TRANSPLANT

also called graft, in medicine, a section of tissue or a complete organ that is removed from its original natural site and transferred to a new position in the same person or in a separate individual. The term, like the synonym graft, was borrowed by surgeons from horticulture. Both words imply that success will result in a healthy and flourishing graft or transplant, which will gain its nourishment from its new environment. also called graft in medicine, a portion of the body or a complete organ that is artificially removed from its natural site and transferred to a separate site on the same or a different individual. Transplants in humans and other animals are classified as autografts, allografts (or homografts), or xenografts (or heterografts), according to whether the tissue or organ is obtained from the recipient himself, from another member of the same species, or from a member of another species, respectively. The fate of a living autograft depends on whether its nutritional requirements are adequately met and thus, as with most tissues, depends on the early reestablishment of a blood supply. Pieces of skin (either whole thickness or partial thickness) or small pieces of other tissues may be transplanted freely to suitable sites and soon become permeated by new vessels. Autografts of skin and subcutaneous tissue may be left connected by a pedicle containing blood vessels, at least until they acquire a new blood supply, and transplants of organs may be handled similarly or by vascular anastomosisi.e., by connecting the artery and vein to suitable vessels in the new site. Allografts, as a rule, evoke an immune reaction in the recipient and, in consequence, are destroyed after a few days or weeks. Exceptionally, allografts may survive for a long time or even permanently, notably (1) when the donor and recipient are unusually compatible, (2) when the tissue, such as cornea and cartilage, is devoid of blood vessels, (3) when the recipient has been treated with immunosuppressive agents such as alkylating agents, antimetabolites, corticosteroids, cyclosporine, or other drugs, and (4) when the recipient has been made specifically tolerant of donor tissue. Complete or nearly complete compatibility occurs when the donor and recipient are identical twins or, in the case of animals, members of the same sex of a closely inbred strain, and in this event immunosuppressive agents may not be required. In other cases, the degree of immunosuppression necessary to prevent rejection is related inversely to the degree of compatibility. Xenografts, as a rule, are destroyed even more quickly than allografts, and it is more difficult to prevent their rejection. In surgery, free (i.e., unattached) autografts of skin, bone, and cartilage are used extensively. Skin transplants are of special importance in the treatment of deep burns. They often consist of only part of the thickness of the skin, and in this event the donor site normally will heal spontaneously (see skin graft). Free nerve transplants also are used, sometimes in the form of multistrand or cable grafts made from small sensory nerves that can conveniently be sacrificed. Successful replacement of severed limbs (hands and arms or legs and feet), called replantation, is increasing. Guillotine-type injuries have a better prognosis than do infected or avulsed injuries. Upper extremities are more successfully reattached than are lower extremities. Prompt cooling of the severed limb and transporting it in sterile gauze and plastic also improve the prognosis. Pedicled autografts of stomach or bowel are used in reconstruction of the gastrointestinal tract after resection for cancer and other disorders, and similar transplants of bowel are used also in reconstruction of the urinary tract. Allografts of cornea are used to restore sight in patients with corneal opacities and keratoconus (conical cornea). They may be of partial or full thickness and will remain clear provided that blood vessels do not enter them. Skin allografts survive for only a few weeks but may be lifesaving in patients with extensive burns. They are replaced by autografts when the patient's general condition is satisfactory. Allografts of bone are used in orthopedic surgery; the living cells of the donor bone are usually rejected, but the remaining noncellular bone matrix provides a structural lattice upon which the recipient's body forms new bone. Allografts of other tissues and of organs usually require close matching of the donor and recipient and the subsequent use of immunosuppressive agents to prevent rejection. As in blood transfusions, the donor and recipient must be of compatible ABO red-blood-cell groups. This, however, is not sufficient; the donor and recipient must also be matched in terms of histocompatibility antigens. The primary human histocompatibility antigens are those of the HLA (human leukocyte group A) system; lymphocytes (a class of white blood cells) from the donor and recipient are tested to determine HLA compatibility. Allografts of bone marrow are used to treat patients with aplastic anemia, congenital immunodeficiency syndromes, and certain forms of leukemia. Because the grafted marrow may contain immunologically active donor cells, there is a risk of the transplant attacking the recipient's tissues. This often fatal graft-versus-host reaction is one of the major complications of bone-marrow transplants. Kidneys for transplantation have been obtained from living donors or cadavers; other organs can be obtained only from cadavers. Organs from cadavers must be obtained very soon after death; they may, however, be preserved for some hours by cooling and other procedures. See kidney transplant. Liver transplantation is technically very difficult, and the transplant must begin to function at once if the patient is to survive, because there is no satisfactory artificial liver; on the other hand, rejection is more easily prevented than in the case of the kidney. Heart transplantation resembles liver transplantation in that the patient's life depends on the transplant being able to function at once; it is technically easier than liver transplantation, but rejection is hard to recognize early and appears to be more difficult to prevent. See heart transplant. Other human organs that have been transplanted with at least some success include the pancreas and the lungs; the latter have been grafted most successfully when combined with the heart in a heart-and-lung transplant. The discovery of the immunosuppressive agent cyclosporine, which controls rejection with only limited suppression of the body's defenses against infection, has helped make organ transplants more feasible. The development of highly specific monoclonal antibodies, which can be targeted to immobilize the immune-system cells responsible for rejection, holds great promise for the future of organ transplantation. in horticulture, plant or tree removed from one location and reset in the ground at another. Most small deciduous trees may be moved with no soil attached to their roots. Trees of more than 7.5 cm (3 inches) in trunk diameter, however, are best moved balled and burlapped, that is, with a ball of earth enclosing the roots held in place with burlap. The tree is usually set out at approximately the depth it stood before moving, and planting is done as quickly as possible after digging, protecting the roots from sun and wind and keeping them moist. Holes must be wide and deep enough to permit the roots to spread naturally or, in the case of balled and burlapped stock, to receive the ball. The hole is filled around the transplanted tree with fertile soil of good texture, worked around the roots and tamped to eliminate air pockets. A shallow, saucerlike depression is formed around the tree to retain water. Trees that are transplanted in the fall should be mulched with 1012.5 cm of straw, moist leaves, or hay. Broken or damaged branches should be pruned. In preparing a native tree for transplantation, both top growth and roots should be pruned back. The trunk is wrapped with tree wrap paper to prevent damage from borers, animals, sunscald, or windburn. Vegetables and flowers that have been started indoors may be transplanted when all danger of frost has passed. Plants must be handled carefully to avoid shock. Seedlings are hardened up for a day or two outside before transplanting. A day that is cloudy or rainy, windless, and cool is ideal for transplanting garden plants. The roots must be kept moist and intact. Newly transplanted small plants require a few days of protection from direct sunlight. Additional reading Francis D. Moore, Give and Take (1964), an account of the history of organ transplantation; Ethics in Medical Progress, ed. by G.E.W. Wolstenholme and Maeve O' Connor (1966), proceedings of a symposium sponsored by the Ciba Foundation, discussing the ethical aspects of transplantation; Roy Y. Calne, Renal Transplantation, 2nd ed. (1967), a technical account of kidney grafting with a discussion of immunological aspects; his A Gift of Life (1970), a book for the nonspecialist, covering the immunological and clinical aspects and the ethics of organ grafting; Russell Scott, The Body As Property (1981), a comprehensive examination of the ethical and legal aspects of organ transplantation. Thomas E. Starzl, Experience in Hepatic Transplantation (1969), the first full account of the pioneer work on liver grafting; Liver Transplantation: The Cambridge-King's College Hospital Experience, ed. by Roy Y. Calne (1983), a later source on liver grafting; Christopher Pallis, ABC of Brain Stem Death (1983), a collection of articles from the British Medical Journal, with a description of brain-stem destruction and how it is recognized; Peter J. Morris (ed.), Kidney Transplantation: Principles and Practice, 2nd ed. (1984), a work on theory and methods; Roberta G. Simmons, Susan D. Klein, and Richard L. Simmons, Gift of Life: The Social and Psychological Impact of Organ Transplantation (1977), a work based on exhaustive studies. Sir Roy Yorke Calne