The best outcomes for organ transplants are achieved when the donor is the identical twin of the individual who needs a transplant. Transplantation is a procedure in which an organ or tissue that is damaged is not functioning and is surgically replaced with an organ obtained from another person. Transplants from identical twin donors are hard to reject, because all the genes are identical. HLA are genes that are passed down from parent to child and used in finding matches for transplants.
Kidneys are sensitive and susceptible to rejection.
Therefore, more efforts are placed to transplant the best possible matches in kidney transplants. Obviously identical twins are the best possible donors for a kidney transplant. Bone marrow transplants require a higher level of HLA matching. They are easily susceptible to rejection and also require the best possible matches. Livers are less sensitive to rejection, so HLA matching is not as important.