Use of an anti-apoptotic CHO cell line for transient gene expression.

Transient gene expression in mammalian cells allows for rapid production of recombinant proteins for research and preclinical studies. Here, we describe the development of a polyethylenimine (PEI) transient transfection system using an anti-apoptotic host cell line. The host cell line, referred to as the Double Knockout (DKO), was generated by deleting two pro-apoptotic factors, Bax and Bak, in a CHO-K1 cell line using zinc finger nuclease mediated gene disruption. Optimized DNA and PEI volumes for DKO transfections were 50% and 30% lower than CHO-K1, respectively. During transfection DKO cells produced relatively high levels of lactate, but this was mitigated by a temperature shift to 31°C which further enhanced productivity. DKO cells expressed ∼3- to 4-fold higher antibody titers than CHO-K1 cells. As evidence of their anti-apoptotic properties post-transfection, DKO cells maintained higher viability and had reduced levels of active caspase-3 compared to CHO-K1 cells. Nuclear plasmid DNA copy numbers and message levels were significantly elevated in DKO cells. Although DNA uptake levels, as early as 40 min post-transfection, were higher in DKO cells this was not due to differences in cell surface heparan sulfate (HS) or initial endocytosis mechanism as both cell types utilized caveolae- and clathrin-mediated endocytosis to internalize DNA:PEI complexes. These results suggest that the increased transfection efficiency and titers from DKO cells are attributed to their resistance to transfection-induced apoptosis and not differences in endocytosis mechanism.