Generation and Characterization of a CE1-Modified mCherry-Expressing Influenza A Virus for In Vivo Imaging and Antiviral Drug Evaluation

Influenza reporter viruses are essential for studying viral infection dynamics and assessing antiviral drug efficacy. However, insertion of exogenous reporter genes can impair both viral replication and reporter expression, limiting the development of these systems. In this study, CE1 compensatory mutation <i>(G3A</i>/<i>C8U)</i> was introduced into the 3' non-coding region of the NS segment of influenza A/Puerto Rico/8/1934 using reverse genetics, generating the recombinant reporter virus H1N1-PR8-NS_CE1-mCherry. Compared with H1N1-PR8-NS_WT-mCherry, H1N1-PR8-NS_CE1-mCherry produced approximately 2.7-fold more infectious particles. CE1 compensatory mutation partially restored impaired replication kinetics in vitro, as evidenced by higher titers of H1N1-PR8-NS_CE1-mCherry at 48 h post-infection in MDCK cells. Additionally, H1N1-PR8-NS_CE1-mCherry maintained the intact mCherry gene insertion and high viral titers during serial passaging. Additionally, a real-time, non-invasive in vivo imaging of influenza A viruses was established using H1N1-PR8-NS_CE1-mCherry. A significant correlation was observed between lung fluorescence intensity and viral load, indicating that fluorescence signals serve as a reliable indicator of lung viral load in infected mice. Finally, utility of this model for in vivo drug screening was confirmed by antiviral drug oseltamivir phosphate. Above all, H1N1-PR8-NS_CE1-mCherry provides a tool for visualizing influenza A virus infection and evaluating antiviral drug efficacy.