Multiple gene segments control the temperature sensitivity and attenuation phenotypes of ca B/Ann Arbor/1/66

Area of Science:

• Virology
• Molecular Biology
• Vaccinology

Background:

• Cold-adapted (ca) B/Ann Arbor/1/66 is the master donor virus for FluMist, a live attenuated influenza vaccine.
• This strain exhibits temperature sensitivity (ts) and attenuation (att) in animal models, unlike virulent wild-type (wt) influenza B viruses.

Purpose of the Study:

• To define the minimal genetic components responsible for the ts and att phenotypes of ca B/Ann Arbor/1/66.
• To understand the genetic basis of attenuation for live attenuated influenza vaccines.

Main Methods:

• Amino acid sequence alignment of internal genes of ca B/Ann Arbor/1/66 with other influenza B viruses.
• Engineering of eight unique amino acids into a recombinant virus using reverse genetics.
• Detailed mutational analysis to pinpoint specific residues controlling ts and att phenotypes.

Main Results:

• Eight unique amino acids were identified in PA, M1, and NP proteins.
• Engineering these eight amino acids back into the wild-type virus reverted the ts and att phenotypes.
• A specific subset of these mutations in NP and PA controlled ts, while additional mutations in M1 controlled att.

Conclusions:

• A small, complex genetic signature comprising specific amino acid changes in NP, PA, and M1 proteins encodes the essential elements for temperature sensitivity and attenuation in influenza B virus.
• This signature can confer ts and att phenotypes to divergent wild-type strains, highlighting its significance for live attenuated vaccine development.