HLA
When you register as a stem cell donor, your HLA typing is determined. Based on this typing, we can see if there is a match between you as a donor and a patient. The HLA typing is done in a laboratory using the cheek swabs made with three cotton swabs during the registration process. On this page, we explain what exactly HLA is.
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What is HLA?
HLA is short for Human Leukocyte Antigens. HLA consist of different proteins found on the outside of virtually all cells in your body. HLA are shaped like little ‘grabbers’ and are part of your body’s immune system. These grabbers can determine whether something is a part of your body or a foreign object. For example, they allow your body to recognize and attack bacteria to keep you healthy.
The components that make up HLA proteins can have tens of thousands of variants. All these components can be combined in different ways. Together, they form your specific HLA profile. In other words, there are huge numbers of different HLA profiles. That is what makes it so difficult to find someone with exactly the same combinations as a patient in need. Finding a single match for a patient therefore requires a very large group of donors.
Why do the donor's and the patient's HLA typing need to match?
During a stem cell transplantation, a donor's stem cells are introduced into the patient's body. The goal is to trigger a minor immune response in the patient's body. This means that the donor cells see the patient's body cells as foreign objects. That allows the donor cells to recognize and attack the patient's sick cells.
When the donor cells destroy the patient's sick cells, it gives the patient a chance of recovery. At the same time, this immune response should not be too severe and cause the donor cells to also attack and destroy the patient's healthy cells. If that happens and the donor cells start attacking the patient's body, this can have serious consequences for the patient's health. It is therefore vitally important that a donor's HLA typing matches that of the patient as closely as possible.
What is the chance of finding a match within a patient's family?
A patient must receive stem cells from a donor with the same HLA typing. The genetic information for the HLA is hereditary. Everyone receives half their HLA from their father and half from their mother. This means you are unlikely to be a full match with your father and/or your mother, but only half. The chance of matching with one of your siblings is 25%.
Other family members
In most cases, cousins share no more than 50% of their HLA profile. Sometimes, certain HLA profiles are so common in a population that the same profile occurs multiple times in one family. In such cases, it is possible to find a full match between parents/children/cousins. However, the chance of this happening is small.
