TRANSPLANTING ANIMAL ORGANS INTO HUMANS IS FEASIBLE.

• Author: FUNG, JOHN J.

With the success of human-to-human transplantation, e need for organ replacement as grown to critical levels. (An estimated 65,000 Americans suffering from end-stage organ failure currently are awaiting organ transplantation and the number is growing each year.) The demand for organs has inspired concerted research efforts in the field of xenotransplantation--the use of animal organs as replacements for human organs. Nearly 5,000 people die each year because suitable donors are not found in time, so any progress toward expanding the pool of organs--including the use of animal organs--has implications that literally translate into human lives.

Despite heightened public awareness to address the need for organ donation, there appears to be little prospect of increasing supplies to meet current shortages satisfactorily. The ability to use animal organs successfully as permanent replacements for failing human organs would end the suffering and death of patients awaiting transplantation. (More than 10% of patients awaiting transplantation die each year because of lack of human organs.) While artificial organs may become a reality with future developments, their ability to replace complex organs, such as the liver, is likely to be years away. Recent developments in understanding the barriers to successful xenotransplantation, along with access to novel drugs and approaches to manipulate the immune system, are making xenotransplantation more clinically feasible and bringing it much closer to reality.

Case reports of using animal kidneys appeared in the early 1900s from sources including pigs, goats, nonhuman primates, and lambs, but they met with failure, as did the earliest attempts at human-to-human transplantation. In the 1960s, a number of nonhuman primate-to-human kidney transplants were attempted, due to the pressing need for organs prior to the adoption of legislation that defined brain death and allowed cadaveric donation. Even with relatively ineffective forms of immunosuppression, function of non-human primate xenografts could be demonstrated, in one patient up to nine months after transplantation of a chimpanzee kidney.

In 1963, seven patients received baboon kidneys, all of which functioned immediately. These xenografts maintained dialysis-free function for up to 60 days before failing from rejection. With advances in immunosuppression and facing a severe shortage of pediatric donor hearts, Dr. Leonard Bailey transplanted a baboon heart...