Recombinant NDV-vectored vaccine expressing mosaic HA and M2e confers broad and early protection against H9N2 avian influenza virus

The development of a universal H9N2 avian influenza vaccine is essential to reduce the occurrence of disease and economic losses in the poultry industry. In this study, we developed a recombinant vaccine rTS-mH9-3M2e based on Newcastle disease virus (NDV) avirulent strain TS09-C, containing a chimeric mosaic H9 HA and three copies of H9N2 avian influenza virus (AIV) M2e. The 1-day-old chickens were vaccinated with rTS-mH9-3M2e, which induced broad neutralizing antibody activity against H9N2 AIV, effectively reduced viral load and virus shedding, and reduced clinical signs and tissue damage. Furthermore, rTS-mH9-3M2e can induce cross-neutralizing response to the heterologous subtype AIV H3N2 and conferred cross-protection against H3N2 AIV. When rTS-mH9-3M2e was used as in ovo vaccine, it conferred the earlier protection against NDV and H9N2 AIV compared with post-hatch vaccination. rTS-mH9-3M2e in ovo vaccination significantly increased the level of splenic CD8 + T cells in chickens at 7 days of age and provided 100% protection against H9N2 AIV and 80% protection for NDV virulent strain. These results support that rTS-mH9-3M2e is a promising candidate for development as a broad H9N2 avian influenza vaccine and an in ovo vaccine.