Using stem cells and iPS cells to discover new treatments for Parkinson's disease.

Fetal cell transplantation can improve the symptoms of Parkinson's disease (PD) patients for more than a decade. In some patients, alpha-synuclein aggregates and Lewy bodies have been observed in the transplanted neurons without functional significance. Recently stem cells have emerged as an ethically acceptable source of cells for transplantation but, importantly, the type of stem cell matters. While the lineage restriction of adult neural stem cells limits their clinical applicability for patients with PD, human pluripotent stem cells provide an opportunity to replace specific types of degenerating neurons. Now, cellular reprogramming technology can provide patient-specific neurons for neural transplantation and problems with cell fate specification and safety are resolving. Induced pluripotent stem (iPS) cell-derived neurons are also a unique tool for interpreting the genetic basis for an individual's risk of developing PD into clinically meaningful information. For example, clinical trials for neuroprotective molecules need to be tested in presymptomatic individuals when the neurons can still be protected. Patient-specific neural cells can also be used to identify an individual's responsiveness to drugs and to understand the mechanisms of the disease. Along these avenues of investigation, stem cells are enabling research for new treatments in PD.