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Organ Transplants

Heart and liver transplants are used when a person's own organs are irreparably damaged, such as by a heart attack or cirrhosis of the liver. The cornea is transplanted to cure blindness. Pancreas transplants have been attempted in persons with diabetes mellitus. Bone marrow is transplanted to persons with cancer of the blood-forming organs, or leukaemia. The most successful and widely practised transplants are those of kidneys and corneas, which are accepted medical procedures, but pancreas and liver transplants are also becoming increasingly common. Transplants of hearts and bone marrow are done with some success, but they are only performed at medical centres that are able to handle such surgery. Grafting involves the transplanting or implanting of living tissue from one part of the body to another in order to make the tissue adhere and grow to supply a missing part. Skin and bone grafting, which involves advanced plastic surgery techniques, are prime examples of self-grafts; in cases of severe burns, however, the patient will receive donor skin tissue which, although selected for its genetic compatibility, may eventually be rejected by the patient's immune system.

Problems of Organ Rejection

In most types of transplants the difficulties that arise are not ones of surgical technique. Instead, they are due to rejection of the new organ by the recipient's immune system. This occurs because each person's tissues bear a unique set of substances called antigens. Some of these substances are considered to be foreign bodies by the recipient's immune system, which mounts an attack against them. Successful transplants have been due largely to the development of ways of temporarily suppressing this immune attack until the organ establishes itself in its new host. Immunosuppressive drugs, in particular cyclosporin, are used; cyclosporin inhibits replication of immune cells known as lymphocytes, without depressing bone marrow function. It is therefore particularly helpful in bone marrow transplants.

Suppressing the immune system, however, leaves the transplant recipient susceptible to viral and fungal infections. Such infections cause many transplants to fail and sometimes cause the death of the recipient. The problem of immune rejection is greatly lessened when the organ comes from a close relative, who is more likely to have the same tissue antigens as the recipient. In the case of liver and pancreas transplants, failures also occur because of the difficulty of reconnecting the many ducts and blood vessels leading into and out of the transplanted organ. As transplantation depends greatly on donor organs, people who have decided to become donors carry special donor cards on them which indicate which of their organs may be used in the event of their death.