New cell line development for antibody-producing Chinese hamster ovary cells using split green fluorescent protein

The establishment of high producer is an important issue in Chinese hamster ovary (CHO) cell culture considering increased heterogeneity by the random integration of a transfected foreign gene and the altered position of the integrated gene. Fluorescence-activated cell sorting (FACS)-based cell line development is an efficient strategy for the selection of CHO cells in high therapeutic protein production. An internal ribosome entry site (IRES) was introduced for using two green fluorescence protein (GFP) fragments as a reporter to both antibody chains, the heavy chain and the light chain. The cells co-transfected with two GFP fragments showed the emission of green fluorescence by the reconstitution of split GFP. The FACS-sorted pool with GFP expression had a higher specific antibody productivity (q(Ab)) than that of the unsorted pool. The q(Ab) was highly correlated with the fluorescence intensity with a high correlation coefficient, evidenced from the analysis of median GFP and q(Ab) in individual selected clones. This study proved that the fragment complementation for split GFP could be an efficient indication for antibody production on the basis of high correlation of q(Ab) with reconstitution of GFP. Taken together, we developed an efficient FACS-based screening method for high antibody-producing CHO cells with the benefits of the split GFP system.