Efficacy of intranasal administration of a truncated NS1 modified live influenza virus vaccine in swine

Abstract

In the U.S., despite available swine influenza virus (SIV) vaccines, multiple influenza subtypes as well as antigenic and genetic variants within subtypes continue to circulate in the swine population. One of the challenges to control and eliminate SIV is that the currently used inactivated influenza virus vaccines do not provide adequate cross-protection against multiple antigenic variants of SIV in the field. We previously generated a recombinant H3N2 swine influenza virus (SIV) based on the influenza A/SW/TX/4199-2/98 virus (TX98) containing an NS1 gene expressing a truncated NS1 protein of 126 amino acids, TX98-NS1Δ126 virus. This recombinant strain was demonstrated to be highly attenuated in swine and showed potential for use as a modified live-virus vaccine (MLV) after intratracheal application in pigs. However, this route of inoculation is not practical for vaccination in the field. In the present study, we first compared intramuscular and intranasal routes of application of the MLV, and found that the intranasal route was superior in priming the local (mucosal) immune response. Pigs were then vaccinated via the intranasal route and challenged with wild type homologous TX98 H3N2 virus, with a genetic and antigenic variant H3N2 SIV (influenza A/SW/ CO/23619/99 virus, CO99) and a heterosubtypic H1N1 SIV (influenza A/SW/IA/00239/2004 virus, IA04). The intranasally vaccinated pigs were completely protected against homologous challenge. In addition, MLV vaccination provided nearly complete protection against the antigenic H3N2 variant CO99 virus. When challenged with the H1N1 IA04 virus, MLV vaccinated animals displayed reduced fever and virus titers despite minimal reduction in lung lesions. In vaccinated pigs, there was no serologic cross-reactivity by HI assays with the heterologous or heterosubtypic viruses. However, there appeared to be substantial cross-reactivity in antibodies at the mucosal level with the CO99 virus in MLV vaccinated pigs.

Vaccination with NS1-truncated H3N2 swine influenza virus primes T cells and confers cross-protection against an H1N1 heterosubtypic challenge in pigs

“…Previous work showed that intranasal NS1 126 TX98 elicited significant IgG and IgA antibody titers in lungs, and the vaccine protected pigs against challenge with TX98 or a similar H3N2 strain [21]. In that study, NS1 126 TX98 vaccination conferred partial protection against the heterosubtypic IA04 challenge.…”

“…Pigs were euthanized and necropsied 5 days post challenge. Bronchoalveolar lavage fluid (BALF) was collected for virus titration as described previously, using 50 ml Minimum Essential Medium per lung lavage [21]. Viral titers were analyzed in nasal swab and BALF samples by a standard tissue culture infectious dose assay on MDCK cell monolayers.…”

“…Truncation of NS1 protein in triple reassortant H3N2 strain A/Sw/Texas/4199-2/98, from a length of 230 amino acids to 126, produced a mutant with restricted replication in the swine respiratory tract but strong immunogenic properties [20]. Intranasal inoculation of pigs with this virus (NS1 126 TX98) resulted in robust protection against homologous challenge and significantly reduced viral replication and clinical signs upon challenge with a drift variant strain [21]. One likely factor in the partial heterologous protection was the production of mucosal IgA antibodies that had significant crossreactivity against the drift variant.…”

Genome plasticity of triple-reassortant H1N1 influenza A virus during infection of vaccinated pigs

“…The A/Swine/IA/00239/2004(H1N1) clusters within the b H1 swine IAVs (Lorusso et al, 2011). This virus was selected because it has been fully characterized, genetically and antigenically (Anderson et al, 2015), and it has been used in several pathogenesis (Vincent et al, 2007) and transmission studies Diaz et al, 2013;Romagosa et al, 2011). The challenge virus was 91.5 and 73.7 % identical at the nucleotide level to the H1 c and d vaccine virus strains, respectively.…”

An Eight-Segment Swine Influenza Virus Harboring H1 and H3 Hemagglutinins Is Attenuated and Protective against H1N1 and H3N2 Subtypes in Pigs

“…Previously, it was shown that SIVs generated by genetic modifications within the hemagglutinin (HA) or nonstructural (NS) genes are attenuated in pigs (12,13). These viruses demonstrated the ability to induce strong cell-mediated and humoral immunity and to provide full protection against homologous SIVs and partial protection against heterologous SIVs (11,(14)(15)(16)(17). In this study, we describe a novel approach that generates a LAIV candidate containing an H3 subtype of HA derived from a circulating SIV in the genetic background of H1N1 SIV.…”