How far are induced pluripotent stem cells from the clinic?

Induced pluripotent stem cells (iPSCs) can be derived from diverse different somatic cells and share many of the characteristics of embryonic stem cells (ESCs). Because iPSCs avoid many of the ethical concerns associated with the use of embryonic or fetal material, iPSCs have great potential in cell-based regenerative medicine. However, several hurdles will need to be surmounted before their potential can be realized in therapeutic applications. For example, the use of viral vectors, some of which are oncogenes raises the risk of tumor formation in patients, the differentiation of iPSCs into required functional cells in vivo remains to be established, the obtaining of pure populations of target cells from iPSCs is still difficult. Of these, some are shared by both iPSCs and ESCs, others are unique to iPSCs. We will describe these stumbling blocks in detail and discuss possible ways to overcome them. Despite many significant advances, there is as yet no technological framework that would allow the exploitation of iPSCs in a clinical setting in the immediate future. Further research will be required before directed reprogramming can provide a source of cells suitable for application in regenerative medicine.