It would be wonderful if patients who needed bone marrow or blood stem cells for a transplant could ask any willing relative or friend to be their donor. Unfortunately, it’s not that simple.
Both patient and donor must have similar genetic markers on their white blood cells in order for the transplant to be successful.
What Are They Matching?
On the surface of your cells lie sets of proteins. Like a fingerprint, these proteins enable your immune system to distinguish between cells that belong in your body and cells that do not. If your immune system cells encounter a cell with the wrong "fingerprint", they orchestrate an immune system attack to destroy it.
Several different proteins on the surface of white blood cells, called human leukocyte antigens (HLA), play an important role in stem cell transplantation. Your donor’s HLA type needs to match yours as closely as possible.
Finding a Related Donor
Typically, a patient’s siblings are tested first to determine if they inherited the same HLA proteins from each parent as the patient. The HLA test is painless and requires only a blood sample or a swab of the inside of the donor’s cheeks.
You inherit two sets of HLA proteins from your biological parents: one set from your mother and a second set from your father. Therefore, you are a half-match with each of your parents, and your children will be a half-match with you.
Each sibling who has the same two biological parents as the patient has a 25% chance of being a ‘perfect’ match for the patient. A ‘perfect match’ means that the HLA proteins are similar.
If no sibling is a perfect match, your parents, children or a sibling who is not a perfect match may be tested as a potential donor, or your transplant team may search for an unrelated donor.
Haploidentical Related Donors
If none of your siblings is a perfect match, your doctor may suggest a haploidentical transplant. A haploidentical transplant is a transplant using cells from a related donor who only half matches your HLA type.
Finding an Unrelated Donor
In the United States, NMDP® (formerly Be The Match®) coordinates the recruitment of unrelated donors. Patients have access to more than 41 million potential adult donors and more than 800,000 cord blood units through the registry.
Your doctor can do a preliminary search of the NMDP registry to assess the likelihood of finding a donor for you. Donors with the same ethnic background as you are more likely to match you than those from a different ethnic background.
If potential donors are identified in the preliminary search, the transplant center may then request a formal search.
Once the best donor is identified, he or she will receive extensive counseling by an NMDP representative before giving final consent to donate. Potential donors undergo a complete medical evaluation to ensure they are healthy enough to donate and don’t have any medical problems that could pose a risk to you or themselves.
To learn more about being or finding an unrelated donor visit NMDP.org.
Cord Blood Units for Transplant
A transplant using blood stem cells from an umbilical cord is an option for some patients. Cord blood units do not need to match your HLA-type as closely as bone marrow or peripheral blood stem cells. They can also be made available more quickly for transplant, since they have already been collected and stored for later use.
Finding a Cord Blood Donor
A transplant using blood stem cells from an umbilical cord is an option for some patients. Cord blood units do not need to match your HLA-type as closely as bone marrow or peripheral blood stem cells. They can also be made available more quickly for transplant, since they have already been collected and stored for later use.
If More Than One Donor is Found
If more than one potential donor is available, several other factors will help your doctor determine the most suitable donor.
- Younger donors are usually preferred over older donors.
- Donors who have not been exposed to CMV.cytomegalovirus (CMV) are preferable if you, too, have not been exposed to CMV
- Some studies suggest that gender is important. Male patients transplanted with cells from a female, especially one who bore children, appear to have a higher risk of developing a complication after transplant called chronic GVHD
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Next Page: Being a Related Bone Marrow or Stem Cell Donor
Updated June 2024
