Advancing Parkinson's disease treatment: cell replacement therapy with neurons derived from pluripotent stem cells.

The motor symptoms of Parkinson's disease (PD) are caused by the progressive loss of dopamine neurons from the substantia nigra. There are currently no treatments that can slow or reverse the neurodegeneration. To restore the lost neurons, international groups have initiated clinical trials using human embryonic or induced pluripotent stem cells (PSCs) to derive dopamine neuron precursors that are used as transplants to replace the lost neurons. Proof of principle experiments in the 1980s and 1990s showed that grafts of fetal ventral mesencephalon, which contains the precursors of the substantial nigra, could, under rare circumstances, reverse symptoms of the disease. Improvements in PSC technology and genomics have inspired researchers to design clinical trials using PSC-derived dopamine neuron precursors as cell replacement therapy for PD. We focus here on four such first-in-human clinical trials that have begun in the US, Europe, and Japan. We provide an overview of the sources of PSCs and the methods used to generate cells for transplantation. We discuss pros and cons of strategies for allogeneic, immune-matched, and autologous approaches and novel methods for overcoming rejection by the immune system. We consider challenges for safety and efficacy of the cells for durable engraftment, focusing on the genomics-based quality control methods to assure that the cells will not become cancerous. Finally, since clinical trials like these have never been undertaken before, we comment on the value of cooperation among rivals to contribute to advancements that will finally provide relief for the millions suffering from the symptoms of PD.