Trimeric SARS-CoV-2 Spike proteins produced from CHO-cells in bioreactors are high quality antigens

Pino, Paco; Kint, Joeri; Kiseljak, Divor; Agnolon, Valentina; Corradin, Giampietro; Kajava, Andrey V.; Rovero, Paolo; Dijkman, Ronald; den Hartog, Gerco; McLellan, Jason S.; Byrne, Patrick O.; Wurm, Maria J; Wurm, Florian M

The Spike protein of SARS-CoV-2 is essential for virus entry into human cells. In fact, most neutralizing antibodies against SARS-CoV-2 are directed against the Spike, making it the antigen of choice for use in vaccines and diagnostic tests. In the current pandemic context, global demand for Spike proteins has rapidly increased and could exceed hundreds of grams to kilograms annually. Coronavirus Spikes are large, heavily glycosylated, homotrimeric complexes, with inherent instability. Their poor manufacturability now threatens availability of these proteins for vaccines and diagnostic tests. Here, we outline a scalable, GMP-compliant, chemically defined process for production of a cell secreted, stabilized form of the trimeric Spike protein. The process is chemically defined and based on clonal, suspension-CHO cell populations and on protein purification via a two-step, scalable downstream process. The trimeric conformation was confirmed using electron microscopy and HPLC analysis. Binding to susceptible cells was shown using a virus-inhibition assay. The diagnostic sensitivity and specificity for detection of serum SARS-CoV-2 specific IgG1 was investigated and found to exceed that of Spike fragments (S1 and RBD). The process described here will enable production of sufficient high-quality trimeric Spike protein to meet the global demand for SARS-CoV-2 vaccines and diagnostic tests.