Human Leukocyte Antigen(HLA) Matching

A more common problem is that when the donor stem cells make their own immune cells, the new cells may see the patient’s cells as foreign and turn against their new home. This type of attack is called graft-versus-host disease. The grafted stem cells attack the body of the person who got the transplant. This is another reason it’s so important to find the closest match possible. HLA matching Many factors play a role in how the immune system knows the difference between self and non-self, but the most important for transplants is the human leukocyte antigen (HLA) system. Human leukocyte antigens are proteins found on the surface of most cells. They make up a person’stissue type, which is different from a person’s blood type. Each person has a number of pairs of HLA antigens. We inherit one of each of these pairs from each of our parents (and pass one of each pair on to each of our children). Doctors try to match these antigens when finding a donor for a person getting a stem cell transplant. How well the donor’s and recipient’s HLA tissue types match plays a large part in whether the transplant will work. A match is better when all 6 of the known major HLA antigens are the same — a 6 out of 6 match. People with these matches have a lower chance of graft-versus-host disease, graft rejection, having a weak immune system, and getting serious infections. For bone marrow and peripheral blood stem cell transplants, sometimes a donor with a single mismatched antigen is used — a 5 out of 6 match. For cord blood transplants a perfect HLA match doesn’t seem to be as crucial for success, and even a sample with a couple of mismatched proteins may be OK. Doctors keep learning more about better ways to match donors. Today, fewer tests may be needed, for siblings since their cells vary less than an unrelated donor. But more than the basic 6 HLA antigens are often tested on unrelated donors to reduce the risks of mismatched types. Sometimes doctors will want to look at 5 pairs of antigens, for example, to try and get a 10 out of 10 match. Certain transplant centers now require high-resolution matching, which looks more deeply into tissue types. Other centers are doing clinical trials with related half-matched donors and different chemotherapy schedules. This is an active area of research because it’s often hard to find a good HLA match.