Bone marrow, a soft tissue inside bones, produces essential blood cells: red blood cells (oxygen), white blood cells (infection), and platelets (clotting). A bone marrow transplant replaces diseased or damaged marrow with healthy cells, treating conditions like leukemia, lymphoma, and other blood/immune disorders. Success depends on finding a compatible donor match.
The Science of Matching
Successful bone marrow transplantation relies on Human Leukocyte Antigen (HLA) compatibility. HLAs are proteins on cell surfaces that help the immune system distinguish self from foreign. Thousands of HLA types exist, inherited from parents, making genetic relatives, especially siblings, often the closest matches.
A close HLA match prevents graft-versus-host disease (GVHD), where donor cells attack the patient, and transplant rejection, where the patient’s immune system attacks donor cells. For success, doctors aim for a match of 8 to 10 specific HLA markers.
The Search for a Donor
The search for a bone marrow donor starts with immediate family. Siblings have about a 25% chance of being a perfect HLA match. If no family match is found, the search expands to national and international registries, like Be The Match in the U.S., which maintain databases of volunteer donors with recorded HLA types.
For unrelated donors, transplant centers submit the patient’s HLA type to registries. Registries conduct a computer search for potential matches. Identified donors undergo further blood tests to confirm HLA compatibility and suitability for donation.
Becoming a Donor
Registering as a potential bone marrow donor involves a cheek swab or blood sample. These are analyzed for HLA type and added to a registry database. Registration signifies a commitment to donate if a compatible match is found, and donors confirm their general health and willingness.
If identified as a match, donors undergo a health screening. Two primary methods exist: Peripheral Blood Stem Cell (PBSC) donation, used in over 85% of cases, involves injections to move stem cells into the bloodstream for collection via an apheresis machine. Traditional bone marrow donation is a surgical procedure collecting liquid marrow from the hip bone under anesthesia. Both are generally safe, with mild, temporary side effects.
When a Perfect Match Isn’t Found
Finding a perfect 10/10 HLA match is challenging, especially for patients from diverse ethnic backgrounds due to HLA type variations. If a fully matched unrelated donor isn’t available, alternative options exist. One is a haploidentical transplant, using a half-match donor (e.g., parent, child, sibling). This is more viable due to advancements in immunosuppressive therapies managing GVHD risk.
Another alternative is umbilical cord blood transplants. Cord blood, collected after birth, is rich in blood-forming stem cells and stored in public banks. Cord blood units require a less stringent HLA match than adult bone marrow, making them a valuable option. Researchers continue exploring new stem cell sources to expand transplant possibilities.