That's not quite what's happening in Roger Pedersen's lab at the University of California in San Francisco--at least not yet. But he has managed to turn a group of carefully tended progenitor cells into a patch of thriving, beating cardiac muscle. "It's amazing," Pedersen says, "when you put unspecialized cells away, come back after the weekend and there's a clump of heartlike cells beating before your eyes in a dish."
And that's just the beginning. Someday, scientists hope to use cells like these to cure diabetes, Parkinson's disease and multiple sclerosis, as well as to reverse congestive heart failure and heal spinal-cord injuries. But there are some aspects of this story that are brave new world-ish. Known scientifically as stem cells, Pedersen's marvelously pliable cells are derived from seven-day-old human embryos, which are destroyed in the process. Although not all stem cells are produced this way, embryonic stem cells seem for now to have the greatest potential for medical miracles.
Pedersen--and the handful of other scientists working with human embryonic stem cells--uses embryos left over from fertility attempts that would otherwise be thrown away. Still, treating human embryos like so many tissue factories seems straight out of Huxley. It certainly doesn't sit well with antiabortion activists--or, in many cases, with lawmakers. In 1996 Congress banned human-embryo research by federally supported scientists, forcing researchers like Pedersen to seek private funding (most of which has been provided by Geron, a Menlo Park, Calif., biotech company).
A lot has changed in the past couple of years, however, that might persuade Congress to reconsider. Last September the National Bioethics Advisory Commission concluded that harvesting stem cells from discarded embryos is morally akin to removing organs from dead people for transplant. Also, the National Institutes of Health has seized on a possible loophole. In their view, federally funded scientists can do research on stem cells as long as someone else--say, in the private sector--actually dismantles the embryos. Most important, a small but influential group of Republicans and Democrats on Capitol Hill has started pushing for a relaxation of federal policy.
This week, Senator Arlen Specter of Pennsylvania, who has called stem cells "a veritable fountain of youth," will convene a hearing on Capitol Hill to review both the science and the ethics of the research. "Finally there is a very possible solution to conquering diseases that were always thought incurable," says actor Christopher Reeve, who has been paralyzed since his spinal cord was crushed in a fall from a horse in 1995, and who, along with former Senator Bob Dole and others, is scheduled to testify. "This research should go forward as fast as possible," Reeve says (see his accompanying Viewpoint). To that end, Senators Specter, a Republican, and Tom Harkin of Iowa, a Democrat, have introduced a bill to lift the ban. Just how far they'll get in an election year is anyone's guess.
To critics, anything that requires the destruction of human embryos--no matter what the reason--is abhorrent. Calling that "worse than abortion," Richard Doerflinger, a director of policy for the National Conference of Catholic Bishops, says, "If [the embryo] is a member of the human family, you cannot destroy that being for the sake of others."
The ethical considerations aside, researchers have so far offered promises aplenty about what stem cells can do but very little proof. Scientists acknowledge that many "nontrivial" technical obstacles remain to be overcome, and they are worried that stem-cell therapy has been so overhyped that it can't help but disappoint. There has even been one death from a related treatment.
To complicate matters, adults have stem cells too. Lurking in the microscopic nooks and crannies of the brain, bone marrow and other organs, these stem cells live in a state of perpetual readiness. Then when, say, the lining of the intestine becomes worn, the body signals the appropriate stem cells to start a process called differentiation, in which they divide and give rise to lots of mature, fully functioning intestinal cells.
These adult stem cells appear to be fairly restricted in what they can become. (Stem cells in the bone marrow usually give rise to different types of blood cells; stem cells in the muscles generally give rise to muscle.) Otherwise, Kafkaesque as it may seem, you could wake up one morning to find that your foot had turned itself into a liver. In any case, while there's no controversy over the use of adult stem cells, their potential benefit as a therapy seems limited.
Stem cells derived from embryos, on the other hand, can become just about anything--from teeth to muscle to neurons. In fact, they're so strongly primed to differentiate that scientists have a tough time keeping them in their original state. James Thomson of the University of Wisconsin was the first to pull off the feat in 1998. He now has an entire tissue bank of stem cells that he hopes one day to turn into specialized tissue almost at will--eliminating the need for fresh embryos.