Scalable bioprocess for high-yield production of SARS-CoV-2 trimeric spike protein-based immunogen (IMT-CVAX) using suspension CHO cells

The COVID-19 pandemic has brought global attention towards the readiness of biotechnology platforms for rapid development of immunogens to be used as vaccine antigens, in diagnostics and in fundamental research. In the present study we provide a bioprocess that is both robust and industry-compatible for high level expression, efficient purification, and scale-up of IMT-CVAX, a prefusion-stabilized trimeric spike protein of SARS-CoV-2. The recombinant IMT-CVAX protein was produced using stable cell pool of Chinese Hamster Ovary (CHO-S) cells that were banked in compliance with cGMP (Current Good Manufacturing Practices) regulations. High quantity expression of IMT-CVAX was achieved through optimization of the shake flask-based process with regards to media, nutrient feeding regimen, incubation temperature, viable cell density and cell viability. We employed refined expression procedures to scale up IMT-CVAX using bioreactor, resulting in a significantly higher yield of around 500 mg/L. Subsequently, a straightforward and simple purification process was developed to produce high-quality IMT-CVAX protein. This procedure consisted of centrifugation, tangential flow filtration (TFF), and either one- or two-step liquid chromatography. A robust anti-spike IgG response was observed in mice after immunization with purified adjuvanted IMT-CVAX. In pseudoviral neutralization assay, mice-generated anti-IMT-CVAX sera could neutralize various SARS-CoV-2 variants. The human convalescent sera from COVID-19-recovered patients recognized IMT-CVAX effectively, which confirms the conformational integrity of IMT-CVAX epitopes. The bioprocess demonstrated here is able to produce sufficient quantities of biopharmaceutical-quality spike protein, which can be used as immunogen against emerging SARS-CoV-2 variants, and can aid in the rapid response to any other pandemic-potential pathogens.