iPS cells: a more critical review.

Over the past 20 months, reports claiming the generation of induced pluripotent stem (iPS) cells with characteristics identical to those of embryonic stem (ES) cells from nonembryonic tissue have captured great attention in both the scientific community and the general public. In the light of the continuing controversy over the use of ES cells, these reports have profound ramifications. This review calls into question the validity of many claims made in these reports--claims that have led to the rapid and premature acceptance of using iPS cells as a viable alternative to using normal stem cells for regenerative therapy. How convincing is the evidence supporting the various claims made for the iPS cells? Are there other more plausible explanations for the same observations? What are these iPS cells? Are they really safe for therapeutic use? Should the iPS technique be considered, in the absence of any direct evidence for induction and reprogramming, as a realistic alternative for somatic cell nuclear transfer (SCNT) to generate ES-like cells? This review attempts to encourage reflections on and offer alternative views for key aspects of iPS cells and studies.