The effect of the G141R egg-adaptive substitution on the biological properties of currently circulating B/Victoria-lineage influenza B viruses

Despite the continuing interest in influenza infection and relevant pathogens, a significant number of publications in this field are devoted to influenza A viruses, while influenza B viruses receive less attention. In PubMed database, there are 10 times fewer articles on influenza B vs. influenza A viruses. However, despite the complete disappearance of influenza B/Yamagata lineage viruses in the post-COVID-19 pandemic period, B/Victoria lineage viruses continue to circulate, posing a problem for national health. The fact that only B/Victoria lineage circulate currently in human population gives a reason to believe that it should be closely investigated. An important place among the major properties of influenza virus hemagglutinin (HA) is referred to its potential to shape antigenic diversity of influenza viruses. It has been reliably proven that mutations in specific positions of HA1 receptor-binding site affect antigenic specificity. Therefore, assessing key amino acid positions located in this area is of substantial scientific and practical interest. This is especially important in practice, e.g., in influenza vaccine production that includes passaging in a sensitive substrate (usually in developing chicken embryos) within manufacturing technology. During passaging, substrate-adapting substitutions may occur in the region of the receptor-binding pocket, which may lead to undesirable changes in antigenic and biological properties of vaccine preparation. Our study is aimed at assessing a role of one of such egg-adapting substitutions (G141R). It was found that passaging of two currently circulating influenza B/Victoria viruses, B/Austria/1359417/2021 and B/Catalonia/2279261NS/2023, and LAIV vaccine strains prepared on their platform in developing chicken embryos resulted in HA1 G141R substitution that increased cold-adaptation of LAIV candidates, but not affecting their antigenic properties, temperature-sensitive phenotype, or degree of HA thermostability. The data presented in the article indicate that it is necessary to pay close attention to the emergence of mutations in the genome of influenza vaccine strains during their preparation, monitoring their possible impact on the key properties of such strains.