Cre‐Mediated Transgene Integration in Chinese Hamster Ovary Cells Using Minicircle DNA Vectors

Bacterial backbone sequences of conventional plasmid vectors have been reported to exhibit negative effects on transgene expression in mammalian cells, such as cytotoxicity and gene silencing. Minicircle DNA vectors can be employed to overcome these issues and to improve the transfection efficiency because of their smaller size. In this study, transgenes are integrated into the hypoxanthine phosphoribosyltransferase (hprt) locus of Chinese hamster ovary (CHO) cells by the Cre-loxP system using minicircle DNA vectors as transgene donors. The targeted transgene integration efficiency is improved 2-3-fold (≈1.4%) using minicircle DNA vectors compared with conventional plasmid vectors. Moreover, clones with expected structures after transgene integration are obtained with a high frequency. When a transgene together with bacterial sequences derived from a plasmid vector is integrated into the hprt locus, the cell growth rate and antibody titer decrease. These results indicate that minicircle DNA vectors are more suitable than conventional plasmid vectors for transgene delivery in recombinant protein production using CHO cells.