Stem cells and neurological disease.

here has recently been a great deal of interest in stem cells and the nervous system, in terms of their potential for deciphering developmental issues as well as their therapeutic potential. In this editorial we will critically appraise the different types of stem cells, their therapeutic implications, and the applications to which they have been put, with the hope that the hype that surround these cells can be distinguished from the scientific reality. Stem cells were originally defined in the haematological system, but more recently have been found in a multitude of other sites, including the brain. These cells all share the same properties of self-renewal and multipotentiality 1 and various different types and therapeutic strategies have been defined with respect to the nervous system (Table 1, fig 1). The reasons for these cells receiving such attention for the treatment of neurological disorders relates to their: (a) capacity to proliferate in culture with the prospect that large numbers of cells can be derived from a limited source; (b) potential to be harvested from the patients themselves; (c) ability to migrate and disseminate following implantation within the adult CNS; (d) possible tropism for areas of pathology ; (e) ease of manipulation using viral and non-viral gene transfer methods; (f) ability to better integrate into normal brain cytoarchitecture with the potential for physiologically regulated release of substances. We will briefly discuss the different types of stem cells and how they have been applied to neurological disease, especially Parkinson's disease, given the accepted view that this is the disease most amenable to cell replacement therapy. Embryonic stem cells are derived from the inner cell mass of the embryonic blastula and are pluripotent with great proliferative potential, although with this comes the risk of teratomas. Much of the work to date has concentrated on mouse derived embryonic stem cells, which can be made to differentiate into neurons, including dopaminergic neurons. 2 These latter cells have been shown to survive and ameliorate behav-ioural deficits in an animal mode of Par-kinson's disease, 3 although in this study 20% of rats still developed teratomas at the transplant site. In contrast, Kim et al, using a different approach that relies on transfection with Nurr1 (a transcription factor involved in the differentiation of dopaminergic cells), have demonstrated functional efficacy without tumour formation. 4 Human embryonic stem cells have now been isolated 5 and grown in culture with enrichment for …