Reverse genetics-generated elastase-dependent swine influenza viruses are attenuated in pigs

Area of Science:

• Veterinary Virology
• Molecular Biology
• Immunology

Background:

• Swine influenza virus (SIV) causes significant economic losses and poses public health risks.
• Modifying the hemagglutinin (HA) cleavage site to be elastase-sensitive has shown promise for viral attenuation in mouse models.
• Previous attempts to apply this attenuation strategy in natural hosts have been unsuccessful.

Purpose of the Study:

• To generate and characterize SIV mutants with modified HA cleavage sites for potential use as live attenuated vaccines.
• To assess the attenuation and safety of these SIV mutants in a natural host (pigs).

Main Methods:

• Reverse genetics was used to create two SIV mutants (A/SW/SK-R345V and A/SW/SK-R345A) from a wild-type H1N1 strain.
• Mutant viruses were characterized for their dependence on neutrophil elastase for cleavage in tissue culture.
• Growth properties, genetic stability, and attenuation in pigs were evaluated.

Main Results:

• Both SIV mutants exhibited exclusive dependence on neutrophil elastase for cleavage in vitro.
• The mutants displayed comparable plaque sizes and growth kinetics to the wild-type SIV.
• Mutant SIVs maintained genetic stability after multiple passages in cell culture and were highly attenuated in pigs.

Conclusions:

• Engineered SIV mutants dependent on neutrophil elastase cleavage are highly attenuated in pigs.
• These findings support the potential of these SIV mutants as live attenuated vaccines for controlling swine influenza.