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.

3D printing: Economical and supply chain independent single-use plasticware for cell culture

3D printing represents a democratization of manufacturing processes, and inexpensive 3D printed parts for cell culture have been tested as replacements for single-use plastics currently unavailable due to worldwide supply chain issues. In addition, such distributed manufacturing of cell culture laboratory materials helps remote areas and developing countries with limited resources. HEK293 cells were used to test printed shake flasks for cell culture applications and their ease of manufacture. Recorded growth curves showed that renewable biodegradable poly(lactic acid) (PLA) thermoplastic is an excellent and economical replacement for single-use plastic shake flasks, which have shipment lead times during pandemic situations or other supply chain disruptions of over 6 months. With a price of 0.60 € in materials, and printing machines with prices lower than one box of single-use pre-sterilized plastic shake flasks (<350€), the use of PLA is very affordable. Low-cost photopolymerization resins were also tested, but the inherent cytotoxicity of these materials prevented cell growth. This was also true for plant-based resins marketed as having low volatile organic compounds (VOC). Treatment of parts to reduce VOC content was partially successful, but not sufficient to sustain prolonged cell growth. A high-cost medical device IIa-class material showed no improved cell growth. Nevertheless, with PLA a low-cost printing material was identified and the use as cell culture compatible material was demonstrated, providing low-cost supply chain independence. In the future, the printing of pilot-scale bioreactors with PLA as a green sustainable material at the point of its use will be possible.