Morbidity and mortality resulting from influenza-like disease are a threat, especially for older adults. To improve case management, next-generation broad-spectrum antiviral therapeutics that are efficacious against major drivers of influenza-like disease, including influenza viruses and respiratory syncytial virus (RSV), are urgently needed. Using a dual-pathogen high-throughput screening protocol for influenza A virus (IAV) and RSV inhibitors, we have identified -hydroxycytidine (NHC) as a potent inhibitor of RSV, influenza B viruses, and IAVs of human, avian, and swine origins. Biochemical polymerase assays and viral RNA sequencing revealed that the ribonucleotide analog is incorporated into nascent viral RNAs in place of cytidine, increasing the frequency of viral mutagenesis. Viral passaging in cell culture in the presence of an inhibitor did not induce robust resistance. Pharmacokinetic profiling demonstrated dose-dependent oral bioavailability of 36 to 56%, sustained levels of the active 5'-triphosphate anabolite in primary human airway cells and mouse lung tissue, and good tolerability after extended dosing at 800 mg/kg of body weight/day. The compound was orally efficacious against RSV and both seasonal and highly pathogenic avian IAVs in mouse models, reducing lung virus loads and alleviating disease biomarkers. Oral dosing reduced IAV burdens in a guinea pig transmission model and suppressed virus spread to uninfected contact animals through direct transmission. Based on its broad-spectrum efficacy and pharmacokinetic properties, NHC is a promising candidate for future clinical development as a treatment option for influenza-like diseases.
The stem of the influenza A virus hemagglutinin (HA) is highly conserved and represents an attractive target for a universal influenza vaccine. The 18 HA subtypes of influenza A are phylogenetically divided into two groups, and while protection with group 1 HA stem vaccines has been demonstrated in animal models, studies on group 2 stem vaccines are limited. Thus, we engineered group 2 HA stem-immunogen (SI) vaccines targeting the epitope for the broadly neutralizing monoclonal antibody CR9114 and evaluated vaccine efficacy in mice and ferrets. Immunization induced antibodies that bound to recombinant HA protein and viral particles, and competed with CR9114 for binding to the HA stem. Mice vaccinated with H3 and H7-SI were protected from lethal homologous challenge with X-79 (H3N2) or A/Anhui/1/2013 (H7N9), and displayed moderate heterologous protection. In ferrets, H7-SI vaccination did not significantly reduce weight loss or nasal wash titers after robust 107 TCID50 H7N9 virus challenge. Epitope mapping revealed ferrets developed lower titers of antibodies that bound a narrow range of HA stem epitopes compared to mice, and this likely explains the lower efficacy in ferrets. Collectively, these findings indicate that while group 2 SI vaccines show promise, their immunogenicity and efficacy are reduced in larger outbred species, and will have to be enhanced for successful translation to a universal vaccine.
22implicated the PA gene segment as a major driver of this phenotype and quantification of viral 33RNA synthesis indicated that both replication and transcription were affected. These findings 34 indicate that multiple distinct mechanisms underlie IAV reliance on multiple infection and 35 underscore the importance of virus-virus interactions in IAV infection, evolution and emergence. 36Importantly, multiple infection with identical viral genomes can also alter infection 58 outcomes. Such cooperation was documented for VSV and HIV, where rates of transcription and 59 replication were enhanced with increasing multiplicity of infection (MOI) 23,24 . Similarly, faster 60 kinetics of virus production were seen at high MOI for poliovirus and IAV 19,25 . In these instances, 61 it is thought that increased copy number of infecting viral genomes provides a kinetic benefit 62 important in the race to establish infection before innate antiviral responses take hold. Indeed, it 63 has been suggested that multiple infection may be particularly relevant for facilitating viral growth 64 under adverse conditions, such as antiviral drug treatment 3,26 . 65For IAV, an important adverse condition to consider is that of a novel host environment. 66IAVs occupy a broad host range, including multiple species of wild waterfowl, poultry, swine, 67 humans and other mammals 27,28 . Host barriers to infection typically confine a given lineage to 68 circulation in one species or a small number of related species 29,30 . Spillovers occur occasionally, 69 however, and can seed novel lineages. When a novel IAV lineage is established in humans, the 70 result is a pandemic of major public health consequence 31,32 . The likelihood of successful cross-71 species transfer of IAV is determined largely by the presence, absence, and compatibility of host 72 factors on which the virus relies to complete its life cycle, and on the viruses' ability to overcome 73 antiviral defenses in the novel host [33][34][35] . 74Our objective herein was to assess the degree to which IAV relies on the delivery of 75 multiple viral genomes to a cell to ensure production of progeny. In particular, we sought to 76 determine whether this phenotype varies with host species. We therefore examined the 77 multiplicity dependence of one human and a panel of avian-origin viruses in multiple host systems. 78Results from all virus/cell combinations tested confirm prior reports that cells multiply-infected with 79 IAV produce more viral progeny than singly-infected cells. Importantly, however, the extent to 80 which viral progeny production is concentrated within the multiply-infected fraction of a cell 81 population varies greatly with virus-host context. Two poultry-adapted H9N2 viruses (A/guinea 82 fowl/HK/WF10/99 (GFHK99) and A/quail/HK/A28945/88 (QaHK88)) exhibit an acute dependence 83 on multiple infection in mammalian systems that is greatly diminished in natural host systems. 84This strong dependence on multiple infection is not seen for the human strain, influenza 85 ...
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