LAIV Mutations Selectively Alter Influenza Viral RNA Polymerase Function, Favoring Transcription over Genome...

Area of Science:

• Virology
• Molecular Biology
• Vaccinology

Background:

• Influenza viruses cause significant respiratory illness, necessitating effective vaccines.
• Live attenuated influenza vaccines (LAIVs) are a key prophylactic strategy, offering robust immune responses.
• LAIVs possess temperature-sensitive and cold-adapted mutations, primarily in PB1 and PB2 polymerase subunits, but their attenuation mechanism remains unclear.

Purpose of the Study:

• To investigate the mechanism of viral attenuation by LAIV mutations in the influenza RNA polymerase.
• To characterize the functional impact of specific LAIV mutations on viral polymerase activity and replication.

Main Methods:

• Introduced LAIV-derived PB1 and PB2 mutations from H2N2 strains into the A/Puerto Rico/8/1934 H1N1 (PR8) model strain.
• Assessed viral RNA polymerase activity (replicase and transcription) of wild-type (WT) and mutant PR8 viruses at different temperatures.
• Quantified viral protein production and infectious viral progeny yield in infected MDCK cells at 37 °C.

Main Results:

• PR8-LAIV polymerase complexes showed maximal activity at cold temperatures (30-32 °C) and reduced activity at elevated temperatures (>37 °C).
• Mutant viruses exhibited temperature-dependent defects in RNA replicase activity but enhanced transcriptional activity at 37 °C.
• Infectious viral progeny production was significantly reduced (2-3 log10) at 37 °C, despite similar viral protein levels compared to WT PR8.

Conclusions:

• LAIV mutations in PB1 and PB2 selectively alter influenza viral RNA polymerase function.
• These mutations favor viral transcription over genome synthesis at physiological temperatures (37 °C).
• This functional shift contributes to viral attenuation by reducing infectious progeny while maintaining antigen production, enhancing vaccine efficacy.