The Niche

Correspondence: iPS cell safety data needs tracking

The following letter, from University of Tokyo’s Hisashi Moriguchi, responds to a recent news feature in Nature describing the scientific race for the assessment and production of induced pluripotent stem cells.

In your News Feature ‘Fast and furious’ (Nature 458, 962–965; 2009), the safety issues concerning induced pluripotent stem (iPS) cells are well summarized. However, reviewing some published manuscripts for iPS cells, I have found that the reports on the cells’ safety are very different among nations.

The follow-up data needed to evaluate the cancerous transformations of iPS cells have been shown in most original manuscripts from Japan (Cell 131, 861–872; 2007. Nature Biotechnol. 26, 101–106; 2008. Science 321, 699–702; 2008). On the other hand, such follow-up data have not been provided in most manuscripts from other nations (Nature 458, 766–770; 2009. Science 324, 797–801; 2009).

Now, new technologies to lower the risk of cancerous transformations by iPS cells have been reported (Nature 458, 962–965; 2009). However, which of the technologies most consistently produces the iPS cells with the least chance of tumourigenicity? The evidence has not been shown.

As Monya Baker indicated, Shinya Yamanaka thinks that iPS cells will be used widely for drug screening and toxicity testing within three or four years (Nature 458, 962–965; 2009). However, if tumourigenic human iPS cells are used as a research tool, more complex epigenetic modifications may arise in the disease-specific iPS cells. As a result, their value as a research tool may be limited. Therefore, the international disclosure of long-term follow-up data for the chimera mouse–derived iPS cells should be provided to determine the best iPS cells.

On the other hand, for human iPS cells, researchers cannot ethically establish chimera human cells. Thus, it is important for researchers to find new methods to predict the tumourigenicity of human iPS cells. In order to promote international disclosure of long term follow-up data for mouse iPS cells, Nature should take the initiative in supporting the plan.

Hisashi Moriguchi

Research Center for Advanced Science and Technology, The University of Tokyo, Japan.

e-mail: moriguchi[at]


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