MIT and Harvard scientists have shown that induced pluripotent stem (iPS) cells can become functioning neurons when transplanted into the brains of mice and rats; they also showed that the cells can improve symptoms in a rat model of Parkinson’s disease.

They used a previously developed method for reprogramming cells, in which skin cells of a mouse can be made pluripotent when infected with a retrovirus carrying four genes. Those cells were turned into neurons.

When rats with a Parkinson’s-like condition were given these neurons derived from iPS cells, the motor defect improved. The researchers also learned that injecting undifferentiated iPS cells caused tumors, but careful cell sorting prevented tumors.