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By Fred Guterl
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By the time Californians go to the polls this week, they will have endured months of Biology 101 lectures from celebrity activists such as eBay founder Pierre Omidyar and producer Doug Wick. Seeing Hollywood and Silicon Valley types pushing their favorite causes--in this case, Proposition 71, a $3 billion research initiative for human embryonic stem cells--is nothing new in California. Seeing scientists do so is another matter. Hans Kierstead of the University of California's Reeve-Irvine Research Center announced shortly before Election Day that he had succeeded in coaxing human embryonic stem cells into producing highly purified brain cells called oligodendrocytes, then injected them into rodents with bruised spines. After nine weeks, the rats regained their ability to walk and run. The results were "thrilling and humbling," said Kierstead. "The humbling part is that the cells are so incredibly powerful."
A decade ago not one person in a million had heard of stem cells. Most people probably still don't know what stems cells are, but they know that the cells are special, and that they hold the power to cure some of the most intractable human diseases. All this is true--with the proper caveats. Scientists are usually the ones pointing them out, but not in the highly politicized atmosphere of stem-cell research. Aside from the ethical questions--should we tamper with embryonic cells, or perform nonreproductive human cloning?--there are more utilitarian ones: Will stem cells deliver? Is the public being sold a bill of goods? Scientists acknowledge the challenges but also tend to be incorrigibly upbeat. It's hard to tell if they're being seduced by their own rhetoric.
Judging from the hype in the run-up to Proposition 71, you might think that the chief obstacles to turning stem cells into cures were political. But the technical ones are legion. Stem cells taken from days-old embryos have the ability to produce any type of human cell, which makes them potentially so useful. But harnessing this ability has proved to be challenging. Left on their own, a clump of stem cells begins to form a hodgepodge of human cells, which won't do much to repair a damaged spinal cord. Scientists have had some success in using chemicals to direct stem cells to grow into various types of tissue, but the cells have an annoying tendency to disobey, preferring certain types of cells over others. Perhaps the cells get subtle cues from surrounding tissue? Nobody yet knows.
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Even if the levers were found to make stem cells grow into replacement parts, scientists would still have to get them to work together with surrounding cells. To be a functioning replacement for damaged brain or spinal-cord tissue, for instance, neurons grown from stem cells would have to connect to the body's neural networks.
If these problems sound tough, consider that scientists at present don't really even know how to identify stem cells. They can test cells by injecting them into animal tissue to see if they form embryonic tissue, but such tests are cumbersome. Scientists would like a way to identify whatever DNA mechanism makes a cell a true stem cell, but they don't yet know what that might be.
Authors Robert Lanza and Nadia Rosenthal spell out all these obstacles and more in the June issue of Scientific American. But you don't hear much about them elsewhere, perhaps because the debate has gotten so shrill. "I am aghast that it has turned into such a huge issue," says Dr. Stephen Minger, director of the stem-cell laboratory at London's King's College. "I just find the level of debate rather juvenile." Let's hope the breakthroughs come before the backlash.
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