Will a bone marrow transplant change one's blood type?
Or is the donor blood type matched with the person before transplant?
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Bone Marrow transplants are extensively matched in order to prevent rejection. Current matching methodology is HLA matching: Stanford Children's Hospital Guidelines
How are a donor and recipient matched?
Matching involves typing human leukocyte antigen (HLA) tissue. The antigens on the surface of these special white blood cells determine the genetic make-up of a person's immune system. There are at least 100 HLA antigens; however, it is believed that there are a few major antigens that determine whether a donor and recipient match. The others are considered minor and their effect on a successful transplant is not as well defined.
Medical research is still investigating the role all antigens play in the process of a bone marrow transplant. The more antigens that match, the better the engraftment of donated marrow. Engraftment of the stem cells occurs when the donated cells make their way to the marrow and begin reproducing new blood cells.
However, because the HLA matching doesn't utilize blood-type and the recipient's marrow is destroyed in the process, then if the donor's marrow produces different red blood cells - then so will the recipient with time:
Does my blood type change after SCT or [Bone Marrow Transplant]?
Yes. The recipients blood type eventually changes to the donor type. That means if you had a blood type of A+ prior to transplant and your donor had a blood type of O, eventually your blood type would become O. I may take several weeks, possibly months for your original blood type to disappear, but eventually it will.
What's interesting is that blood-typing is not be expressly necessary with the modern bone marrow transplant process. The danger of mixing two antagonistic blood types in vivo is that the recipient's immune system attacks the foreign red blood cells resulting in body-wide rejection. However, because the immune system's response capabilities are decimated by the destruction of the recipient's bone marrow (usually accomplished via chemotherapy or radiation), it can't mount much of an attack in the first place. That's not to say the body can't mount an attack, or that the donor's tissue can't mount an attack on the recipient (Graft-Versus-Host-Disease [GVHD]) - but the better the HLA match the less likely issues are to arise, which is why we do the more accurate and relevant HLA matching instead of blood-typing.