Cellular immunotherapy has achieved incremental success in recent years. Varieties of cell products are undergoing fundamental research and clinical trials, among which CAR-T cell therapy is approved for marketing. As research progresses, these cells need to be modified to promote their safety and efficacy. Gene-editing technologies have evolved from RNA interference (RNAi), including small interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs), to new generations of zinc finger nucleases (ZFNs), transcription-activator-like effector nucleases (TALENs), and clusters of regularly spaced short palindromic repeats (CRISPR/Cas9), and delivery methods are widely used. Here, we summarize the ongoing clinical trials and fundamental research for genome editing therapy. Additionally, we highlight existing in vivo delivery systems and their limitations to find a better method to deliver genes.