Transplantation of dopaminergic progenitor cells derived from human induced pluripotent stem cells is safe and could be effective in Parkinson disease (PD), according to a recent study published in Nature. In the phase I/II trial, seven people with PD underwent transplantation with the main aim of assessing the safety of the treatment. No serious adverse events occurred, and transplantation did not lead to tumours or inflammation over 2 years of monitoring. Improvements in motor function were seen in five of the participants over the same period, suggesting that the transplanted cells compensated for disease-associated loss of dopaminergic neurons.