The Uncommon Surgical Procedures - Organ transplants

T he ability to rebuild human bodies from the parts of other humans or from artificial organs is one of modern medicine's greatest accomplishments, and its oldest dreams. Some of the most ancient documents, thousands of years old, tell of medical efforts to transplant organs, limbs, and other tissues to save lives or enable disabled persons to pursue normal activities. In the twentieth century, medical scientists discovered how to overcome a number of obstacles to the transplanting of organs, and today the transplantation of a variety of organs has become commonplace.

Tissue Compatibility

A major obstacle to organ transplants has been one of histoincompatibility ( histo means “tissue”): the tissues of the person receiving the transplant tend to reject the tissues of the transplanted organs. The problem is quite similar to that of allergies or the body's reaction to foreign bodies, including infectious organisms. Each individual has a set of antigens that are peculiar to that person, because of genetic variations among different persons. The histoincompatible antigens are on the surfaces of the tissue cells. But in most cases the antigens on the cells of the transplanted organ do not match those of the person receiving the transplant, so the recipient's body in effect refuses to accept the transplant.

The major exception to this rule is found in identical twins, who are born with the same sets of antigens. The organs of one twin can be transplanted to the body of the other twin with a minimum risk of rejection. Antigens on the tissue cells of brothers and sisters and of the parents will be similar, because of the biological relationship, but they will not be as compatible as those of identical twins. Even less compatible are antigens of people who are not related.

Types of Grafts

There is virtually no problem in transferring tissues from one area to another of the same patient. Skin grafts, bone grafts, and blood-vessel transplants are commonly made with a patient's own tissues, which have the same antigens, as in spinal fusions, repair of diseased leg arteries, and so on. Tissue transplants within an individual's body are called autografts . Transplants of tissues or organs from one human to another are called homografts , or allografts . Heterografts , or xenografts , are tissues from one species that are transplanted to another; they offer the greatest risk of histoincompatibility and are used mainly as a temporary measure, such as covering a severely burned area of a person with specially treated pieces of pigskin. The heterograft will be rejected, but it will provide some protection during the recovery period.

Much of the experience of surgeons in handling tissue transplants between humans came from early experiments in skin grafting. It was found that histoincompatibility in transplants of skin appeared to sensitize the recipient tissues in the same way that allergy sensitivity rises.

Thus, when a second skin graft from the same donor is attempted, the graft is rejected more rapidly than the first graft because of the buildup of antibodies from the first rejection. The same sort of rejection reaction can occur in transplants of kidneys, hearts, and other organs unless the problem of histoincompatibility is overcome.

Immunosuppressive Chemicals

In order to make the host body more receptive to an organ transplant, immunosuppressive chemicals are injected into the recipient's tissues to suppress their natural tendency to reject the foreign tissue. However, the technique of suppressing the immune response of the host tissues is not without hazards. By suppressing the natural rejection phenomenon, the transplant recipient is made vulnerable to other diseases. It has been found, for example, that persons who receive the immune response suppression chemicals as part of transplant surgery develop cancers at a rate that is 15 times that of the general population. Transplant patients also can become extremely vulnerable to infections, such as pneumonia.

Antigen Matching

The breakthrough in human organ transplantation was helped by the development of a system of matching antigens related to lymphocytes—a type of white blood cell—of the donor and recipient. At least a dozen lymphocyte antigens have been identified, and it is possible to match them by a process similar to matching blood factors of patients before making a blood transfusion. If all or most of the antigens of the donor tissue and the recipient match, the chances for a successful transplanting procedure are greatly enhanced.

Antigen matching is less important in some kinds of homografts, such as replacing the cornea of the eye. The cornea is a unique kind of tissue with no blood vessels, and therefore is unlikely to be invaded by antibodies of the recipient. Pieces of human bone also may be used in homografts with a minimum risk of rejection, although surgeons usually prefer to use bone from the patient's own body in repairing fractures and in other orthopedic procedures.

Types of Transplants

Cornea Transplant

Cornea transplants helped to pioneer the art of homografts. The first successful cornea transplants were made during the 1930s. In addition to the absence of rejection problems because of incompatible antigens, cornea transplants probably succeeded in the early days of homografts because only small pieces of the tissue were used.

Kidney Transplant

Kidney transplants began in the 1950s. Antigen typing was unknown at that time, but physicians had learned of the genetic factors of blood groups and found from experience that although kidney transplants from siblings and parents could eventually be rejected, the rejection phenomenon was delayed. The first truly successful kidney transplant operation was performed in Boston in 1954 between twin brothers; doctors had tested the tissue compatibility of the twins first by making a small skin transplant to see if it would be rejected. Knowledge acquired later of immunosuppressive drugs enabled surgeons to make kidney transplants between persons who were not twins.

More than 5,000 kidney transplant operations have been performed with an 82 percent survival rate of two years or more when the donor was related to the recipient. When a cadaver kidney was transplanted, the two-year survival rate was 65 percent. It has been estimated that as many as 10,000 kidney disease patients each year could benefit from a transplanted organ, but a lack of available kidneys in satisfactory condition restricts the number of transplants. An alternative for some kidney patients awaiting an organ transplant is hemodialysis, a process that performs as an artificial kidney.

Heart Transplant

The first successful human heart transplant was performed by Dr. Christiaan Barnard in Cape Town, South Africa, in 1968. The patient survived more than 18 months and led a relatively active life until the second heart failed because of a rejection reaction. Many heart transplant operations have been performed since 1968, with varying success, sometimes leading to complete recovery and sometimes to recovery for long periods of time. Heart transplants were found to be more difficult than some other organ transplants, such as of the kidney, because the heart must be taken from the donor at virtually the moment of death and immediately placed in the body of the recipient. Because of concern about determining the moment of death, the medical profession has offered guidelines for answering this complex ethical and legal question.

Success of a heart transplant operation may depend on the health of other organ systems in the patient's body; persons in need of heart transplants usually have medical problems involving the lungs and kidneys as a result of the diseased heart. And heart transplant patients frequently seem less able to tolerate the use of immunosuppressive drugs that must be administered after surgery. The introduction of cyclosporine as an immunosuppressant changed the picture substantially, however. Medical evidence indicated that cyclosporine would lead to a five-year survival rate among heart transplant patients of 50 percent or more. Because cyclosporine speeds rehabilitation after an operation, average hospital stays for patients receiving the immunosup-pressant have been reduced from 72 to 42 days.

Conducted before cyclosporine came into common use, one study of a group of transplant patients showed that fewer than 40 percent survived beyond the first year. Several lived more than two years after the operation.

Bone-Marrow Transplant

Limited success has been reported in efforts to perform bone-marrow transplants. Bone-marrow transplants are performed to supply patients with active leukocytes to fight cancer and other diseases. The successful early cases have involved transplants between sisters and brothers who had been typed for tissue compatibility.

Other Kinds of Transplants

Surgeons also have experimented with varying success with human transplants of livers, lungs, and pancreas tissue. Lung transplant efforts have been hampered by infection, rejection, and hemorrhage. Because the lungs are exposed to pathogenic organisms in the environment they are especially vulnerable to infections when the host tissues have been treated with immunosuppressive chemicals. Liver transplants are difficult to perform because of a lack of satisfactory donor organs and the complex circuitry of arteries, veins, and bile duct that must be connected to the recipient before the liver can begin to function.

Most major organ transplants are considered only in terms of a “last ditch” effort to prolong the life of a patient who is critically ill. While homografts are not always a perfect success and may lengthen a patient's life by only a few years, remarkable strides in these surgical techniques have been made over a relatively short period of time. Surgeons who specialize in organ transplants state that even greater progress could be made if a greater supply of donor organs were available.