Pseudorabies virus production using a serum-free medium in fixed-bed bioreactors with low cell inoculum density

Fixed-bed bioreactors packed with macrocarriers show great potential to be used for vaccine process development and large-scale production due to distinguishing features of low shear force, high cell adhering surface area, and easy replacement of culture media in situ. As an initial step of utilizing this type of bioreactors for Pseudorabies virus production (PRV) by African green monkey kidney (Vero) cells, we developed a tube-fixed-bed bioreactor in the previous study, which represents a scale-down model for further process optimization. By using this scale-down model, here we evaluated impacts of two strategies (use of serum-free medium and low cell inoculum density) on PRV production, which have benefits of simplifying downstream process and reducing risk of contamination. We first compared Vero cell cultures with different media, bioreactors and inoculum densities, and conclude that cell growth with serum-free medium is comparable to that with serum-containing medium in tube-fixed-bed bioreactor, and low inoculum density supports cell growth only in this bioreactor. Next, we applied serum-free medium and low inoculum cell density for PRV production. By optimization of time of infection (TOI), multiplicity of infection (MOI) and the harvesting strategy, we obtained total amount of virus particles ~ 9 log₁₀ TCID₅₀ at 5 days post-infection (dpi) in the tube-fixed-bed bioreactor. This process was then scaled up by 25-fold to a Xcell 1-L fixed-bed bioreactor, which yields totally virus particles of 10.5 log₁₀ TCID_50, corresponding to ~ 3 × 10⁵ doses of vaccine. The process studied in this work holds promise to be developed as a generic platform for the production of vaccines for animal and human health.