At a time when the first regenerative medicine clinical trials are being performed using pluripotent stem cells, teams from the I-Stem Institute, are continuing to explore the quality criteria that must be adopted to best ensure patient safety. Three years ago, an I-Stem team identified a genomic anomaly that very frequently appeared in undifferentiated cell lines when the latter were forced to perform too great a number of proliferation cycles. The same team has today demonstrated the systematic occurrence of a genomic anomaly in differentiated neural stem cells, beginning at these lines, after several dozen replication cycles. The details of this research are published in the Journal of Clinical Investigation, dated 24 January. This research received backing from Inserm and the AFM thanks to donations from a Telethon.