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On the Caribbean Island of St. Kitts, these surgeons are implanting several million human neural stem cells into the brain of an African green monkey. When the human cells mature -- the black dots in the picture -- they function as living partners with the billions of monkey brain cells that are already there.
Dr. Eugene Redmond hopes the implanted cells in monkeys like this one, which come from federally approved lines of stem cells cultured in U.S. laboratories, will eventually help supply a chemical called dopamine. That chemical is missing from the brains of people who have Parkinson's disease, which afflicts up to a million Americans.
EUGENE REDMOND: We find that we can get stem cells to survive for long periods of time in the brain. They make into different types of cells. And we have some preliminary results in functionally impaired animals that the stem cells improve their Parkinsonism and make them better.
TOM BEARDEN: Will this eventually lead to a cure for Parkinson's disease?
EUGENE REDMOND: Well, we would like to think so. This and maybe some other techniques that are coming along will have to be combined in order to make a real cure.
The chimera
TOM BEARDEN: Dr. Redmond's implanted animals don't look or act differently, but they're now something called chimeras. It's a reference to ancient Greek mythology. A chimera was a combination of goat, lion and snake. To modern science, it's an animal that combines components of two different species in one body. Chimeras themselves aren't really new. In the 1980s, Scottish scientists used cloning techniques to create a half sheep, half goat, a geep. But bringing embryonic human stem cells into the mix is new, and has raised a host of ethical questions that the scientific community is now trying to grapple with.
Biologist Stuart Newman was so concerned he applied for a patent on a human-animal chimera in hopes of drawing public attention to what he saw as the dangers of such research. The patent was denied, which is just what he wanted.
STUART NEWMAN: The goal was to alert the public as to what the technology was capable of, to point out that because of the biological continuity between all different living species, there's really no obstacle to making something that is midway or part way between different species.
TOM BEARDEN: For example?
STUART NEWMAN: Well, a half human, half chimpanzee
Putting human cells into animal brains
TOM BEARDEN: Newman and others are concerned that if enough human cells are integrated into the brains of animals, humanlike consciousness might develop. But Redmond and his associates are keeping a close watch on their monkeys, like this one, dubbed XO-47. Redmond hasn't seen anything remotely like human behavior in this or any of his test subjects.
EUGENE REDMOND: We're putting maybe eight to ten million cells in a brain that maybe has twenty to forty billion cells. So this is an extremely small impact. It's not going to make a monkey into a humanized monkey.
TOM BEARDEN: This mouse also has human neural stem cells its brain. Like Redmond, Dr. Irving Weissman and his colleagues at Stanford University are also looking for ways to cure several neurological diseases, including brain cancer.
IRVING WEISSMAN: We put a few thousand cells in this ventricle of the mouse. It seeded here. The cancer cells came out here.
TOM BEARDEN: Weissman's eventual goal is to create a mouse with a brain made entirely of human cells. He suspects it would still be a mouse brain in every other way -- structure, form and function -- but theoretically would react to new treatments the same way it would in a human body. It would provide a platform to test new drugs without subjecting a human subject to potential harm.
IRVING WEISSMAN: If you have a human set of neurons -- pain, hippocampus, learning, whatever -- in the context of the mouse brain you could try a drug and say, What does this do to a simple learning task? What does this do to perception of a smell -- and so on.
