Live-attenuated influenza virus vaccine strain with an engineered temperature-sensitive and genetically stable viral...

Vaccination against seasonal influenza is considered an effective means of reducing morbidity and mortality. Live-attenuated vaccines offer more protection against influenza than inactivated vaccines as they efficiently induce cellular immunity and provide cross-immunogenicity against various antigenic subtypes. For the production of safer live-attenuated vaccines, it is important to develop a common master donor vaccine strain in which pathogenic revertants are much less likely to appear. In this study, we introduced a single amino acid substitution of Lys471 into the PB1 polymerase subunit of influenza A virus and succeeded in isolating an attenuated mutant virus that exhibits a temperature-sensitive phenotype. The Lys471 residue is located in the polymerase motif D on PB1 and is positioned near the entrance tunnel domain for incoming nucleotide triphosphate. Although 10 viable PB1-Lys471 mutants did not proliferate at 37°C, their variants could replicate at 31°C and 34°C. Moreover, we found that PB1-Lys471Pro variant induces a genetically stable influenza virus phenotype; this mutant virus did not revert to wild-type phenotype from the temperature-sensitive phenotype by serial virus passages. Animal experiments have demonstrated that these PB1 mutant strains work effectively as live-attenuated vaccines. Application of the PB1-Lys471 substitution to a master donor strain is expected to lead to the development of a safer, high-performance, and widely used live-attenuated vaccine with the antigen of circulating influenza viruses.

Influenza virus elicits respiratory tract disease and is a threat to global human health. Vaccination is considered an effective tool for reducing the morbidity and mortality caused by influenza disease. The only licensed live-attenuated influenza vaccine that has been proven safe and effective is FluMist. In this study, we isolated an attenuated influenza mutant virus with a Lys471 single amino acid substitution in PB1, which displayed a temperature-sensitive and a low-pathogenicity phenotype. By applying the PB1-Lys471 substitution to the vaccine mother strain or the circulating influenza virus using reverse genetic technology, a high-performance and safe live-attenuated vaccine carrying the viral antigens of the vaccine-targeted strain can be developed.