For potential use in regenerative medicine both iPS and iN cell approaches would provide autologous neuronal donor cells for transplantation. Expandability is obviously a major advantage of iPS cells over postmitotic iN cells and may very well be a limiting factor. However, the postmitotic state of iN cells would have the advantage of a much lower risk of cancer and teratoma formation. Integration-free iN cells would be preferable for clinical use. Along those lines will it be exciting to see whether small molecules can be found to replace some or all transcription factors, similar to the recent successes for iPS cells. Finally, future studies will need to improve iN cell generation from adult human fibroblast since the current low efficiencies represent another hurdle for any of these translational applications.
