It is clear that fetal nigral transplantation remains an experimental procedure and cannot be presently recommended as a therapy for PD. It is not certain why benefits were observed in open label studies but not in two double-blind studies, despite using similar protocols and evidence of graft survival on both PET studies and post-mortem examination. It is certainly possible that benefits observed in open label studies were exaggerated by placebo effect or bias. It is also not certain why transplanted patients developed off-medication dyskinesias. Insight into the cause of this complication and the development of methods to prevent this complication from occurring are required before further trials of fetal nigral transplantation or other forms of cell-based therapy can be resumed. While these results are disappointing, these studies provide some clues that might permit better results to be obtained with a variety of protocol modifications (Winkler et al., 2005). These are discussed below.
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