Bioprocess characterization of virus-like particle production with the insect cell baculovirus expression system at nanoparticle level

Background. Virus-like particles (VLPs) are a multivalent platform showing great promise for the development of vaccines, gene therapy, diagnostic, and drug delivery approaches. Particularly, HIV-1 Gag VLPs provide a robust and flexible scaffold for the presentation of a variety of antigens. The insect cell baculovirus expression vector system (BEVS) is nowadays one of the reference systems to produce these complex nanoparticles, but information about VLP quality, quantity, stability, as well as cell performance is scarce, especially at bioreactor scale. Results. VLPs produced in the reference High Five and Sf9 insect cell lines share similar physicochemical properties, with VLPs produced in Sf9 cells showing lower levels of double stranded DNA and protein contaminants, and a higher degree of VLP assembly. Besides VLPs, other nanoparticle populations are divergently encountered in each cell line. Hi5 supernatants contain a higher load of extracellular vesicles, while Sf9 supernatants exhibit higher concentrations of baculovirus particles. Similar titers are achieved when comparing Gag to Gag-eGFP VLP production, with the size of most of the nanoparticles produced comprised at the 150-250 nm range. Eventually, Gag VLP production in a 2 L stirred tank bioreactor is successfully demonstrated, validating bioprocess transference to the final product candidate. Conclusions. This work provides two potentially valuable strategies for the production of HIV-1 Gag VLPs and a detailed analysis of the different nanoparticle populations produced.