Figure 3.

Promotion of myelin repair by exogenous cells. Cells may be derived from developmentally distinct stages: embryonic, foetal and adult. Two classes of cells have generated particular interest, each with their own benefits and drawbacks: NPCs and adult non-neural stem cells. NPCs may be generated by ex vivo manipulation from human embryonic stem cells, or directly from primary foetal or adult brain samples. Adult mesenchymal stem cells can be generated from readily accessible sources such as skin and bone marrow. Other cell types that are potentially capable of myelination include olfactory ensheathing cells and Schwann cells. Exogenous cells may promote remyelination directly or indirectly by differentiation into myelinating cells and/or promotion of endogenous remyelination. In addition, grafted cells can be neuroprotective by means independent of differentiation such as immune modulation and trophic support (see text for details).