Reprogrammed iPS cells are pluripotent. Credit: Katie Ris-Vicari

When, a year ago, we picked induced pluripotent (iPS) stem cells as an area worth watching, it had only recently been demonstrated that the basic approach—expressing a defined set of factors in somatic cells to render them pluripotent—worked in human.

The potential of this system, for understanding early development, as a research model for disease, or even in future applications in the clinic, was apparent, but several questions remained.

There has since been progress in many directions, in work from several labs. By starting with different cell types, or by using small molecules, the efficiency of reprogramming has been improved up to 100-fold and has allowed iPS cells to be generated without one or more of the reprogramming factors. Screens for small molecules that can improve the results even further will doubtless continue.

The range of cell types that have been rendered pluripotent has also increased and now includes pancreatic beta cells, neural stem cells and human keratinocytes, among others. Human iPS cells have in addition been generated by reprogramming somatic cells from individuals affected with genetic disease. And recently, transient expression of the reprogramming factors has been used to generate mouse iPS cells, circumventing problems that can result from viral integration into the genome.

In addition to further technical improvement, continued studies of iPS stem cell biology, whether at the level of gene expression, epigenetics or differentiation, will be critical for harnessing their full potential. This is still an area worth watching, we bet.