Organ Transplants from Animals

by Food and Drug Administration (FDA)

"You'll need a liver transplant," Dr. Zeno says. She scribbles quickly on her prescription pad and dates it: April 17, 2025. "Take this to the hospital pharmacy and we'll schedule the surgery for Friday morning."

The patient sighs — he's visibly relieved that his body will be rid of hepatitis forever.

"What kind of liver will it be?" he asks.

"Well, it's from a pig," Zeno replies. "But it will be genetically altered with your DNA. Your body won't even know the difference."

Obviously, this is science fiction. But according to some scientists, it could be a reality someday. An animal organ, probably from a pig, could be genetically altered with human genes to trick a patient's immune system into accepting it as its own flesh and blood.

Called "xenotransplants," such animal-to-human procedures would be lifesaving for the thousands of people waiting for organ donations. There have been about 30 experimental xenotransplants since the turn of the century.

Rebuilding Bodies

Xenotransplants are on the cutting edge of medical science, and some scientists think they hold the key not only to replacing organs, but to curing other deadly diseases as well.

Last December, for example, after getting permission from the Food and Drug Administration, researchers at the University of California, San Francisco, injected an AIDS patient with baboon bone marrow. The hope was that the baboon bone marrow, which is resistant to HIV and a source of immune cells, could provide a replacement for the patient's damaged immune system.

In April 1995, also with FDA permission, doctors at Lahey Hitchcock Medical Center in Burlington, Mass., injected fetal pig brain cells into the brains of patients with advanced Parkinson's disease. The hope was that the fetal tissue would produce dopamine, which the patients' brains lack. Both experiments were primarily to test the safety of such procedures, not whether they are effective.

Other xenotransplant experiments have involved implanting animal hearts, livers and kidneys into humans.

According to Scott McCartney's book on transplantation, Defying the Gods: Inside the New Frontiers of Organ Transplants, the first organ transplant was performed in the early twentieth century by Alexis Carrel, a French physician practicing in Chicago. He had developed a technique to sew blood vessels together, and in 1906 he transplanted a new heart into a dog and a new kidney into a cat.

The first animal-to-human transplant was in the same year, when the French surgeon Mathieu Jaboulay implanted a pig's kidney into one woman and a goat's liver into another. Neither survived.

Today, human organ transplants are commonplace. For example, more than 10,000 Americans received kidney transplants last year, with a three-year life expectancy of more than 85 percent, according to the United Network for Organ Sharing (UNOS), an organization of transplant programs and laboratories in the United States. Under contract to the U.S. Department of Health and Human Services, UNOS administers a national organ network, and its members set policies for equitable organ allocation.

Surgeons have made great strides in perfecting transplant techniques, but two problems endure. First, there are never enough organs to go around (see "Transplant Organs: Too Little, Too Late"). Second, once patients receive organs, it is a constant battle to keep their immune systems from rejecting them. Both problems may be eventually solved by xenotransplants and the genetic engineering techniques developed from such experiments.

Of all animals, baboons and pigs are the favored xenotransplant donors. Baboons are genetically close to humans, so they're most often used for initial experiments. Six baboon kidneys were transplanted into humans in 1964, a baboon heart into a baby in 1984, and two baboon livers into patients in 1992.

Although all the patients died within weeks after their operations, they did not die of organ rejection. Rather, they died of infections common to patients on immunosuppressive drugs.

One drawback to using baboons is that they harbor many viruses. They also reproduce slowly, carrying only one offspring at a time. Some people have raised ethical objections, especially since baboons are so similar to humans. They have human-like faces and hands and a highly developed social structure. Although it's conceivable that baboons could donate bone marrow without being killed, recent experiments have required extensive tissue studies, and the animals have been sacrificed.

For long-term use, pigs may be a better choice. Pigs have anatomies strikingly similar to that of humans. Pigs are generally healthier than most primates and they're extremely easy to breed, producing a whole litter of piglets at a time. Moral objections to killing pigs are fewer since they're slaughtered for food.

About the Author

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