BMT: Matching Donors and Recipients

• Why is it necessary to 'match' bone marrow donors and recipients?
  • Bone marrow transplantation (BMT) involves transfer of bone marrow cells from a donor to a recipient.
  • In order for such a transfer to be successful, it is important that the transplanted cells and the recipient's body recognize one another as 'self,' and not as foreign material to be attacked and rejected.
  • Self-recognition is more likely to occur is there is a close match between the donor and the recipient.
• How does the body recognize self?
  • Most cells of the body carry inherited surface markers which the body's immune system recognizes as 'self.'
  • These markers, referred to as human leukocyte antigens (HLAs), are present in 6 pairs.
  • One copy (or allele) of each pair is inherited from the mother and one copy is inherited from the father.
  • The 6 pairs of HLAs are termed:
    • HLA-A
    • HLA-B
    • HLA-C
    • HLA-DP
    • HLA-DQ
    • HLA-DR
• How is a person's HLA type determined?
  • First, a blood sample is obtained.
  • Leukocytes (a type of white blood cell with clearly identifiable HLA markers) are isolated from the sample.
  • Laboratory tests are performed in order to determine which HLA markers are present on the cells.
• What makes for a close match between donor and recipient?
  • For purposes of matching bone marrow donors and recipients, 3 HLA pairs (for a total of 6 antigens) are tested:
    • HLA-A
    • HLA-B
    • HLA-DR
  • The USA National Marrow Donor Program (NMDP) requires a '5 of 6' antigen match between donors and recipients: 5 of the 6 antigens tested (two HLA-A, two HLA-B, two HLA-DR) must match exactly.
  • In some cases, transplant centers may require a '6 of 6' antigen match, depending upon factors such as:
    • Patient's age
    • Patient's diagnosis
    • Patient's general health/overall condition
    • Transplant center's policies
• How are matching donors and recipients identified?
  • A small sample of blood is taken from potential bone marrow donors, then tested for HLA type (HLA-A and HLA-B).
  • HLA type is entered into the NMDP Registry, a computerized database of all potential donors.
  • When a patient search of the NMDP Registry identifies a donor as a preliminary match, the donor is contacted.
  • The donor gives another sample of blood, to be tested for HLA-DR type.
  • If HLA-A, HLA-B, and HLA-DR types all match, a sample of the donor's blood is sent directly to the patient's transplant center to confirm the match between donor and recipient (confirmatory typing, or CT).
  • Once CT has identified a single potential donor as the best possible match, the donor undergoes:
    • Counseling, including a full explanation of the donation process
    • Thorough physical examination/medical history
    • Signing of an 'Intent to Donate' or 'Consent' form
  • If the potential donor passes all medical tests and signs the consent form:
    • Bone marrow collection is scheduled.
    • The patient begins preparation for the transplant.

The material in this article is provided for informational purposes only. For specific medical advice or diagnosis, consult a healthcare provider.