Cas9 exo-endonuclease eliminates chromosomal translocations during genome editing

Chromosomal structural variations induced by CRISPR/Cas hinder its application in clinics. Here, the authors fuse Cas9 with optimized TREX2 to generate Cas9TX, which can prevent perfect repair and inhibit repeated cleavage. The mechanism underlying unwanted structural variations induced by CRISPR-Cas9 remains poorly understood, and no effective strategy is available to inhibit the generation of these byproducts. Here we find that the generation of a high level of translocations is dependent on repeated cleavage at the Cas9-targeting sites. Therefore, we employ a strategy in which Cas9 is fused with optimized TREX2 to generate Cas9TX, a Cas9 exo-endonuclease, which prevents perfect DNA repair and thereby avoids repeated cleavage. In comparison with CRISPR-Cas9, CRISPR-Cas9TX greatly suppressed translocation levels and enhanced the editing efficiency of single-site editing. The number of large deletions associated with Cas9TX was also reduced to very low level. The application of CRISPR-Cas9TX for multiplex gene editing in chimeric antigen receptor T cells nearly eliminated deleterious chromosomal translocations. We report the mechanism underlying translocations induced by Cas9, and propose a general strategy for reducing chromosomal abnormalities induced by CRISPR-RNA-guided endonucleases.

Automated summary

The authors fused Cas9 with optimized TREX2 to generate Cas9TX, which effectively inhibits chromosomal structural variations induced by CRISPR/Cas and improves editing efficiency.