Human leukocyte antigen (HLA) typing is used to match you with a donor for your bone marrow or cord blood transplant. This is not the same as ABO blood typing. HLA is a protein – or marker – found on most cells in your body. Your immune system uses HLA markers to know which cells belong in your body and which do not.
Be The Match Registry® is a listing of potential donors and cord blood units and their HLA types. The best transplant outcome happens when a patient’s HLA and the donor’s HLA closely match.
HLA matching basics
Half of your HLA markers are inherited from your mother and half from your father. Each brother and sister has a 25%, or 1 in 4, chance of matching you, if you have the same mother and father. It is highly unlikely that other family members will match you. Under very rare circumstances, family members other than siblings may be tested.
About 70%, or 7 out of 10, patients who need a transplant do not have a suitable donor in their family. If you do not have a donor in your family, your transplant team may look for an unrelated donor or cord blood unit for you on Be The Match Registry. When a search is done on the Be The Match Registry, it includes a search of more than 21 million potential adult donors and more than 590,000 cord blood units on lists from around the world.
Role of HLA matching
HLA matching is important because a close HLA match:
- Increases the likelihood of a successful transplant.
- Improves engraftment—when the donated cells start to grow and make new blood cells in you.
- Reduces the risk of complications after transplant, especially graft-versus-host disease (GVHD). GVHD is a potentially serious complication. GVHD occurs when the immune cells, which are part of the donated marrow or cord blood, attack your body.
HLA matching requirements
There are many HLA markers. Each HLA marker has a name. The names are letters or combinations of letters and numbers. Doctors review at least 8 HLA markers for these minimum requirements: two A markers, two B markers, two C markers, and two DRB1 markers. Some doctors look for an additional marker, called DQ, to match.
An adult donor must match at least 6 of these 8 HLA markers. Many transplant centers require at least a 7 of 8 match. Because cord blood cells are less mature than adult donor cells they have less strict matching criteria. A cord blood unit must match at least 4 of 6 markers at HLA-A, -B, and -DRB1. These guidelines are based on scientific studies of transplant results.
Example A shows that the patient's markers match the donor's. When HLA markers A, B, C, and DRB1 from the patient and the donor match, it is called an 8 of 8 match. When A, B, C, DRB1, and DQ markers all match, it’s called a 10 of 10 match.
Example B shows that one of the patient's A markers does not match one of the donor's A markers. Therefore, this is a 7 of 8 match or, if the DQ marker matches, a 9 of 10 match.
Confirmatory HLA Typing
HLA typing is a complex process that can be done at different levels of detail. Patients always have HLA typing done at a high level of detail. Blood is tested using laboratory methods that check the exact HLA markers.
Every potential donor has a special type of detailed HLA typing (also called confirmatory typing) done before being chosen as the best match for a patient. Confirmatory typing is done to make sure the patient and potential donor match at a detailed level.
View your potential matches
If you know your HLA typing, you may use MatchView® to view potential matches for your HLA type. This tool will show you how many potential donors and cord blood units may be available on the registry at the time that you use the tool. Keep in mind that there are many factors that go into choosing the very best possible match for you. You may have more or fewer actual donors than what is shown. MatchView does not search our partner international registries. Ask your doctor to go over the results with you.
Other factors for a successful transplant
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HLA matching is the most important factor but not the only factor that can affect your chances of having a successful transplant.
- The number of blood-forming cells needs to be suitable for the size of the patient. Larger patients need more blood-forming cells. Cord blood units have fewer cells than adult donors. Sometimes, more than one cord blood unit is needed for a patient.
- Different donor characteristics have an impact on a transplant’s success. These include the donor’s:
- Blood type
- Body size
- The number of times a female donor has been pregnant
If more than one well-matched adult donor is found for you, your doctor will look at these factors.
- Infection history can also affect transplant outcomes and choice of a donor. Before transplant, doctors test patients and donors for a common virus called cytomegalovirus (CMV).
Finding donors for patients with less common HLA types
Transplant centers may face a greater challenge finding a match for some patients because some HLA types are less common. HLA types are inherited, so the best chance of finding a suitable donor may be with someone of a similar racial or ethnic background. Some people have very diverse tissue types that reduce the chances of finding suitably matching donors.
Be The Match® focuses on adding potential donors and cord blood units from diverse backgrounds to the registry so that all patients in need of a transplant can receive one.
Be The Match uses state-of-the-art technology to help transplant centers predict which donors are most likely to match an individual patient when tested further. Be The Match has HLA experts that can assist your transplant team if your search is especially challenging.