CRISPR-Cas9 is the third generation of gene editing technology after ZFN and TALENs, which has the advantages of high editing efficiency, low cost, and easy operation, and has become the most mainstream gene editing method today. At present, several cell and gene therapy drugs based on CRISPR-Cas9 technology have been approved for clinical trials. In in vitro gene therapy, cells modified by the CRISPR-Cas9 system are tested for extracellular or intracellular Cas9 nuclease residues before being infused back into the body.
