Some fear animal organ transplants might unleash new infections
By Associated Press, 08/04/01
BOSTON -- One worry about putting pig hearts and kidneys into people is that the organs might carry along a dangerous germ, perhaps even one that could later spread from person to person.
See how pig organs can be used in humans
Pig organs eyed for transplants into humans
Some key dates in the development of animal-to-human transplants:
1954: Dr. Joseph Murray performs the world's first successful human organ transplant at Peter Bent Brigham Hospital in Boston, transferring a kidney from one identical twin to the other.
1963: Dr. Keith Reemtsma at Tulane University transplants more than a dozen kidneys from chimps to humans. One woman survives for nine months. At the University of Colorado, Dr. Thomas Starzl does six more transplants with baboon kidneys, but all eventually die.
1964: At the University of Mississippi, Dr. James Hardy attempts the first heart xenotransplant. The chimpanzee heart is too small to support circulation, and the patient dies after two hours.
1968: Doctors at the National Heart Hospital in London attempt a pig-to-human heart transplant. The heart is rejected and stops working within minutes.
1979: Dr. Christian Barnard, the South African surgeon who performed the first successful human heart transplant, tries to use baboon and chimp hearts as temporary backup pumps. Both patients die.
1983: The antirejection drug cyclosporine is introduced, making human-to-human transplants much more routine.
1984: At California's Loma Linda University, doctors replace 12-day-old Baby Fae's malformed heart with a baboon's. She dies 20 days later when the heart is rejected.
1992: Starzl, now at the University of Pittsburgh, performs two transplants using baboon livers. Both patients die from the effects of antirejection drugs.
1992: Researchers at Massachusetts General Hospital discover that a sugar on the surface of cells from pigs and many other animals provokes the body to immediately reject transplanted organs.
1995: Jeff Getty of San Francisco received a baboon bone marrow transplant in an attempt to restore immune system function damaged by the AIDS virus. The transplant fails, but Getty survives.
Source: The Associated Press
In many ways, pig organs are likely to be safer than human ones. The pigs would be raised in exceedingly clean, air-filtered barns and kept free of the viruses that can spread in human-to-human transplants, such as cytomegalovirus, Epstein-Barr virus or even more serious worries, such as hepatitis and the AIDS virus.
However, pigs, like all creatures, have viruses that uniquely infect them. And no one can be quite sure what will happen when these are put inside people.
The best known of these are the porcine endogenous retroviruses, or PERV. These viruses are permanently stitched into the pigs' genetic makeup. They take up about 1 percent of all the genetic material inside every pig cell. In a test tube, at least, PERV can be transferred into human cells.
"To our knowledge, these are not harmful to humans, but we are not absolutely sure," says Dr. Robert Mendez, president of the National Institute of Transplantation at St. Vincent Medical Center in Los Angeles.
Doctors have examined patients exposed to pig tissue in various ways, such as experimental transplants of fetal pig cells into the brain. None show any sign of infection with PERV.
Still, skeptics point out this does not mean it cannot happen. Nor does it rule out the possibility that pigs may carry other microbes that scientists do not even know about. One hypothetical concern is that pigs might pass along a virus that is harmless to them but deadly to people, and this germ in turn could be transmitted to others, perhaps through sex.
Before genetically engineered pig organs are tested in people, researchers will have to convince the Food and Drug Administration that the approach is safe. Nevertheless, many expect some restrictions to be placed on transplant recipients, such as a willingness to undergo regular testing for infections.
"The risk is really the unknown risk," says Dr. Fritz Bach of Beth Israel Deaconess Medical Center in Boston. "What a catastrophe if we suddenly start a new AIDS. Maybe the risk is one in 100,000. But what if it happens?"