Stem cells for central nervous system repair and rehabilitation.

The central nervous system (CNS) has limited capacity for self-repair. Current treatments are often incapable of reversing the debilitating effects of CNS diseases that result in permanent and/or progressive physical and cognitive impairments. One promising repair strategy is transplantation of stem cells, which can potentially replace lost neurons and/or glia or promote repair through secretion of trophic factors. Various types of stem cells exist, each with their own advantages and disadvantages. Although no consensus exists regarding the optimal cell type to use, moderate functional improvements have been shown in animal models of CNS diseases using different types of stem cells. However, the precise mechanism of action behind their beneficial effects remains unknown. In addition, many barriers to clinical use still need to be resolved before transplantation of stem cells can be used as effective biologics. These barriers include--depending on the stem cell type--possible tumor formation, difficulty with harvest, limited in vivo differentiation and integration, and ethical issues regarding use.