Efficacy of Live-Attenuated H9N2 Influenza Vaccine Candidates Containing NS1 Truncations against H9N2 Avian Influenza Viruses

Abstract

H9N2 avian influenza virus is a zoonotic agent with a broad host range that can contribute genetic information to H5 or H7N9 subtype viruses, which are significant threats to both humans and birds. Thus, there is a great need for a vaccine to control H9N2 avian influenza. Three mutant viruses of an H9N2 virus A/chicken/Taixing/10/2010 (rTX-NS1-73, rTX-NS1-100, and rTX-NS1-128) were constructed with different NS1 gene truncations and confirmed by western blot analysis. The genetic stability, pathogenicity, transmissibility, and host immune responses toward these mutants were evaluated. The mutant virus rTX-NS1-128 exhibited the most attenuated phenotype and lost transmissibility. The expression levels of interleukin 12 in the nasal and tracheal tissues from chickens immunized with rTX-NS1-128 were significantly upregulated on day 3 post-immunization and the IgA and IgG antibody levels were significantly increased on days 7, 14, and 21 post-immunization when compared to chickens that received an inactivated vaccine. rTX-NS1-128 also protected chickens from challenge by homologous and heterologous H9N2 avian influenza viruses. The results indicate that rTX-NS1-128 can be used as a potential live-attenuated vaccine against H9N2 avian influenza.

A Live Attenuated H9N2 Avian Influenza Vaccine Prevents the Viral Reassortment by Exchanging the HA and NS1 Packaging Signals

“…H9N2 AIVs A/chicken/Shanghai/F/98 (H9N2), A/chicken/Taixing/10/2010 (H9N2, rTX), and the NS1 truncated virus (rTX-NS1-128) ( Chen et al, 2017 ) were identified and stored by our laboratory and were cultured in the 9- to 11-day-old embryonated SPF chicken eggs at 37°C. Allantoic fluids were harvested 72 h post-inoculation and stored at −70°C.…”

“…In our previous study, H9N2 live attenuated vaccine candidate strain with a truncated NS1 gene was constructed, verified by animal experiments that provide good protection for both specific pathogen-free (SPF) chickens ( Chen et al, 2017 ). On the basis of this vaccine virus (rTX-NS1-128 strain), the HA packaging signal, including NCR, the 80 nucleotides (nt) of 5′ORF, and the 9 nt of 3′ORF ( Watanabe et al, 2003 ), and the NS packaging signal, including NCR, 150 nt of 5′ORF, and 150 nt of 3′ORF ( Fujii et al, 2005 ), were exchanged to avoid viral recombination and to construct safe and high-efficiency live attenuated vaccines.…”

“…Attenuated influenza viruses have been developed based on the deletion of truncation of the NS1 gene that interferes with interferon ( Kochs et al, 2007 ). Previously, we developed a live attenuated H9N2 vaccine by truncating the NS1 gene (named rTX-NS1-128), which can protect chickens against homologous and heterologous H9N2 AIVs challenge ( Chen et al, 2017 ). Therefore, the live attenuated vaccine has more advantages compared with the inactivated vaccine.…”

Live poultry vaccines against highly pathogenic avian influenza viruses

“…The mutant virus of H9N2 subtype with NS1-128 truncation was more immunogenic than the corresponding inactivated vaccine and protected chickens from challenge by homologous and heterologous H9N2 avian influenza viruses [38].…”

A modified live bat influenza A virus-based vaccine prototype provides full protection against HPAIV H5N1

“…The current MLIVs are based on apathogenic influenza viruses, and attenuation is, e.g. achieved by using truncated NS1 proteins 21 or restricted replication capacities due to cold-adaptation 22 or the introduction of elastasespecific cleavage sites into the HA precursor protein 23 . Although cold-adapted MLIVs have been licensed for several years for use in humans, there are no MLIVs licensed for poultry yet, and only two types of vector-based live vaccines are on the market 18 .…”