Although several limitations exist in current 3D technology as detailed in the section of “human iPSC-based disease modeling”198,199, combining disease-specific iPSCs with 3D technology allows the examination of spatiotemporal cellular interactions that could reveal the physiological disease status, thus providing an unprecedented drug-screening platform and offering a new option for tissue-replacement therapy. However, transplantation of human stem cell-derived organoids into animals to derive human tissues or organs may bring new issues in biomedical ethics that warrant further attention200, such as the potential of transplanted human stem cells to mix with host cells and development in the nervous system and germlines of host animals.
