Xenotransplantation: Using Animal Organs for Humans

Procedure could save lives, but virus transmission is a threat

| January-February 2000

The idea of using animal organs to rebuild humans was once the stuff of Gothic horror stories. Even the medical term for the practice—xenotransplantation—has a sci-fi ring. But now, two pharmaceutical companies and their scientific partners are poised to make fiction into fact by transplanting genetically engineered pig organs into humans for the first time.

As creepy as it sounds, surgeons could potentially save thousands of lives if they could “harvest” organs from animals instead of the occasional accident victim. Once a delicate operation, transplants are now nearly routine. But, while patients are living longer, the supply of organs cannot meet the demand. About 5,000 people on the U.S. transplant waiting list died in 1998 for lack of a donor.

Animal rights activists, of course, say xenotransplantation is cruel, but biomedical researchers tend to brush off their concerns. In this case, however, critics raise another issue that potential pig transplanters can’t ignore. Xenotransplantation, they say, has the potential to cause a devastating epidemic by introducing animal viruses into the human population.

To make their point, the critics refer to the devastating Ebola virus and HIV, both of which probably began in apes and made the jump to humans. And those viruses had no help. In order for a transplant to take, doctors must chemically subdue the immune system. Without their natural defenses, humans could be more vulnerable to infection by once harmless, organ-borne animal viruses. So while animal-to-human transplants could save thousands, they could kill thousands or more as well, says Laura Purdy, a bioethicist from the University of Toronto, writing in Free Inquiry (Fall 1999). “In this respect, xenotransplantation looks different from previous experimental treatments, where patients have both stood to gain and undertaken most of the risk,” she notes.

Virus fears pretty much eliminated apes as organ donor candidates, even though the human body would be less likely to reject organs from our primate cousins. Instead, researchers began working with pigs in the hope that they could use genetic engineering to overcome rejection problems. But two years ago, scientists concluded that pigs carry something called porcine endogenous retrovirus, or PERV, which is so deeply embedded in their DNA that there is no way to breed it out.

Now, researchers for one of the companies working on the genetically altered pigs have produced a study suggesting that these viruses may not be an obstacle. Scientists from Imutran Ltd. of Cambridge, England, rounded up 160 patients from around the world who had been treated with cells and tissue from pigs. The group included burn victims who had received pig skin grafts and liver failure patients whose blood had been filtered through pig livers rather than a dialysis machine.