The application of iPSCs seems so good so far and all these mentioned results raise great clinical expectations. However, it should be noted that safety-related concerns for such iPSCs cell therapy should be resolved prior to clinical application. A main concern after iPSC therapy is tumor formation as a result of residual or remaining undifferentiated iPSCs that were not successfully induced into differentiation. Moreover, there is the chance that the reprogramming was not necessarily complete (Nakamura and Okano, 2013; Kim et al., 2014). Long term safety issues also include deteriorated motor function accompanied by a tumor formation (Nori et al., 2015). However, Tsuji et al. used the neurospheres 3D culturing of iPSCs obtained from mice fibroblasts, and injected them into the injured spinal cord. Those neurospheres were able to differentiate into three neuronal lineages: astrocytes, oligodendrocytes, and neurons, promoting recovery and improving locomotor functional loss with no tumor formation for the observation period of more than 120 days (Tsuji et al., 2010). Besides, an in vivo study has shown that 3 rats have died out of 12 rats that received
