Rapid, high-yield production of full-length SARS-CoV-2 spike ectodomain by transient gene expression in CHO cells
- J Biotechnol. 2021 Jan 20:326:21-27. doi: 10.1016/j.jbiotec.2020.12.005.
- 1. Human Health Therapeutics Research Centre, National Research Council Canada, 6100 Royalmount Avenue, Montreal, QC, H4P 2R2, Canada.
- 2. Human Health Therapeutics Research Centre, National Research Council Canada, 6100 Royalmount Avenue, Montreal, QC, H4P 2R2, Canada. Electronic address: [email protected].
Recombinant forms of the spike protein of SARS-CoV-2 and related viruses have proven difficult to produce with good yields in mammalian cells. Given the panoply of potential COVID-19 diagnostic tools and therapeutic candidates that require purified spike protein and its importance for ongoing SARS-CoV-2 research, we have explored new approaches for spike production and purification. Three transient gene expression methods based on PEI-mediated transfection of CHO or HEK293 cells in suspension culture in chemically-defined media were compared for rapid production of full-length SARS-CoV-2 spike ectodomain. A high-cell-density protocol using DXB11-derived CHOBRI/55E1 cells gave substantially better yields than the other methods. Different forms of the spike ectodomain were expressed, including the wild-type SARS-CoV-2 sequence and a mutated form (to favor expression of the full-length spike ectodomain stabilized in pre-fusion conformation), with and without fusion to putative trimerization domains. An efficient two-step affinity purification method was also developed. Ultimately, we have been able to produce highly homogenous preparations of full-length spike, both monomeric and trimeric, with yields of 100-150 mg/L in the harvested medium. The speed and productivity of this method support further development of CHO-based approaches for Recombinant spike protein manufacturing.