Dissecting divergent outcomes in stem cell-derived dopamine cell therapy trials for Parkinson's disease.

Fetal tissue transplantation established proof-of-concept for dopamine cell replacement in Parkinson's disease but yielded inconsistent outcomes due to limited tissue availability and cellular heterogeneity. Advances in generating high-purity dopamine progenitors from pluripotent stem cells have enabled standardized products that show safety and motor improvement in clinical trials. However, these trials revealed divergent outcomes arising at three levels: between clinical studies, driven by differences in cell products, baseline patient characteristics, or immunosuppressants; between patients, influenced by alloimmune factors, genetic background, or co-pathology; and within patients, where graft survival varies across transplantation sites due to the local microenvironment or surgical technique.