These cells are then stored in a cryogenic freezer until the patient is ready for transplant. Allogeneic transplantation uses marrow from a family member or unrelated donor. The ideal donor has a tissue type which matches the patient's tissue type as closely as possible. If no suitable family-member donor is available in some cases an unrelated donor may be identified. These donors come from the general population and are identified through marrow-donor registries.
Syngeneic transplantation uses the marrow from an identical twin.
A. Human leukocyte antigens are a series of protein molecules on the surface of all cells. In HLA typing the proteins on the cells of the patient and potential donor are compared. There are two antigens encoded by each gene. There are other genes outside of the HLA system that play a lesser role in transplantation. The only perfectly matched individuals are identical twins.