Steam cells: solution to the problem of transplants in Parkinson's disease?

The use of neural transplantation or cellular therapies for Parkinson's disease (PD) is based on the idea of substituting nigral dopaminergic neurons lost as a consequence of the degenerative process. More than 400 people with PD have received a transplant with highly variable results. Success of cellular therapy depends on the survival of a sufficient number of trasplanted dopaminergic cells and on the restoration of normal striatal circuitry, disrupted by the disease process. None of the currently used cellular sources can generate an unlimited number of dopaminergic cells. Stem cells (SC) are pluripotent cells which may be obtained from embryonic, fetal or adult tissues. SC can be isolated, expanded in culture during long periods of time and induced to differentiate into dopaminergic cells. Cellular lines can be created and can be stored. Therefore, a large amount of dopaminergic cells can be obtained from a single SC and they can be used when necessary. Embryonic SC seems to be more plastic than adult SC; however, the plasticity of adult SC may be higher than initially thought due to a phenomenon called transdifferentiation. Several studies carried out in experimental models have shown that SC therapy is viable. SC may be also the ideal vehicle for gene therapy. However, much work remains to be done before SC can be applied to human beings. Different aspects of neural development should be elucidated and important practical problems should be overcome, particularly those related to the development of germinal tumors and immunological rejection. Finally, ethical controversies should be carefully managed.