Comparative study of the propagation and plaque titration conditions for human coronavirus OC43 as a surrogate for SARS-CoV-2.

The ongoing COVID-19 pandemic is threatening human health globally. The development of effective drugs and vaccines against SARS-CoV-2 is hindered by the limited access to high-biosafety-level facilities. Although human coronavirus (HCoV) OC43, a low-pathogenic endemic human coronavirus, has been used as a surrogate virus for SARS-CoV-2 research, a standard technique for HCoV-OC43 culture and plaque titration has not been established. Our objective was to establish optimized culture and titration protocols for HCoV-OC43. The growth kinetics and permissibility to HCoV-OC43 infection of seven different cell lines were examined concurrently at two different temperatures, 33°C and 37°C. Cell lines exhibiting a cytopathic effect (CPE) were selected for plaque titration. No significant difference in the rate of cell growth was observed at the two temperatures tested. Interestingly, HCoV-OC43 was found not to be a high-temperature-sensitive virus, since it grew well at 37°C. Although RD, LLC-MK2, MRC-5, and HCT-8 cell lines supported virus growth with an obvious cytopathic effect and a high yield of virus after two days of infection, only RD cells were suitable for producing countable plaques. The incubation of the cells with 1.2% low-viscosity Avicel as an overlay medium at 37°C for 4 days appeared to promote clearer and sharper plaque morphology. However, further optimization of the plaque titration protocol is still required due to the continued observation of plaque size variation and hazy zones. We propose a cost-effective protocol for HCoV-OC43 culture and plaque titration that can be implemented at a standard conventional temperature without the need for additional special equipment.

The host protease KLK5 primes and activates spike proteins to promote human betacoronavirus replication and lung inflammation.

Coronaviruses rely on host proteases to activate the viral spike protein, which facilitates fusion with the host cell membrane and the release of viral genomic RNAs into the host cell cytoplasm. The distribution of specific host proteases in the host determines the host, tissue, and cellular tropism of these viruses. Here, we identified the kallikrein (KLK) family member KLK5 as a major host protease secreted by human airway cells and exploited by multiple human betacoronaviruses. KLK5 cleaved both the priming (S1/S2) and activation (S2') sites of spike proteins from various human betacoronaviruses in vitro. In contrast, KLK12 and KLK13 displayed preferences for either the S2' or S1/S2 site, respectively. Whereas KLK12 and KLK13 worked in concert to activate SARS-CoV-2 and MERS-CoV spike proteins, KLK5 by itself efficiently activated spike proteins from several human betacoronaviruses, including SARS-CoV-2. Infection of differentiated human bronchial epithelial cells (HBECs) with human betacoronaviruses induced an increase in KLK5 that promoted virus replication. Furthermore, ursolic acid and other related plant-derived triterpenoids that inhibit KLK5 effectively suppressed the replication of SARS-CoV, MERS-CoV, and SARS-CoV-2 in HBECs and mitigated lung inflammation in mice infected with MERS-CoV or SARS-CoV-2. We propose that KLK5 is a pancoronavirus host factor and a promising therapeutic target for current and future coronavirus-induced diseases.

NK cells modulate in vivo control of SARS-CoV-2 replication and suppression of lung damage.

Natural killer (NK) cells play a critical role in virus control. However, it has remained largely unclear whether NK cell mobilization in SARS-CoV-2 infections is beneficial or pathologic. To address this deficit, we employed a validated experimental NK cell depletion non-human primate (NHP) model with SARS-CoV-2 Delta variant B.1.617.2 challenge. Viral loads (VL), NK cell numbers, activation, proliferation, and functional measures were evaluated in blood and tissues. In non-depleted (control) animals, infection rapidly induced NK cell expansion, activation, and increased tissue trafficking associated with VL. Strikingly, we report that experimental NK cell depletion leads to higher VL, longer duration of viral shedding, significantly increased levels of pro-inflammatory cytokines in the lungs, and overt lung damage. Overall, we find the first significant and conclusive evidence for NK cell-mediated control of SARS-CoV-2 virus replication and disease pathology. These data indicate that adjunct therapies for infection could largely benefit from NK cell-targeted approaches.

A BSL-2 compliant mouse model of SARS-CoV-2 infection for efficient and convenient antiviral evaluation.

Animal models of authentic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection require operation in biosafety level 3 (BSL-3) containment. In the present study, we established a mouse model employing a single-cycle infectious virus replicon particle (VRP) system of SARS-CoV-2 that can be safely handled in BSL-2 laboratories. The VRP [ΔS-VRP(G)-Luc] contains a SARS-CoV-2 genome in which the spike gene was replaced by a firefly luciferase (Fluc) reporter gene (Rep-Luci), and incorporates the vesicular stomatitis virus glycoprotein on the surface. Intranasal inoculation of ΔS-VRP(G)-Luc can successfully transduce the Rep-Luci genome into mouse lungs, initiating self-replication of Rep-Luci and, accordingly, inducing acute lung injury mimicking the authentic SARS-CoV-2 pathology. In addition, the reporter Fluc expression can be monitored using a bioluminescence imaging approach, allowing a rapid and convenient determination of viral replication in ΔS-VRP(G)-Luc-infected mouse lungs. Upon treatment with an approved anti-SARS-CoV-2 drug, VV116, the viral replication in infected mouse lungs was significantly reduced, suggesting that the animal model is feasible for antiviral evaluation. In summary, we have developed a BSL-2-compliant mouse model of SARS-CoV-2 infection, providing an advanced approach to study aspects of the viral pathogenesis, viral-host interactions, as well as the efficacy of antiviral therapeutics in the future.IMPORTANCESevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly contagious and pathogenic in humans; thus, research on authentic SARS-CoV-2 has been restricted to biosafety level 3 (BSL-3) laboratories. However, due to the scarcity of BSL-3 facilities and trained personnel, the participation of a broad scientific community in SARS-CoV-2 research had been greatly limited, hindering the advancement of our understanding on the basic virology as well as the urgently necessitated drug development. Previously, our colleagues Jin et al. had generated a SARS-CoV-2 replicon by replacing the essential spike gene in the viral genome with a Fluc reporter (Rep-Luci), which can be safely operated under BSL-2 conditions. By incorporating the Rep-Luci into viral replicon particles carrying vesicular stomatitis virus glycoprotein on their surface, and via intranasal inoculation, we successfully transduced the Rep-Luci into mouse lungs, developing a mouse model mimicking SARS-CoV-2 infection. Our model can serve as a useful platform for SARS-CoV-2 pathological studies and antiviral evaluation under BSL2 containment.

The coagulation process for enveloped and non-enveloped virus removal in turbid water: Removal efficiencies, mechanisms and its application to SARS-CoV-2 Omicron BA.2.

The coagulation process has a high potential as a treatment method that can handle pathogenic viruses including emerging enveloped viruses in drinking water treatment process which can lower infection risk through drinking water consumption. In this study, a surrogate enveloped virus, bacteriophage Փ6, and surrogate non-enveloped viruses, including bacteriophage MS-2, T4, ՓX174, were used to evaluate removal efficiencies and mechanisms by the conventional coagulation process with alum, poly­aluminum chloride, and ferric chloride at pH 5, 7, and 9 in turbid water. Also, treatability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a recent virus of global concern by coagulation was evaluated as SARS-CoV-2 can presence in drinking water sources. It was observed that an increase in the coagulant dose enhanced the removal efficiency of turbidity and viruses, and the condition that provided the highest removal efficiency of enveloped and non-enveloped viruses was 50 mg/L of coagulants at pH 5. In addition, the coagulation process was more effective for enveloped virus removal than for the non-enveloped viruses, and it demonstrated reduction of SARS-CoV-2 Omicron BA.2 over 0.83-log with alum. According to culture- and molecular-based assays (qPCR and CDDP-qPCR), the virus removal mechanisms were floc adsorption and coagulant inactivation. Through inactivation with coagulants, coagulants caused capsid destruction, followed by genome damage in non-enveloped viruses; however, damage to a lipid envelope is suggested to contribute to a great extend for enveloped virus inactivation. We demonstrated that conventional coagulation is a promising method for controlling emerging and re-emerging viruses in drinking water.

Identification of a membrane-associated element (MAE) in the C-terminal region of SARS-CoV-2 nsp6 that is essential for viral replication.

The coronavirus disease 2019 (COVID-19) pandemic, caused by the novel coronavirus severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), has rapidly spread worldwide since its emergence in late 2019. Its ongoing evolution poses challenges for antiviral drug development. Coronavirus nsp6, a multiple-spanning transmembrane protein, participates in the biogenesis of the viral replication complex, which accommodates the viral replication-transcription complex. The roles of its structural domains in viral replication are not well studied. Herein, we predicted the structure of the SARS-CoV-2 nsp6 protein using AlphaFold2 and identified a highly folded C-terminal region (nsp6C) downstream of the transmembrane helices. The enhanced green fluorescent protein (EGFP)-fused nsp6C was found to cluster in the cytoplasm and associate with membranes. Functional mapping identified a minimal membrane-associated element (MAE) as the region from amino acids 237 to 276 (LGV-KLL), which is mainly composed of the α-helix H1 and the α-helix H2; the latter exhibits characteristics of an amphipathic helix (AH). Mutagenesis studies and membrane flotation experiments demonstrate that AH-like H2 is required for MAE-mediated membrane association. This MAE was functionally conserved across MERS-CoV, HCoV-OC43, HCoV-229E, HCoV-HKU1, and HCoV-NL63, all capable of mediating membrane association. In a SARS-CoV-2 replicon system, mutagenesis studies of H2 and replacements of H1 and H2 with their homologous counterparts demonstrated requirements of residues on both sides of the H2 and properly paired H1-H2 for MAE-mediated membrane association and viral replication. Notably, mutations I266A and K274A significantly attenuated viral replication without dramatically affecting membrane association, suggesting a dual role of the MAE in viral replication: mediating membrane association as well as participating in protein-protein interactions.IMPORTANCESevere acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) assembles a double-membrane vesicle (DMV) by the viral non-structural proteins for viral replication. Understanding the mechanisms of the DMV assembly is of paramount importance for antiviral development. Nsp6, a multiple-spanning transmembrane protein, plays an important role in the DMV biogenesis. Herein, we predicted the nsp6 structure of SARS-CoV-2 and other human coronaviruses using AlphaFold2 and identified a putative membrane-associated element (MAE) in the highly conserved C-terminal regions of nsp6. Experimentally, we verified a functionally conserved minimal MAE composed of two α-helices, the H1, and the amphipathic helix-like H2. Mutagenesis studies confirmed the requirement of H2 for MAE-mediated membrane association and viral replication and demonstrated a dual role of the MAE in viral replication, by mediating membrane association and participating in residue-specific interactions. This functionally conserved MAE may serve as a novel anti-viral target.

SARS-CoV-2 infects cells lining the blood-retinal barrier and induces a hyperinflammatory immune response in the retina via systemic exposure.

SARS-CoV-2 has been shown to cause wide-ranging ocular abnormalities and vision impairment in COVID-19 patients. However, there is limited understanding of SARS-CoV-2 in ocular transmission, tropism, and associated pathologies. The presence of viral RNA in corneal/conjunctival tissue and tears, along with the evidence of viral entry receptors on the ocular surface, has led to speculation that the eye may serve as a potential route of SARS-CoV-2 transmission. Here, we investigated the interaction of SARS-CoV-2 with cells lining the blood-retinal barrier (BRB) and the role of the eye in its transmission and tropism. The results from our study suggest that SARS-CoV-2 ocular exposure does not cause lung infection and moribund illness in K18-hACE2 mice despite the extended presence of viral remnants in various ocular tissues. In contrast, intranasal exposure not only resulted in SARS-CoV-2 spike (S) protein presence in different ocular tissues but also induces a hyperinflammatory immune response in the retina. Additionally, the long-term exposure to viral S-protein caused microaneurysm, retinal pigmented epithelium (RPE) mottling, retinal atrophy, and vein occlusion in mouse eyes. Notably, cells lining the BRB, the outer barrier, RPE, and the inner barrier, retinal vascular endothelium, were highly permissive to SARS-CoV-2 replication. Unexpectedly, primary human corneal epithelial cells were comparatively resistant to SARS-CoV-2 infection. The cells lining the BRB showed induced expression of viral entry receptors and increased susceptibility towards SARS-CoV-2-induced cell death. Furthermore, hyperglycemic conditions enhanced the viral entry receptor expression, infectivity, and susceptibility of SARS-CoV-2-induced cell death in the BRB cells, confirming the reported heightened pathological manifestations in comorbid populations. Collectively, our study provides the first evidence of SARS-CoV-2 ocular tropism via cells lining the BRB and that the virus can infect the retina via systemic permeation and induce retinal inflammation.

The role of SARS-CoV-2 ORF7a in autophagy flux disruption: implications for viral infection and pathogenesis.

Although alterations in the autophagy-lysosome pathway have been observed in the SARS-CoV-2 infection and invasion process since the outbreak of the coronavirus disease in 2019, the in-depth mechanism of autophagic and lysosomal reprogramming by SARS-CoV-2 has yet to be well identified. Our recent study unveiled a pivotal role played by the open reading frame 7a (ORF7a) protein in the SARS-CoV-2 genome, particularly in the modulation of macroautophagy/autophagy flux and function during viral infection and pathogenesis. Our study elucidated the underlying molecular mechanisms by which SARS-CoV-2 ORF7a intercepts autophagic flux, evades host autophagy-lysosome degradation, and accelerates viral infection and progeny germination. Furthermore, our study highlights that ORF7a can be a therapeutic target, and glecaprevir may hold potential as a drug against SARS-CoV-2 by targeting ORF7a. The key observations revealed in this study also contribute to a growing understanding of the function of SARS-CoV-2 ORF7a and the mechanisms underlying COVID-2019 treatment.

Glyceraldehyde-3-Phosphate Dehydrogenase Binds with Spike Protein and Inhibits the Entry of SARS-CoV-2 into Host Cells.

INTRODUCTION: Coronavirus disease 2019 caused by coronavirus-2 (SARS-CoV-2) has emerged as an aggressive viral pandemic. Health care providers confront a challenging task for rapid development of effective strategies to combat this and its long-term after effects. Virus entry into host cells involves interaction between receptor-binding domain (RBD) of spike (S) protein S1 subunit with angiotensin converting enzyme present on host cells. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a moonlighting enzyme involved in cellular glycolytic energy metabolism and micronutrient homeostasis. It is deployed in various cellular compartments and the extra cellular milieu. Though it is known to moonlight as a component of mammalian innate immune defense machinery, till date its role in viral restriction remains unknown. METHOD: Recombinant S protein, the RBD, and human GAPDH protein were used for solid phase binding assays and biolayer interferometry. Pseudovirus particles expressing four different strain variants of S protein all harboring ZsGreen gene as marker of infection were used for flow cytometry-based infectivity assays. RESULTS: Pseudovirus entry into target cells in culture was significantly inhibited by addition of human GAPDH into the extracellular medium. Binding assays demonstrated that human GAPDH binds to S protein and RBD of SARS-CoV-2 with nanomolar affinity. CONCLUSIONS: Our investigations suggest that this interaction of GAPDH interferes in the viral docking with hACE2 receptors, thereby affecting viral ingress into mammalian cells.

Coronavirus takeover of host cell translation and intracellular antiviral response: a molecular perspective.

Coronaviruses are a group of related RNA viruses that cause respiratory diseases in humans and animals. Understanding the mechanisms of translation regulation during coronaviral infections is critical for developing antiviral therapies and preventing viral spread. Translation of the viral single-stranded RNA genome in the host cell cytoplasm is an essential step in the life cycle of coronaviruses, which affects the cellular mRNA translation landscape in many ways. Here we discuss various viral strategies of translation control, including how members of the Betacoronavirus genus shut down host cell translation and suppress host innate immune functions, as well as the role of the viral non-structural protein 1 (Nsp1) in the process. We also outline the fate of viral RNA, considering stress response mechanisms triggered in infected cells, and describe how unique viral RNA features contribute to programmed ribosomal -1 frameshifting, RNA editing, and translation shutdown evasion.

Pre-COVID-19 Immunity to Common Cold Human Coronaviruses Induces a Recall-Type IgG Response to SARS-CoV-2 Antigens Without Cross-Neutralisation.

The capacity of pre-existing immunity to human common coronaviruses (HCoV) to cross-protect against de novo COVID-19is yet unknown. In this work, we studied the sera of 175 COVID-19 patients, 76 healthy donors and 3 intravenous immunoglobulins (IVIG) batches. We found that most COVID-19 patients developed anti-SARS-CoV-2 IgG antibodies before IgM. Moreover, the capacity of their IgGs to react to beta-HCoV, was present in the early sera of most patients before the appearance of anti-SARS-CoV-2 IgG. This implied that a recall-type antibody response was generated. In comparison, the patients that mounted an anti-SARS-COV2 IgM response, prior to IgG responses had lower titres of anti-beta-HCoV IgG antibodies. This indicated that pre-existing immunity to beta-HCoV was conducive to the generation of memory type responses to SARS-COV-2. Finally, we also found that pre-COVID-19-era sera and IVIG cross-reacted with SARS-CoV-2 antigens without neutralising SARS-CoV-2 infectivity in vitro. Put together, these results indicate that whilst pre-existing immunity to HCoV is responsible for recall-type IgG responses to SARS-CoV-2, it does not lead to cross-protection against COVID-19.

Immunizations with diverse sarbecovirus receptor-binding domains elicit SARS-CoV-2 neutralizing antibodies against a conserved site of vulnerability.

Viral mutations are an emerging concern in reducing SARS-CoV-2 vaccination efficacy. Second-generation vaccines will need to elicit neutralizing antibodies against sites that are evolutionarily conserved across the sarbecovirus subgenus. Here, we immunized mice containing a human antibody repertoire with diverse sarbecovirus receptor-binding domains (RBDs) to identify antibodies targeting conserved sites of vulnerability. Antibodies with broad reactivity against diverse clade B RBDs targeting the conserved class 4 epitope, with recurring IGHV/IGKV pairs, were readily elicited but were non-neutralizing. However, rare class 4 antibodies binding this conserved RBD supersite showed potent neutralization of SARS-CoV-2 and all variants of concern. Structural analysis revealed that the neutralizing ability of cross-reactive antibodies was reserved only for those with an elongated CDRH3 that extends the antiparallel beta-sheet RBD core and orients the antibody light chain to obstruct ACE2-RBD interactions. These results identify a structurally defined pathway for vaccine strategies eliciting escape-resistant SARS-CoV-2 neutralizing antibodies.

Chimeric spike mRNA vaccines protect against Sarbecovirus challenge in mice.

The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003 and SARS-CoV-2 in 2019 highlights the need to develop universal vaccination strategies against the broader Sarbecovirus subgenus. Using chimeric spike designs, we demonstrate protection against challenge from SARS-CoV, SARS-CoV-2, SARS-CoV-2 B.1.351, bat CoV (Bt-CoV) RsSHC014, and a heterologous Bt-CoV WIV-1 in vulnerable aged mice. Chimeric spike messenger RNAs (mRNAs) induced high levels of broadly protective neutralizing antibodies against high-risk Sarbecoviruses. By contrast, SARS-CoV-2 mRNA vaccination not only showed a marked reduction in neutralizing titers against heterologous Sarbecoviruses, but SARS-CoV and WIV-1 challenge in mice resulted in breakthrough infections. Chimeric spike mRNA vaccines efficiently neutralized D614G, mink cluster five, and the UK B.1.1.7 and South African B.1.351 variants of concern. Thus, multiplexed-chimeric spikes can prevent SARS-like zoonotic coronavirus infections with pandemic potential.

A Comparison of the Clinical, Viral, Pathologic, and Immunologic Features of Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and Coronavirus 2019 (COVID-19) Diseases.

CONTEXT.­: The purpose of this review was to compare 3 coronavirus diseases, including severe acute respiratory syndrome, Middle East respiratory syndrome, and COVID-19 caused by SARS-CoV, MERS-CoV, and SARS-CoV-2 viruses, respectively. OBJECTIVE.­: To cover the following topics: clinical considerations, viral characteristics, pathology, immune response, pathogenesis, and the prognosis associated with each coronavirus disease in humans. DATA SOURCES.­: Clinically, flu-like symptoms are usual at the time of presentation for all 3 diseases, but these vary from asymptomatic to severe multisystem involvement. The pathology associated with symptomatic severe acute respiratory syndrome and COVID-19 has been well described, the most prominent of which is diffuse alveolar damage. The immune response to each of these viruses is highly complex and includes both humoral and cellular components that can have a significant impact on prognosis. In severe cases of COVID-19, a dysregulated innate host immune system can initiate a hyperinflammatory syndrome dominated by endothelial dysfunction that can lead to a hypercoagulable state with microthrombi, resulting in a systemic microvascular and macrovascular disease. CONCLUSIONS.­: The severe acute respiratory syndrome and Middle East respiratory syndrome epidemics have been limited, involving approximately 8000 and 2500 individuals, respectively. In contrast, COVID-19 has resulted in a worldwide pandemic with more than 177 million cases and 3.9 million deaths as of June 15, 2021, and fatality rates ranging from less than 0.1% to approximately 10% depending upon the country. Ending on a positive note, the development of a number of vaccines, at least 6 of which now are in clinical use, should mitigate and eventually control the devastating COVID-19 pandemic.

Molecular basis of cross-species ACE2 interactions with SARS-CoV-2-like viruses of pangolin origin.

Pangolins have been suggested as potential reservoir of zoonotic viruses, including SARS-CoV-2 causing the global COVID-19 outbreak. Here, we study the binding of two SARS-CoV-2-like viruses isolated from pangolins, GX/P2V/2017 and GD/1/2019, to human angiotensin-converting enzyme 2 (hACE2), the receptor of SARS-CoV-2. We find that the spike protein receptor-binding domain (RBD) of pangolin CoVs binds to hACE2 as efficiently as the SARS-CoV-2 RBD in vitro. Furthermore, incorporation of pangolin CoV RBDs allows entry of pseudotyped VSV particles into hACE2-expressing cells. A screen for binding of pangolin CoV RBDs to ACE2 orthologs from various species suggests a broader host range than that of SARS-CoV-2. Additionally, cryo-EM structures of GX/P2V/2017 and GD/1/2019 RBDs in complex with hACE2 show their molecular binding in modes similar to SARS-CoV-2 RBD. Introducing the Q498H substitution found in pangolin CoVs into the SARS-CoV-2 RBD expands its binding capacity to ACE2 homologs of mouse, rat, and European hedgehog. These findings suggest that these two pangolin CoVs may infect humans, highlighting the necessity of further surveillance of pangolin CoVs.

An application of slow feature analysis to the genetic sequences of coronaviruses and influenza viruses.

BACKGROUND: Mathematical approaches have been for decades used to probe the structure of DNA sequences. This has led to the development of Bioinformatics. In this exploratory work, a novel mathematical method is applied to probe the DNA structure of two related viral families: those of coronaviruses and those of influenza viruses. The coronaviruses are SARS-CoV-2, SARS-CoV-1, and MERS. The influenza viruses include H1N1-1918, H1N1-2009, H2N2-1957, and H3N2-1968. METHODS: The mathematical method used is the slow feature analysis (SFA), a rather new but promising method to delineate complex structure in DNA sequences. RESULTS: The analysis indicates that the DNA sequences exhibit an elaborate and convoluted structure akin to complex networks. We define a measure of complexity and show that each DNA sequence exhibits a certain degree of complexity within itself, while at the same time there exists complex inter-relationships between the sequences within a family and between the two families. From these relationships, we find evidence, especially for the coronavirus family, that increasing complexity in a sequence is associated with higher transmission rate but with lower mortality. CONCLUSIONS: The complexity measure defined here may hold a promise and could become a useful tool in the prediction of transmission and mortality rates in future new viral strains.

The green tea catechin epigallocatechin gallate inhibits SARS-CoV-2 infection.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has caused a pandemic with tens of millions of cases and more than a million deaths. The infection causes COVID-19, a disease of the respiratory system of divergent severity. No treatment exists. Epigallocatechin-3-gallate (EGCG), the major component of green tea, has several beneficial properties, including antiviral activities. Therefore, we examined whether EGCG has antiviral activity against SARS-CoV-2. EGCG blocked not only the entry of SARS-CoV-2, but also MERS- and SARS-CoV pseudotyped lentiviral vectors and inhibited virus infections in vitro. Mechanistically, inhibition of the SARS-CoV-2 spike-receptor interaction was observed. Thus, EGCG might be suitable for use as a lead structure to develop more effective anti-COVID-19 drugs.

A quantitative model used to compare within-host SARS-CoV-2, MERS-CoV, and SARS-CoV dynamics provides insights into the pathogenesis and treatment of SARS-CoV-2.

The scientific community is focused on developing antiviral therapies to mitigate the impacts of the ongoing novel coronavirus disease 2019 (COVID-19) outbreak. This will be facilitated by improved understanding of viral dynamics within infected hosts. Here, using a mathematical model in combination with published viral load data, we compare within-host viral dynamics of SARS-CoV-2 with analogous dynamics of MERS-CoV and SARS-CoV. Our quantitative analyses using a mathematical model revealed that the within-host reproduction number at symptom onset of SARS-CoV-2 was statistically significantly larger than that of MERS-CoV and similar to that of SARS-CoV. In addition, the time from symptom onset to the viral load peak for SARS-CoV-2 infection was shorter than those of MERS-CoV and SARS-CoV. These findings suggest the difficulty of controlling SARS-CoV-2 infection by antivirals. We further used the viral dynamics model to predict the efficacy of potential antiviral drugs that have different modes of action. The efficacy was measured by the reduction in the viral load area under the curve (AUC). Our results indicate that therapies that block de novo infection or virus production are likely to be effective if and only if initiated before the viral load peak (which appears 2-3 days after symptom onset), but therapies that promote cytotoxicity of infected cells are likely to have effects with less sensitivity to the timing of treatment initiation. Furthermore, combining a therapy that promotes cytotoxicity and one that blocks de novo infection or virus production synergistically reduces the AUC with early treatment. Our unique modeling approach provides insights into the pathogenesis of SARS-CoV-2 and may be useful for development of antiviral therapies.

A comparative review of pathogenesis and host innate immunity evasion strategies among the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV).

COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put the global public health at its highest threat around the world. Previous epidemic caused by the acute respiratory syndrome coronavirus (SARS-CoV) in 2002 is also considered since both the coronaviruses resulted in the similar clinical complications. The outbreak caused by the Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 had a low rate of disease transmission and death cases. Modes of entry by MERS and SARS coronaviruses are similar to that of SARS-CoV-2, except MERS-CoV utilize different receptor. They all belong to the lineage C of ß-coronavirus. Based on the information from the previous reports, the present review is mainly focused on the mechanisms of disease progression by each of these viruses in association to their strategies to escape the host immunity. The viral entry is the first step of pathogenesis associated with attachment of viral spike protein with host receptor help releasing the viral RNA into the host cell. Models of molecular pathogenesis are outlined with virus strategies escaping the host immunity along with the role of various inflammatory cytokines and chemokines in the process. The molecular aspects of pathogenesis have also been discussed.

Critical ACE2 Determinants of SARS-CoV-2 and Group 2B Coronavirus Infection and Replication.

The angiotensin-converting enzyme 2 (ACE2) receptor is a major severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) host range determinant, and understanding SARS-CoV-2-ACE2 interactions will provide important insights into COVID-19 pathogenesis and animal model development. SARS-CoV-2 cannot infect mice due to incompatibility between its receptor binding domain and the murine ACE2 receptor. Through molecular modeling and empirical in vitro validation, we identified 5 key amino acid differences between murine and human ACE2 that mediate SARS-CoV-2 infection, generating a chimeric humanized murine ACE2. Additionally, we examined the ability of the humanized murine ACE2 receptor to permit infection by an additional preemergent group 2B coronavirus, WIV-1, providing evidence for the potential pan-virus capabilities of this chimeric receptor. Finally, we predicted the ability of these determinants to inform host range identification of preemergent coronaviruses by evaluating hot spot contacts between SARS-CoV-2 and additional potential host receptors. Our results identify residue determinants that mediate coronavirus receptor usage and host range for application in SARS-CoV-2 and emerging coronavirus animal model development.IMPORTANCE SARS-CoV-2 (the causative agent of COVID-19) is a major public health threat and one of two related coronaviruses that have caused epidemics in modern history. A method of screening potential infectible hosts for preemergent and future emergent coronaviruses would aid in mounting rapid response and intervention strategies during future emergence events. Here, we evaluated determinants of SARS-CoV-2 receptor interactions, identifying key changes that enable or prevent infection. The analysis detailed in this study will aid in the development of model systems to screen emergent coronaviruses as well as treatments to counteract infections.