Allogeneic Hematopoietic Stem Cell Donor
Choosing a donor
HLA Typing
Potential recipients of a HSCT will have HLA typing done before a donor search is initiated.
HLA typing is now done on peripheral blood samples using highly sensitive high-resolution DNA typing techniques.
This produces a HLA typing for each patient that looks something like this:
A |
B |
C |
DRB1 |
0101 |
1501 |
0802 |
4601 |
0403 |
1602 |
0901 |
5201 |
The first two numbers refer to the HLA-antigen and the last two numbers refer to the HLA-allele.
HLA-allele level typing is now accepted as the gold standard for HLA-typing and is used to match recipients to donors (exceptions may include umbilical cord transplants).
In most transplants a patient’s siblings and parents are also HLA typed. First preference is usually given to a fully HLA-allele level matched sibling. Each sibling has a 25% chance of being a perfect match to the person who needs a transplant (since there is a 50% chance that sibling will have received the same haplotype from mom and 50% chance of receiving the same haplotype from dad. 0.50 multiplied by 0.50 = 0.25).
Only rarely is a parent a perfect HLA match with their children. This is because they have given only one haplotype to their offspring. Most often, they are only 50% HLA similar to their offspring.
Parental haploidentical mismatched HSCT
- Possible to transplant from a 50% matched parent (parental haploidentical mismatched HSCT), but high risk.
- Only rarely performed due to concerns about:
- Severe GVHD
- Graft rejection
- Poor immune reconstitution following transplant.
- On rare occasion, because of random crossover events during miosis or because certain haplotypes tend to cluster in particular ethnic groups, a parent will be a perfect match for their child (around 2% of the time). In these situations using a parent as the donor may be possible.
