And What About The Science?

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But even if the research proceeds apace, can stem cells ever live up to their promise? On this question, it's the science of the thing that matters, not the politics, and the science is uncertain. Investigators have already made significant advances in stem-cell research--the latest being the announcement from researchers at the Israel Institute of Technology (Technion) that they'd used a batch of embryonic stem cells to grow heart cells that actually beat and insulin-producing cells that mimic those in the pancreas. But there are plenty of steps between these advances and actual treatments--and any or all of them could pose difficulties. Says Dr. Karl Skorecki, director of Technion's Rappaport Research Institute: "We are at the beginning of a long process."

The first major hurdle is that while embryonic stem cells can develop into just about any type of tissue, scientists have little control over which one. Both the insulin-producing cells and heart cells, for example, came about by spontaneous differentiation. Scientists had to let the cells grow on their own, then pick out the ones they wanted.

But creating the appropriate cells is just part of the problem. Scientists then have to ensure that the new cells can survive in a host and do the job they're supposed to do. Dr. Lior Gepstein, leader of the team that developed the heart cells, has doubts. "If they stay in the damaged area and don't combine with the other heart tissue, they won't contract simultaneously, and they won't do any good."

Preliminary research in this area has yielded mixed results. When primitive cells are injected into rats with spinal-cord injuries, reports Dietrich, the animals' motor function frequently improves. But if you look at the rats' spinal cords at the end of the experiment, you don't see a big increase in the number of nerve cells or connections per cell. One theory about what's going on: the injected stem cells are releasing growth-promoting factors that may help the nerve cells that were already there reroute signals around the injury. Unfortunately, they may also be releasing chemicals that prevent the repair from being complete. And these are just animal experiments. Researchers will almost certainly face a whole new set of obstacles when they begin experiments on human subjects.

So given the tortuous road to stem-cell therapy, how long will patients have to wait? For some areas of research, things could move quickly, with scientists churning out lab-grown cells within a year or two. But moving into animal models and then human trials could take much longer. "There is no reason to think that this will happen overnight," says Dr. Christopher Saudek, president of the American Diabetes Association.

While research will now move faster than it would have if Bush had banned stem-cell work outright, it will also move more slowly than it would have if he had approved unrestricted funding. As the President himself allowed, there's no telling whether stem cells will be the panacea some people say. When the answers do start to come, they could be far in the future--and far beyond U.S. shores.

--Reported by David Bjerklie and Alice Park/New York, Anthee Carassava/London and John Dickerson/Washington