Brave New Cells

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Stem cells can also be obtained from aborted fetuses in a process developed two years ago by John Gearhart at the Johns Hopkins School of Medicine in Baltimore. Gearhart harvested cells from the region that gives rise to the testes or ovaries. Such fetal stem cells appear to be as malleable as embryonic ones.

One feature that all stem cells share is an urge to travel. Evan Snyder, a neurologist at Harvard Medical School in Boston, has found that stem cells are attracted to injured tissues, perhaps because of biological cues released by dying or diseased cells. Indeed, one of Snyder's lab colleagues found that a batch of stem cells had migrated from one side of a rat's brain to the other to infiltrate a tumor.

Stem cells are also highly responsive to their surroundings. Researchers have taken adult stem cells from the brains of rats and put them in bone marrow and watched, in astonishment, as they spewed out blood cells. True, they did not form all the different blood-cell types, just a few. But until then no one had known that adult stem cells could adapt even that much to their environment.

And the extraordinary thing is that it's the specialized cells surrounding them--their older brothers and sisters, if you will--that provide the directions. Not in words but in biological signals, like growth factors and surface proteins, and by simply touching them.

David Anderson and his colleagues at Cal Tech have, for example, identified many environmental triggers that get the nervous system's stem cells to turn into neurons or into their supporting glial cells. They've also gone inside stem cells to isolate the genes responsible for the transformations. As with most adult stem cells, these cells appear, so far, to be limited in the types of tissue into which they can differentiate. Yet they still give rise to many different kinds of neurons--from sensory cells in your nose to touch receptors on your fingertips. The next step, Anderson says, is to figure out how that happens.

Pretty heady stuff, especially for neurologists who have spent most of their professional lives believing that even if the adult brain had stem cells, they'd never yield new neurons. Now the scientists have at least two options to consider. They can train stem cells to produce nerve tissue in a petri dish and then implant the new tissue in an ailing brain. Or, as Fred Gage at the Salk Institute in La Jolla, Calif., suggests, they can tweak the brain's stem cells to start churning out new neurons. If you could do that, Gage says, "it would take away the controversy over embryonic research."

There's much more to learn, of course, and many pitfalls to avoid. Consider the case of a 52-year-old American athlete with Parkinson's disease, who in 1989--before human stem cells had been isolated from the brain--traveled to China for a fetal-cell transplant. The goal was to replace some of the diseased neurons in his brain with newly differentiated fetal nerve tissue. While that approach has been at least partly successful in hundreds of other cases, something went dreadfully wrong this time. About two years later, the man suddenly developed trouble breathing and died.

An autopsy uncovered a hard mass of tissue pressing on his brain stem, which controls breathing, among other things. Apparently, the surgeons had scooped up a few extra fetal cells that then migrated and became cartilage, skin and hair cells.

Clearly, researchers don't know enough to start injecting stem cells into humans anytime soon, despite predictions that the first human trials could begin in the next couple of years. Just don't expect to hear a lot about what's going on behind closed lab doors, if the current congressional ban continues and stem-cell research remains almost entirely in the hands of biotech companies. "That's actually the worst-case scenario because now the public has no input," says Larry Goldstein, a cell biologist at University of California at San Diego. "Companies have to be motivated by profit, so they aren't necessarily going to tell us what they're doing."

With or without federal funding, stem-cell research will continue. Scientists may even sidestep the abortion issue by figuring out how to make adult cells act more like embryonic ones. But the private sector isn't going to wait to find out if that's feasible. Tens of thousands of embryos are created in in-vitro fertilization clinics each year and never implanted. If the Federal Government wants to have a say in how they get used, it will have to pay for the privilege.