Model-based analysis of influenza A virus replication in genetically engineered cell lines elucidates the impact of host cell factors on key kinetic parameters of virus growth.

The best measure to limit spread of contagious diseases caused by influenza A viruses (IAVs) is annual vaccination. The growing global demand for low-cost vaccines requires the establishment of high-yield production processes. One possible option to address this challenge is the engineering of novel vaccine producer cell lines by manipulating gene expression of host cell factors relevant for virus replication. To support detailed characterization of engineered cell lines, we fitted an ordinary differential equation (ODE)-based model of intracellular IAV replication previously established by our group to experimental data obtained from infection studies in human A549 cells. Model predictions indicate that steps of viral RNA synthesis, their regulation and particle assembly and virus budding are promising targets for cell line engineering. The importance of these steps was confirmed in four of five single gene overexpression cell lines (SGOs) that showed small, but reproducible changes in early dynamics of RNA synthesis and virus release. Model-based analysis suggests, however, that overexpression of the selected host cell factors negatively influences specific RNA synthesis rates. Still, virus yield was rescued by an increase in the virus release rate. Based on parameter estimations obtained for SGOs, we predicted that there is a potential benefit associated with overexpressing multiple host cell genes in one cell line, which was validated experimentally. Overall, this model-based study on IAV replication in engineered cell lines provides a step forward in the dynamic and quantitative characterization of IAV-host cell interactions. Furthermore, it suggests targets for gene editing and indicates that overexpression of multiple host cell factors may be beneficial for the design of novel producer cell lines. Author summary Influenza viruses depend on cellular functions at every step of their life cycle and a comprehensive picture of virus-host cell interactions is the key to understand influenza disease and establish antiviral therapies. Over the past decade, this was supported by numerous screening approaches, which identified cellular factors relevant for intracellular virus replication. Ideally, the identification of pro-viral targets should also support the generation of cell lines to optimize influenza virus replication in cell cultures. As a first approach towards this goal, we used a mathematical model to identify mechanisms of viral growth that would be most promising targets for host cell factor manipulation. Based on predictions, we expected a significant increase in virus production if RNA synthesis and virus assembly and virus budding were perturbed, which was partially confirmed by cell lines overexpressing single and multiple selected host cell factors. However, the cell-specific productivity of engineered cell lines was not improved significantly and, according to model-based analysis, this can be explained by adverse changes in kinetic parameters of intracellular replication steps. Finally, results indicate that screening approaches should focus on late time points post infection to identify targets for engineering of cell lines that support high-yield vaccine production processes.