Large-Scale Transient Transfection of Suspension-Adapted Chinese Hamster Ovary Cells for the Production of the Trimeric SARS-CoV-2 Spike Protein.

The production and purification of the secreted ectodomain of SARS-CoV-2 spike protein (S protein) were performed by transiently transfecting suspension-adapted Chinese hamster ovary cells (ExpiCHO). The method involved the separate addition of plasmid DNA expressing the S protein and polyethyleneimine to a suspension culture at a density of 5 × 106 cells/mL; and the subsequent addition of dimethyl sulfoxide at 2% (v/v). The transfected ExpiCHO cells were cultivated at 31 °C with agitation by orbital shaking under 5% CO2. On day six post-transfection, the culture was centrifuged, and the supernatant was filtered to remove cells and cell debris. Finally, the secreted recombinant S protein was recovered from the supernatant by a single step of affinity chromatography to the Twin-Strep-Tag of the recombinant S protein.