A bone marrow transplant, also known as a hematopoietic stem cell transplant, replaces damaged or diseased bone marrow with healthy stem cells. This procedure restores the body’s ability to produce healthy blood cells. It treats various conditions, including cancers like leukemia and lymphoma, and non-cancerous blood disorders such as aplastic anemia or sickle cell anemia.
Understanding Blood Types
Blood types are determined by specific proteins, called antigens, on the surface of red blood cells. The ABO blood group system classifies blood into four main types: A, B, AB, and O. Type A blood has A antigens, type B has B antigens, type AB has both, and type O has neither. The Rh factor further classifies blood as Rh-positive or Rh-negative, based on the RhD antigen. Both ABO and Rh status are routinely checked for blood transfusion compatibility.
Blood Type and Bone Marrow Transplant
Blood type is not the primary factor for a successful bone marrow transplant. While blood type compatibility is important for red blood cell transfusions, the stem cells used in a transplant are immature blood-forming cells. These donor stem cells will eventually produce all types of blood cells, changing the recipient’s blood type to match the donor’s. If an ABO blood type mismatch occurs, medical teams can manage it with specific procedures, such as removing plasma or depleting red blood cells from the donor’s marrow. These steps are manageable and do not prevent a necessary transplant.
The Importance of HLA Matching
The most significant factor for a successful bone marrow transplant is Human Leukocyte Antigen (HLA) compatibility. HLA proteins on cell surfaces help the immune system distinguish “self” from “non-self,” identifying foreign invaders. A close HLA match between donor and recipient prevents severe complications after transplant. These include Graft-versus-Host Disease (GVHD), where donor immune cells attack the recipient’s tissues, and transplant rejection, where the recipient’s immune system attacks donor cells. More matching HLA markers lower the risk of these complications and increase the likelihood of successful engraftment. HLA matching is more complex than ABO blood typing due to the vast number of possible types. Doctors assess multiple HLA markers, aiming for high compatibility, often 8 to 10 or even 12 different markers. This genetic diversity makes finding a perfect match challenging.
Finding a Compatible Donor
Finding a compatible donor for a bone marrow transplant, especially one with a close HLA match, is complex due to the diversity of HLA types. Siblings have the highest probability of being a match, with about a 25% chance of a full HLA match. However, most patients do not find a suitable donor within their family. Parents are always a half-match with their children, but rarely a full match. For most patients, finding an unrelated donor through national and international registries is necessary. Organizations like Be The Match (National Marrow Donor Program, NMDP) maintain large registries of volunteer donors and umbilical cord blood units. These registries facilitate searches by comparing the patient’s HLA profile with registered donors worldwide. The process of finding a match can take time, sometimes months, particularly if the patient has a less common HLA type.