In Vivo Characterization of Avian Influenza A (H5N1) and (H7N9) Viruses Isolated from Canadian Travelers

Evaluating the epizootic and zoonotic threat of an H7N9 low-pathogenicity avian influenza virus (LPAIV) variant associated with enhanced pathogenicity in turkeys

Between 2013 and 2017, the A/Anhui/1/13-lineage (H7N9) low-pathogenicity avian influenza virus (LPAIV) was epizootic in chickens in China, causing mild disease, with 616 fatal human cases. Despite poultry vaccination, H7N9 has not been eradicated. Previously, we demonstrated increased pathogenesis in turkeys infected with H7N9, correlating with the emergence of the L217Q (L226Q H3 numbering) polymorphism in the haemagglutinin (HA) protein. A Q217-containing virus also arose and is now dominant in China following vaccination. We compared infection and transmission of this Q217-containing 'turkey-adapted' (ty-ad) isolate alongside the H7N9 (L217) wild-type (wt) virus in different poultry species and investigated the zoonotic potential in the ferret model. Both wt and ty-ad viruses demonstrated similar shedding and transmission in turkeys and chickens. However, the ty-ad virus was significantly more pathogenic than the wt virus in turkeys but not in chickens, causing 100 and 33% mortality in turkeys respectively. Expanded tissue tropism was seen for the ty-ad virus in turkeys but not in chickens, yet the viral cell receptor distribution was broadly similar in the visceral organs of both species. The ty-ad virus required exogenous trypsin for in vitro replication yet had increased replication in primary avian cells. Replication was comparable in mammalian cells, and the ty-ad virus replicated successfully in ferrets. The L217Q polymorphism also affected antigenicity. Therefore, H7N9 infection in turkeys can generate novel variants with increased risk through altered pathogenicity and potential HA antigenic escape. These findings emphasize the requirement for enhanced surveillance and understanding of A/Anhui/1/13-lineage viruses and their risk to different species.

Inhibition of Influenza Virus Polymerase by Interfering with Its Protein-Protein Interactions

Influenza (flu) virus is a serious threat to global health with the potential to generate devastating pandemics. The availability of broad spectrum antiviral drugs is an unequaled weapon during pandemic events, especially when a vaccine is still not available. One of the most promising targets for the development of new antiflu therapeutics is the viral RNA-dependent RNA polymerase (RdRP). The assembly of the flu RdRP heterotrimeric complex from the individual polymerase acidic protein (PA), polymerase basic protein 1 (PB1), and polymerase basic protein 2 (PB2) subunits is a prerequisite for RdRP functions, such as mRNA synthesis and genome replication. In this Review, we report the known protein-protein interactions (PPIs) occurring by RdRP that could be disrupted by small molecules and analyze their benefits and drawbacks as drug targets. An overview of small molecules able to interfere with flu RdRP functions exploiting the PPI inhibition approach is described. In particular, an update on the most recent inhibitors targeting the well-consolidated RdRP PA-PB1 subunit heterodimerization is mainly reported, together with pioneer inhibitors targeting other virus-virus or virus-host interactions involving RdRP subunits. As demonstrated by the PA-PB1 interaction inhibitors discussed herein, the inhibition of flu RdRP functions by PPI disrupters clearly represents a valid means to identify compounds endowed with a broad spectrum of action and a reduced propensity to develop drug resistance, which are the main issues of antiviral drugs.

A Replication-Defective Influenza Virus Harboring H5 and H7 Hemagglutinins Provides Protection against H5N1 and H7N9 Infection in Mice

The recent highly pathogenic avian influenza (HPAI) H5N1 and H7N9 viruses have caused hundreds of human infections with high mortality rates. Although H5N1 and H7N9 viruses have been limited mainly to avian species, there is high potential for these viruses to acquire human-to-human transmission and initiate a pandemic. A highly safe and effective vaccine is needed to protect against a potential H5N1 or H7N9 influenza pandemic. Here, we report the generation and evaluation of two reassortant influenza viruses, PR8-H5-H7_NA and PR8-H7-H5_NA These viruses contain six internal segments from A/Puerto Rico/8/1934 (PR8), the HA segment from either A/Alberta/01/2014 (H5N1) [AB14 (H5N1)] or A/British Columbia/01/2015 (H7N9) [BC15 (H7N9)], and a chimeric NA segment with either the BC15 (H7N9) HA gene or the AB14 (H5N1) HA gene flanked by the NA packaging signals of PR8. These viruses expressed both H5 and H7 HAs in infected cells, replicated to high titers when exogenous NA was added to the culture medium in vitro, and were replication defective and nonvirulent when administered intranasally in mice. Moreover, intranasal vaccination with PR8-H5-H7_NA elicited robust immune responses to both H5 and H7 viruses, conferring complete protection against both AB14 (H5N1) and BC15 (H7N9) challenges in mice. Conversely, vaccination with PR8-H7-H5_NA only elicited robust immune responses toward the H7 virus, which conferred complete protection against BC15 (H7N9) but not against AB14 (H5N1) in mice. Therefore, PR8-H5-H7_NA has strong potential to serve as a vaccine candidate against both H5 and H7 subtypes of influenza viruses.IMPORTANCE Avian influenza H5N1 and H7N9 viruses infected humans with high mortality rates. A highly safe and effective vaccine is needed to protect against a potential pandemic. We generated and evaluated two reassortant influenza viruses, PR8-H5-H7_NA and PR8-H7-H5_NA, as vaccine candidates. Each virus contains one type of HA in segment 4 and the other subtype of HA in segment 6, thereby expressing both H5 and H7 subtypes of the HA molecule. The replication of viruses is dependent on the addition of exogenous NA in cell culture and is replication defective in vivo Vaccination of PR8-H5-H7_NA virus confers protection to both H5N1 and H7N9 virus challenge; conversely, vaccination of PR8-H7-H5_NA provides protection only to H7N9 virus challenge. Our data revealed that when engineering such a virus, the H5 or H7 HA in segment 6 affects the immunogenicity. PR8-H5-H7_NA has strong potential to serve as a vaccine candidate against both H5 and H7 subtypes of influenza viruses.

A bivalent live attenuated influenza virus vaccine protects against H1N2 and H3N2 viral infection in swine

Swine Influenza A virus (swIAV) poses a substantial burden to the swine industry due to its highly contagious nature, acute viral disease, and ability to cause up to 100 % morbidity. Currently, North American swine are predominately infected with three subtypes of swIAV: H1N1, H1N2, and H3N2. The ability of influenza viruses to cross both directions between humans and swine means that both human and swine-origin viruses as well as new reassortant viruses can pose a substantial public health or pandemic threat. Since the primary method of protection and control against influenza is through vaccination, more effective, new vaccine platforms need to be developed. This study uses two Canadian swIAV isolates, A/Swine/Alberta/SD0191/2016 (H1N2) [SD191] and A/Swine/Saskatchewan/SD0069/2015 (H3N2) [SD69] to design a bivalent live attenuated influenza virus vaccine (LAIV) through reverse genetics. The hemagglutinin (HA) cleavage site from both SD191-WT and SD69-WT were engineered from a trypsin-sensitive to an elastase-sensitive motif, to generate SD191-R342V and SD69-K345V, respectively. The elastase dependent SD191-R342V virus possesses a mutation from arginine to valine at amino acid (aa) 342 on HA, whereas the elastase dependent SD69-K345V virus possesses a mutation from lysine to valine at aa 345 on HA. Both elastase dependent swIAVs are completely dependent on elastase, display comparable growth properties to the wild type (WT) viruses, are genetically stable in vitro, and entirely non-virulent in pigs. Moreover, when these elastase dependent swIAVs were administered together in pigs, they were found to stimulate antibody responses and IFN-γ secreting cells, as well as prevent viral replication and lung pathology associated with WT H1N2 and H3N2 swIAV challenge. Therefore, this bivalent LAIV demonstrates the strong candidacy to protect swine against the predominant influenza subtypes in North America.

Bone marrow-derived mesenchymal stem cells attenuate pulmonary inflammation and lung damage caused by highly pathogenic avian influenza A/H5N1 virus in BALB/c mice

BACKGROUND

The highly pathogenic avian influenza A/H5N1 virus is one of the causative agents of acute lung injury (ALI) with high mortality rate. Studies on therapeutic administration of bone marrow-derived mesenchymal stem cells (MSCs) in ALI caused by the viral infection have been limited in number and have shown conflicting results. The aim of the present investigation is to evaluate the therapeutic potential of MSC administration in A/H5N1-caused ALI, using a mouse model.

METHODS

MSCs were prepared from the bone marrow of 9 to 12 week-old BALB/c mice. An H5N1 virus of A/turkey/East Java/Av154/2013 was intranasally inoculated into BALB/c mice. On days 2, 4, and 6 after virus inoculation, MSCs were intravenously administered into the mice. To evaluate effects of the treatment, we examined for lung alveolar protein as an indicator for lung injury, PaO₂/FiO₂ ratio for lung functioning, and lung histopathology. Expressions of NF-κB, RAGE (transmembrane receptor for damage associated molecular patterns), TNFα, IL-1β, Sftpc (alveolar cell type II marker), and Aqp5+ (alveolar cell type I marker) were examined by immunohistochemistry. In addition, body weight, virus growth in lung and brain, and duration of survival were measured.

RESULTS

The administration of MSCs lowered the level of lung damage in the virus-infected mice, as shown by measuring lung alveolar protein, PaO₂/FiO₂ ratio, and histopathological score. In the MSC-treated group, the expressions of NF-κB, RAGE, TNFα, and IL-1β were significantly suppressed in comparison with a mock-treated group, while those of Sftpc and Aqp5+ were enhanced. Body weight, virus growth, and survival period were not significantly different between the groups.

CONCLUSION

The administration of MSCs prevented further lung injury and inflammation, and enhanced alveolar cell type II and I regeneration, while it did not significantly affect viral proliferation and mouse morbidity and mortality. The results suggested that MSC administration was a promissing strategy for treatment of acute lung injuries caused by the highly pathogenic avian influenza A/H5N1 virus, although further optimization and combination use of anti-viral drugs will be obviously required to achieve the goal of reducing mortality.

Synthesis and characterization of 1,2,4-triazolo[1,5-a]pyrimidine-2-carboxamide-based compounds targeting the PA-PB1 interface of influenza A virus polymerase

Influenza viruses (Flu) are responsible for seasonal epidemics causing high rates of morbidity, which can dramatically increase during severe pandemic outbreaks. Antiviral drugs are an indispensable weapon to treat infected people and reduce the impact on human health, nevertheless anti-Flu armamentarium still remains inadequate. In search for new anti-Flu drugs, our group has focused on viral RNA-dependent RNA polymerase (RdRP) developing disruptors of PA-PB1 subunits interface with the best compounds characterized by cycloheptathiophene-3-carboxamide and 1,2,4-triazolo[1,5-a]pyrimidine-2-carboxamide scaffolds. By merging these moieties, two very interesting hybrid compounds were recently identified, starting from which, in this paper, a series of analogues were designed and synthesized. In particular, a thorough exploration of the cycloheptathiophene-3-carboxamide moiety led to acquire important SAR insight and identify new active compounds showing both the ability to inhibit PA-PB1 interaction and viral replication in the micromolar range and at non-toxic concentrations. For few compounds, the ability to efficiently inhibit PA-PB1 subunits interaction did not translate into anti-Flu activity. Chemical/physical properties were investigated for a couple of compounds suggesting that the low solubility of compound 14, due to a strong crystal lattice, may have impaired its antiviral activity. Finally, computational studies performed on compound 23, in which the phenyl ring suitably replaced the cycloheptathiophene, suggested that, in addition to hydrophobic interactions, H-bonds enhanced its binding within the PA_C cavity.

A Replication-Defective Influenza Virus Vaccine Confers Complete Protection against H7N9 Viral Infection in Mice

Avian influenza H7N9 viruses continue to pose a great threat to public health, which is evident by their high case-fatality rates. Although H7N9 was first isolated in humans in China in 2013, to date, there is no commercial vaccine available against this particular strain. Our previous studies developed a replication-defective influenza virus through mutation of the hemagglutinin (HA) cleavage site from a trypsin-sensitive to an elastase-sensitive motif. In this study, we report the development of a reassortant mutant influenza virus derived from the human isolate A/British Columbia/01/2015 (H7N9) [BC15 (H7N9)], which is the QVT virus. The HA gene of this virus possesses three mutations at the cleavage site, Lys-Gly-Arg were mutated to Gln-Thr-Val at amino acid (aa) positions 337, 338, and 339, respectively. We report this virus to rely on elastase in vitro, possess unaltered replication abilities when elastase was provided compared to the wild type virus in vitro, and to be non-virulent and replication-defective in mice. In addition, we report this virus to induce significant levels of antibodies and IFN-γ and IL-5 secreting cells, and to protect mice against a lethal challenge of the BC15 (H7N9) virus. This protection is demonstrated through the lack of body weight loss, 100% survival rate, and the prevention of BC15 (H7N9) viral replication as well as the reduction of proinflammatory cytokines induced in the mouse lung associated with the influenza disease. Therefore, these results provide strong evidence for the use of this reassortant mutant H7N9 virus as a replication-defective virus vaccine candidate against H7N9 viruses.

Innate immunemodulator containing adjuvant formulated HA based vaccine protects mice from lethal infection of highly pathogenic avian influenza H5N1 virus

The highly pathogenic avian influenza (HPAI) H5N1 viruses and their spillover into the human population pose substantial economic and public health threats. Although antiviral drugs have some effect in treating influenza infection, vaccination is still the most effective intervention to prevent possible pandemic outbreaks. We have developed a novel H5 influenza vaccine to improve the world's pandemic preparedness. We produced a hemagglutinin (HA) of HPAI H5N1 virus A/Alberta/01/2014 (AB14) using both mammalian (m) and bacterial (b) expression systems. The purified recombinant proteins were formulated with a proprietary adjuvant (TriAdj) and their efficacy as vaccine candidates was evaluated in mice. Intramuscular delivery of two doses of TriAdj formulated mammalian expressed HA (m-HA/TriAdj) was shown to provide full protection against a lethal challenge of AB14 in mice. In contrast, bacterially expressed HA with TriAdj (b-HA/TriAdj), b-HA without adjuvant, and m-HA without adjuvant resulted in no protection in immunized mice. Furthermore, m-HA/TriAdj elicited significantly higher levels of balanced Th1 and Th2 responses and neutralizing antibody titres. All the mice in the m-HA/TriAdj group survived a lethal AB14 H5N1 challenge and showed no signs of disease or infection as demonstrated by no loss of body weight or detectable virus in the lungs. Our results suggest that m-HA formulated with TriAdj has potential to protect against pandemic H5N1 in the event of its cross over to the human host.