Controlled vs. non-controlled culture systems for SARS-CoV-2 VLP production using the baculovirus/SF9 platform

COVID-19 is an infectious disease resulting from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which emerged as a global pandemic in 2020. Virus-like particles (VLP) are artificially generated nanoparticles composed of a subset of viral components that closely mimic the native virus in size, structure, and surface composition. These features contribute to their robust immunogenic potential, stimulating both antibody-mediated and cell-mediated immune responses. This study aimed to evaluate the expression of SARS-CoV-2 structural proteins and the VLP production using a baculovirus-insect cell system. Two monocistronic recombinant baculoviruses, each carrying either the spike (S) or nucleocapsid (N) gene of SARS-CoV-2, were employed in two different culture systems: Schott flasks and a stirred-tank bioreactor. The Sf9 cells showed substantial differences between the Schott flask and stirred tank bioreactor in terms of metabolism, virus titer, and cell death after infection. Both proteins' expressions were confirmed in the two culture systems assessed. However, VLP formation (69.1-78.2 nm) was only confirmed in the co-infection setup with both monocistronic recombinant baculoviruses. In contrast, infection with only the S-protein baculovirus failed to produce VLP in our findings.