MONKEYS with Parkinson’s disease-like symptoms have had their suffering eased by an injection of human embryonic stem cells (hESCs) into their brain.

Jun Takahashi of Kyoto University in Japan and colleagues injected these cells into monkeys whose brains had been damaged by a chemical that destroys dopamine-producing neurons and so causes Parkinson’s symptoms.

Two monkeys received hESCs that had been matured into an early form of neural cell. Six months later, the monkeys had recovered 20 to 45 per cent of the movement they had lost before treatment. Post-mortems a year after treatment showed that the cells had developed into fully functioning dopamine-secreting neurons. Another monkey that received less-mature neural cells also showed improvements (Stem Cells, DOI: 10.1002/stem.1060).

“Monkeys starting with tremors and rigidity [began] to move smoothly, and animals originally confined to sitting down were able to walk around,” says Takahashi.

The team says it will probably be four to six years before clinical trials in humans begin.