A similar strategy of direct induction has enabled the production of oligodendrocytes and oligodendrocyte progenitor cells from murine fibroblasts (Najm et al., 2013; Yang et al., 2013), and although these phenotypes have yet to be directly induced from human somatic cells, one may anticipate the likely accomplishment of this goal as well as work in the field proceeds. Yet despite the promise of this approach, its drawbacks may prevent early clinical adoption. Directly induced terminal phenotypes, whether neurons or oligodendrocytes, are either post-mitotic or nearly so, limiting their expansion capacity, and thus requiring virtual 1:1 stoichiometry between successfully instructed cells and their intended product. Since the transduction and phenotypic instruction efficiencies of this technique remain relatively low, the number of cells of interest produced are similarly low, and unrealistically so for the purpose of any potential clinical use (Goldman, 2013). Moreover, the inherent heterogeneity within such an induced population would complicate assurance of their safety and hence their regulation.
