Current Status and Future Perspectives on Stem Cell-Based Therapies for Parkinson's Disease.

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease, affecting 1%-2% of the population over the age of 65. As the population ages, it is anticipated that the burden on society will significantly escalate. Although symptom reduction by currently available pharmacological and/or surgical treatments improves the quality of life of many PD patients, there are no treatments that can slow down, halt, or reverse disease progression. Because the loss of a specific cell type, midbrain dopamine neurons in the substantia nigra, is the main cause of motor dysfunction in PD, it is considered a promising target for cell replacement therapy. Indeed, numerous preclinical and clinical studies using fetal cell transplantation have provided proof of concept that cell replacement therapy may be a viable therapeutic approach for PD. However, the use of human fetal cells remains fraught with controversy due to fundamental ethical, practical, and clinical limitations. Groundbreaking work on human pluripotent stem cells (hPSCs), including human embryonic stem cells and human induced pluripotent stem cells, coupled with extensive basic research in the stem cell field offers promising potential for hPSC-based cell replacement to become a realistic treatment regimen for PD once several major issues can be successfully addressed. In this review, we will discuss the prospects and challenges of hPSC-based cell therapy for PD.