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Stem cells migrate in primate brains

(CNN) -- A study of unborn monkeys may provide clues to how stem cells behave in the human brain, and could one day help develop therapies based on stem cell transplants, researchers reported Friday.

However, any therapies to treat humans are years away from being developed -- and may not be feasible at all, they cautioned.

The researchers injected human stem cells derived from an aborted fetus into the brains of three unborn monkeys. The injections were given when the monkey fetuses were 12-13 weeks old. When they were 16-17 weeks old, they were delivered by Caesarean section and their brains examined.

The researchers found that the stem cells had spread throughout the monkeys' brains, rather than remain at the injection site. Some had differentiated into neurons and other types of brain cells.

"The remarkable thing we found is that the stem cells we put in did not produce a glob of cells in one place in the brain," researcher Dr. Curt R. Freed of the University of Colorado School of Medicine told the Associated Press. "Instead, they distributed themselves around the fluid-filled spaces and went into an orderly migration to the areas of the brain that were under development."

Other human stem cells did not differentiate but formed a reservoir of cells.

The researchers said these undifferentiated cells might provide a pool of stem cells that are used for repair when the body needs it. The finding could explain why scientists have found similar groups of less-differentiated stem cells in various organs of the body.

The research was published in Friday's edition of the journal Science.

This is not the first time researchers have had success implanting stem cells into animal brains. Research on rats and mice also showed that stem cells would migrate to various parts of the brain. However, this is thought to be the first time such a response has been shown in the larger primate brain.

Therapies 'years away'

The finding suggests stem cells injected into a human brain would also migrate to the appropriate locations. That might mean that scientists could one day use targeted gene therapy or cell replacement approaches using stem cells to treat diseases in the human brain.

But such therapies are years away and might not even work at all, scientists cautioned.

The researchers don't know if the differentiated stem cells are performing properly -- or even performing at all. And the monkeys were too young to determine if they suffered any negative consequences from the procedure.

Moreover, the monkeys used in this experiment were not sick. Scientists were not trying to cure them of any disease; they were only trying to determine how the injected stem cells would behave.

But even if scientists were able to show that stem cell injections could cure sick monkeys before they were born, there would still be many steps before any human cures could be obtained.

Researchers would have to determine exactly what types of cells would be most likely to cure a human fetus. Even if they determine that, they do not know if it is physically possible to implant the cells into a fetus without harming it or the mother. And the question of complications from the procedure also is unanswered.

• National Institutes of Health
• Stem Cells: A Primer
• American Association for the Advancement of Science - Stem Cells

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