Truncation of NS1 Protein Enhances T Cell-Mediated Cross-Protection of a Live Attenuated Influenza Vaccine Virus Expressing Wild-Type Nucleoprotein

Abstract

Current seasonal influenza vaccines have suboptimal effectiveness, especially in seasons dominated by viruses that do not match the vaccine. Therefore, finding new approaches to improve the immunogenicity and efficacy of traditional influenza vaccines is of high priority for public health. Licensed live attenuated influenza vaccine (LAIV) is a promising platform for designing broadly protective vaccines due to its ability to induce cross-reactive T-cell immunity. In this study, we tested the hypothesis that truncation of the nonstructural protein 1 (NS1) and the replacement of the nucleoprotein (NP) of the A/Leningrad/17 master donor virus with a recent NP, i.e., switching to 5:3 genome composition, could improve the cross-protective potential of the LAIV virus. We generated a panel of LAIV candidates differing from the classical vaccine by the source of NP gene and/or by the length of NS1 protein. We showed that NS1-modified LAIV viruses had reduced viral replication in the respiratory tract of mice, indicating a more attenuated phenotype compared to the LAIVs with full-length NS1. Most importantly, the LAIV candidate with both NP and NS genes modified induced a robust systemic and lung-localized memory CD8 T-cell response targeting more recent viruses, and better protected immunized mice against lethal challenge with a heterosubtypic influenza virus than the control LAIV variant. Overall, these data indicate that the 5:3 LAIVs with truncated NS1 may be beneficial for protection against heterologous influenza viruses and warrant further preclinical and clinical development.

Expression of the SARS-CoV-2 receptor-binding domain by live attenuated influenza vaccine virus as a strategy for designing a bivalent vaccine against COVID-19 and influenza

“…The FluCoVac-19 and FluCoVac-20 variants were compared to the classical LAIV virus, and the difference in the replicative activity between chimeric and control viruses suggests that the foreign insert could have interfered with the ability of the LAIV virus to replicate in the mouse URT. For the NS1-modified recombinant viruses, the absence of infectious virus in the mouse respiratory tract is in line with findings that the LAIVs encoding truncated NS1 protein had restricted ability to infect mice [ 17 ]. Therefore, the effect of foreign insertions within the NS1 ORF on the infectivity of the virus in mice could not be elucidated.…”

“…The replicative activity of the recombinant viruses in chicken embryos was compared to that of the modified H7N9 LAIV virus encoding truncated to 126 residues NS1 protein, which was characterized earlier [ 17 ]. Most of the chimeric influenza viruses replicated efficiently in eggs, except FluCoVac-79 variant (Table 2 ).…”

“…One of the reasons for the lower immunogenicity of the RBD-based recombinant influenza viruses based on A/Leningrad/17 backbone compared to the other backbones could be the inability of the Len/17-based viruses to efficiently replicate in the mouse respiratory tract, especially with NS1 modifications [ 17 ]. For example, A/PR/8/34-based influenza viruses, even in the case of truncated NS1, replicate well in the lungs [ 65 ], thus producing higher levels of virus-specific serum antibodies.…”

“…A previously rescued live attenuated influenza vaccine (LAIV) virus served as a viral vector for generation of recombinant influenza viruses expressing immunogenic fragments of SARS-CoV-2 [ 17 ]. This virus carries hemagglutinin (HA) and neuraminidase (NA) genes of A/17/Anhui/2013/61 (A/Anhui/1/2013-based LAIV strain) and the remaining six genes from A/Leningrad/134/17/57 (H2N2), a master donor virus for LAIV.…”

“…This virus carries hemagglutinin (HA) and neuraminidase (NA) genes of A/17/Anhui/2013/61 (A/Anhui/1/2013-based LAIV strain) and the remaining six genes from A/Leningrad/134/17/57 (H2N2), a master donor virus for LAIV. An H7N9 LAIV virus expressing truncated NS1 protein was used here as an additional vector control; generation and main characteristics of this vaccine virus were previously reported [ 17 ].…”