HLA testing is used to match patients and donors for stem cell transplants
Your HLA type is a series of genes that controls your immune system. There are many different possible combinations, which means that it's difficult to find someone with the exact same HLA type as you.
HLA types are determined by a complex inheritance pattern. There are three general groups of HLA: HLA-A, HLA-B, and HLA-DR. Within these groups, there are many different types of proteins. For example, HLA-A contains 59 different proteins; HLA-B has 118 proteins.
Your parents each have two haplotypes (combinations of genes) of HLA. You inherited one from each parent, so you have a 25% chance of having a matched HLA type with a sibling.
When a patient receives a stem cell transplant, their HLA type must match that of the donor. Only 30% of patients have a match within their family; 70% need an unrelated donor like you!
Your body uses HLAs to determine if cells are part of your body or foreign. It's critical for the patient and the donor to have compatible HLA types because otherwise, the patient's immune system will reject the transplant and the treatment will fail.