Cell Engineering for Vaccine Production

Cell-based production of influenza virus

Influenza is an infectious disease that affects millions of people worldwide. Due to its rapid mutation rate, new influenza vaccines are formulated ever year. Currently, trivalent inactivated viral vaccines are manufactured from chicken embryonated eggs and this production process requires extensive planning, laborious preparations, and reliable egg supplies. To give a sense of the time requirement for manufacturing egg-based vaccines, typically strains for vaccine preparation are selected in the month of February in the northern hemisphere and the shipment of the final products will not take place until August/September. Although egg-based production has been used for the past 60 years, it will be insufficient in responding to a pandemic outbreak. In recent decades, many studies have geared toward the development of cell-based production of influenza vaccine, which potentially have many advantages such as rapid scale-up and retaining similar antigenic activities. Among the cell lines tested, Madin Darby Canine Kidney (MDCK) is one of the most promising cell substrates for influenza virus propagation due to its consistently high viral titers. However, In order to be commercially viable, cell lines are typically adapted or transformed to suspension cultures so they can be grown in production-scale bioreactors. Some studies have attempted to use microcarrier beads to overcome this barrier, but nevertheless, the use of these beads introduces another layer of process optimization, and at large scales, would be quite cumbersome. Based the previous microarray data, we have identify a human gene that can affect cell adhesion. We then introduce this human gene to the MDCK cells and observed a correlation between the decrease in tight-junction formation on monolayer cultures and the expression of this human gene. Subsequently, these genetically modified cells were tested in shake flask culture and were found to be able to survive and proliferate under anchorage-independent conditions. Preliminary tumorigenicity studies have shown that these anchorage-independent MDCK cells did not become much more aggressive, in contrast to other groups have observed when cell lines were transformed. Influenza B virus were tested in these modified cells and were found that under an optimized infection strategy, hemagglutinin titers were almost 20-fold higher than those in parental MDCK cells. This work demonstrates that this novel MDCK cell line has high potentials to serve as an alternative to chicken embryonated eggs.

 

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