Transduction of HEK293 Cells with BacMam Baculovirus Is an Efficient System for the Production of HIV-1 Virus-like Particles

Gag virus-like particles (VLPs) are promising vaccine candidates against infectious diseases. VLPs are generally produced using the insect cell/baculovirus expression vector system (BEVS), or in mammalian cells by plasmid DNA transient gene expression (TGE). However, VLPs produced with the insect cell/BEVS are difficult to purify and might not display the appropriate post-translational modifications, whereas plasmid DNA TGE approaches are expensive and have a limited scale-up capability. In this study, the production of Gag VLPs with the BacMam expression system in a suspension culture of HEK293 cells is addressed. The optimal conditions of multiplicity of infection (MOI), viable cell density (VCD) at infection, and butyric acid (BA) concentration that maximize cell transduction and VLP production are determined. In these conditions, a maximum cell transduction efficiency of 91.5 +/- 1.1%, and a VLP titer of 2.8 +/- 0.1 x 10(9) VLPs/mL are achieved. Successful VLP generation in transduced HEK293 cells is validated using super-resolution fluorescence microscopy, with VLPs produced resembling immature HIV-1 virions and with an average size comprised in the 100-200 nm range. Additionally, evidence that BacMam transduction occurs via different pathways including dynamin-mediated endocytosis and macropinocytosis is provided. This work puts the basis for future studies aiming at scaling up the BacMam baculovirus system as an alternative strategy for VLP production.