What is HLA?

Human leukocyte antigens (HLA) are proteins found on most cells in the human body. Your immune system uses HLA to identify which cells belong in your body and which do not. Doctors use HLA typing to match blood stem cell donors with patients, but it’s not as simple as it sounds. Your body has 12 unique HLA markers (proteins), creating millions of possible combinations for doctors to consider when searching for a match.

HLA typing

HLA typing begins with having your blood drawn or the inside of your cheek swabbed. Your doctor will send the blood sample or cheek swab to a lab where it’s tested to determine your HLA type.

Your doctor may ask some of your family members to get HLA typed too, since you’re more likely to find a match from someone who shares your ethnic background.

HLA matching

Once your HLA type has been confirmed, your doctor will compare it to your family members and potential donors and cord blood units (CBU) on the NMDP Registry^SM to see if there is a suitable match. When pairing a donor and patient for a blood stem cell transplant, there are three different types of matches doctors can use.

Full match - When a patient and donor share all the same HLA markers, it is considered a full match. This is the best possible type of match, but it’s also the hardest to find.

Partial match - With advances in transplant, it’s also possible for some patients to safely receive a transplant from a donor that’s a partial match. In a partial match type, the donor matches most, but not all of the recipient’s HLA.

Haploidentical match - For other patients, a haploidentical (haplo) match is the best option. A haplo match is when a patient and donor share half of the same HLA.

Clinical trials and research are making it easier to find a suitable match for everyone who needs a blood stem cell transplant. Your doctor will use detailed testing to choose the best donor for you within your family or on the NMDP Registry. If you don’t have a fully matched donor, ask your doctor if joining an NMDP^SM-sponsored Donor for All clinical trial could be right for you.

You can also get help finding and joining a clinical trial through the no-cost Jason Carter Clinical Trials Search and Support (Opens in a new tab) program.

HLA is inherited, so you are most likely to match a sibling or an unrelated donor of a similar ethnic background. Sometimes it’s hard to find a fully matched donor because some HLA types are less common.

Matching with siblings

In your family, each brother and sister who shares the same parents as you has a 25% chance (1 in 4) of being a full HLA match. About 70% (7 out of 10) of patients who need a transplant won’t have a fully matched donor in their immediate family. Extended family members are not likely to be full HLA matches.

Matching with parents

Because you inherit half of your HLA from your mother and half from your father, parents and children share half of the same HLA. This means your parent or child could be a potential donor for a haploidentical transplant.

Matching with donors from similar ethnic backgrounds

A person’s ethnic background plays an important role in finding a match. In the same way patients are more likely to match with a sibling because HLA is inherited, they have a better chance of finding a match from an unrelated donor of the same ethnicity.

HLA typing can be performed at:

• A transplant center
• A cancer clinic or cancer center

HLA typing should be done as soon as possible after your diagnosis. If you haven't been to a transplant center yet, your doctor can have your HLA typing done for free through our NMDP HLA Today program (Opens in a new tab).

If you still have questions or concerns, please contact our Patient Support Center for assistance:

• Call or text: 1 (888) 999-6743
• Email: patientinfo@nmdp.org

If you are a hematologist or oncologist who would like to learn more about our HLA Today program, visit network.nmdp.org (Opens in a new tab) or email us at HLAToday@nmdp.org.

Your doctor wants to find the best possible donor or cord blood unit match for you because it:

• Improves the chances for a successful transplant.
• Helps your donor cells engraft and make new blood cells in your body.
• Reduces the risk of complications like graft-versus-host disease (GVHD). GVHD happens when the immune cells from donated cells (the graft) attack the recipient’s cells (the host).

Based on your HLA markers, your best match could be a full, partial or haplo match. There are factors beyond HLA that also help your doctor decide on the best donor or cord blood unit for you. If you have questions, talk to your transplant team. They’ll be able to answer any questions specific to your case about HLA matching or how they’ll choose a donor.