Multiplicity of infection and culture medium on the SARS-CoV-2 virus like-particles production by baculovirus/insect system

This work aimed to assess the SARS-CoV-2 structural proteins' expression and virus-like particles (VLP) production by Baculovirus/Insect cell platform using two levels of Multiplicity of Infection (MOI), and two culture media, one of them a serum-free medium and the other one chemically defined. Two SARS-CoV-2 VLP were obtained from Sf9 cells coinfection using in both cases, three monocistronic recombinant baculoviruses holding the genes of Nucleocapsid (N; MOI = 2 or 0.2), Membrane (M; MOI = 1 or 0.1), and Envelope (E; MOI = 1 or 0.1) viral proteins, and the fourth one was changed between a baculovirus bearing Spike protein (S; MOI = 3 or 0.3) or receptor-binding domain (RBD; MOI = 3 or 0.3) genes of SARS-CoV-2. Similar performance was verified for both culture media in SARS-CoV-2 VLP production bearing four structural virus proteins or RBD domain. The SARS-CoV-2 structural proteins' expression was comparable at different MOIs (tenfold) as well as SARS-CoV-2 VLP size (around 100 nm). The increase in specific death rates over the coinfection phase was confirmed in relatively high MOI assays. This finding was related to an exponential virus titer profile for high MOIs over the entire infection phase, meanwhile, a viral peak was observed at low MOIs, confirming a secondary infection. The SARS-CoV-2 VLP improved production carrying immunogenic S protein was confirmed concerning others holding RBD. However, the protein composition of produced VLP should be studied further to assess the VLP homogeneity when different culture media and MOIs are used.