Current advances in the treatment of Parkinson's disease with stem cells.

Stem cell replacement has emerged as the novel therapeutic strategy for Parkinson's disease (PD). Control of motor behavior is lost in PD due to the selective degeneration of mesencephalic dopamine neurons (DA) in the substantia nigra. This progressive loss of DA neurons results in devastating symptoms for which there is no cure. Debilitating side effects often result from chronic pharmacological treatment, hence current investigations into cell transplantation therapy as a substitute and/or adjuvant to other therapeutics. Clinical trials with fetal DA tissue have provided evidence that cell transplantation could be a viable alternative. Limited availability of fetal tissue, combined with variable outcome led to emphasis on other sources of cells, such as stem cells. This review focuses on three stem cell sources (embryonic, neural, and adult mesenchymal). Also discussed is the molecular differentiation into mature DA neurons, the various protocols that have been developed to generate DA neurons from various stem cells, and the current state of stem cell therapy for PD.