Organ transplantation is the practice of removing a usable organ from a person who has just died, usually in an accident,
and giving it to a severely ill person who needs it to replace a damaged organ. Transplanted hearts, livers, kidneys, and pancreases save lives of patients who are healthy except for the failure of one organ. Every year about 20,000 organ
transplants take place worldwide, but the need for organs far outstrips the supply from donors who die with healthy reusable parts. Living donors can be used for organs such as the kidney or bone marrow, since a person can live with one kidney, and the bone marrow cells naturally regenerate.
Early Research
The field of organ transplantation started in 1945 when Peter Brian Medawar and his colleagues first showed that tissue grafts, or transplants, from one individual to another would be rejected by an immunological
reaction to the foreign tissue. This was discovered to be a reaction of the body's lymphoid organs (lymph nodes, spleen, and bone marrow), similar in principle to the immunity resulting from exposure to a virus (see immune system; lymphatic system). A foreign graft triggers a complicated response, in which antibodies are produced that act specifically against the foreign organ. Other cells directly infiltrate the organ and proceed to damage its blood vessels and substance, leading to rapid destruction of the graft. In bone-marrow transplants cells with immune responses are infused, and the graft may attack the host, called a graft-versus-host reaction.