Mechanism of human antibody-mediated neutralization of Marburg virus.

The mechanisms by which neutralizing antibodies inhibit Marburg virus (MARV) are not known. We isolated a panel of neutralizing antibodies from a human MARV survivor that bind to MARV glycoprotein (GP) and compete for binding to a single major antigenic site. Remarkably, several of the antibodies also bind to Ebola virus (EBOV) GP. Single-particle EM structures of antibody-GP complexes reveal that all of the neutralizing antibodies bind to MARV GP at or near the predicted region of the receptor-binding site. The presence of the glycan cap or mucin-like domain blocks binding of neutralizing antibodies to EBOV GP, but not to MARV GP. The data suggest that MARV-neutralizing antibodies inhibit virus by binding to infectious virions at the exposed MARV receptor-binding site, revealing a mechanism of filovirus inhibition.

Characterization of Ebola Virus Mucosal Challenge Routes in Cynomolgus Macaques.

Zaïre ebolavirus (EBOV) causes Ebola virus disease (EVD), a devastating viral hemorrhagic fever in humans. Nonhuman primate (NHP) models of EVD traditionally use intramuscular infection with higher case fatality rates and reduced mean time-to-death compared to contact transmission typical of human cases of EVD. A cynomolgus macaque model of oral and conjunctival EBOV was used to further characterize the more clinically relevant contact transmission of EVD. NHPs challenged via the oral route had an overall 50% survival rate. NHPs challenged with a target dose of 1 × 102 PFU or 1 × 104 PFU of EBOV via the conjunctival route had 40% and 100% mortality, respectively. Classic signs of lethal EVD-like disease were observed in all NHPs that succumbed to EBOV infection including viremia, hematological abnormalities, clinical chemistries indicative of hepatic and renal disease, and histopathological findings. Evidence of EBOV viral persistence in the eye was observed in NHPs challenged via the conjunctival route. IMPORTANCE This study is the first to examine the Kikwit strain of EBOV, the most commonly used strain, in the gold-standard macaque model of infection. Additionally, this is the first description of the detection of virus in the vitreous fluid, an immune privileged site that has been proposed as a viral reservoir, following conjunctival challenge. The oral and conjunctival macaque challenge model of EVD described here more faithfully recapitulates the prodrome that has been reported for human EVD. This work paves the way for more advanced studies to model contact transmission of EVD, including early events in mucosal infection and immunity, as well as the establishment of persistent viral infection and the emergence from these reservoirs.

Characterization and Demonstration of the Value of a Lethal Mouse Model of Middle East Respiratory Syndrome Coronavirus Infection and Disease.

UNLABELLED: Characterized animal models are needed for studying the pathogenesis of and evaluating medical countermeasures for persisting Middle East respiratory syndrome-coronavirus (MERS-CoV) infections. Here, we further characterized a lethal transgenic mouse model of MERS-CoV infection and disease that globally expresses human CD26 (hCD26)/DPP4. The 50% infectious dose (ID50) and lethal dose (LD50) of virus were estimated to be <1 and 10 TCID50 of MERS-CoV, respectively. Neutralizing antibody developed in the surviving mice from the ID50/LD50 determinations, and all were fully immune to challenge with 100 LD50 of MERS-CoV. The tissue distribution and histopathology in mice challenged with a potential working dose of 10 LD50 of MERS-CoV were subsequently evaluated. In contrast to the overwhelming infection seen in the mice challenged with 10(5) LD50 of MERS-CoV, we were able to recover infectious virus from these mice only infrequently, although quantitative reverse transcription-PCR (qRT-PCR) tests indicated early and persistent lung infection and delayed occurrence of brain infection. Persistent inflammatory infiltrates were seen in the lungs and brain stems at day 2 and day 6 after infection, respectively. While focal infiltrates were also noted in the liver, definite pathology was not seen in other tissues. Finally, using a receptor binding domain protein vaccine and a MERS-CoV fusion inhibitor, we demonstrated the value of this model for evaluating vaccines and antivirals against MERS. As outcomes of MERS-CoV infection in patients differ greatly, ranging from asymptomatic to overwhelming disease and death, having available both an infection model and a lethal model makes this transgenic mouse model relevant for advancing MERS research. IMPORTANCE: Fully characterized animal models are essential for studying pathogenesis and for preclinical screening of vaccines and drugs against MERS-CoV infection and disease. When given a high dose of MERS-CoV, our transgenic mice expressing hCD26/DPP4 viral receptor uniformly succumbed to death within 6 days, making it difficult to evaluate host responses to infection and disease. We further characterized this model by determining both the ID50 and the LD50 of MERS-CoV in order to establish both an infection model and a lethal model for MERS and followed this by investigating the antibody responses and immunity of the mice that survived MERS-CoV infection. Using the estimated LD50 and ID50 data, we dissected the kinetics of viral tissue distribution and pathology in mice challenged with 10 LD50 of virus and utilized the model for preclinical evaluation of a vaccine and drug for treatment of MERS-CoV infection. This further-characterized transgenic mouse model will be useful for advancing MERS research.

Generation of a transgenic mouse model of Middle East respiratory syndrome coronavirus infection and disease.

UNLABELLED: The emergence of Middle East respiratory syndrome-coronavirus (MERS-CoV) in the Middle East since 2012 has caused more than 900 human infections with ∼40% mortality to date. Animal models are needed for studying pathogenesis and for development of preventive and therapeutic agents against MERS-CoV infection. Nonhuman primates (rhesus macaques and marmosets) are expensive models of limited availability. Although a mouse lung infection model has been described using adenovirus vectors expressing human CD26/dipeptidyl peptidase 4 (DPP4), it is believed that a transgenic mouse model is needed for MERS-CoV research. We have developed this transgenic mouse model as indicated in this study. We show that transgenic mice globally expressing hCD26/DPP4 were fully permissive to MERS-CoV infection, resulting in relentless weight loss and death within days postinfection. High infectious virus titers were recovered primarily from the lungs and brains of mice at 2 and 4 days postinfection, respectively, whereas viral RNAs were also detected in the heart, spleen, and intestine, indicating a disseminating viral infection. Infected Tg(+) mice developed a progressive pneumonia, characterized by extensive inflammatory infiltration. In contrast, an inconsistent mild perivascular cuffing was the only pathological change associated with the infected brains. Moreover, infected Tg(+) mice were able to activate genes encoding for many antiviral and inflammatory mediators within the lungs and brains, coinciding with the high levels of viral replication. This new and unique transgenic mouse model will be useful for furthering knowledge of MERS pathogenesis and for the development of vaccine and treatments against MERS-CoV infection. IMPORTANCE: Small and economical animal models are required for the controlled and extensive studies needed for elucidating pathogenesis and development of vaccines and antivirals against MERS. Mice are the most desirable small-animal species for this purpose because of availability and the existence of a thorough knowledge base, particularly of genetics and immunology. The standard small animals, mice, hamsters, and ferrets, all lack the functional MERS-CoV receptor and are not susceptible to infection. So, initial studies were done with nonhuman primates, expensive models of limited availability. A mouse lung infection model was described where a mouse adenovirus was used to transfect lung cells for receptor expression. Nevertheless, all generally agree that a transgenic mouse model expressing the DPP4 receptor is needed for MERS-CoV research. We have developed this transgenic mouse model as indicated in this study. This new and unique transgenic mouse model will be useful for furthering MERS research.

Role of protein phosphatase 1 in dephosphorylation of Ebola virus VP30 protein and its targeting for the inhibition of viral transcription.

The filovirus Ebola (EBOV) causes the most severe hemorrhagic fever known. The EBOV RNA-dependent polymerase complex includes a filovirus-specific VP30, which is critical for the transcriptional but not replication activity of EBOV polymerase; to support transcription, VP30 must be in a dephosphorylated form. Here we show that EBOV VP30 is phosphorylated not only at the N-terminal serine clusters identified previously but also at the threonine residues at positions 143 and 146. We also show that host cell protein phosphatase 1 (PP1) controls VP30 dephosphorylation because expression of a PP1-binding peptide cdNIPP1 increased VP30 phosphorylation. Moreover, targeting PP1 mRNA by shRNA resulted in the overexpression of SIPP1, a cytoplasm-shuttling regulatory subunit of PP1, and increased EBOV transcription, suggesting that cytoplasmic accumulation of PP1 induces EBOV transcription. Furthermore, we developed a small molecule compound, 1E7-03, that targeted a non-catalytic site of PP1 and increased VP30 dephosphorylation. The compound inhibited the transcription but increased replication of the viral genome and completely suppressed replication of EBOV in cultured cells. Finally, mutations of Thr(143) and Thr(146) of VP30 significantly inhibited EBOV transcription and strongly induced VP30 phosphorylation in the N-terminal Ser residues 29-46, suggesting a novel mechanism of regulation of VP30 phosphorylation. Our findings suggest that targeting PP1 with small molecules is a feasible approach to achieve dysregulation of the EBOV polymerase activity. This novel approach may be used for the development of antivirals against EBOV and other filovirus species.

Evaluation of molnupiravir (EIDD-2801) efficacy against SARS-CoV-2 in the rhesus macaque model.

Molnupiravir (EIDD-2801) is a prodrug of a ribonucleoside analogue that is currently being used under a US FDA emergency use authorization for the treatment of mild to moderate COVID-19. We evaluated molnupiravir for efficacy as an oral treatment in the rhesus macaque model of SARS-CoV-2 infection. Twenty non-human primates (NHPs) were challenged with SARS-CoV-2 and treated with 75 mg/kg (n = 8) or 250 mg/kg (n = 8) of molnupiravir twice daily by oral gavage for 7 days. The NHPs were observed for 14 days post-challenge and monitored for clinical signs of disease. After challenge, all groups showed a trend toward increased respiration rates. Treatment with molnupiravir significantly reduced viral RNA levels in bronchoalveolar lavage (BAL) samples at Days 7 and 10. Considering the mild to moderate nature of SARS-CoV-2 infection in the rhesus macaque model, this study highlights the importance of monitoring the viral load in the lung as an indicator of pharmaceutical efficacy for COVID-19 treatments. Additionally, this study provides evidence of the efficacy of molnupiravir which supplements the current ongoing clinical trials of this drug.

Cell-Type Apoptosis in Lung during SARS-CoV-2 Infection.

The SARS-CoV-2 pandemic has inspired renewed interest in understanding the fundamental pathology of acute respiratory distress syndrome (ARDS) following infection. However, the pathogenesis of ARDS following SRAS-CoV-2 infection remains largely unknown. In the present study, we examined apoptosis in postmortem lung sections from COVID-19 patients and in lung tissues from a non-human primate model of SARS-CoV-2 infection, in a cell-type manner, including type 1 and 2 alveolar cells and vascular endothelial cells (ECs), macrophages, and T cells. Multiple-target immunofluorescence assays and Western blotting suggest both intrinsic and extrinsic apoptotic pathways are activated during SARS-CoV-2 infection. Furthermore, we observed that SARS-CoV-2 fails to induce apoptosis in human bronchial epithelial cells (i.e., BEAS2B cells) and primary human umbilical vein endothelial cells (HUVECs), which are refractory to SARS-CoV-2 infection. However, infection of co-cultured Vero cells and HUVECs or Vero cells and BEAS2B cells with SARS-CoV-2 induced apoptosis in both Vero cells and HUVECs/BEAS2B cells but did not alter the permissiveness of HUVECs or BEAS2B cells to the virus. Post-exposure treatment of the co-culture of Vero cells and HUVECs with a novel non-cyclic nucleotide small molecule EPAC1-specific activator reduced apoptosis in HUVECs. These findings may help to delineate a novel insight into the pathogenesis of ARDS following SARS-CoV-2 infection.

Cell-type apoptosis in lung during SARS-CoV-2 infection.

The SARS-CoV-2 pandemic has inspired renewed interest in understanding the fundamental pathology of acute respiratory distress syndrome (ARDS) following infection because fatal COVID-19 cases are commonly linked to respiratory failure due to ARDS. The pathologic alteration known as diffuse alveolar damage in endothelial and epithelial cells is a critical feature of acute lung injury in ARDS. However, the pathogenesis of ARDS following SRAS-CoV-2 infection remains largely unknown. In the present study, we examined apoptosis in post-mortem lung sections from COVID-19 patients and lung tissues from a non-human primate model of SARS-CoV-2 infection, in a cell-type manner, including type 1 and 2 alveolar cells and vascular endothelial cells (ECs), macrophages, and T cells. Multiple-target immunofluorescence (IF) assays and western blotting suggest both intrinsic and extrinsic apoptotic pathways are activated during SARS-CoV-2 infection. Furthermore, we observed that SARS-CoV-2 fails to induce apoptosis in human bronchial epithelial cells (i.e., BEAS2B cells) and primary human umbilical vein endothelial cells (HUVECs), which are refractory to SARS-CoV-2 infection. However, infection of co-cultured Vero cells and HUVECs or Vero cells and BEAS2B cells with SARS-CoV-2 induced apoptosis in both Vero cells and HUVECs/BEAS2B cells, but did not alter the permissiveness of HUVECs or BEAS2B cells to the virus. Post-exposure treatment of the co-culture of Vero cells and HUVECs with an EPAC1-specific activator ameliorated apoptosis in HUVECs. These findings may help to delineate a novel insight into the pathogenesis of ARDS following SARS-CoV-2 infection.

Recombinant Human Decorin Inhibits TGF-b1 Induced Contraction of Collagen Lattice by Keloid Fibroblasts.

While wound contraction plays an important role in healing, it may lead to excessive scar formation and pathological wound contracture in extreme conditions. To date, the key regulator of wound contraction and keloid formation is transforming growth factor-beta (TGF-b1). Decorin has been reported to bind TGF-b1 and neutralize some of its activities. The present study investigated whether decorin affected TGF-b1-induced fibroblast contractile activity by using fibroblast-populated collagen lattice (FPCL), which has been generally used as an in-vitro model thought to mimic wound contraction in vivo, modified by the incorporation of recombinant human decorin into collagen gel. As expected, TGF-b1 significantly enhanced the contraction of collagen gel at hour 12, 24, 48, 72, and 96 (P < 0.05). Recombinant human decorin inhibited both the basal and TGF-b1-enhanced contraction of collagen gel by keloid fibroblasts (P < 0.05). These inhibitory effects of recombinant human decorin were associated with suppression of TGF-b1-induced filamentous actin (F-actin) expression in keloid fibroblasts. Furthermore, recombinant human decorin inhibited TGF-b1 induced a-smooth muscle actin (a-SMA), PAI-1 (plasminogen activator inhibitor-1) protein, and mRNA expressions in keloid fibroblasts (P < 0.05). These data indicate that recombinant human decorin can suppress TGF-b1-induced contraction of collagen gel by keloid fibroblasts. Moreover, decorin can inhibit basal contraction of collagen gel by keloid fibroblasts. These results suggest that decorin may have therapeutic potential for excessive skin contraction as observed in a keloid. .

Immunization with inactivated Middle East Respiratory Syndrome coronavirus vaccine leads to lung immunopathology on challenge with live virus.

To determine if a hypersensitive-type lung pathology might occur when mice were given an inactivated MERS-CoV vaccine and challenged with infectious virus as was seen with SARS-CoV vaccines, we prepared and vaccinated mice with an inactivated MERS-CoV vaccine. Neutralizing antibody was induced by vaccine with and without adjuvant and lung virus was reduced in vaccinated mice after challenge. Lung mononuclear infiltrates occurred in all groups after virus challenge but with increased infiltrates that contained eosinophils and increases in the eosinophil promoting IL-5 and IL-13 cytokines only in the vaccine groups. Inactivated MERS-CoV vaccine appears to carry a hypersensitive-type lung pathology risk from MERS-CoV infection that is similar to that found with inactivated SARS-CoV vaccines from SARS-CoV infection.

Passive Transfer of A Germline-like Neutralizing Human Monoclonal Antibody Protects Transgenic Mice Against Lethal Middle East Respiratory Syndrome Coronavirus Infection.

Middle East Respiratory Syndrome coronavirus (MERS-CoV) has repeatedly caused outbreaks in the Arabian Peninsula. To date, no approved medical countermeasures (MCM) are available to combat MERS-CoV infections. Several neutralizing human monoclonal antibodies (mAbs), including m336, a germline-like human mAb, have been chosen as promising MCM for MERS-CoV. However, their clinical development has been hindered by the lack of a robust animal model that recapitulate the morbidity and mortality of human infections. We assessed the prophylactic and therapeutic efficacy of m336 by using well-characterized transgenic mice shown to be highly sensitive to MERS-CoV infection and disease. We found that mice treated with m336 prior to or post lethal MERS-CoV challenging were fully protected, compared to control mice which sufferered from profound weight loss and uniform death within days after infection. Taken together, these results support further development of m336 and other human monoclonal antibodies as potential therapeutics for MERS-CoV infection.

Identification of an ideal adjuvant for receptor-binding domain-based subunit vaccines against Middle East respiratory syndrome coronavirus.

Middle East respiratory syndrome (MERS), an emerging infectious disease caused by MERS coronavirus (MERS-CoV), has garnered worldwide attention as a consequence of its continuous spread and pandemic potential, making the development of effective vaccines a high priority. We previously demonstrated that residues 377-588 of MERS-CoV spike (S) protein receptor-binding domain (RBD) is a very promising MERS subunit vaccine candidate, capable of inducing potent neutralization antibody responses. In this study, we sought to identify an adjuvant that optimally enhanced the immunogenicity of S377-588 protein fused with Fc of human IgG (S377-588-Fc). Specifically, we compared several commercially available adjuvants, including Freund's adjuvant, aluminum, Monophosphoryl lipid A, Montanide ISA51 and MF59 with regard to their capacity to enhance the immunogenicity of this subunit vaccine. In the absence of adjuvant, S377-588-Fc alone induced readily detectable neutralizing antibody and T-cell responses in immunized mice. However, incorporating an adjuvant improved its immunogenicity. Particularly, among the aforementioned adjuvants evaluated, MF59 is the most potent as judged by its superior ability to induce the highest titers of IgG, IgG1 and IgG2a subtypes, and neutralizing antibodies. The addition of MF59 significantly augmented the immunogenicity of S377-588-Fc to induce strong IgG and neutralizing antibody responses as well as protection against MERS-CoV infection in mice, suggesting that MF59 is an optimal adjuvant for MERS-CoV RBD-based subunit vaccines.

Aerosolized Ebola vaccine protects primates and elicits lung-resident T cell responses.

Direct delivery of aerosolized vaccines to the respiratory mucosa elicits both systemic and mucosal responses. This vaccine strategy has not been tested for Ebola virus (EBOV) or other hemorrhagic fever viruses. Here, we examined the immunogenicity and protective efficacy of an aerosolized human parainfluenza virus type 3-vectored vaccine that expresses the glycoprotein (GP) of EBOV (HPIV3/EboGP) delivered to the respiratory tract. Rhesus macaques were vaccinated with aerosolized HPIV3/EboGP, liquid HPIV3/EboGP, or an unrelated, intramuscular, Venezuelan equine encephalitis replicon vaccine expressing EBOV GP. Serum and mucosal samples from aerosolized HPIV3/EboGP recipients exhibited high EBOV-specific IgG, IgA, and neutralizing antibody titers, which exceeded or equaled titers observed in liquid recipients. The HPIV3/EboGP vaccine induced an EBOV-specific cellular response that was greatest in the lungs and yielded polyfunctional CD8+ T cells, including a subset that expressed CD103 (αE integrin), and CD4+ T helper cells that were predominately type 1. The magnitude of the CD4+ T cell response was greater in aerosol vaccinees. The HPIV3/EboGP vaccine produced a more robust cell-mediated and humoral immune response than the systemic replicon vaccine. Moreover, 1 aerosol HPIV3/EboGP dose conferred 100% protection to macaques exposed to EBOV. Aerosol vaccination represents a useful and feasible vaccination mode that can be implemented with ease in a filovirus disease outbreak situation.

Immunization with SARS coronavirus vaccines leads to pulmonary immunopathology on challenge with the SARS virus.

BACKGROUND: Severe acute respiratory syndrome (SARS) emerged in China in 2002 and spread to other countries before brought under control. Because of a concern for reemergence or a deliberate release of the SARS coronavirus, vaccine development was initiated. Evaluations of an inactivated whole virus vaccine in ferrets and nonhuman primates and a virus-like-particle vaccine in mice induced protection against infection but challenged animals exhibited an immunopathologic-type lung disease. DESIGN: Four candidate vaccines for humans with or without alum adjuvant were evaluated in a mouse model of SARS, a VLP vaccine, the vaccine given to ferrets and NHP, another whole virus vaccine and an rDNA-produced S protein. Balb/c or C57BL/6 mice were vaccinated i.m. on day 0 and 28 and sacrificed for serum antibody measurements or challenged with live virus on day 56. On day 58, challenged mice were sacrificed and lungs obtained for virus and histopathology. RESULTS: All vaccines induced serum neutralizing antibody with increasing dosages and/or alum significantly increasing responses. Significant reductions of SARS-CoV two days after challenge was seen for all vaccines and prior live SARS-CoV. All mice exhibited histopathologic changes in lungs two days after challenge including all animals vaccinated (Balb/C and C57BL/6) or given live virus, influenza vaccine, or PBS suggesting infection occurred in all. Histopathology seen in animals given one of the SARS-CoV vaccines was uniformly a Th2-type immunopathology with prominent eosinophil infiltration, confirmed with special eosinophil stains. The pathologic changes seen in all control groups lacked the eosinophil prominence. CONCLUSIONS: These SARS-CoV vaccines all induced antibody and protection against infection with SARS-CoV. However, challenge of mice given any of the vaccines led to occurrence of Th2-type immunopathology suggesting hypersensitivity to SARS-CoV components was induced. Caution in proceeding to application of a SARS-CoV vaccine in humans is indicated.

Recombinant human decorin inhibits TGF-beta1-induced contraction of collagen lattice by hypertrophic scar fibroblasts.

Decorin was reported to bind transforming growth factor-beta (TGF-beta(1)) and neutralise some of its activity as a key regulator of wound contraction and hypertrophic scar formation. In this study, we investigated whether recombinant human decorin affected TGF-beta(1)-induced fibroblast contractile activity, by using fibroblast-populated collagen lattice with decorin added to the collagen gel. Hypertrophic scar fibroblasts showed greater basal contraction of collagen gels than normal fibroblasts, and the addition of TGF-beta(1) significantly enhanced this. Decorin inhibited both the basal and TGF-beta(1)-enhanced contraction of collagen gel by both normal and hypertrophic scar fibroblasts. Decorin also inhibited TGF-beta(1)-induced alpha-smooth muscle actin (alpha-SMA), plasminogen activator inhibitor-1 (PAI-1) protein and mRNA expressions in normal and hypertrophic scar fibroblasts. These results suggest that decorin may have therapeutic potential for excessive skin contraction as observed in hypertrophic scarring.