WASHINGTON--As the size of the American family declines, the number of transplants from donors other than human leukocyte antigen (HLA) identical siblings can be expected to rise sharply in coming years, John A. Hansen, MD, said at a meeting on blood and marrow transplantation, sponsored by the Leukemia Society of America.
"As families get smaller, the average American has less than a 30% chance of finding an HLA match among his or her siblings," said Dr. Hansen, of the Fred Hutchinson Cancer Research Center and the University of Washington.
Dr. Hansen, along with Craig W. S. Howe, MD, PhD, CEO of the National Marrow Donor Program (NMDP), called for an expanded pool of donors to help provide matches for these patients.
Since the risk of acute graft-versus-host disease (GVHD) rises with the number of incompatible HLA loci, bone marrow transplant (BMT) specialists must look for ways to overcome inevitable mismatches and reduce the incidence and severity of GVHD.
An initial search of the NMDP registry will uncover an HLA-A, B, or DR identical match for 61% of transplant patients. At the Fred Hutchinson Cancer Research Center, higher resolution testing has shown that just 34% of patients will have at least one identical HLA-A, B, DRB1 donor, while the rest will have a donor with a minor mismatch in one antigen. Another 11% of patients will have a potential donor with at least one major mismatch.
A close match has significant implications for BMT outcomes. With a DRB1 match, the 5-year survival rate is 63%, Dr. Hansen said, but a mismatch offers a 5-year survival rate of only 37%. Moreover, a DRB1 mismatch results in more acute GVHD than do HLA-A or HLA-B mismatches.
In his presentation, Dr. Howe cited an analysis of transplants at 35 centers between 1988 and 1992. The study showed the following prognostic factors to be statistically significant in predicting a favorable outcome: a complete serological match, male donor sex, younger donor age, shorter disease duration, younger recipient age, and higher Karnofsky score.