Homologous PB1 gene promotes the replication efficiency of avian influenza H7N4 candidate vaccine virus

Abstract

Background The first and only case of human infection with the avian influenza A (H7N4) virus in China emerged in 2018. The H7N4 virus was distinct from previous H7N9 viruses and raised public concerns. Therefore, developing a suitable H7N4 candidate vaccine virus (CVV) remains crucial for potential pandemic preparedness. Methods We constructed a reassortant virus with a (6 + 2) genome composition, then introduced the polymerase basic protein 1 (PB1) from a wild‐type virus to develop a (5 + 3) reassortant virus through reverse genetics. We performed whole‐genome sequencing to confirm the genome stability, assessed the growth ability in MDCK cells, and analyzed virus antigenicity using hemagglutination inhibition assays. Subsequently, the effect of homologous PB1 on polymerase activity, viral protein yield, and pathogenicity was assessed. Results The (5 + 3) virus harbouring the homologous PB1 gene exhibited significantly improved growth characteristics, higher viral protein yield, and polymerase activity than the (6 + 2) virus. After successive passage in embryonated eggs, glutamic acid (E) substituted glycine(G) at position 218 (H3 numbering) in the hemagglutinin (HA) gene of both (5 + 3) and (6 + 2) viruses. The substitution improved the growth of the (6 + 2) virus but exhibited no significant effect or alteration on the antigenicity of the (5 + 3) virus. Moreover, the (5 + 3) virus exhibited low pathogenicity in chickens and ferrets. Conclusion Homologous PB1 of the H7N4 virus improves the growth ability while sustaining low pathogenicity. Collectively, the gene composition of the (5 + 3) reassortant virus is a suitable H7N4 CVV for potential pandemic preparedness.

Development of an Enhanced High-Yield Influenza Vaccine Backbone in Embryonated Chicken Eggs

“…The M vRNA segment almost always originates from PR8 [ 10 , 16 , 17 ] and has been shown to confer a higher yield [ 11 ]. Analysis of 5:3 reassortants has revealed that the PB1 vRNA segment is frequently derived from the circulating virus [ 10 , 16 , 17 ] by conferring a higher yield [ 18 , 19 , 20 , 21 ]. Thus, the high yield of a candidate vaccine virus is often conferred by the PR8 M vRNA segment and the PB1 vRNA segment of the circulating virus.…”