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Summary Human induced pluripotent stem cells (iPSCs) are promising in regenerative medicine. However, the risks of teratoma formation and the overgrowth of the transplanted cells continue to be major hurdles that must be overcome. Here, we examined the efficacy of the inducible caspase-9 (iCaspase9) gene as a fail-safe against undesired tumorigenic transformation of iPSC-derived somatic cells. We used a lentiviral vector to transduce iCaspase9 into two iPSC lines and assessed its efficacy in vitro and in vivo. In vitro, the iCaspase9 system induced apoptosis in approximately 95% of both iPSCs and iPSC-derived neural stem/progenitor cells (iPSC-NS/PCs). To determine in vivo function, we transplanted iPSC-NS/PCs into the injured spinal cord of NOD/SCID mice. All transplanted cells whose mass effect was hindering motor function recovery were ablated upon transduction of iCaspase9. Our results suggest that the iCaspase9 system may serve as an important countermeasure against post-transplantation adverse events in stem cell transplant therapies., Highlights • The iCaspase9 system induced apoptosis of iPSCs and all iPSC derivatives in vitro • Grafted iPSC-NS/PCs formed teratomas and non-teratomatous neural tumors • The iCaspase9 system prevented tumor progression and adverse effects with tumor • CID was demonstrated to be an effective inducer even in the CNS protected by the BBB, In this article, Okano, Nakamura and colleagues report that the iCaspase9 system abolished hiPSC-NS/PCs-derived tumors and controlled adverse events. The iCaspase system may serve as an important countermeasure against post-transplantation adverse events in stem cell transplant therapies.

Neural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs) are expected to be a valuable cell source for cell therapies that target central nervous system disorders. For clinical applications, NS/PCs should be induced and maintained under clinical grade conditions, which are challenging to achieve. In the present study, we established a procedure to obtain xeno-free long-term self-renewing neuroepithelial-like stem cells (xf-lt-NES cells) from feeder-free hiPSCs using a newly developed xeno-free medium, StemFit(®)AS200. xf-lt-NES cells were cultured for long periods in StemFit(®)AS200 while retaining normal karyotypes, NS/PC marker expression and differentiation capacity for neuronal and glial differentiation in vitro and in vivo. Furthermore, the cells were cryopreserved using a defined serum-free freezing reagent, which demonstrated the feasibility of this xeno-free culture system for large-scale lt-NES cell production and cell banking. Taken together, our system represents a promising approach for the manufacture of clinically relevant products for cell therapy using NS/PCs.