If you had to pick the likely stroke victim from a lineup, Amanda Davis is not the person you'd choose. On the eve of her 20th birthday, the sweet-faced New Englander was driving home from college to visit her parents when she started feeling queasy and uncoordinated. She pulled over and asked her friend to drive. Then she woke up in a hospital bed. A stroke had paralyzed the entire left side of her body. No one expected her to walk again.
Two years later Davis not only walks but runs short distances. She has gotten rid of her leg brace and regained use of her left arm. Her only lingering impairment is a paralyzed hand. It's hard to say exactly what causes such a stellar recovery, but here's a possibility. Last year doctors at Boston's Brigham and Women's Hospital drilled two holes in Davis's skull and injected fetal-pig cells--about 80 million of them--into her brain. The cells seem to have taken root and formed connections with her own surviving neurons, reversing much of the damage caused by the stroke.
Pig-cell transplants are still a work in progress, and porcine organ transplants are only an idea. But as producers Frank Simmonds and Michael Chrisman of Britain's Carlton Television make clear in a new documentary titled "Organ Farm," the barriers to cross-species medical procedures are slowly coming down. Despite doubts about the safety and ethics of "xenotransplantation" (the prefix means "foreign"), biotech and pharmaceutical companies are pouring millions into the endeavor, and their technologies are steadily improving. If the enthusiasts are right, people with pig hearts will be pacing hospital corridors five years from now, and organ production will become a new form of agriculture.
The idea of putting pig parts in people is not a new one; physicians have long used porcine heart valves and hormones in people. But with the advent of fetal-cell research, the practice has reached a whole new level. Today, researchers are testing fetal-pig cells as a treatment for a range of brain conditions--not only stroke but also Parkinson's disease, Huntington's disease, epilepsy, chronic pain and spinal-cord injury. Only a few dozen patients have received brain cells from fetal pigs. But preliminary studies of Parkinson's patients suggest that pig cells may work as well as those from human fetuses.
That's not saying much. During the past few weeks, scientists have reported disappointing results with both approaches. In one study, researchers at the Boston-based companies Genzyme and Diacrin treated 10 Parkinson's sufferers with fetal-pig cells, then charted them against patients who got sham operations (burr holes and brain jabs but no neurons). The treated subjects deteriorated at the same average rate as the controls. Just a week earlier researchers at Columbia and the University of Colorado reported similar findings from a study in which 20 Parkinson's patients received human fetal neurons. Despite the disappointing averages, however, both studies included patients who responded dramatically to treatment. In "Organ Farm"--which will air on PBS's "Frontline" March 27 and April 3--we see a 52-year-old man named Jim Finn walk briskly, drive a car and work around his house. The same Jim Finn was in the final stages of Parkinson's four years ago, barely able to stand or even speak, but everything changed after surgery. The next challenge, says Diacrin CEO Tom Fraser, is to determine what makes certain people so responsive, and build on it.
Though whole-organ transplants are not yet feasible, the prospects are improving almost monthly. When a regular pig organ is attached to a person or a primate, the immune system destroys it within hours. But in recent years, scientists have created pigs whose cells display antigens--flags, basically--that human cells use to show the immune system they belong in the body. Organs from those partially "humanized" animals have survived up to eight weeks in baboons--and they're sometimes used (externally) to sustain people for brief periods while they await human-organ transplants. Despite the human camouflage, these organs still sport a pig antigen called Gal, which flags them as foreigners and speeds immune rejection. Several companies are now racing to develop Gal-free pigs. And Infigen Inc. of DeForest, Wis., recently succeeded at cloning a partially humanized pig. That's important because breeding could dilute the qualities that make a pig medically useful.
The race to reinvent the pig is not hard to fathom. This year 53,000 of the 75,000 Americans who might benefit from a transplant will die waiting for a donor. Transplantable pig organs could generate billions for biotech while extending thousands of lives. But what would the net effect be? Many experts worry that cross-species organ sharing could trigger plagues by infecting people with obscure but transmissible pathogens. As Amherst College biologist Paul Ewald observes, the bugs that cause AIDS, tuberculosis, typhus and measles all reached us through animals. Plagues aside, many critics see xenotransplantation as a colossal waste of resources. "You could save more lives for less money by improving access to basic health care," says Alan Berger of the Sacramento-based Animal Protection Institute. True enough. But that argument has yet to slow the quest for higher-tech treatments, and this race is far from over.