Conventional gene targeting approaches based on homologous recombination (HR), which occurs in nature when sperms and eggs are generated, can be used to achieve targeted genetic modification in human cells (Smithies, Gregg, Boggs, Koralewski, & Kucherlapati, 1985; Song, Schwartz, Maeda, Smithies, & Kucherlapati, 1987). However, the efficiency of HR is extremely low, necessitating elaborate positive and negative selection to obtain cells that contain the desired modification.Double-strand breaks (DSBs) at the target site can increase the efficiency of HR by at least two orders of magnitude (Rouet, Smih, & Jasin, 1994). Furthermore, error-prone repair of these DSBs through nonhomologous end joining (NHEJ) can lead to targeted mutagenesis (Bibikova, Golic, Golic, & Carroll, 2002). DSBs at specific genomic loci can be generated by specific sequence-recognizing programmable nucleases, which include zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and RNA-guided engineered nucleases (RGENs) (Kim & Kim, 2014).