The neurons show adequate release of DA into the host18 and, most importantly, they gradually provide substantial clinical improvement, with up to 50% to 60% reductions in the Unified Parkinson’s Disease Rating Scale (UPDRS). Moreover, the clinical improvements strongly correlate with recovery of movement-related activation of the host premotor and supplementary motor cortex.14 Most of the early transplantation Inhibitors,research,lifescience,medical efforts for PD were carried out as open-label trials. These trials gave similar results and

suggested the potential benefits of cell transplantation, but concerns were raised about their validity because of the relative limited number of patients, the variable inclusion criteria, and the lack

of adequate control groups. In 1992, to circumvent these issues, the National Institutes of Health (NIH) agreed to sponsor two larger controlled clinical trials. These were designed as doubleblind clinical trials and even included highly controversial sham surgeries as placebo controls. The results of the first trial were published in 200131 Inhibitors,research,lifescience,medical and the results of the second trial have recently been reported.32 To transplantation enthusiasts, the results were rather disappointing – even troubling. The first study showed no overall improvement on a subjective global Inhibitors,research,lifescience,medical rating scale; however, some reductions in UPDRS score were found in patients Inhibitors,research,lifescience,medical who had responded well to L-dopa treatment prior to surgery.14,31,33 The most troubling result was that 15% of the grafted patients showed severe dyskinesias as a side effect of treatment. The second study also failed to show any significant improvements after grafting and, in this study, more than

50% of the patients developed dyskinesias.32 In spite of the disappointing and troubling results of these recent NIH trials, most of the scientists involved seem to agree that more basic research and clinical trials are needed to be fully able to evaluate the benefits from this highly novel and still experimental treatment. A more detailed discussion of these Inhibitors,research,lifescience,medical Epothilone B molecular weight issues can be found in Bjôrklund et al.14 One issue that, becomes very clear from the discussion about cell transplantation for PD is that, the current method of using fetal DA neurons has major technical and practical limitations, including the limited and ethically controversial availability of human fetal DA neurons, and the potential immunological and virological complications of using nonhuman species as fetal cell sources. Therefore, most, of the scientific community agree that this Stem Cells inhibitor approach now requires a better source of transplantable DA neurons if cell therapy is ever to become a realistic and accessible treatment modality for PD. This review will focus on the various types of stem or progenitor cells currently under investigation as potential sources for cell replacement, in PD.