increased donor-recipient disparity at major and minor HLA loci). Graft rejection may also be observed in reduced-intensity regimens, especially in patients who are not pretreated heavily.

• In many patients with aplastic anemia, the underlying pathophysiology reflects an autoimmune recognition of the stem cells by an aberrant immune response. Most conditioning regimens used in aplastic anemia are reduced-intensity regimens. If the conditioning regimen does not fully eliminate the abnormal immune response, the graft may fail by the same mechanism that resulted in aplastic anemia in the first place. Prior to matched related donor transplantation, family member, directed donor transfusions should not be administered to avoid alloimmunization of the patient against minor histocompatibility antigens that are common to other family members.