As a potential blood stem cell donor, your tissue type will be matched using human leukocyte antigen (HLA) typing. HLA are proteins or markers found on all cells in your body. These proteins are used by your immune system to recognise which cells belong in your body and which cells do not. If these proteins do not match, the patient’s body would reject the given stem cells of the donor. A close match means that the patient’s immune system would recognise your blood system as its own.
With more than 20,000 known characteristics that can occur in millions of combinations, finding a match is extremely rare. Approximately two thirds of patients who need a transplant do not have a suitable donor within their family and rely on the register to find an unrelated donor. In these cases, the patient’s doctor will search for an unrelated donor. To be considered a match, the patient and donor must have at least 8 out of 10 tissue characteristics in common, but ideally should have 10. The rarity of having matching HLA tissue-type characteristics is the reason finding matching donors is so difficult.