Highly Efficient Production of an Influenza H9N2 Vaccine Using MDCK Suspension Cells

H9N2 subtype avian influenza virus poses a constant threat to the poultry industry and the control of the disease leans upon the use of effective vaccines. As an alternative to the conventional chicken embryonated eggs, animal cell culture could overcome the limitations of egg supplies and upgrade the manufacturing of avian influenza vaccines for poultry. Development of serum-free suspension cell culture could allow even higher virus productivity, where a suspension cell line with good growth and production performance is required. In this work, an adherent MDCK cell line was adapted to suspension growth to cell concentration up to 12 × 106 cells/mL in a serum-free medium in batch cultures. Subsequently, the influenza virus propagation in this MDCK cell line was evaluated and was improved with the medium exchange at time of infection as well as optimization of infection conditions in terms of MOI and cell concentration for infection. Furthermore, various feed strategies were tested in the infection phase for improved virus titer and a maximum hemagglutinin titer of 13 log2 (HAU/50 μL) was obtained using the 1:2 medium dilution strategy. Evaluation of MDCK cell growth and H9N2 virus propagation in the bioreactors with optimized operating conditions showed comparable cell performance and virus yield compared to shake flasks, with a high cell-specific virus yield above 14000 virions/cell. With the purified H9N2 virus harvested from the bioreactor, the MDCK cell-derived vaccine was able to induce high titers of neutralizing antibodies in chickens. Overall, the results demonstrate the promising application of the highly efficient MDCK cell-based production platform for the avian influenza vaccine manufacturing.