Characterization of site-specific recombination mediated by Cre recombinase during the development of erythropoietin producing CHO cell lines

The establishment of erythropoietin (EPO) producing Chinese hamster ovary (CHO) cell lines was conducted using Cre-mediated cassette exchange. The characterization of site-specific recombination mediated by Cre-recombinase during the cell line development was also performed. A total of six parental clones, which had various green fluorescence levels ranging from high to low and containing a single copy of insertion vector (pEGFP-m2), were screened. The EPO targeting vector (pIC-m2-EPO) was targeted into the 6 parental clones by Cre-mediated cassette exchange. Correctly targeted clones were obtained from 4 out of 6 parental clones with 0∼15% of targeting efficiencies. Moreover, there was a positive relationship (R² = 0.87) between fluorescence levels of the parental clones before Cre-mediated cassette exchange and specific EPO productivities (q _EPO ) of the correctly targeted clones after Cre-mediated cassette exchange. Therefore, it was verified that the chromosomal loci’s characteristic gene expression level was not modified even after cassette exchange mediated by Cre recombinase during the development of EPO producing CHO cell lines. This finding implies that the reproducible development of CHO cell lines largely producing a desired protein is expected to be achieved by Cre-mediated cassette exchange.