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Human leukocyte antigen (HLA) typing
To improve the chance of a successful stem cell transplant, and to lower the risk of complications, the donor’s stem cells need to match the recipient’s as closely as possible. A process called HLA typing makes sure that the donor and recipient are closely matched.
Everyone has a set of proteins called human leukocyte antigens (HLAs) on the surface of their cells. These antigens help the body’s immune system tell what belongs in the body and what doesn’t. For a stem cell transplant to work, the recipient’s immune system must think that the new stem cells belong so that it doesn’t try to destroy them. The higher the number of antigens that both the donor and the recipient share, the better the chance that the recipient’s body will accept the donated stem cells.
HLA typing is usually done by a special blood test that checks the antigens. Antigens on the donated stem cells need to be exactly the same as, or very similar to, those on the recipient’s cells. At least 6–10 specific antigens need to match. A perfect match is 6 out of 6 (6/6) or 10/10, but a transplant may be done if there is a less than perfect match (5/6 or 9/10). The highest likelihood of finding a perfect match is within the recipient’s own family (usually a brother or sister).
The recipient’s immune system might think that the new stem cells don’t belong and attack them. This is called a graft rejection. Rejection is more likely if the match is not close. This usually doesn’t happen because the treatment given before the transplant weakens the recipient’s immune system. More often, the donor stem cells think that the recipient’s cells don’t belong and attack them. This is called graft-versus-host disease (GVHD).