Parkinson’s disease patients treated with fetal tissue are assessed three years after surgery. The TransEuro open-label trial of human fetal ventral mesencephalic transplantation in patients with moderate Parkinson’s disease

Transplantation of human fetal ventral mesencephalic (hfVM) tissue in patients with Parkinson’s disease (PD) has yielded clinical benefits but also side effects such as graft-induced dyskinesias (GIDs). The open-label TransEuro trial (NCT01898390) was designed to determine whether this approach could be further developed into a clinically useful treatment. Owing to poor availability of hfVM, only 11 patients were grafted at two centres, using the same tissue preparation protocol but different implantation devices. No overall clinical effect was seen for the primary end point 3 years after grafting. No major GIDs were seen but we observed differences in outcome related to transplant device and/or site. Dopamine uptake improved at 18 months in 7 patients according to [18F]-fluorodopa PET imaging but was restored to near-normal levels in only one patient. Our findings highlight the need for a stem-cell source of dopamine neurons for potential PD cell therapy and provide critical insights into how such clinical studies should be approached.