Advances in human stem cell therapies: pre-clinical studies and the outlook for central nervous system regeneration

Cell transplantation has come to the forefront of regenerative medicine alongside the discovery and application of stem cells in both research and clinical settings. There are several types of stem cells currently being used for pre-clinical regenerative therapies, each with unique characteristics, benefits and limitations. This brief review will focus on recent basic science advancements made with embryonic stem cells and induced pluripotent stem cells. Both embryonic stem cells and induced pluripotent stem cells provide platforms for new neurons to replace dead and/or dying cells following injury. Due to their capacity for reprogramming and differentiation into any neuronal type, research in preclinical rodent models has shown that embryonic stem cells and induced pluripotent stem cells can integrate, survive and form connections in the nervous system similar to de novo cells. Going forward however, there are some limitations to consider with the use of either stem cell type. Ethically, embryonic stem cells are not an ideal source of cells, genetically, induced pluripotent stem cells are not ideal in terms of personalized treatment for those with certain genetic diseases the latter of which may guide regenerative medicine away from personalized stem cell based therapies and into optimized stem cell banks. Nonetheless, the potential of these stem cells in central nervous system regenerative therapy is only beginning to be appreciated. For example, through genetic modification, stem cells serve as ideal platforms to reintroduce missing or downregulated molecules into the nervous system to further induce regenerative growth. In this review, we highlight the limitations of stem cell based therapies whilst discussing some of the means of overcoming these limitations.