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

Abstract

Swine influenza virus (SIV) infections continue to cause production losses in the agricultural industry in addition to being a human public health concern. The primary method of controlling SIV is through vaccination. The killed SIV vaccines currently in use must be closely matched to the challenge virus, and their protective efficacy is limited. Live attenuated influenza vaccines (LAIV) provide strong, long-lived cell-mediated and humoral immunity against different influenza virus subtypes with no need for antigen matching. Here we report the generation of a new potential LAIV, an eight-segment SIV harboring two different SIV hemagglutinins (HAs), H1 and H3, in the genetic background of H1N1 SIV. This mutant SIV was generated by fusing the H3 HA ectodomain from A/Swine/Texas/4199-2/98 (H3N2) to the cytoplasmic tail, transmembrane domain, and stalk region of neuraminidase (NA) from A/Swine/Saskatchewan/18789/02 (H1N1) SIV. While this H1-H3 chimeric SIV, when propagated in vitro in the presence of exogenous neuraminidase, showed kinetics and growth properties similar to those of the parental wild-type virus, in vivo it was highly attenuated in pigs, demonstrating a great potential for serving as a dual LAIV. Furthermore, vaccination with the H1-H3 virus elicited robust immune responses, which conferred complete protection against infections with both H1 and H3 SIV subtypes in pigs.

Development and applications of single-cycle infectious influenza A virus (sciIAV)

“…Evidence for this was first provided by showing the presence of anti-GFP Abs in mice following immunization with a GFP-expressing sciIAV ΔPB2 (Victor et al, 2012). Furthering this data, when a reporter gene from a sciIAV was replaced by an inactive HA gene from a heterologous IAV, both mice and swine were protected against heterologous influenza virus infections (Masic et al, 2013; Uraki et al, 2013). However, no NAbs were detected against the heterologous strain in mice even though they were detected in swine.…”

“…Moreover ferrets, which have upper respiratory physiology more closely related to humans than mice and can transmit influenza via aerosol droplets, were also protected by sciIAV against infection and transmitting virus (Baker et al, 2013). Vaccination with sciIAV in swine was also shown to be protective and immunogenic (Masic et al, 2013; Pyo and Zhou, 2014). …”

“…However, no NAbs were detected against the heterologous strain in mice even though they were detected in swine. Whether these bivalent sciIAV had different protective efficacies than reporter-expressing sciIAV was not addressed (Masic et al, 2013; Uraki et al, 2013). Amenability of sciIAV as a bivalent vaccine was further shown when Streptococcus pneumoniae surface protein A (PspA), HPIV-3 HN protein, or RSV F protein replaced the reporter gene in sciIAV (Fonseca et al, 2014; Katsura et al, 2014; Kobayashi et al, 2013).…”

Pregnancy and infection: using disease pathogenesis to inform vaccine strategy

“…Studies in nonpregnant mice have demonstrated that a single dose of sciIAV vaccine confers protection against heterosubtypic lethal challenge without any adverse effects. 136 – 141 Similar safety and efficacy profiles of sciIAV have been replicated in ferret and pig models, 136 , 142 but studies in pregnant animals have not been performed. Compared with the risks associated with live virus vaccination and concerns of efficacy with inactivated vaccines, novel vaccine platforms, such as nanoparticle-based technologies, VLPs and replication-deficient viruses have proven benefits.…”

Animal Models for Influenza Viruses: Implications for Universal Vaccine Development

“…Traditionally, pigs have mostly been used for the development of swine influenza virus vaccines, for which several novel approaches are under investigation [ 160 , 161 , 162 ]. Similarly to humans [ 163 ], mice [ 128 ] and ferrets [ 164 , 165 ], seasonal H1N1 vaccination (inactivated or live-attenuated) induced minimal cross-reactive humoral responses, and showed marginal efficacy against a pandemic H1N1 challenge [ 166 ].…”