If an allogeneic transplant is to succeed, the donor and recipient must be similar in their genetic make-up.
We all have special proteins (antigens) on the surface of our WBCs and other cells, called human leukocyte antigens (HLA); the combination of antigens we have gives us our “tissue type.”
Testing for HLA antigens, also called tissue typing, is a blood test used to find out which antigens we have (usually six are checked). Other than a twin (which is a perfect match), the best match is a person who has all six matching antigens. Even so, because the transplant comes from another person, there is a possibility of immunologic complications. If a donor cannot be found who matches all six antigens, doctors may use a donor with five, or possibly even four matching antigens, but because there is greater incompatibility, there is a greater risk of more severe GVHD.