You can find a summary of some of the research and discussion from CIRM's Amy Adams here. Paul Knoepfler of UC Davis said,
"So if iPS cells are not that similar to ESC, what does this mean?(Editor's note: An earlier version of this item contained typos in the material that was inserted from Knoepfler's original post. He corrected those typos on his blog, and we have altered his quote above to reflect those changes.)
"First, it is not the end of the world. Many of us had assumed that iPS cells are similar to ESC in some ways, but distinct in others. These studies simply validate that notion.
"Second, iPS cells are still very useful even if they are not quite so close siblings of ESC. In fact, iPS cells do not need to be extremely similar to ESC to be useful. The pluripotency and self-renewal of iPS cells makes them a powerful tool regardless.
"Third, iPS cells are a distinct type of stem cell from ESC and should be considered as such.
"Fourth, these studies also highlight that every iPS cell line made is distinct from the others made. The heterogeneity amongst iPS cell lines is probably more substantial than the differences between ESC lines, but ESC lines also vary between each other quite a lot as well.
"Finally, the tumorigenicity of iPS cells is a serious concern. A remaining open question is how prone iPS cells are to form malignant tumors (although don't forget that teratoma can be malignant!). We predict that iPS cells are dramatically more prone to produce malignant tumors compared to ESC."