Quantification of intracellular influenza A virus protein dynamics in different host cells after seed virus adaptation

Various hosts are considered for cell culture-based influenza vaccine production. In order to obtain a deeper understanding for differences in virus production capabilities, characterization of the viral replication mechanisms in the context of a given host cell is crucial. Quantitative experimental data on the intracellular dynamics of viral RNAs and viral proteins, together with extracellular virus titers, can be used to build mathematical. In this study, we report results obtained from an optimized mass spectrometry assay for the quantification of viral proteins that was applied to compare the production of influenza A virus HA, NP, NA, M1 and NS1 proteins. With an MDCK cell-adapted seed virus, a maximum of about 1.0E+08 copies/cell were found for all five viral proteins after infection of avian AGE1.CR and human HEK293 cells. Such intracellular levels are about five-fold lower than in MDCK cells. However, after five passages for seed virus adaptation, intracellular protein copy numbers comparable to those in MDCK cells were achieved. Highest levels were found for the NS1 protein with about 1.0E+09 copies/cell. While the onset of virus particle release started earlier for both cell lines (about 3–6 h), the maximum virus titers did not change after seed virus adaptation for AGE1.CR cells but increased for HEK293 cells. Even after adaptation, the highest HA titers were still obtained for MDCK cells. The experimental data point to differences in host cell immune response and protein synthesis, consumption and degradation rates that impact virus production in cells of different origin.