Accelerated homology-directed targeted integration of transgenes in Chinese hamster ovary cells via CRISPR/Cas9 and fluorescent enrichment

ABSTRACT Targeted gene integration into site‐specific loci can be achieved in Chinese hamster ovary (CHO) cells via CRISPR/Cas9 genome editing technology and the homology‐directed repair (HDR) pathway. The low efficiency of HDR often requires antibiotic selection, which limits targeted integration of multiple genes at multiple sites. To improve HDR‐mediated targeted integration, while avoiding the use of selection markers, chemical treatment for increased HDR, and fluorescent enrichment of genome‐edited cells was assessed in CHO cells. Chemical treatment did not improve HDR‐mediated targeted integration. In contrast, fluorescent markers in Cas9 and donor constructs enable FACS enrichment, resulting in a threefold increase in the number of cells with HDR‐mediated genome editing. Combined with this enrichment method, large transgenes encoding model proteins (including an antibody) were successfully targeted integrated. This approach provides a simple and fast strategy for targeted generation of stable CHO production cell lines in a rational way. Biotechnol. Bioeng. 2016;113: 2518–2523. © 2016 Wiley Periodicals, Inc. The authors have developed a method for selection marker‐free HDR‐mediated targeted integration in CHO cells by using fluorescent markers and FACS sorting. The fluorescent enrichment facilitated precise and site‐specific integration of large transgenes encoding biopharmaceutical proteins into the CHO genome without using antibiotic selection. The fast and simple method presented in this study has a large potential to both assess future HDR optimization efforts and to accelerate controlled generation of stable CHO production cell lines.