An avian-origin internal backbone effectively increases the H5 subtype avian influenza vaccine candidate yield in both chicken embryonated eggs and MDCK cells.

Inactivated vaccines play an important role in preventing and controlling the epidemic caused by the H5 subtype avian influenza virus. The vaccine strains are updated in response to alterations in surface protein antigens, while an avian-derived vaccine internal backbone with a high replicative capacity in chicken embryonated eggs and MDCK cells is essential for vaccine development. In this study, we constructed recombinant viruses using the clade 2.3.4.4d A/chicken/Jiangsu/GY5/2017(H5N6, CkG) strain as the surface protein donor and the clade 2.3.4.4b A/duck/Jiangsu/84512/2017(H5N6, Dk8) strain with high replicative ability as an internal donor. After optimization, the integration of the M gene from the CkG into the internal genes from Dk8 (8G) was selected as the high-yield vaccine internal backbone, as the combination improved the hemagglutinin1/nucleoprotein (HA1/NP) ratio in recombinant viruses. The r8GΔG with attenuated hemagglutinin and neuraminidase from the CkG exhibited high-growth capacity in both chicken embryos and MDCK cell cultures. The inactivated r8GΔG vaccine candidate also induced a higher hemagglutination inhibition antibody titer and microneutralization titer than the vaccine strain using PR8 as the internal backbone. Further, the inactivated r8GΔG vaccine candidate provided complete protection against wild-type strain challenge. Therefore, our study provides a high-yield, easy-to-cultivate candidate donor as an internal gene backbone for vaccine development.