Because its HLA antigens are the same, the tissue is not rejected. Tissue transplanted from one location to the other in the same indiviual is called an autograft. If a tissue or organ is taken from a donor and transplanted to the body of a unrelated host, several of the HLA antigens are likely to be different. Such a graft made between the members of the same species but of different genetic makeup is called a homograft. The host's immune system regards the graft as foreign and launches an effective immune response called a graft rejection.
T lymphocytes attack the transplanted tissue and can destroy it within a few days.
Before transplants are performed, tissues from the patient and from potential donors must be typed and matched as well as possible.