Robust and resource-efficient production process suitable for large-scale production of baculovirus through high cell density seed train and optimized infection strategy

The aim of this study was the development of a scalable production process for high titer (108 pfu/mL and above) recombinant baculovirus stocks with low cell line-derived impurities for the production of virus-like particles (VLP). To achieve this, we developed a high cell density (HCD) culture for low footprint cell proliferation, compared different infection strategies at multiplicity of infection (MOI) 0.05 and 0.005, different infection strategies and validated generally applicable harvest criteria of cell viability <= 80%. We also investigated online measurable parameters to observe the baculovirus production. The infection strategy employing a very low virus inoculum of MOI 0.005 and a 1:2 dilution with fresh medium one day after infection proved to be the most resource efficient. There, we achieved higher cell-specific titers and lower host cell protein concentrations at harvest than other tested infection strategies with the same MOI, while saving half of the virus stock for infecting the culture compared to other tested infection strategies. HCD culture by daily medium exchange was confirmed as suitable for seed train propagation, infection, and baculovirus production, equally efficient as the conventionally propagated seed train. Online measurable parameters for cell concentration and average cell diameter were found to be effective in monitoring the production process. The study concluded that a more efficient VLP production process in large scale can be achieved using this virus stock production strategy, which could also be extended to produce other proteins or extracellular vesicles with the baculovirus expression system.