Monkeys with a Parkinson's disease–like disorder showed signs of improvement after receiving transplants of human-brain stem cells. The treated monkeys began to walk and eat again, while their untreated companions continued to degenerate.
In Parkinson's, neurons that produce the nerve-signal transmitter dopamine die off. Researchers have implanted fully mature dopamine-producing neurons into the brains of a few people with Parkinson's, but those cells sometimes produced too much of the chemical, causing spasms.
Hoping to bypass that problem, D. Eugene Redmond Jr. of the Yale University School of Medicine and his colleagues deployed immature brain stem cells collected from fetuses. Such cells have the potential to mature into the whole array of brain-cell types, including dopamine producers.