Optimization of a high-cell-density polyethylenimine transfection method for rapid protein production in CHO-EBNA1 cells

For pre-clinical evaluation of biotherapeutic candidates, protein production by transient gene expression (TGE) in Chinese Hamster Ovary (CHO) cells offers important advantages, including the capability of rapidly and cost-effectively generating recombinant proteins that are highly similar to those produced in stable CHO clones. We have established a novel CHO clone (CHO-3E7) expressing a form of the Epstein-Barr virus nuclear antigen-1 (EBNA-1) with improved TGE productivity relative to parental CHO cells. Taking advantage of a new transfection-compatible media formulation that permits prolonged, high-density culture, we optimized transfection parameters (cell density, plasmid vector and polyethylenimine concentrations) and post-transfection culture conditions to establish a new, high-performing process for rapid protein production. The growth media is chemically defined, and a single hydrolysate feed is added post-transfection, followed by periodic glucose supplementation. This method gave significantly higher yields than our standard low-cell density, F17-based CHO-3E7 TGE method, averaging several hundred mg/l for a panel of recombinant proteins and antibodies. Purified antibodies produced using the two methods had distinct glycosylation profiles but showed identical target binding kinetics by SPR. Key advantages of this new protein production platform include the cost-effectiveness of the transfection reagent, the commercial availability of the culture media and the ability to perform high-cell-density transfection without media change.