First-in-human clinical trial for age-related macular degeneration using iPSC-derived retinal pigment epithelium (RPE) cells was conducted in 2014,showing no serious adverse effects to date,including tumor formation.This appears to be attributable to relatively small number of transplanted cells,and distinct morphology of RPE cells;it might be relatively easy to minimize contamination of undifferentiated cells.However,in the case of clinical trial using iPSC-derived cardiomyocytes,108-109 cells would be required for transplantation;strict control of residual undifferentiated cells should be necessary for safer clinical application.