Stem cell transplantation research - the remaining hurdles

Despite the public interest in stem cell treatment for Parkinson's disease, the field is in its infancy with many issues still to be addressed.In a review of recent advances in the use of stem cells for Parkinson's disease, Drs Snyder and Olanow from New York also list a number of hurdles to be overcome. They say that political debate and "the outspoken involvement of celebrities" has not only increased awareness of the possible benefits of stem cell therapy, but also created unrealistic expectations. Factors still requiring resolution include determination of the most appropriate type of stem cell for transplantation and the optimal method for expanding and differentiating stem cells into functioning dopamine neurones. Embryonic stem cells are currently considered the most appropriate for transplantation in Parkinson's disease. These cells can spontaneously differentiate into neurones after transplantation with a few showing features of dopamine neurones. "A major concern is the potential of undifferentiated cells to develop into undesired cell phenotypes with tumor formation (e.g. teratomas) and other unanticipated complications," the authors say. They also refer to two clinical trials of fetal nigral neurone transplantation where dyskinesia persisted after withdrawal of levodopa and say that studies are required to assess the risk of off-medication dyskinesia with stem cell transplantation. "Enthusiasm for stem cells must be tempered by the experience with fetal nigral transplantation, which remains a sobering reminder of the importance of preclinical basic science in preparing for a clinical trial," they warn.The authors point out that it is important to remember that non-dopaminergic lesions also play a role in Parkinson's disease and that stem cells may not address this aspect of the disease. They say it is possible that early transplantation may prevent degeneration in non-dopamine neurones that occurs secondary to dopamine deficiency. However, the conclude, "It remains a concern, nonetheless, that therapies based exclusively on dopamine replacement will not meaningfully improve disability in Parkinson's disease patients beyond that which can already be achieved."Reference...