Of patients needing a transplant using cells from someone else, only about 30 percent have an available match within their family.
The remaining 70 percent of patients have to find a donor through a search in the network of donor registries. Luckily, for most patients, at least one good match will be found. In fact, approximately 95 percent of patients will find an acceptable match.
However, the chance of finding a match can be much lower for people of color. Because the human leukocyte antigens (HLA) used for determining a match are linked to ethnicity, patients are most likely to find a match within their own ethnic group.
Unfortunately, the number of available donors in non-white ethnic groups is considerably smaller than in white ethnic groups. To improve the chance of finding a match for everyone, it is vitally important that registries include donors from all possible ethnic groups.
Matching a patient to a bone marrow/stem cell donor relies on testing of specific proteins on the surface of white blood cells called human leukocyte antigens (HLA). This is also called histocompatibility testing or tissue typing.
These antigens play an important role in the body’s immune system by recognizing foreign cells. Even with apparently “perfect” matching, differences between the patient and donor HLA molecules can provoke graft rejection or graft-vs.-host disease.
These life-threatening complications must be controlled with immune suppressing medications until the recipient becomes tolerant of the donor cells and the donor cells become tolerant of the recipient.
Between 6 and 10 different antigens are tested for a stem cell transplant. The quality of the match is stated in terms of the number of antigens that match out of the number of possible matches, depending on the system used.
A 6 out of 6 (6/6) or 10 out of 10 (10/10) match is the best. However, many successful transplants are done with 5/6 matches using donor marrow or stem cells or 4/6 matches using cord blood. Siblings have a 1 in 4 chance of having a 6/6 match because they inherited their HLA from the same parents. Finding a good match outside of the immediate family is much more difficult.
Most marrow registries have a mechanism that allows patients and donors to contact each other if they wish to do so. If you were matched to a donor or patient registered with the NMDP, contact will be facilitated by the registry and transplant center no sooner than one year after the transplant.
Both parties will need to fill out a form stating that they wish to make contact. Hutchinson Center/SCCA patients who wish to correspond with or meet their donor after the one-year waiting period may contact Janel Minty at 206-288-6585 or email@example.com to begin the process.
If the donor does not wish to make direct contact, patients may still send an anonymous card or letter, which will be forwarded to the donor by the registry. Rules regarding contact may differ for donors registered though other organizations, even if the match was facilitated through the NMDP.