The development of programmable site-specific nucleases, including the zinc-finger nuclease (ZFN)15,16, transcription activator-like effector nucleases (TALENs)17–19, and the CRISPR/Cas9 system20–22,23 (Table 1), has improved gene editing efficiency in human ESCs and iPSCs substantially by inducing DNA double-strand breaks at the site of gene modification. The CRISPR/Cas9 technology in particular has attracted much attention and gained wide usage in gene editing of human ESCs and iPSCs due to its simplicity in design and ease of use. This gene editing technology allows researchers to introduce disease-causing mutations to WT iPSCs and eliminate such mutations in patient iPSCs to create isogenic controls for iPSC-based disease modeling (Fig. 1).
