ILAR Journal Online, Volume 37(1) 1995: Perspectives on Xenotransplantation

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ILAR Journal V37(1) 1995
Perspectives on Xenotransplantation

Xenotransplantation: A Historical Perspective
Keith Reemtsma

Keith Reemtsma, M.D., is professor of surgery at Columbia University, College of Physicians and Surgeons, New York, New York.

INTRODUCTION

The increasing success of organ transplantation over the past several decades has had the paradoxical effect of highlighting the scarcity of human donors. One response to the need for organs has been an increased effort in research into cross-species transplantation, usually referred to as xenotransplantation.

While the donor-organ shortage is the most frequently cited reason for renewed interest in xenotransplantation, there are other compelling reasons for pursuing this approach, such as the logistic advantages and the ability to prepare the donor, the recipient, or both should preoperative immunologic modification prove feasible.

The overriding question often asked about xenotransplantation is: Will it work'? The answer is that xenotransplantation has worked, and the appropriate questions, therefore are: Under what circumstances can we predict success? And which species, which organs, and which form of immune suppression or immune modification should be used?

The history of xenotransplantation is both interesting and informative. Although the modem history can be dated to 1963, the earlier work provides some background for more recent efforts.

THE MYTHOLOGY OF TRANSPLANTATION

The idea of transplanting organs from animals to humans has intrigued humanity for as long as he recorded his myths and his history. Daedelus, who grafted bird feathers to his arms, was perhaps the first to transplant across the species barrier successfully. He escaped from his island prison in Crete and flew to the mainland of Greece. A similar experiment by his son, Icarus, ended in acute graft rejection, attributed to a thermolabile adhesive. After flying too close to the sun he plunged into the water which is now called, in his honor, the Icaran Sea (Hamilton 1940).

EARLY ATTEMPTS AT RENAL XENOGRAFTING

Early in the twentieth century reports on cross-species grafting (then called heterotransplantation) appeared in the scientific literature. In 1905 in France, Princeteau inserted slices of rabbit kidney into a nephrotomy in a child with renal insufficiency. "The immediate results were excellent," he wrote. "The volume of the urine increased; vomiting stopped. . . . On the 16th the child died of pulmonary congestion. . ." (Princeteau 1905).

In the following year, Jaboulay, also in France, attempted renal heterotransplantation into humans on two occasions, using vascular anastomoses (Jaboulay 1906). The xenografts, one from a pig and another from a goat, were inserted into the antecubital space. Neither graft functioned, and failure was attributed to vascular thromboses.

In 1910, Unger, in Germany, described his attempt at transplantation of kidneys from a nonhuman primate into man. The patient died 32 hours after transplantation, and autopsy showed venous thromboses (Unger 1910).

In New York in 1923, Neuhof attempted treatment of a patient with mercury bichloride poisoning by renal heterotransplantation. When he was unable to obtain a human kidney, he transplanted the kidney of a lamb into the patient. The patient died 9 days later, but Neuhof was not totally discouraged. He wrote, "[This case] proves, however, that a heterografted kidney in a human being does not necessarily become gangrenous and the procedure is, therefore, not necessarily a dangerous one, as had been supposed. It also demonstrates that thrombosis or hemorrhage at the anastomosis is not inevitable. I believe that this case report should turn attention anew..." (Neuhof 1923).

However, scientific interest in transplantation declined when the immunological basis of the rejection process was established. With the demonstration of effectiveness of immunosuppressive drugs, there was renewed interest in transplantation. An accelerated effort in renal allotransplantation was accompanied by problems in procuring organs. Ethical considerations posed difficult problems, particularly in the use of volunteer human donors. The use of organs harvested from human cadavers depended on rapid transfer or preservation and imposed restrictions of supply, selection, and scheduling.

THE TULANE UNIVERSITY CHIMPANZEE-TO-MAN RENAL XENOGRAFT EXPERIENCE

In our renal allografting at Tulane University in New Orleans, we had increasing difficulty obtaining donor organs. Attempts to use cadaveric kidneys were inadequate. We were reluctant to press the use of volunteer humans for ethical, scientific, and legal reasons. Chronic dialysis was not available.

As this impasse was developing, we decided to explore the use of nonhuman sources for clinical renal transplantation. This decision was prompted, in part, by clinical urgency. Additionally, a regional primate center in the vicinity brought scientists experienced in primatology. Furthermore, an active program in transplantation immunology had been developed to give an added base to the study.

Our basic conjuncture was that kidneys from nonhuman sources closely related to humans would respond similarly to human kidneys following transplantation into man. The problem of presumably more strenuous immune suppression was balanced against the advantages in the use of nonhuman donors.

In practice, all patients were terminal uremics, maintained on dialysis, who were presented with the following alternatives: (1) supportive treatment only, (2) an allograft from a relative, (3) a cadaveric allograft if available, or (4) a heterograft (xenograft).

The risks, the uncertainties, and the experimental nature of the work were discussed with the patients and their families. If they chose to proceed with transplantation and had no volunteer donor, a search was made for a cadaveric kidney. If no suitable cadaver kidney became available, a xenograft was used, with the patient's understanding and consent.

The Chimpanzee as Donor

The chimpanzee was selected as the donor for several reasons. They included (1) the chimpanzee's close taxonomic relationship to man; (2) its range of size, which approximates that of man, a factor that might have significance in the transplantation of other organs in addition to kidneys; (3) its renal function corresponds closely to that of man; and (4) chimpanzees have been found to be of blood types A and O, thereby offering the possibility of the universal donor from the standpoint of blood groups.

Between November 5, 1963, and February 10, 1964, six patients received renal heterotransplants from chimpanzees. All patients were in terminal uremia necessitating dialysis and all patients received pretransplantation treatment with azathioprine, actinomycin C, and steroids. The donor was selected based on body size and blood typing of both donor and recipient. Creatinine clearance was determined in each donor.

In each instance the donor received general endotracheal anesthesia with monitoring of blood pressure, electrocardiogram, and body temperature. A moderate hypothermia (about 30°C) of the entire renal complex, including both kidneys and ureters, aorta, and vena cava, was removed en bloc after anticoagulation and was irrigated. Patients were prepared simultaneously by extraperitoneal exposure of the external iliac artery and vein. In each instance the aorta and vena cava of the graft were anastomosed to the recipient's external iliac artery and vein, respectively, in an end-to-side fashion. The periods of ischemia, from the time of vessel clamping in the donor until blood flow was restored through the graft in the recipient, varied from 36 to 43 minutes.

All patients received postoperative azathioprine, actinomycin C, steroids, and X-irradiation to the graft. Two cases are summarized below.

Case 1

A 43-year-old former dock worker with a history of hypertension since 1957 was admitted to the Veterans Administration Hospital, New Orleans, in 1959. Renal biopsies showed nephrosclerosis and chronic glomerulonephritis. He was treated with dietary management, including salt restriction. He was readmitted in June 1963 because of progressive uremia, hypertension, and congestive heart failure. Laboratory studies included the following: blood urea nitrogen (BUN) 240 mg%, creatinine 14 mg%, and creatinine clearance 8 ml/min. There was no improvement with dietary management, and peritoneal dialysis was required.

On November 5, 1963, he received a renal xenograft. During the first 14 hours after transplantation, the urinary output was 5700 ml. The BUN, which was 112 mg% on the day of operation, decreased to 39 mg% by the 4th day of operation, and fell to 1.5 mg% 48 hours after transplantation. Four days after transplantation, rejection occurred, but was reversed following local irradiation to the graft and increased doses of immunosuppressive drugs. His early course has been reported previously in detail. Function of the graft was confirmed by renograms, scans, and intravenous urogram.

Serial renograms demonstrated a progressive delay in the appearance of the peak uptake. Changes in the renogram, however, were not correlated with biochemical changes in renal function.

Hemagglutination studies demonstrated a precipitous rise in titer beginning on the 4th day following transplantation. The titer fell to pretransplantation levels at the end of 1 month and remained at this level throughout the 2d month. Data on cytotoxicity studies are shown.

On December 18, he was allowed to leave the hospital because he was asymptomatic and had normal renal function. He was readmitred on December 20 with a temperature of 39.4°C, and radiographic evidence of an infiltrate in the right middle lobe with pleural effusion. Culture of the sputum revealed Aerobacter aerogenes. The dosage of azahioprine was lowered because of leukopenia, but renal function continued satisfactorily. The patient's condition later deteriorated rapidly, and he died 63 days after transplantation following a period of shock, apparently due to sepsis.

Autopsy showed acute bronchopneumonia (right lower lobe) and acute tracheobronchitis with resolving abscess (right middle lobe). The transplanted kidneys showed acute tubular necrosis, consistent with shock. There were no cellular infiltrates or changes in the blood vessels (Reemtsma and others 1964).

Case 2

A 23-year-old schoolteacher was admitted in November 1963 with chronic glomerulonephritis and progressive uremia. She had experienced an episode of acute glomerulonephritis at age 14, and demonstrated persisting proteinuria. She had remained asymptomatic until approximately 5 months before admission, when she noted weakness and dizziness.

On admission her blood pressure was 190/120 mmHg, and laboratory studies included BUN of 184 mg%, creatinine of 40 rog%, and creatinine clearance of 4 ml/min. Rapid deterioration of her condition necessitated peritoneal dialysis.

On January 13, 1964, she received a renal heterotransplant. Diuresis occurred with a urinary output on the day of operation of 7 liters. By the 3d day following transplantation the BUN had fallen from a preoperative level of 116 mg% to 12 mg%, and the serum creatinine from a preoperative level of 21 mg% to 0.9 mg%. Creatinine clearance was 50 ml/min. Her blood pressure fell to normotensive levels (110/70 mmHg). Her subsequent course demonstrated satisfactory renal function until the 23d day following operation when threatened rejection was expected.

Urinary output decreased to 1,000 ml/24 h, BUN creatinine rose to 28 and 1.9 mg%, respectively. Creatinine clearance fell to 23 ml/min, and urinary sodium content to 11.6 mEq for a 24-hour period. Gradual reversal of rejection occurred during the following 2 weeks, although unexplained fever persisted for 3 months. She became asymptomatic and had normal renal function 8 months after transplantation.

Serial renograms in this patient demonstrated a delay in peak activity, which coincided with clinical and biochemical evidence of threatened rejection. Following reversal of rejection, the renogram resumed a more normal pattern. An intravenous urogram 12 weeks after transplantation showed function of both transplanted kidneys.

Agglutination studies demonstrated a slight rise in titer at approximately 3 weeks after transplantation. The agglutation titer subsequently returned to previous levels.

This patient died 9 months after transplantation. The cause of death was thought to be acute electrolyte imbalance. Autopsy showed no other cause of death. Histology of the transplanted kidneys showed no other cellular infiltration, but subintimal hyperplasia of the arterioles (Reemtsma and others 1964).

SUBSEQUENT CLINICAL STUDIES

Following the initial experience in New Orleans, there was a flurry of activity in the field of primate-to-man transplantation. In December, 1964, three distinguished transplant surgeons, Drs. J.D. Hardy, D.M. Hume, and T.E. Starzl, were attending a surgical meeting in New Orleans. At the end of the meeting I showed these three surgeons the first patient, who was doing well with normal renal function 7 weeks after transplantation. Each of these three surgeons began working in clinical xenografting.

Hardy and others (1964) reported a few months later the first case of heart transplantation in man. He used the heart of a chimpanzee, but was unsuccessful in this attempt. Hume (1964) did a chimpanzee-to-man renal transplant, and the patient died the following day of excessive diuresis.

Starzl (1964) began a series of baboon-to-man renal transplants which were studied extensively and have been reported in detail. The histopathological studies in our chimpanzee-to-man work and in Starzl's baboon-to-man cases were all carried out by Dr. Ken Porter of London.

By 1965 we had dialysis facilities available at Tulane University, and we had developed a successful cadaver organ procurement program. For these reasons we discontinued our clinical renal xenotransplantation.

I have subsequently, however, maintained experimental programs in xenotransplantation, including transplantation of islet cells in several animal models, and xenotransplantation of the heart between different species of primate.

ETHICAL CONSIDERATIONS

In considering the use of nonhuman species as donors for transplants into humans there are ethical issues concerning both the recipient and the donor, and, in addition, the process of experimental procedures in general.

For this discussion, I shall confine my remarks to the use of nonhuman donors. The questions that arise are these:

Is it ever acceptable, from an ethical point of view, to use nonhuman animals to treat human illness?
What species should we use?
Which organs and tissues should be used?
Under what circumstances should xenotransplantation be moved from the laboratory to the clinical setting?

The general use of animals for treating human illnesses now is widely accepted. Insulin from animal sources has been used to treat diabetes in humans for most of this century. Heart valves from animals now are routinely used in cardiac surgery worldwide.

The selection of the species poses several problems. From an immunologic standpoint, we would prefer species most closely related to man. The chimpanzee, however, is an endangered species and cannot be used in terminal experiments. The baboon is more distant from humans and does not reach the size of the chimpanzee or adult human. Although the baboon is not an endangered species, it is, nevertheless, a primate, and as such this work raises ethical concerns.

The use of nonprimate donors, such as pigs, reduces ethical concerns, but the use of organs and tissues from pigs into humans involves a higher immunologic barrier than with primates. Extensive studies now are underway to modify pig donors, such as with transgenic techniques to reduce problems involved in transplantation.

The final, and most difficult question, involves the transfer of work from the laboratory to the clinical setting. There is no single criterion that can be applied to this decision. The variables include success of laboratory work, the applicability of animal studies to clinical experiments, the degree of urgency, and the availability of alternate solutions.

Xenotransplantation in the future may involve a broad spectrum of tissues, from cells and subcellular components to organ grafts. Some problems, such as transmission of microorganisms, may be similar across this spectrum, but other aspects of xenotransplantation may vary with the organ or tissue used. Furthermore, with the immunologic approaches to xenotransplantation continuing to undergo rapid evolution, it would be premature to prescribe guidelines or regulations governing the translation of work from the laboratory to the clinic.

The current increase in interest in xenotransplantation is based both on clinical needs and on promising leads being pursued in different laboratories. When and how these advances are translated into clinical programs are decisions best left to the groups of investigators involved in this work. The trend is unmistakable, and clinical success is probable, although not assured, in the near future.

REFERENCES

Hamilton, E. 1940. Mythology. Boston: Little, Brown and Co.

Hardy, J. D., C. M. Chavez, F. D. Kurrus, W. A. Neely, S. Eraslan, M. D. Tumer, L. W. Fabian, and T. D. Labecki. 1964. Heart transplantation in man. J. Am. Med. Assoc. 188:1132.

Hume, D. M. 1964. Discussion of paper by Reemtsma and others. Ann.Surg. 160:384.

Jaboulay, M. 1906. Greffe de reins au pli coude par soudres artielles et veincuses. Lyon Med. 107:575.

Neuhof, H. 1923. The Transplantation of Tissues. New York: Appleton and Co., p. 260.

Princeteau, M. 1905. Greffe renale. J. Med. Bordeaux 26:549.

Reemtsma, K., B. H. McCracken, J. U. Schlegel, M. A. Pearl, C. W. Pearce, C. W. DeWitt, P. E. Smith, R. L. Hewitt, R. L. Flinner, and O. Creech.1964. Renal heterotransplantation in man. Ann. Surg. 160:384.

Starzl, T. E. 1964. Discussion of paper by Reemtsma and others. Ann. Surg. 160:384.

Unger, E. 1910. Nierentransplantation. Klin. Wschr. 47:573.