Translation of stem cell therapy for neurological diseases.

"Regenerative medicine" hopefully will provide novel therapies for diseases that remain without effective therapy. This development is also true for most neurodegenerative disorders including Alzheimer's disease, Huntington's disease, or Parkinson's disease. Transplantation of new neurons to the brain has been performed in Parkinson's disease and in Huntington's disease. The restoration of dopaminergic neurons in patients with Parkinson's disease via implantation of embryonic midbrain tissue was taken from animal experiments to clinical applications, showing a limited efficacy. Clinical trials in patients with Huntington's disease using fetal striatal tissue currently are underway. Today, it seems possible to generate functional dopaminergic or striatal neurons form a variety of stem cells including embryonic or neural stem cells as well as induced pluripotent stem cells. First clinical trials using neural stem cell or embryonic-stem-cell-derived tissue are approved or already underway. Such cells allow for extensive in vitro and in vivo testing as well as "good manufacturing production," reducing the risks in clinical application.