Procedure of Matching (HLA)
The use of marrow from another person requires careful testing to ensure the match between the patient and donor is very close. On most cells of the body, there are protein molecules (antigens) that mark the cells as being “Of self.” These unique markers are what the immune system will recognize as “Belonging”. One of the immune system’s jobs is to constantly run a surveillance throughout the body, trying to find and destroy items that do not display the individual’s unique antigens. Objects that the immune system looks for and destroys are, infection–causing bacteria, viruses, tumor cells and foreign objects such as splinters.
Human Leukocyte Antigen (HLA) is the name given to the system used to identify the unique markers (antigens) that the immune system recognizes. The markers are easily found on a white blood cell called leukocyte. To determine a person’s HLA type, the leukocytes are isolated from a blood sample and testing is performed to identify which HLA markers are present.
You inherit your HLA typing through the genes passed down from your parents. The genes are linked together in strands of three: you get three antigens from your mother and three from your father. These markers provide a shorthand way to identify the part of the inheritance important for marrow compatibility testing. One set of three is called a haplotype (half of your inheritance). Two haplotypes create one’s phenotype.
The three locations on the gene that are tested are the A, B, and DR. Each location has the potential to express two specificities, for a total of six markers. There are more areas in between these locations (C, DQ, DP), but in most cases, the A, B, and DR locations are the landmarks of the unique set of a person’s antigens that are matched for bone marrow transplants. During a search, these A, B, and DR designations are used to match a patient and donor.
The Correct Match
Of the six HLA antigens (two at A, two at B, and two at DR) there should not be more than one antigen mismatch between the patient and donor antigens. In other words, a donor and patient are considered sufficiently HLA matched if they are a “Five of six” antigen match. However, not all transplant centers will perform “Five of six” transplants. Some centers may require “Six of six” antigen matches depending upon the patient’s age, condition, diagnosis, or the transplant center’s criteria. Some transplant centers will perform haploid–identical transplants, or half matches, with related donors.
(0 vote)
