Previous studies demonstrated the principal feasibility of converting non-neuronal human cells into iN cells, but also described a low conversion efficiency and a diminished capacity of the resulting iN cells for synapse formation (Pang et al., 2011; Ambasudhan et al., 2011; Qiang et al., 2011; Pfisterer et al., 2011a and 2011b; Yoo et al., 2011; Caiazzo et al., 2011; Son et al., 2011). However, realization of the potential of iN cells for studying the pathogenesis of neurological diseases, for developing drug screening systems, and for producing neurons for regenerative medicine requires the capability of producing human iN cells at a large scale and high yield, and necessitates the generation of iN cells that readily form synapses. Moreover, such goals would be facilitated by a high degree of reproducibility of iN cell generation independent of the starting cell line, and by production of a relatively homogeneous population of functional iN cells for experiments.
