Regenerative medicine is fraught with safety concerns about whether using, for example, induced pluripotent stem cell (iPSC)-derived material poses a risk of developing cancer from that material. To investigate these safety concerns, Hong, Winkler et al. developed a non-human primate model. They used autologous iPSCs and showed that undifferentiated iPSCs formed teratomas in vivo, which activated an inflammatory immune response. However, when the iPSCs were first differentiated into mesodermal stromal-like cells, they formed new bone in vivo, without any evidence of teratoma formation, suggesting that differentiated iPSCs may be safe to use in vivo.