Transplantation HLA Types Just as red blood cells have A, B, O types, leukocytes have HLA types. HLA stands for human leukocyte antigens, and the success of a transplantation depends mainly on HLA matching. There are tens of thousands of patterns of HLA types. Because HLA is transmitted equally from the parents, the odds of a person's HLA matching that of his or her brothers or sisters are 1 out of 4, or 25%. The odds of HLA matching the parents' are very slim and with unrelated people the odds are, as mentioned before, 1 out of several hundreds to many thousands.

Children can inherit 4 possible HLA types
　〔example〕The case of one family showing why siblings have
　　a higher possibility of matching each other's HLA.

Various types of HLA

Key to Success in Bone Marrow Transplantation:HLA

If the HLA does not match, the transplantation will not succeed due to rejection. In order to carry out a successful transplantation, loci A, B and DR have to match (2 in 1 locus, 6 in total).