Stem Cells to the Rescue?

A favorite tactic of right-wing activists opposed to research with human embryonic stem cells is to sneer something like, “ah, it’ll never work, and you’ll have killed (sic) all those babies (sic) for nothing.” While scientists have been known to exaggerate the potential benefits of their research, when it comes to stem cells they have actually been pulling back, trying to inject a dose of reality into the hope/hype machine that has convinced big chunks of the public that cures for stroke, Alzheimer’s, Parkinson’s and other awful brain diseases are just around the corner—the corner where stem cell studies break free of the shackles President George Bush imposed on them in August 2001.

Except that their studies keep showing that barriers to using stem cells therapeutically are not insurmountable at all. In the latest coup, researchers have transplanted human neural stem cells into the brains of rats and mice, traced the cells’ travels, and found that they navigate toward areas damaged by stroke. Stanford neuroscientist Gary Steinberg and colleagues were able to trace the cells’ travels because they slipped minuscule bits of iron inside the cells so that MRI could detect them. As the scientists are reporting tonight in the online edition of the Proceedings of the National Academy of Sciences, the iron doesn’t hurt the cells: the neural cells behaved just as they without the iron. That suggests that a similar tag could be used safely if stem cells are transplanted into human patients, allowing physicians to track their progress.

Where the cells went was just as encouraging. Last year Steinberg and his team reported that human neural stem cells migrated toward a brain region in rats that mimicked a human stroke. Moreover, the stem cells matured into cells indigenous to that damaged region, suggesting they had insinuated themselves into existing tissue in a way that could well prove therapeutic.

“I think it’s critical that we are applying this technique in human stem cells that can be used in human clinical trials,” said Stanford’s Raphael Guzman.

In a fascinating twist, the scientists found that when they transplanted human neural stem cells into the brains of healthy adult rats, the cells stayed put rather than migrating anywhere. That suggests that it is only when the animal’s brain has been damaged, as by a stroke, that the damaged region emits “help!” signals that attract neural stem cells. All the hand-wringing about brain diseases and injuries being too complicated to be treated by stem cells—how would they know where to go and how to make functional circuits?, as the critics say—may be misplaced.