Antibodies targeting a quaternary site on SARS-CoV-2 spike glycoprotein prevent viral receptor engagement by conformational locking.

SARS-CoV-2 continues to evolve, with many variants evading clinically authorized antibodies. To isolate monoclonal antibodies (mAbs) with broadly neutralizing capacities against the virus, we screened serum samples from convalescing COVID-19 patients. We isolated two mAbs, 12-16 and 12-19, which neutralized all SARS-CoV-2 variants tested, including the XBB subvariants, and prevented infection in hamsters challenged with Omicron BA.1 intranasally. Structurally, both antibodies targeted a conserved quaternary epitope located at the interface between the N-terminal domain and subdomain 1, uncovering a site of vulnerability on SARS-CoV-2 spike. These antibodies prevented viral receptor engagement by locking the receptor-binding domain (RBD) of spike in the down conformation, revealing a mechanism of virus neutralization for non-RBD antibodies. Deep mutational scanning showed that SARS-CoV-2 could mutate to escape 12-19, but such mutations are rarely found in circulating viruses. Antibodies 12-16 and 12-19 hold promise as prophylactic agents for immunocompromised persons who do not respond robustly to COVID-19 vaccines.

Coronaviruses exploit a host cysteine-aspartic protease for replication.

Highly pathogenic coronaviruses, including severe acute respiratory syndrome coronavirus 2 (refs. 1,2) (SARS-CoV-2), Middle East respiratory syndrome coronavirus3 (MERS-CoV) and SARS-CoV-1 (ref. 4), vary in their transmissibility and pathogenicity. However, infection by all three viruses results in substantial apoptosis in cell culture5-7 and in patient tissues8-10, suggesting a potential link between apoptosis and pathogenesis of coronaviruses. Here we show that caspase-6, a cysteine-aspartic protease of the apoptosis cascade, serves as an important host factor for efficient coronavirus replication. We demonstrate that caspase-6 cleaves coronavirus nucleocapsid proteins, generating fragments that serve as interferon antagonists, thus facilitating virus replication. Inhibition of caspase-6 substantially attenuates lung pathology and body weight loss in golden Syrian hamsters infected with SARS-CoV-2 and improves the survival of mice expressing human DPP4 that are infected with mouse-adapted MERS-CoV. Our study reveals how coronaviruses exploit a component of the host apoptosis cascade to facilitate virus replication.

Clofazimine broadly inhibits coronaviruses including SARS-CoV-2.

The COVID-19 pandemic is the third outbreak this century of a zoonotic disease caused by a coronavirus, following the emergence of severe acute respiratory syndrome (SARS) in 20031 and Middle East respiratory syndrome (MERS) in 20122. Treatment options for coronaviruses are limited. Here we show that clofazimine-an anti-leprosy drug with a favourable safety profile3-possesses inhibitory activity against several coronaviruses, and can antagonize the replication of SARS-CoV-2 and MERS-CoV in a range of in vitro systems. We found that this molecule, which has been approved by the US Food and Drug Administration, inhibits cell fusion mediated by the viral spike glycoprotein, as well as activity of the viral helicase. Prophylactic or therapeutic administration of clofazimine in a hamster model of SARS-CoV-2 pathogenesis led to reduced viral loads in the lung and viral shedding in faeces, and also alleviated the inflammation associated with viral infection. Combinations of clofazimine and remdesivir exhibited antiviral synergy in vitro and in vivo, and restricted viral shedding from the upper respiratory tract. Clofazimine, which is orally bioavailable and comparatively cheap to manufacture, is an attractive clinical candidate for the treatment of outpatients and-when combined with remdesivir-in therapy for hospitalized patients with COVID-19, particularly in contexts in which costs are an important factor or specialized medical facilities are limited. Our data provide evidence that clofazimine may have a role in the control of the current pandemic of COVID-19 and-possibly more importantly-in dealing with coronavirus diseases that may emerge in the future.

Low Environmental Temperature Exacerbates Severe Acute Respiratory Syndrome Coronavirus 2 Infection in Golden Syrian Hamsters.

BACKGROUND: The effect of low environmental temperature on viral shedding and disease severity of Coronavirus Disease 2019 (COVID-19) is uncertain. METHODS: We investigated the virological, clinical, pathological, and immunological changes in hamsters housed at room (21°C), low (12-15°C), and high (30-33°C) temperature after challenge by 105 plaque-forming units of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). RESULTS: The nasal turbinate, trachea, and lung viral load and live virus titer were significantly higher (~0.5-log10 gene copies/ß-actin, P < .05) in the low-temperature group at 7 days postinfection (dpi). The low-temperature group also demonstrated significantly higher level of tumor necrosis factor-α, interferon-γ (IFN-γ), interleukin-1ß, and C-C motif chemokine ligand 3, and lower level of the antiviral IFN-α in lung tissues at 4 dpi than the other 2 groups. Their lungs were grossly and diffusely hemorrhagic, with more severe and diffuse alveolar and peribronchiolar inflammatory infiltration, bronchial epithelial cell death, and significantly higher mean total lung histology scores. By 7 dpi, the low-temperature group still showed persistent and severe alveolar inflammation and hemorrhage, and little alveolar cell proliferative changes of recovery. The viral loads in the oral swabs of the low-temperature group were significantly higher than those of the other two groups from 10 to 17 dpi by about 0.5-1.0 log10 gene copies/ß-actin. The mean neutralizing antibody titer of the low-temperature group was significantly (P < .05) lower than that of the room temperature group at 7 dpi and 30 dpi. CONCLUSIONS: This study provided in vivo evidence that low environmental temperature exacerbated the degree of virus shedding, disease severity, and tissue proinflammatory cytokines/chemokines expression, and suppressed the neutralizing antibody response of SARS-CoV-2-infected hamsters. Keeping warm in winter may reduce the severity of COVID-19.

Probable Animal-to-Human Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Delta Variant AY.127 Causing a Pet Shop-Related Coronavirus Disease 2019 (COVID-19) Outbreak in Hong Kong.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect human and other mammals, including hamsters. Syrian (Mesocricetus auratus) and dwarf (Phodopus sp.) hamsters are susceptible to SARS-CoV-2 infection in the laboratory setting. However, pet shop-related Coronavirus Disease 2019 (COVID-19) outbreaks have not been reported. METHODS: We conducted an investigation of a pet shop-related COVID-19 outbreak due to Delta variant AY.127 involving at least 3 patients in Hong Kong. We tested samples collected from the patients, environment, and hamsters linked to this outbreak and performed whole genome sequencing analysis of the reverse transcription polymerase chain reaction (RT-PCR)-positive samples. RESULTS: The patients included a pet shop keeper (Patient 1), a female customer of the pet shop (Patient 2), and the husband of Patient 2 (Patient 3). Investigation showed that 17.2% (5/29) and 25.5% (13/51) environmental specimens collected from the pet shop and its related warehouse, respectively, tested positive for SARS-CoV-2 RNA by RT-PCR. Among euthanized hamsters randomly collected from the storehouse, 3% (3/100) tested positive for SARS-CoV-2 RNA by RT-PCR and seropositive for anti-SARS-CoV-2 antibody by enzyme immunoassay. Whole genome analysis showed that although all genomes from the outbreak belonged to the Delta variant AY.127, there were at least 3 nucleotide differences among the genomes from different patients and the hamster cages. Genomic analysis suggests that multiple strains have emerged within the hamster population, and these different strains have likely transmitted to human either via direct contact or via the environment. CONCLUSIONS: Our study demonstrated probable hamster-to-human transmission of SARS-CoV-2. As pet trading is common around the world, this can represent a route of international spread of this pandemic virus.

Severe Acute Respiratory Syndrome Coronavirus 2 Infects and Damages the Mature and Immature Olfactory Sensory Neurons of Hamsters.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is primarily an acute respiratory tract infection. Distinctively, a substantial proportion of COVID-19 patients develop olfactory dysfunction. Especially in young patients, loss of smell can be the first or only symptom. The roles of inflammatory obstruction of the olfactory clefts, inflammatory cytokines affecting olfactory neuronal function, destruction of olfactory neurons or their supporting cells, and direct invasion of olfactory bulbs in causing olfactory dysfunction are uncertain. METHODS: We investigated the location for the pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from the olfactory epithelium (OE) to the olfactory bulb in golden Syrian hamsters. RESULTS: After intranasal inoculation with SARS-CoV-2, inflammatory cell infiltration and proinflammatory cytokine/chemokine responses were detected in the nasal turbinate tissues. The responses peaked between 2 and 4 days postinfection, with the highest viral load detected at day 2 postinfection. In addition to the pseudo-columnar ciliated respiratory epithelial cells, SARS-CoV-2 viral antigens were also detected in the mature olfactory sensory neurons labeled by olfactory marker protein, in the less mature olfactory neurons labeled by neuron-specific class III ß-tubulin at the more basal position, and in the sustentacular cells, resulting in apoptosis and severe destruction of the OE. During the entire course of infection, SARS-CoV-2 viral antigens were not detected in the olfactory bulb. CONCLUSIONS: In addition to acute inflammation at the OE, infection of mature and immature olfactory neurons and the supporting sustentacular cells by SARS-CoV-2 may contribute to the unique olfactory dysfunction related to COVID-19, which is not reported with SARS-CoV-2.

Coinfection by Severe Acute Respiratory Syndrome Coronavirus 2 and Influenza A(H1N1)pdm09 Virus Enhances the Severity of Pneumonia in Golden Syrian Hamsters.

BACKGROUND: Clinical outcomes of the interaction between the co-circulating pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and seasonal influenza viruses are unknown. METHODS: We established a golden Syrian hamster model coinfected by SARS-CoV-2 and mouse-adapted A(H1N1)pdm09 simultaneously or sequentially. The weight loss, clinical scores, histopathological changes, viral load and titer, and serum neutralizing antibody titer were compared with hamsters challenged by either virus. RESULTS: Coinfected hamsters had more weight loss, more severe lung inflammatory damage, and tissue cytokine/chemokine expression. Lung viral load, infectious virus titers, and virus antigen expression suggested that hamsters were generally more susceptible to SARS-CoV-2 than to A(H1N1)pdm09. Sequential coinfection with A(H1N1)pdm09 one day prior to SARS-CoV-2 exposure resulted in a lower lung SARS-CoV-2 titer and viral load than with SARS-CoV-2 monoinfection, but a higher lung A(H1N1)pdm09 viral load. Coinfection also increased intestinal inflammation with more SARS-CoV-2 nucleoprotein expression in enterocytes. Simultaneous coinfection was associated with delay in resolution of lung damage, lower serum SARS-CoV-2 neutralizing antibody, and longer SARS-CoV-2 shedding in oral swabs compared to that of SARS-CoV-2 monoinfection. CONCLUSIONS: Simultaneous or sequential coinfection by SARS-CoV-2 and A(H1N1)pdm09 caused more severe disease than monoinfection by either virus in hamsters. Prior A(H1N1)pdm09 infection lowered SARS-CoV-2 pulmonary viral loads but enhanced lung damage. Whole-population influenza vaccination for prevention of coinfection, and multiplex molecular diagnostics for both viruses to achieve early initiation of antiviral treatment for improvement of clinical outcome should be considered.

Simulation of the Clinical and Pathological Manifestations of Coronavirus Disease 2019 (COVID-19) in a Golden Syrian Hamster Model: Implications for Disease Pathogenesis and Transmissibility.

BACKGROUND: A physiological small-animal model that resembles COVID-19 with low mortality is lacking. METHODS: Molecular docking on the binding between angiotensin-converting enzyme 2 (ACE2) of common laboratory mammals and the receptor-binding domain of the surface spike protein of SARS-CoV-2 suggested that the golden Syrian hamster is an option. Virus challenge, contact transmission, and passive immunoprophylaxis studies were performed. Serial organ tissues and blood were harvested for histopathology, viral load and titer, chemokine/cytokine level, and neutralizing antibody titer. RESULTS: The Syrian hamster could be consistently infected by SARS-CoV-2. Maximal clinical signs of rapid breathing, weight loss, histopathological changes from the initial exudative phase of diffuse alveolar damage with extensive apoptosis to the later proliferative phase of tissue repair, airway and intestinal involvement with viral nucleocapsid protein expression, high lung viral load, and spleen and lymphoid atrophy associated with marked chemokine/cytokine activation were observed within the first week of virus challenge. The mean lung virus titer was between 105 and 107 TCID50/g. Challenged index hamsters consistently infected naive contact hamsters housed within the same cages, resulting in similar pathology but not weight loss. All infected hamsters recovered and developed mean serum neutralizing antibody titers ≥1:427 14 days postchallenge. Immunoprophylaxis with early convalescent serum achieved significant decrease in lung viral load but not in lung pathology. No consistent nonsynonymous adaptive mutation of the spike was found in viruses isolated from the infected hamsters. CONCLUSIONS: Besides satisfying Koch's postulates, this readily available hamster model is an important tool for studying transmission, pathogenesis, treatment, and vaccination against SARS-CoV-2.

Surgical Mask Partition Reduces the Risk of Noncontact Transmission in a Golden Syrian Hamster Model for Coronavirus Disease 2019 (COVID-19).

BACKGROUND: Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is believed to be mostly transmitted by medium- to large-sized respiratory droplets, although airborne transmission may be possible in healthcare settings involving aerosol-generating procedures. Exposure to respiratory droplets can theoretically be reduced by surgical mask usage. However, there is a lack of experimental evidence supporting surgical mask usage for prevention of COVID-19. METHODS: We used a well-established golden Syrian hamster SARS-CoV-2 model. We placed SARS-CoV-2-challenged index hamsters and naive hamsters into closed system units each comprising 2 different cages separated by a polyvinyl chloride air porous partition with unidirectional airflow within the isolator. The effect of a surgical mask partition placed between the cages was investigated. Besides clinical scoring, hamster specimens were tested for viral load, histopathology, and viral nucleocapsid antigen expression. RESULTS: Noncontact transmission was found in 66.7% (10/15) of exposed naive hamsters. Surgical mask partition for challenged index or naive hamsters significantly reduced transmission to 25% (6/24, P = .018). Surgical mask partition for challenged index hamsters significantly reduced transmission to only 16.7% (2/12, P = .019) of exposed naive hamsters. Unlike the severe manifestations of challenged hamsters, infected naive hamsters had lower clinical scores, milder histopathological changes, and lower viral nucleocapsid antigen expression in respiratory tract tissues. CONCLUSIONS: SARS-CoV-2 could be transmitted by respiratory droplets or airborne droplet nuclei which could be reduced by surgical mask partition in the hamster model. This is the first in vivo experimental evidence to support the possible benefit of surgical mask in prevention of COVID-19 transmission, especially when masks were worn by infected individuals.

Immunization With a Novel Human Type 5 Adenovirus-Vectored Vaccine Expressing the Premembrane and Envelope Proteins of Zika Virus Provides Consistent and Sterilizing Protection in Multiple Immunocompetent and Immunocompromised Animal Models.

Background: Zika virus (ZIKV) infection may be associated with severe complications and disseminated via both vector-borne and nonvector-borne routes. Adenovirus-vectored vaccines represent a favorable controlling measure for the ZIKV epidemic because they have been shown to be safe, immunogenic, and rapidly generable for other emerging viral infections. Evaluations of 2 previously reported adenovirus-vectored ZIKV vaccines were performed using nonlethal animal models and/or nonepidemic ZIKV strain. Methods: We constructed 2 novel human adenovirus 5 (Ad5)-vectored vaccines containing the ZIKV premembrane-envelope (Ad5-Sig-prM-Env) and envelope (Ad5-Env) proteins, respectively, and evaluated them in multiple nonlethal and lethal animal models using epidemic ZIKV strains. Results: Both vaccines elicited robust humoral and cellular immune responses in immunocompetent BALB/c mice. Dexamethasone-immunosuppressed mice vaccinated with either vaccine demonstrated robust and durable antibody responses and significantly lower blood and tissue viral loads than controls (P < .05). Similar findings were also observed in interferon-α/ß receptor-deficient A129 mice. In both of these immunocompromised animal models, Ad5-Sig-prM-Env-vaccinated mice had significantly (P < .05) higher titers of anti-ZIKV-specific neutralizing antibody titers and lower (undetectable) viral loads than Ad5-Env-vaccinated mice. The close correlation between the neutralizing antibody titer and viral load helped to explain the better protective effect of Ad5-Sig-prM-Env than Ad5-Env. Anamnestic response was absent in Ad5-Sig-prM-Env-vaccinated A129 mice. Conclusions: Ad5-Sig-prM-Env provided sterilizing protection against ZIKV infection in mice.

Improved detection of Zika virus RNA in human and animal specimens by a novel, highly sensitive and specific real-time RT-PCR assay targeting the 5'-untranslated region of Zika virus.

OBJECTIVE AND METHOD: We developed and evaluated five novel real-time RT-PCR assays targeting conserved regions in the 5'-untranslated region (5'-UTR), envelope (E'), non-structural protein 2A (NS2A), NS5 and 3'-UTR of the ZIKV genome. RESULTS: The ZIKV-5'-UTR assay exhibited the lowest in vitro limit of detection (5-10 RNA copies/reaction and 3.0 × 10-1 plaque-forming units/ml). Compared to the modified version of a widely adopted RT-PCR assay targeting the ZIKV-E gene, the ZIKV-5'-UTR assay showed better sensitivity in human clinical specimens, and representative mouse specimens, including many organs which are known to be involved in human ZIKV infection but difficult to obtain in clinical settings. The ZIKV-5'-UTR assay detected ZIKV RNA in 84/84 (100.0%) ZIKV-E'-positive and an additional 30/296 (10.1%, P < 0.01) ZIKV-E'-negative mouse specimens. The higher sensitivity of the ZIKV-5'-UTR assay was most significant in kidney and testis/epididymis specimens (P < 0.01). No in vitro or in vivo cross-reactivity was found between the ZIKV-5'-UTR assay and dengue virus, yellow fever virus, Japanese encephalitis virus, West Nile virus, hepatitis C virus and Chikungunya virus. CONCLUSIONS: The highly sensitive and specific ZIKV-5'-UTR assay may help to improve the laboratory diagnosis of ZIKV infection.

P21-activated kinase 1 (PAK1)-mediated cytoskeleton rearrangement promotes SARS-CoV-2 entry and ACE2 autophagic degradation.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has had a significant impact on healthcare systems and economies worldwide. The continuous emergence of new viral strains presents a major challenge in the development of effective antiviral agents. Strategies that possess broad-spectrum antiviral activities are desirable to control SARS-CoV-2 infection. ACE2, an angiotensin-containing enzyme that prevents the overactivation of the renin angiotensin system, is the receptor for SARS-CoV-2. ACE2 interacts with the spike protein and facilitates viral attachment and entry into host cells. Yet, SARS-CoV-2 infection also promotes ACE2 degradation. Whether restoring ACE2 surface expression has an impact on SARS-CoV-2 infection is yet to be determined. Here, we show that the ACE2-spike complex is endocytosed and degraded via autophagy in a manner that depends on clathrin-mediated endocytosis and PAK1-mediated cytoskeleton rearrangement. In contrast, free cellular spike protein is selectively cleaved into S1 and S2 subunits in a lysosomal-dependent manner. Importantly, we show that the pan-PAK inhibitor FRAX-486 restores ACE2 surface expression and suppresses infection by different SARS-CoV-2 strains. FRAX-486-treated Syrian hamsters exhibit significantly decreased lung viral load and alleviated pulmonary inflammation compared with untreated hamsters. In summary, our findings have identified novel pathways regulating viral entry, as well as therapeutic targets and candidate compounds for controlling the emerging strains of SARS-CoV-2 infection.

Antibodies that neutralize all current SARS-CoV-2 variants of concern by conformational locking.

SARS-CoV-2 continues to evolve and evade most existing neutralizing antibodies, including all clinically authorized antibodies. We have isolated and characterized two human monoclonal antibodies, 12-16 and 12-19, which exhibited neutralizing activities against all SARS-CoV-2 variants tested, including BQ.1.1 and XBB.1.5. They also blocked infection in hamsters challenged with Omicron BA.1 intranasally. Structural analyses revealed both antibodies targeted a conserved quaternary epitope located at the interface between the N-terminal domain and subdomain 1, revealing a previously unrecognized site of vulnerability on SARS-CoV-2 spike. These antibodies prevent viral receptor engagement by locking the receptor-binding domain of spike in the down conformation, revealing a novel mechanism of virus neutralization for non-RBD antibodies. Deep mutational scanning showed that SARS-CoV-2 could mutate to escape 12-19, but the responsible mutations are rarely found in circulating viruses. Antibodies 12-16 and 12-19 hold promise as prophylactic agents for immunocompromised persons who do not respond robustly to COVID-19 vaccines.

SARS-CoV-2 hijacks neutralizing dimeric IgA for nasal infection and injury in Syrian hamsters1.

Prevention of robust severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in nasal turbinate (NT) requires in vivo evaluation of IgA neutralizing antibodies. Here, we report the efficacy of receptor binding domain (RBD)-specific monomeric B8-mIgA1 and B8-mIgA2, and dimeric B8-dIgA1, B8-dIgA2 and TH335-dIgA1 against intranasal SARS-CoV-2 challenge in Syrian hamsters. These antibodies exhibited comparable neutralization potency against authentic virus by competing with human angiotensin converting enzyme-2 (ACE2) receptor for RBD binding. While reducing viral loads in lungs significantly, prophylactic intranasal B8-dIgA unexpectedly led to high amount of infectious viruses and extended damage in NT compared to controls. Mechanistically, B8-dIgA failed to inhibit SARS-CoV-2 cell-to-cell transmission, but was hijacked by the virus through dendritic cell-mediated trans-infection of NT epithelia leading to robust nasal infection. Cryo-EM further revealed B8 as a class II antibody binding trimeric RBDs in 3-up or 2-up/1-down conformation. Neutralizing dIgA, therefore, may engage an unexpected mode of SARS-CoV-2 nasal infection and injury.

SARS-CoV-2 infection induces inflammatory bone loss in golden Syrian hamsters.

Extrapulmonary complications of different organ systems have been increasingly recognized in patients with severe or chronic Coronavirus Disease 2019 (COVID-19). However, limited information on the skeletal complications of COVID-19 is known, even though inflammatory diseases of the respiratory tract have been known to perturb bone metabolism and cause pathological bone loss. In this study, we characterize the effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on bone metabolism in an established golden Syrian hamster model for COVID-19. SARS-CoV-2 causes significant multifocal loss of bone trabeculae in the long bones and lumbar vertebrae of all infected hamsters. Moreover, we show that the bone loss is associated with SARS-CoV-2-induced cytokine dysregulation, as the circulating pro-inflammatory cytokines not only upregulate osteoclastic differentiation in bone tissues, but also trigger an amplified pro-inflammatory cascade in the skeletal tissues to augment their pro-osteoclastogenesis effect. Our findings suggest that pathological bone loss may be a neglected complication which warrants more extensive investigations during the long-term follow-up of COVID-19 patients. The benefits of potential prophylactic and therapeutic interventions against pathological bone loss should be further evaluated.

The spike receptor-binding motif G496S substitution determines the replication fitness of SARS-CoV-2 Omicron sublineage.

The replication and pathogenicity of SARS-CoV-2 Omicron BA.2 are comparable to that of BA.1 in experimental animal models. However, BA.2 has rapidly emerged to overtake BA.1 to become the predominant circulating SARS-CoV-2 variant worldwide. Here, we compared the replication fitness of BA.1 and BA.2 in cell culture and in the Syrian hamster model of COVID-19. Using a reverse genetics approach, we found that the BA.1-specific spike mutation G496S compromises its replication fitness, which may contribute to BA.1 being outcompeted by BA.2 in the real world. Additionally, the BA.1-unique G496S substitution confers differentiated sensitivity to therapeutic monoclonal antibodies, which partially recapitulates the immunoevasive phenotype of BA.1 and BA.2. In summary, our study identified G496S as an important determinant during the evolutionary trajectory of SARS-CoV-2.

Pathogenicity, transmissibility, and fitness of SARS-CoV-2 Omicron in Syrian hamsters.

The in vivo pathogenicity, transmissibility, and fitness of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron (B.1.1.529) variant are not well understood. We compared these virological attributes of this new variant of concern (VOC) with those of the Delta (B.1.617.2) variant in a Syrian hamster model of COVID-19. Omicron-infected hamsters lost significantly less body weight and exhibited reduced clinical scores, respiratory tract viral burdens, cytokine and chemokine dysregulation, and lung damage than Delta-infected hamsters. Both variants were highly transmissible through contact transmission. In noncontact transmission studies Omicron demonstrated similar or higher transmissibility than Delta. Delta outcompeted Omicron without selection pressure, but this scenario changed once immune selection pressure with neutralizing antibodies-active against Delta but poorly active against Omicron-was introduced. Next-generation vaccines and antivirals effective against this new VOC are therefore urgently needed.

A broadly neutralizing antibody protects Syrian hamsters against SARS-CoV-2 Omicron challenge.

The strikingly high transmissibility and antibody evasion of SARS-CoV-2 Omicron variants have posed great challenges to the efficacy of current vaccines and antibody immunotherapy. Here, we screen 34 BNT162b2-vaccinees and isolate a public broadly neutralizing antibody ZCB11 derived from the IGHV1-58 family. ZCB11 targets viral receptor-binding domain specifically and neutralizes all SARS-CoV-2 variants of concern, especially with great potency against authentic Omicron and Delta variants. Pseudovirus-based mapping of 57 naturally occurred spike mutations or deletions reveals that S371L results in 11-fold neutralization resistance, but it is rescued by compensating mutations in Omicron variants. Cryo-EM analysis demonstrates that ZCB11 heavy chain predominantly interacts with Omicron spike trimer with receptor-binding domain in up conformation blocking ACE2 binding. In addition, prophylactic or therapeutic ZCB11 administration protects lung infection against Omicron viral challenge in golden Syrian hamsters. These results suggest that vaccine-induced ZCB11 is a promising broadly neutralizing antibody for biomedical interventions against pandemic SARS-CoV-2.

A molecularly engineered, broad-spectrum anti-coronavirus lectin inhibits SARS-CoV-2 and MERS-CoV infection in vivo.

"Pan-coronavirus" antivirals targeting conserved viral components can be designed. Here, we show that the rationally engineered H84T-banana lectin (H84T-BanLec), which specifically recognizes high mannose found on viral proteins but seldom on healthy human cells, potently inhibits Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (including Omicron), and other human-pathogenic coronaviruses at nanomolar concentrations. H84T-BanLec protects against MERS-CoV and SARS-CoV-2 infection in vivo. Importantly, intranasally and intraperitoneally administered H84T-BanLec are comparably effective. Mechanistic assays show that H84T-BanLec targets virus entry. High-speed atomic force microscopy depicts real-time multimolecular associations of H84T-BanLec dimers with the SARS-CoV-2 spike trimer. Single-molecule force spectroscopy demonstrates binding of H84T-BanLec to multiple SARS-CoV-2 spike mannose sites with high affinity and that H84T-BanLec competes with SARS-CoV-2 spike for binding to cellular ACE2. Modeling experiments identify distinct high-mannose glycans in spike recognized by H84T-BanLec. The multiple H84T-BanLec binding sites on spike likely account for the drug compound's broad-spectrum antiviral activity and the lack of resistant mutants.

Beneficial effect of combinational methylprednisolone and remdesivir in hamster model of SARS-CoV-2 infection.

Effective treatments for coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are urgently needed. Dexamethasone has been shown to confer survival benefits to certain groups of hospitalized patients, but whether glucocorticoids such as dexamethasone and methylprednisolone should be used together with antivirals to prevent a boost of SARS-CoV-2 replication remains to be determined. Here, we show the beneficial effect of methylprednisolone alone and in combination with remdesivir in the hamster model of SARS-CoV-2 infection. Treatment with methylprednisolone boosted RNA replication of SARS-CoV-2 but suppressed viral induction of proinflammatory cytokines in human monocyte-derived macrophages. Although methylprednisolone monotherapy alleviated body weight loss as well as nasal and pulmonary inflammation, viral loads increased and antibody response against the receptor-binding domain of spike protein attenuated. In contrast, a combination of methylprednisolone with remdesivir not only prevented body weight loss and inflammation, but also dampened viral protein expression and viral loads. In addition, the suppressive effect of methylprednisolone on antibody response was alleviated in the presence of remdesivir. Thus, combinational anti-inflammatory and antiviral therapy might be an effective, safer and more versatile treatment option for COVID-19. These data support testing of the efficacy of a combination of methylprednisolone and remdesivir for the treatment of COVID-19 in randomized controlled clinical trials.