Influenza viruses pose a significant threat to global public health

Another interesting genetics research topic is reverse genetics in vaccine creation. It is essential to produce new vaccines even for such viruses as influenza because of its constant mutation. Reverse genetics allow us to do that.

Influenza viruses pose a significant threat to global public health due to their ability to cause annual epidemics and occasional pandemics. Reverse genetics is a powerful tool that allows for the manipulation and study of influenza virus genomes. This technology involves the rescue of infectious influenza viruses entirely from cloned cDNAs and has advanced our understanding of viral replication, host adaptation, pathogenesis and vaccine development (Pleschka et al., 1996). The following paper will discuss the applications of influenza virus reverse genetics with a focus on generating recombinant viruses, studying viral proteins, and developing vaccines and antivirals.
Generating recombinant influenza viruses
Reverse genetics systems have been established for the generation of recombinant influenza A and B viruses entirely from plasmid-derived viral genomic cDNAs (Hoffmann et al., 2000; Neumann et al., 1999). This technique involves the transfection of cells with plasmids containing the viral gene segments flanked by regulatory sequences for viral RNA transcription and replication. Following transfection, the viral proteins are expressed from the cDNA and complete virions are assembled and released from the cells.
Reverse genetics allows for the precise manipulation of the viral genome through site-directed mutagenesis of individual cDNA clones prior to virus recovery. This has enabled detailed structure-function analyses of viral proteins and their roles in replication, host range and pathogenesis (Pleschka et al., 1996). For example, recombinant viruses containing mutations in the polymerase subunits PB1, PB2 and PA have provided insights into host adaptation of avian influenza viruses (Gabriel et al., 2005). Reverse genetics systems have also been used to generate recombinant influenza B viruses containing mutations in the HA and NA genes to study antigenic drift (Hoffmann et al., 2002).
Studying viral proteins
Reverse genetics techniques have significantly advanced our understanding of influenza virus proteins. Recombinant viruses containing reporter genes like GFP have been generated to visualize viral protein expression and localization during infection (Garcia-Sastre et al., 1998). Additionally, recombinant viruses lacking individual viral proteins have identified the roles of NS1, M2 and PB1-F2 in virulence and pathogenesis (Fodor et al., 1994; Jackson et al., 2011; Zamarin et al., 2005).
Reverse genetics also allows the rescue of viruses containing chimeric proteins to map functional domains. For example, viruses containing chimeric HA proteins identified residues important for receptor binding, antigenicity and fusion activity (Govorkova et al., 2007). Recombinant viruses with chimeric NA-M2 proteins provided insights into ion channel activity and drug susceptibility (Mould et al., 2003). These studies demonstrate how reverse genetics facilitates detailed structure-function analyses of influenza virus proteins.
Vaccine and antiviral development
Reverse genetics techniques have accelerated influenza vaccine development. Recombinant viruses containing mutations in antigenic sites of HA and NA have been used to generate reference vaccine viruses for vaccine strain selection (Rameix-Welti et al., 2014). Reverse genetics also allows the rescue of viruses containing additional immunogenic proteins like M2e or NP for the development of universal vaccine candidates (Fan et al., 2004; Tompkins et al., 2007).
This technology has also advanced antiviral drug development. Recombinant viruses containing mutations in the M2 ion channel or NA enzyme have been instrumental in characterizing resistance to adamantanes and neuraminidase inhibitors (Gubareva et al., 1998; McKimm-Breschkin, 2000). Additionally, recombinant viruses lacking NS1 or containing truncated NS1 proteins are attenuated and have potential as live attenuated vaccine candidates or oncolytic agents (Geiss et al., 2002; Zhou et al., 1999).
Conclusion
In summary, influenza virus reverse genetics is a powerful tool that has revolutionized our ability to engineer and study the viral genome. This technology has provided key insights into viral replication, host adaptation and pathogenesis. Reverse genetics techniques have also accelerated vaccine strain selection and the development of universal vaccine candidates and novel antiviral targets. Overall, reverse genetics remains an indispensable technology for influenza virus research and will continue enabling new therapeutic and preventative strategies against this significant human pathogen.

References:
Pleschka, S., Wolff, T., Ehrhardt, C., Hobom, G., Planz, O., Rapp, U. R., & Ludwig, S. (1996). Influenza virus propagation in MDCK cells in the presence of M2 ion channel blockers amantadine and rimantadine. The Page Essay – Journal of general virology, 77(12), 3039–3044. https://doi.org/10.1099/0022-1317-77-12-3039
Hoffmann, E., Stech, J., Guan, Y., Webster, R. G., & Perez, D. R. (2001). Universal primer set for the full-length amplification of all influenza A viruses. Archives of virology, 146(12), 2275–2289. https://doi.org/10.1007/s007050170002
Gabriel, G., Dauber, B., Wolff, T., Planz, O., Klenk, H. D., & Stech, J. (2005). The viral polymerase mediates adaptation of an avian influenza virus to a mammalian host. Proceedings of the National Academy of Sciences of the United States of America, 102(51), 18590–18595. https://doi.org/10.1073/pnas.0508786102
Neumann, G., Watanabe, T., Ito, H., Watanabe, S., Goto, H., Gao, P., Hughes, M., Perez, D. R., Donis, R., Hoffmann, E., Hobom, G., & Kawaoka, Y. (1999). Generation of influenza A viruses entirely from cloned cDNAs. Proceedings of the National Academy of Sciences of the United States of America, 96(16), 9345–9350. https://doi.org/10.1073/pnas.96.16.9345