Unlike those of bone marrow and peripheral blood stem cells, cord blood stem cell transplants do not require an exact HLA match. This is because cord blood stem cells are more primitive and adaptable cells.
What this means is that it is easier and faster to find a suitable donor for a cord blood transplant – in fact, there’s a one in four chance of a perfect match between siblings and even the possibility of a match with extended family members.
But let’s back up a bit.
Human leukocyte antigens (HLA) are proteins or markers that are located on the surface of most cells and tissues in the body. HLA differ from person to person. Every person has specific HLA markers that recognize which cells belong in the body. Some antigens appear more commonly in certain populations and ethnic groups.
The Importance of a Match
Half of a person’s HLA markers are inherited from their mother, and the other half from their father. When two people share the same HLA, they are referred to as a “full match”. Their tissues are immunologically compatible with each other.
The best transplant outcome is reached when a patient’s HLA and the donor’s HLA closely match. According to bethematch.org, a close HLA match could mean:
- Increased likelihood of a successful transplant
- Improved engraftment rate (when the donated cells start to grow and develop new blood cells within the patient).
- Reduced risk of complications following the transplant – especially graft-versus-host disease (GVHD), a potentially serious complication.
HLA typing is used as a tool to identify the HLA type, which is then used to match patients and donors for bone marrow, peripheral blood and cord blood stem cells.
There are many groups of HLA, but three groups that are typically used for matching. Within each group, there are many different specific HLA proteins:
Here’s a specific demonstration. Mary and John (shown below) each have two sets of three HLA. If John and Mary had a baby, the child would inherit a set of three HLA from each parent. This is one example of four possible combinations that the child could inherit from its parent:
There are thousands of different combinations of possible HLA tissue types, which can make it difficult to find an exact match. As mentioned above, cord blood stem cells have the added benefit of not requiring an exact HLA antigen match between the donor and the recipient.