Live attenuated influenza A virus vaccines with modified NS1 proteins for veterinary use

Abstract

Influenza A viruses (IAV) spread rapidly and can infect a broad range of avian or mammalian species, having a tremendous impact in human and animal health and the global economy. IAV have evolved to develop efficient mechanisms to counteract innate immune responses, the first host mechanism that restricts IAV infection and replication. One key player in this fight against host-induced innate immune responses is the IAV non-structural 1 (NS1) protein that modulates antiviral responses and virus pathogenicity during infection. In the last decades, the implementation of reverse genetics approaches has allowed to modify the viral genome to design recombinant IAV, providing researchers a powerful platform to develop effective vaccine strategies. Among them, different levels of truncation or deletion of the NS1 protein of multiple IAV strains has resulted in attenuated viruses able to induce robust innate and adaptive immune responses, and high levels of protection against wild-type (WT) forms of IAV in multiple animal species and humans. Moreover, this strategy allows the development of novel assays to distinguish between vaccinated and/or infected animals, also known as Differentiating Infected from Vaccinated Animals (DIVA) strategy. In this review, we briefly discuss the potential of NS1 deficient or truncated IAV as safe, immunogenic and protective live-attenuated influenza vaccines (LAIV) to prevent disease caused by this important animal and human pathogen.

Antiviral responses versus virus-induced cellular shutoff: a game of thrones between influenza A virus NS1 and SARS-CoV-2 Nsp1

“…IAV NS1 modulates the inhibition of IFN production through variable interventions ( Baker et al., 2015 ; Cheng et al., 2015 ; Nogales et al., 2017a ; Nogales et al., 2017b ; Nogales et al., 2017c ; Hilimire et al., 2020 ; Martinez-Sobrido et al., 2020 ; Chiem et al., 2022 ; Nogales et al., 2022 ). However, other IAV proteins, including PA-X ( Chiem et al., 2021 ), PB1-F2 ( Varga and Palese, 2011 ; Varga et al., 2012 ), or PB2 have also been shown to be involved in inhibition of host antiviral responses during IAV infection ( Forero et al., 2015 ; Yang et al., 2022 ).…”

“…IAV NS1 has been shown to be implicated in counteracting the host antiviral innate IFN response at multiple levels ( Figures 4 , 5 ) ( Wang et al., 2000 ; Geiss et al., 2002 ; Quinlivan et al., 2005 ; Nogales et al., 2022 ). A direct interaction of IAV NS1 to the CARD domain of RIG-I abrogates the activation of all downstream regulatory transcription factors, including TRIM25 and RIPLET ubiquitin ligases that are essential for the priming of IFN production ( Bharadwaj and Mohana Priya, 2015 ) ( Figures 4A , 5 ).…”

“…Studying the sequence of aa residues located at the linker and disordered CTD of IAV NS1 revealed high variability among different IAV ( Figure 2 ) ( Bornholdt and Prasad, 2008 ). Deletion of five aa residues (80-84) located at the NS1 linker region of H5N1 IAV increased virus virulence in chicken and mice ( Long et al., 2008 ), while several studies revealed the impact of NS1 CTD truncations of different lengths on IAV pathogenicity and infectivity ( Seo et al., 2002 ; Quinlivan et al., 2005 ; Solorzano et al., 2005 ; Li et al., 2006b ; Chambers et al., 2009 ; Nogales et al., 2022 ). Moreover, specific aa residues were reported to be crucial as functional sites to mediate viral transcription upregulation, including R38 and K41 ( Zhang et al., 2023 ).…”

“…Reverse genetics approaches have provided researchers an efficient and powerful platform to introduce specific modifications in the viral genome of IAV ( Martinez-Sobrido et al., 2020 ; Nogales et al., 2022 ) or SARS-CoV-2 ( Ye et al., 2020 ; Mabrouk et al., 2022 ) with the goal to generate recombinant attenuated viruses that can be implemented as effective live-attenuated vaccine (LAV) candidates for the treatment of viral infections. In this review, we briefly discuss the potential of key IAV NS1 and SARS-CoV-2 Nsp1 mutants for their potential implementation as LAV for the prevention of IAV and SARS-CoV-2 infections.…”

Reprogramming viral immune evasion for a rational design of next-generation vaccines for RNA viruses

“…Based on such information, influenza viruses were engineered to modify the NS1 functions. The NS1-modified viruses appeared clinically attenuated and retained the immunogenicity in various species of animals, including mice ( 182 – 185 ), pigs ( 186 – 188 ), horses ( 189 , 190 ), poultry ( 191 – 194 ), macaques ( 195 ) as well as in humans ( 196 – 198 ). Influenza A virus containing a partial deletion in the NS1 gene provides solid evidence for clinical attenuation in animals while providing protective immunity against virulent challenges with the wild-type virus ( 199 ).…”