A COVID-19 vaccine candidate based on SARS-CoV-2 spike protein and immune-stimulating complexes

Abstract

Spike protein form SARS-CoV-2, the etiologic agent of COVID-19 pandemic disease, constitutes a structural protein that proved to be the main responsible for neutralizing antibodies production. Thus, its sequence is highly considered for the design of chimeric proteins that might be used as vaccine candidates. Animal cell culture represents the best option for the production of subunit vaccines based on recombinant proteins since they introduce post-translational modifications that are important to mimic the natural antigenic epitopes. Particularly, the human cell line HEK293T has been explored and used for the production of biotherapeutics since the products derived from them present human-like post translational modifications that are important for the protein´s activity and immunogenicity. In this work, the spike ectodomain (S-ED) was produced in sHEK293T cells using a 1 L stirred tank bioreactor operated in perfusion mode. Harvests were purified and S-ED characterization was performed, revealing the expected size and morphology. High N-glycans content was confirmed. Furthermore, S-ED specific binding with the hACE2 (human Angiotensin Converting Enzyme 2) receptor could be verified Two different adjuvants were used to evaluate the immunogenicity of S-ED: the traditional aluminium hydroxide and immune-stimulating complexes (ISCOMs). Both formulations demonstrated the presence of anti-RBD antibodies in the plasma of immunized mice, being significantly higher for the latter adjuvant. Also, higher levels of IFN-γ and IL-4 were detected after the ex vivo immune stimulation of spleen-derived MNCs from ISCOMs immunized mice. Further analysis confirmed that S-ED/ISCOMs elicits neutralizing antibodies against SARS CoV-2.