The science and ethics of cell-based therapies for Parkinson's disease.

Parkinson's Disease (PD) is an age-related, disabling neurodegenerative disorder. Although sufferers usually respond to dopamine agonists for extended periods, the disease remains progressive and adverse drug effects can compromise effective long term treatment. Cell-based therapies have been the subject of much hype and optimism with regard to PD. Proof of principle was provided in the 1980s with fetal tissue transplantation trials demonstrating successful graft survival. Embryonic stem cells and reprogrammed or transdifferentiated somatic cells may provide alternative sources of tissue with the potential to overcome the material shortages and technical difficulties that have hindered fetal neural transplants. This article will review the state of the science for cell based therapies and examine the ethical issues that societies must negotiate regarding their clinical use.