Long-Term Evaluation of Intranigral Transplantation of Human iPSC-Derived Dopamine Neurons in a Parkinson's Disease Mouse Model.

Parkinson's disease (PD) is a neurodegenerative disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). One strategy for treating PD is transplantation of DA neuroblasts. Significant advances have been made in generating midbrain DA neurons from human pluripotent stem cells. Before these cells can be routinely used in clinical trials, extensive preclinical safety studies are required. One of the main issues to be addressed is the long-term therapeutic effectiveness of these cells. In most transplantation studies using human cells, the maturation of DA neurons has been analyzed over a relatively short period not exceeding 6 months. In present study, we generated midbrain DA neurons from human induced pluripotent stem cells (hiPSCs) and grafted these neurons into the SNpc in an animal model of PD. Graft survival and maturation were analyzed from 1 to 12 months post-transplantation (mpt). We observed long-term survival and functionality of the grafted neurons. However, at 12 mpt, we observed a decrease in the proportion of SNpc DA neuron subtype compared with that at 6 mpt. In addition, at 12 mpt, grafts still contained immature neurons. Our results suggest that longer-term evaluation of the maturation of neurons derived from human stem cells is mandatory for the safe application of cell therapy for PD.