Science & Technology: MEDICINE
A TRANSPLANT BREAKTHROUGH...WITH ONE BIG CATCH
Pig organs with human genes could save thousands, but many fear a viral epidemic
Transplant surgeons are often unable to help many of their patients because of a critical shortage of organs. Each year, 3,000 patients die while languishing on transplant waiting lists. It's a desperate situation that seems to call for desperate measures.
Enter genetically engineered pigs. Raised in solitary confinement in ultra-clean rooms from birth, these high-tech porcines don't nurse because it's too dirty. They wouldn't recognize slop if they fell in it. For the transplant industry, these pigs represent a shining hope. Their organs closely resemble our own. And the pigs have been engineered to carry key human genes that make the organs look nearly human to a recipient's immune system--and therefore less likely to be rejected.
"A REALLY BAD IDEA." Pig hearts have been kept beating in monkeys for as long as 60 days. With recent advances in cloning, scientists could theoretically raise genetically identical pig litters, greatly reducing the variables. Pigs are cleaner than baboons--another potential source of organs--and using pigs is less likely to elicit complaints from animal activists. Pig organs could help save 200,000 lives a year in America, says John J. Fung, transplantation director at the University of Pittsburgh Medical Center.
Recently, however, researchers have pointed to what could be a disastrous drawback to the use of pig organs. Last month, researchers at London's Institute of Cancer Research reported that a virus found in pig cells had crossed over and infected human cells--an event doctors had thought was unlikely. Other groups have observed the same thing. The implications are ominous: The transplantation of pig organs into humans could unleash a new human viral epidemic. "From an infectious disease standpoint, transplanting animal organs is a really bad idea," says Jonathan S. Allan, virologist at the Southwest Foundation for Biomedical Research in San Antonio and a leading critic of the transplant of animal organs into humans, a process called xenotransplantation.
The battle over pig organs pits two groups of doctors against each other--transplant surgeons and virologists. Surgeons who see their patients dying don't worry so much about the long-term risks that virologists find so terrifying. In Britain, the virologists' camp won out: In January, the government placed a moratorium on xenotransplants.
In the U.S., the Food & Drug Administration has given the $4 billion transplant industry the go-ahead, stipulating strict monitoring of tissues, organs, and patients and the establishment of nationwide tissue banks. "We're building more safety into the approach," says Philip D. Noguchi, director of cellular and gene therapies at the FDA.
Livers, hearts, and other intact organs present the greatest risks for the transmission of animal viruses to humans. Such organs can easily spread any viruses they might carry throughout the bloodstream. Most healthy people might have immune systems powerful enough to resist the viruses. But transplant patients are given drugs to suppress their immune systems to prevent rejection of their transplanted organs. That leaves them vulnerable to the animal viruses, which could in turn leap from them to the rest of us.
YEARS OF TESTING. Besides whole organ transplants, researchers are also devising ways to transplant live animal tissues and cells to treat some diseases. Theoretically, it's easier to screen the tissues for the presence of viruses. Doctors in Boston, for example, have inserted fetal pig cells into the brains of 12 Parkinson's disease patients--with startling success. In some cases patients have begun walking again. Biotech companies are rigging up "bioartificial" livers, circulating patients' blood through pig liver cells and then back into the body.
Meanwhile, researchers are experimenting with animal tissues and cells for use against diabetes, multiple sclerosis, and AIDS. Although likely safer, even tissue and cell implants pose unknown risks. Noguchi emphasizes that more research is needed. "It makes it sort of a crapshoot," he says. That could change as scientists develop tests sensitive enough to proclaim tissues virus-free--but that could take years.
Some researchers argue that the FDA must push the industry to build stronger firewalls between species by banning some procedures and demanding the most rigorous testing. Otherwise, in the fight against familiar old diseases, we could end up creating mysterious new ones.By Stephen Baker in Pittsburgh