HLA matching promotes the growth and development of new healthy blood cells called engraftment and reduces the risk of a post-transplant complication called graft-versus-host GVHD disease. Learn more details about HLA matching. HLA basics Human leukocyte antigen HLA typing is used to match patients and donors for bone marrow or cord blood transplants.
There are two antigens for each letter and they are identified by numbers. So, your HLA type might look something like this:. Children born of the same parents may inherit the same combination or a different combination of antigens. Except for identical twins and some brothers and sisters, it is very rare to get an exact match between two people, especially if they are unrelated.
The chance of finding an exact match with an unrelated donor is about one in , Although we try to match antigens as much as possible for kidney and pancreas recipients, we do transplant organs into recipients who have no antigens in common, and these patients do very well. The details of this depend on the specific type of transplant and on other medical circumstances.
Stem cell transplantation is often a greater challenge than solid organ transplantation in terms of the importance of a good HLA match. In both, there is a risk that the cells of transplant recipients may attack the donated tissue.
But in a stem cell transplant, there is also a chance that some of the donated cells may also attack the cells of the transplant recipient. This is known as graft-versus-host disease. For example, 10 years after a kidney transplant, you are more likely to still have a functioning kidney if you received a kidney with a full HLA match than if you received only a half HLA match.
Different healthcare providers and medical institutions may have different guidelines about the number of HLA matches needed to go ahead with a transplant.
But in certain situations, you might still be able to have a transplant with a smaller number of matches. In other cases, you may want to receive other treatments while you wait for a better match to potentially become available. Information about your HLA type is included in databases that link potential donors to recipients.
It is one of many factors that determine who receives them. Similarly, people are encouraged to volunteer to have HLA typing done, so that information can be added to a registry of potential bone marrow donors.
If an HLA match to someone needing bone marrow is found, these people may be contacted to see if they can donate. Ask your healthcare team as many questions as you need to feel comfortable. The bottom line is that HLA typing is an important step in your healthcare treatment plan.
Finding a good match will give you the best chance that your transplant will successfully treat your condition, and that your new tissue will work for years to come. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.
Choo SY. The HLA system: genetics, immunology, clinical testing, and clinical implications. Yonsei Med J. Tiercy JM. How to select the best available related or unrelated donor of hematopoietic stem cells?
Khaddour K, Mewawalla P. Hematopoietic stem cell transplantation. In: StatPearls. Updated March 2, Downing J. The lymphocyte crossmatch by flow cytometry for kidney transplantation.
Methods Mol Biol. Bone Marrow Transplant. American Association for Clinical Chemistry. HLA testing. Updated July 10, Acute graft versus host disease: a comprehensive review. In some cases, one way matching of rare antigens with a closely related common antigen may be permitted due to the relative disadvantage to the patient with rare antigens in receiving a well- matched kidney.
The list of antigens and criteria are reviewed annually. All antigens recognized by the World Health Organization WHO Nomenclature Committee are on the list; in addition, the list includes some 4-digit names representing alleles that may be readily identified by low resolution molecular testing and represent unique antigens, not yet recognized by the WHO serologic nomenclature. Because the criteria have changed over the years and also because the identification of antigens has improved over time, there is some confusion as to how the match algorithm works 7.
In recognition of the problems associated with the identification of rare splits, the Histocompatibility Committee has defined criteria that determine which splits antigen subtypes match only themselves and which match the parent antigen as well. See examples below. These criteria incorporate the consensus typings for antigens reported by several proficiency testing PT and cell exchange programs, as well as data from molecular typing kits. They are based on the premise that antigens identified consistently by participating laboratories should be readily definable during routine cadaver donor testing.
Unfortunately, an obvious consequence of this system is that non-equivalence in matching may occur when one split is commonly identified and the other split is not well defined. When typing potential organ recipients, the laboratory has the time to do additional testing to clear up any ambiguities before the recipient is placed on the waiting list.
However, the rapid typing of cadaver donors does not always allow time to resolve these ambiguities. Therefore, a misinterpretation of data is more likely to occur for difficult-to-assign antigens with a donor than for the recipient type.
This is becoming less of a problem as more labs use molecular typing for donor testing. Nonetheless, the Histocompatibility Committee recognizes the problems inherent in the typing of donors and has tried to address them in the structure of the matching criteria. The criteria used take into account the desire to match donor and recipient as closely as possible, considering those situations where there may be a high degree of difficulty in identifying the correct antigen.
The criteria differ somewhat for Class I and II antigens, so they are discussed separately below. Some splits of DR match other splits and some do not. This is best shown by example:. A donor is entered as a DR The donor will match a recipient with DR15 or the parent antigen, DR2.
A donor is entered as DR The donor will match a recipient with DR2, 15 or. DR and have not reached consensus; nonetheless, some labs have the capability of reporting these antigens, and may do so if they are unequivocally identified. Despite the fact that some DR splits match other splits of the same broad DR antigen, it is highly recommended that ALL identified splits be entered into UNet sm for both donors and recipients.
In most cases, this is routinely done. This number is, in part, due to reporting of molecular typings as DR3 instead of DR17 or However, it is possible to differentiate DR17 from DR 18 using molecular testing. While matching will occur between broad antigens and their splits, it is of importance to the integrity of the UNOS data that whenever DR split antigens can be identified with confidence, they should be reported as splits.
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