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Summary Suppression of innate immune responses during filoviral infection contributes to disease severity. Ebola (EBOV) and Marburg (MARV) viruses each encode a VP35 protein that suppresses RIG-I-like receptor signaling and interferon-α/β (IFN-α/β) production by several mechanisms, including direct binding to double stranded RNA (dsRNA). Here, we demonstrate that in cell culture, MARV infection results in a greater upregulation of IFN responses as compared to EBOV infection. This correlates with differences in the efficiencies by which EBOV and MARV VP35s antagonize RIG-I signaling. Furthermore, structural and biochemical studies suggest that differential recognition of RNA elements by the respective VP35 C-terminal IFN inhibitory domain (IID) rather than affinity for RNA by the respective VP35s is critical for this observation. Our studies reveal functional differences in EBOV versus MARV VP35 RNA binding that result in unexpected differences in the host response to deadly viral pathogens. [ABSTRACT FROM AUTHOR]

Lassa virus (LASV) is recognized by the World Health Organization as one of the top five pathogens likely to cause a severe outbreak. A recent unprecedented resurgence of LASV in Nigeria caused by genetically diverse strains underscores the need for licensed medical countermeasures. Single-injection vaccines that can rapidly control outbreaks and confer long-term immunity are needed. Vaccination of cynomolgus monkeys with a recombinant vesicular stomatitis virus vector expressing the glycoprotein precursor of LASV lineage IV strain Josiah (rVSVΔG-LASV-GPC) induces fast-acting protection in monkeys challenged 3 or 7 days later with a genetically heterologous lineage II isolate of LASV from Nigeria, while nonspecifically vaccinated control animals succumb to challenge. The rVSVΔG-LASV-GPC vaccine induces rapid activation of adaptive immunity and the transcription of natural killer (NK) cell-affiliated mRNAs. This study demonstrates that rVSVΔG-LASV-GPC may provide rapid protection in humans against LASV infections in cases where immediate public-health intervention is required. [Display omitted] • Recombinant VSV vaccine provides rapid immunity to Lassa virus infection in monkeys There are currently no approved vaccines for Lassa fever in humans. Cross et al. show that vaccination with recombinant VSV-LASV-GPC (lineage IV) provides rapid heterologous protection against Lassa (lineage II) infection as early as 3 days post-vaccination. [ABSTRACT FROM AUTHOR]

The glycoprotein (GP) of ebolaviruses participates in a critical membrane fusion process to establish infection of a cell and therefore, represents an important target of both vaccines and antivirals. The latest reports on pan-ebolavirus monoclonal antibodies in small animal models may offer promising outcomes and insight into how best to target the GP in vaccine and antiviral discovery. [ABSTRACT FROM AUTHOR]

Summary: Kelch-like ECH-associated protein 1 (Keap1) is a ubiquitin E3 ligase specificity factor that targets transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) for ubiquitination and degradation. Disrupting Keap1-Nrf2 interaction stabilizes Nrf2, resulting in Nrf2 nuclear accumulation, binding to antioxidant response elements (AREs), and transcription of cytoprotective genes. Marburg virus (MARV) is a zoonotic pathogen that likely uses bats as reservoir hosts. We demonstrate that MARV protein VP24 (mVP24) binds the Kelch domain of either human or bat Keap1. This binding is of high affinity and 1:1 stoichiometry and activates Nrf2. Modeling based on the Zaire ebolavirus (EBOV) VP24 (eVP24) structure identified in mVP24 an acidic loop (K-loop) critical for Keap1 interaction. Transfer of the K-loop to eVP24, which otherwise does not bind Keap1, confers Keap1 binding and Nrf2 activation, and infection by MARV, but not EBOV, activates ARE gene expression. Therefore, MARV targets Keap1 to activate Nrf2-induced cytoprotective responses during infection. [Copyright &y& Elsevier]

Exotic and emerging viral pathogens associated with high morbidity and mortality in humans are being identified annually with recent examples including Lujo virus in southern Africa, Severe Fever with Thrombocytopenia Syndrome virus in China and a SARS-like coronavirus in the Middle East. The sporadic nature of these infections hampers our understanding of these diseases and limits the opportunities to design appropriate medical countermeasures against them. Because of this, animal models are utilized to gain insight into the pathogenesis of disease with the overall goal of identifying potential targets for intervention and evaluating specific therapeutics and vaccines. For these reasons it is imperative that animal models of disease recapitulate the human condition as closely as possible in order to provide the best predictive data with respect to the potential efficacy in humans. In this article we review the current status of disease models for highly pathogenic and emerging viral pathogens. [Copyright &y& Elsevier]

Abstract: Considerable progress has been made over the last decade in developing candidate preventive vaccines that can protect nonhuman primates against Ebola and Marburg viruses. A vaccine based on recombinant vesicular stomatitis virus (VSV) seems to be particularly robust as it can also confer protection when administered as a postexposure treatment. While filoviruses are not thought to be transmitted by aerosol in nature the inhalation route is among the most likely portals of entry in the setting of a bioterrorist event. At present, all candidate filoviral vaccines have been evaluated against parenteral challenges but none have been tested against an aerosol exposure. Here, we evaluated our recombinant VSV-based Zaire ebolavirus (ZEBOV) and Marburg virus (MARV) vaccines against aerosol challenge in cynomolgus macaques. All monkeys vaccinated with a VSV vector expressing the glycoprotein of ZEBOV were completely protected against an aerosol exposure of ZEBOV. Likewise, all monkeys vaccinated with a VSV vector expressing the glycoprotein of MARV were completely protected against an aerosol exposure of MARV. All control animals challenged by the aerosol route with either ZEBOV or MARV succumbed. Interestingly, disease in control animals appeared to progress slower than previously seen in macaques exposed to comparable doses by intramuscular injection. [Copyright &y& Elsevier]

Abstract: Ebola hemorrhagic fever is a severe viral infection characterized by fever, shock and coagulation defects. Recent studies in macaques show that major features of illness are caused by effects of viral replication on macrophages and dendritic cells. Infected macrophages produce proinflammatory cytokines, chemokines and tissue factor, attracting additional target cells and inducing vasodilatation, increased vascular permeability and disseminated intravascular coagulation. However, they cannot restrict viral replication, possibly because of suppression of interferon responses. Infected dendritic cells also secrete proinflammatory mediators, but cannot initiate antigen-specific responses. In consequence, virus disseminates to these and other cell types throughout the body, causing multifocal necrosis and a syndrome resembling septic shock. Massive “bystander” apoptosis of natural killer and T cells further impairs immunity. These findings suggest that modifying host responses would be an effective therapeutic strategy, and treatment of infected macaques with a tissue-factor inhibitor reduced both inflammation and viral replication and improved survival. [Copyright &y& Elsevier]

Hendra virus and Nipah virus (NiV), members of the Henipavirus (HNV) genus, are zoonotic paramyxoviruses known to cause severe disease across six mammalian orders, including humans. We isolated a panel of human monoclonal antibodies (mAbs) from the B cells of an individual with prior exposure to equine Hendra virus (HeV) vaccine, targeting distinct antigenic sites. The most potent class of cross-reactive antibodies achieves neutralization by blocking viral attachment to the host cell receptors ephrin-B2 and ephrin-B3, with a second class being enhanced by receptor binding. mAbs from both classes display synergistic activity in vitro. In a stringent hamster model of NiV Bangladesh (NiV B) infection, antibodies from both classes reduce morbidity and mortality and achieve synergistic protection in combination. These candidate mAbs might be suitable for use in a cocktail therapeutic approach to achieve synergistic potency and reduce the risk of virus escape. [Display omitted] • Antibodies targeting the henipavirus receptor-binding protein (RBP) were isolated • Two potently neutralizing mAbs, HENV-103 and HENV-117, bind to distinct sites on the RPB • HENV-103 and HENV-117 delivered as a cocktail display enhanced protection in hamsters Doyle et al. describe two human monoclonal antibodies that target the henipavirus receptor-binding protein, HENV-103 and HENV-117, that display highly potent activity in vitro and enhanced therapeutic efficacy in vivo when delivered as a cocktail. [ABSTRACT FROM AUTHOR]

Passive transfer of convalescent plasma or serum is a time-honored strategy for treating infectious diseases. Human convalescent plasma containing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently being used to treat patients with coronavirus disease 2019 where clinical efficacy trials are ongoing. Here, we assess therapeutic passive transfer in groups of SARS-CoV-2-infected African green monkeys with convalescent sera containing either high or low anti-SARS-CoV-2 neutralizing antibody titers. Differences in viral load and pathology are minimal between monkeys that receive the lower titer convalescent sera and untreated controls. However, lower levels of SARS-CoV-2 in respiratory compartments, reduced severity of virus-associated lung pathology, and reductions in coagulopathy and inflammatory processes are observed in monkeys that receive high titer sera versus untreated controls. Our data indicate that convalescent plasma therapy in humans may be an effective strategy provided that donor sera contain high anti-SARS-CoV-2 neutralizing titers given in early stages of the disease. • Treatment with convalescent sera mitigates COVID-19 severity in nonhuman primates • Sera with high SARS-CoV-2 neutralizing antibody titers show the greatest benefit • Data suggest passive transfer as a therapy in humans in early stages of disease Rapid development of postexposure therapies is necessary for emerging viral threats such as SARS-CoV-2. Cross et al. demonstrate therapeutic reduction of disease severity using convalescent sera with high concentrations of SARS-CoV-2 neutralizing antibodies in the African green monkey model of COVID-19, suggesting this as a possible treatment approach in humans. [ABSTRACT FROM AUTHOR]

Zaire ebolavirus (EBOV) VP35 protein is a suppressor of type I interferon (IFN) production, an inhibitor of dendritic cell maturation, and a putative virulence determinant. Here, a recombinant EBOV encoding a mutant VP35 virus (VP35m) is demonstrated to activate RIG-I-like receptor signaling and innate antiviral pathways. When inoculated into cynomolgus macaques, VP35m exhibits dramatic attenuation as compared to wild-type EBOV (wtEBOV), with 20 or 300 times the standard 100% lethal challenge dose not causing EBOV disease (EVD). Further, VP35m infection, despite limited replication in vivo , activates antigen presentation and innate immunity pathways and elicits increased frequencies of proliferating memory T cells and B cells and production of anti-EBOV antibodies. Upon wtEBOV challenge, VP35m-immunized animals survive, exhibiting host responses consistent with an orderly immune response and the absence of excessive inflammation. These data demonstrate that VP35 is a critical EBOV immune evasion factor and provide insights into immune mechanisms of EBOV control. • A VP35 mutant Ebola virus (VP35m) induces MAVS-dependent interferon responses • VP35m is highly attenuated in cynomolgus macaques • VP35m elicits robust adaptive immune responses despite minimal replication in vivo • VP35m protects cynomolgus macaques from challenge with wild-type Ebola virus Woolsey et al. demonstrate that immune evasion functions of the Ebola virus VP35 protein are critical for virulence in non-human primates. A VP35 mutant Ebola virus does not cause lethal disease and instead elicits adaptive immune responses that can protect animals from wild-type Ebola virus challenge. [ABSTRACT FROM AUTHOR]

[Display omitted] Although two vaccines for Zaire ebolavirus (EBOV) have been licensed and deployed successfully to combat recurring outbreaks of Ebolavirus Disease in West Africa, there are no vaccines for two other highly pathogenic members of the Filoviridae , Sudan ebolavirus (SUDV) and Marburg marburgvirus (MARV). The results described herein document the immunogenicity and protective efficacy in cynomolgus macaques of a single-vial, thermostabilized (lyophilized) monovalent (SUDV) and bivalent (SUDV & MARV) protein vaccines consisting of recombinant glycoproteins (GP) formulated with a clinical-grade oil-in-water nanoemulsion adjuvant (CoVaccine HT™). Lyophilized formulations of the vaccines were reconstituted with Water for Injection and used to immunize groups of cynomolgus macaques before challenge with a lethal dose of a human SUDV or MARV isolate. Sera collected after each of the three immunizations showed near maximal GP-binding IgG concentrations starting as early as the second dose. Most importantly, the vaccine candidates (monovalent or bivalent) provided 100% protection against severe and lethal filovirus disease after either SUDV or MARV infection. Although mild, subclinical infection was observed in a few macaques, all vaccinated animals remained healthy and survived the filovirus challenge. These results demonstrate the value that thermostabilized protein vaccines could provide for addressing an important gap in preparedness for future filovirus outbreaks. [ABSTRACT FROM AUTHOR]

An abstract of the article "Development of an siRNA Based Therapy for Ebola Virus Infection," by Thomas W. Geisbert and colleagues is presented.

Iminosugars are host-directed antivirals with broad-spectrum activity. The iminosugar, N -butyl-deoxynojirimycin ( N B-DNJ or Miglustat ® ), is used in humans for treatment of Gaucher's disease and has mild antiviral properties. More potent analogs of N B-DNJ have been generated and have demonstrated activity against a variety of viruses including flaviviruses, influenza, herpesviruses and filoviruses. In the current study, a panel of analogs based on N B-DNJ was analyzed for activity against Ebola (EBOV) and Marburg viruses (MARV). The antiviral activity of N B-DNJ (UV-1), UV-2, UV-3, UV-4 and UV-5 against both EBOV and MARV was demonstrated in Vero cells. Subsequent studies to examine the activity of UV-4 and UV-5 using rodent models of EBOV and MARV were performed. In vivo efficacy studies provided inconsistent data following treatment with iminosugars using filovirus mouse models. A tolerability study in nonhuman primates demonstrated that UV-4 could be administered at much higher dose levels than rodents. Since UV-4 was active in vitro , had been demonstrated to be active against influenza and dengue in vivo , and was being tested in a Phase 1 clinical trial, a small proof-of-concept nonhuman primate trial was performed to determine whether this antiviral candidate could provide clinical benefit to EBOV-infected individuals. Administration of UV-4B did not provide a clinical or survival benefit to macaques infected with EBOV–Makona; however, dosing of animals was not optimal in this study. Efficacy may be improved by thrice daily dosing (e.g. by nasogastric tube feeding) to match the efficacious dosing regimens demonstrated against dengue and influenza viruses. [ABSTRACT FROM AUTHOR]

Lassa fever is a significant health threat to West African human populations with hundreds of thousands of annual cases. There are no approved medical countermeasures currently available. Compassionate use of the antiviral drug ribavirin or transfusion of convalescent serum has resulted in mixed success depending on when administered or the donor source, respectively. We previously identified several recombinant human monoclonal antibodies targeting the glycoprotein of Lassa virus with strong neutralization profiles in vitro . Here, we demonstrate remarkable therapeutic efficacy using first-in-class human antibodies in a guinea pig model of Lassa infection thereby presenting a promising treatment alternative. [ABSTRACT FROM AUTHOR]

Nipah virus (NiV) and Hendra virus (HeV) are highly pathogenic, bat-borne paramyxoviruses in the genus Henipavirus that cause severe and often fatal acute respiratory and/or neurologic diseases in humans and livestock. There are currently no approved antiviral therapeutics or vaccines for use in humans to treat or prevent NiV or HeV infection. To facilitate development of henipavirus antivirals, a high-throughput screening (HTS) platform was developed based on a well-characterized recombinant version of the nonpathogenic Henipavirus , Cedar virus (rCedV). Using reverse genetics, a rCedV encoding firefly luciferase (rCedV-Luc) was rescued and its utility evaluated for high-throughput antiviral compound screening. The luciferase reporter gene signal kinetics of rCedV-Luc in different human cell lines was characterized and validated as an authentic real-time measure of viral growth. The rCedV-Luc platform was optimized as an HTS assay that demonstrated high sensitivity with robust Z′ scores, excellent signal-to-background ratios and coefficients of variation. Eight candidate compounds that inhibited rCedV replication were identified for additional validation and demonstrated that 4 compounds inhibited authentic NiV-Bangladesh replication. Further evaluation of 2 of the 4 validated compounds in a 9-point dose response titration demonstrated potent antiviral activity against NiV-Bangladesh and HeV, with minimal cytotoxicity. This rCedV reporter can serve as a surrogate yet authentic BSL-2 henipavirus platform that will dramatically accelerate drug candidate identification in the development of anti-henipavirus therapies. • A high-throughput screening assay using the Henipavirus , Cedar virus, encoding luciferase (rCedV-Luc) was established. • A large diverse small molecule library was screened for compounds that inhibited rCedV-Luc infection and replication. • 4 compounds that inhibited rCedV replication also inhibited authentic Nipah virus replication. • 2 compounds had IC 50 concentrations of less than 10 μM for Nipah virus and less than 20 μM for Hendra virus. • rCedV-Luc is an authentic henipavirus platform that will accelerate the development of anti-henipavirus countermeasures. [ABSTRACT FROM AUTHOR]