Choosing an alternative bone marrow donor among available family members

Bone marrow transplantation (BMT) can be curative for patients with hematological malignancies, marrow failure syndromes, and certain metabolic disorders. However, fewer than half of the patients who could benefit have a donor who is either an HLA-matched sibling or a phenotypically similar unrelated volunteer.

The opportunity for allogeneic bone marrow transplantation is significantly increased by the use of partially mismatched, haploidentical related donors. The likelihood of finding a donor within the family is dependent on the acceptable degree of mismatch on the unshared chromosome. The degree of mismatch is expected to be approximately 10% for a one-antigen mismatch, 20-30% for a two-antigen mismatch, and > 95% for a three-antigen mismatch. Improvements in transplant techniques designed to enhance engraftment and to prevent the development of severe acute and chronic graft-versus-host disease have increased the feasibility of utilizing this readily available donor pool. Obviously, the ability to use a three-antigen mismatched related donor would make bone marrow transplantation available for almost every patient.

Recent studies combining in vitro and in vivo immunomodulation of donor lymphocytes have resulted in consistent engraftment and control of acute graft-versus-host disease.

These findings provide encouragement that there may need be no restriction on the availability of allogeneic marrow transplants as a therapeutic option for appropriate candidates.