Everyone has 2 chromosomes to define the HLA antigens, one of which is inherited from the father and the other from the mother. The closer a donor's HLA antigens match the recipient's the better it will survive and the less immunosuppression will be required.
Parameters:
(1) number of matches between the donor and recipient's major HLA antigens
(2) relatedness of the donor and recipient
The major HLA antigens for tissue transplants are:
(1) HLA-A (Class I antigen)
(2) HLA-B (Class I antigen)
(3) HLA-DR (Class II antigen)
Since there are 2 chromosomes encoding these antigens, a total of 6 HLA antigens are matched. Each difference between a donor and recipient is called a mismatch. The number of mismatches may range from 0 to 6.
If the HLA-A, HLA-B and HLA-DR on one chromosome of the recipient are the same as those on a chromosome of the donor then the haploidentical. This may occur between a parent and child or 2 non-twin siblings.
If both chromosomes match then there is an identical match, which is seen in identical twins.
The presence of 0 mismatches does not always indicate an identical match since the HLA genes may be on different chromosomes.
The donor and recipient may be:
(1) related
(2) unrelated
An unrelated donor who matches or closely matches the recipient is called a matched unrelated donor (MUD).
Limitations:
• Molecular methods are replacing the standard antigen match since the results are more specific.
• Newer drugs and protocols for immunosuppression allow even mismatched organs to be used successfully.
