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.
The researchers induced Parkinson’s symptoms in eight African green monkeys by injecting a toxin into their brains. Later, the team transplanted 3 million cells into the brains of five of the monkeys. Some of those cells indeed began making dopamine, but most grew into astrocytes, which are cells that nourish and support neurons.
The researchers say that the extra astrocytes orchestrated a “protect-and-repair” effort that jump-started the innate healing capabilities of the monkeys’ brains. The astrocytes apparently secreted growth factors that stopped nerve damage, boosted blood vessel growth, and prompted existing neurons to start making dopamine.
Over 4 months, the monkeys receiving the human cells made partial recoveries, the researchers report in the July 17 Proceedings of the National Academy of Sciences.