Regeneration and repair in multiple sclerosis: the role of cell transplantation.

Physiological (spontaneous) and reactive (reparative) regenerative processes are fundamental part of life and greatly differ among the different animals and tissues. While spontaneous regeneration naturally occurs upon cell attrition, reparative regeneration occurs as a consequence of tissue damage. Both spontaneous and reparative regeneration play an important role in maintaining the normal equilibrium of the central nervous system (CNS) as well as in promoting its repair upon injury. Cells play a critical role in reparative regeneration as regenerating structures (cells or tissues) depend on the proliferation without (de)differentiation of parenchymal cells surviving to the injury, proliferation of stem (progenitor) cells resident in the injured tissue, dedifferentiation of mature cells in the remaining tissue, or by the influx of stem cells originating outside the damaged tissue. Considering the central role of stem and progenitor cells in regeneration, a spur of experimental stem cell-based transplantation approaches for tissue (e.g. CNS) repair has been recently generated. This review will focus on the therapeutic efficacy of different sources of somatic stem cells - and in particular on those of neural origin - in promoting CNS repair in a chronic (auto)immune-mediated inflammatory disorder such as multiple sclerosis.