Live attenuated influenza virus production in batch high cell density cultivation of suspension AGE1.CR.pIX cells

Most influenza vaccines are trivalent inactivated split or subunit vaccines administered intramuscular. Alternatively, live attenuated influenza vaccine (LAIV) induce a more efficient immunological response and can be applied intranasal [1]. The attenuated viruses are generated by reassorting 6 backbone genes of cold-adapted (ca) viruses replicating best at 25 °C with the respective genes for HA and NA of the seasonal strains. Vaccine is then produced at 33°C in eggs or cell culture. However, in a screen for possible production cell lines most cell lines exhibited only low permissivities or do not replicate all strains. Only with MDCK and Vero cells high titers of approximately 108 pfu/mL could be achieved [2]. Here, we report on an evaluation of the avian designer cell line AGE1.CR.pIX for LAIV production. Before infection experiments were done, adaptations of Vero-adapted LAIV A and B strains were carried out throughout three passages to improve replication. In scouting experiments, promising titers of ≥108 viruses/mL were achieved in small-scale cultures. In a next step, lab-scale bioreactor production aiming at high cell densities of >4x106 cells/mL in batch mode was evaluated. Up to 5x106 cells/mL could be infected in these studies without loss of cell-specific productivity. Overall, yields achieved with this suspension cell line were comparable to titers obtained with Vero or MDCK cells [3]. Both process steps (cell proliferation and virus production) took place in a chemically defined medium, favoring this approach over processes described for MDCK or Vero cells. In summary, the evaluated cell line AGE1.CR.pIX was shown to be suitable for production of LAIV strains to significant titers and thus provide a fully chemically-defined suspension process