The real-world effectiveness of an intranasal spray A8G6 antibody cocktail in the post-exposure prophylaxis of COVID-19 (preprint)

BackgroundDue to the continuous appearance of novel SARS-CoV-2 variants that are resistant to approved antibodies and leading to the epidemic rebound, several approved neutralizing antibodies have been paused for their usage against COVID-19. Previously, we identified A8G6, an antibody combination of two synergic SARS-CoV-2 neutralizing antibodies 55A8 and 58G6, that showed broad neutralizing activities against Omicron variants. When administrated by the nasal spray delivery system, A8G6 showed promising efficacy in COVID-19 animal models and also showed favorable safety profile in preclinical models as well as in a first-in-human trial. The aim of this study is to evaluate the real-world efficacy of A8G6 neutralizing antibody nasal spray in post-exposure prevention of COVID-19. MethodsFrom November 27, 2022 to January 31, 2023, an open-label, non-randomized, two-arm, blank-controlled, investigator-initiated trial was conducted in Chongqing, China. High-risk healthy participants (18-65 years) within 72 hours after close contact to SARS-CoV-2 infected individuals were recruited and received a three-dose (1.4 mg/dose) A8G6 nasal spray treatment daily or no treatment (blank control) for 7 consecutive days. The primary end points were 1) the occurrence of positive SARS-CoV-2 RT-PCR cases in A8G6 treated group vs blank control group at the end of day 7; 2) time to SARS-CoV-2 positive conversion at the end of day 7. The secondary end points were 1) viral load of SARS-CoV-2 when participants became SARS-CoV-2 positive; 2) the time from SARS-CoV-2 infection to negative COVID-19 conversion. Safety end point of the nasal spray AG86 was analyzed by recording adverse events during the whole course of this trial. This study was registered with Chictr.org (ChiCTR2200066416). FindingsOf 513 enrolled participants, 173 in the A8G6 treatment group and 340 in the blank-control group were included in the analysis. SARS-CoV-2 infection occurred in 151/340 (44.4%) subjects in the blank control group and 12/173 (6.9%) subjects with the A8G6 treatment group. The result indicates that the intranasal spray A8G6 reduces the risk of SARS-CoV-2 infection (HR=0.12, 95% CI, 0.07-0.22; p<0.001). The prevention efficacy of the A8G6 treatment within 72-hours exposure was calculated to be 84.4% (95% CI: 74.4%-90.4%). Moreover, compared to the blank-control group, the time from the SARS-CoV-2 negative to the positive COVID-19 conversion was significantly longer in the AG86 treatment group (mean time: 3.4 days in the A8G6 treatment group vs 2.6 days in the control group, p=0.019). In the secondary end-point analysis, the A8G6 nasal treatment had no effects on the viral load at baseline SARS-CoV-2 RT-PCR positivity and the time of the negative COVID-19 conversion (viral clearance). Finally, 5 participants (3.1%) in the treatment group reported general adverse effects. We did not observe any severe adverse effects related to the A8G6 treatment in this study. InterpretationIn this study, the intranasal spray AG86 antibody cocktail showed potent efficacy for prevention of SARS-CoV-2 infection in close contacts of COVID-19 patients. FundingChongqing Biomedical R&D Major Special Project, Project (No. CSTB2022TIAD-STX0013), Chongqing Science and Health Joint Medical High-end Talent Project (No. 2022GDRC012), Science and Technology Research Program of Chongqing Municipal Education Commission (No. KJZD-K202100402), CQMU Program for Youth Innovation in Future Medicine (No. W0073). Research in contextO_ST_ABSEvidence before the studyC_ST_ABSTwo potent neutralizing antibodies 55A8 and 58G6 against SARS-CoV-2 were identified from the plasma of COVID-19 convalescent patients. In our previous studies, the synergetic neutralization of the antibody combination of 55A8 and 58G6 (A8G6) had been shown in structural mechanism, as well as in vitro and in vivo. Pre-clinical evaluation of A8G6 nasal spray showed promising efficacy against Omicron BA.4/5 infection in golden syrian hamsters challenged with live virus. In a first-in-human trial, A8G6 also showed favorable safety profile and nasal concentration over IC90 of neutralization activity against Omicron BA.4/5. The preliminary data showed that the intranasal spray A8G6 had the excellent efficacy, safety and druggability to protect against COVID-19. Added value of this studyThis is the first human trial showing that a nasal spray of neutralizing antibody cocktail is efficacious in preventing SARS-CoV-2 infection but is not efficacious in the post-infection treatment of COVID-19. In the Omicron wave of the COVID-19 pandemic in China in November, 2022, COVID-19 close contacts receiving the A8G6 treatment in the designated quarantine hotels showed a significantly lower incidence of SARS-CoV-2 infection. Additionally, the A8G6 treatment delayed time from exposure to the diagnosis of the COVID-19 positivity (median time: 3.4 days in the treatment group vs 2.6 days in the control group). Furthermore, we analyzed the effects of the A8G6 treatment on the clinical status of close contacts who became infected with SARS-CoV-2. Results suggests that there were no significant differences in viral load of SARS-CoV-2 at the beginning of positive infection and the time of the viral clearance between A8G6 treatment and blank control groups. Overall, the trial result is consistent with the mechanism of action of nasal spray antibody cocktail for the prevention of SARS-CoV-2 infection. Finally, low safety risk of the nasal spray A8G6 was also shown in the trial. Implications of all the available evidenceWe observed the use of A8G6 to reduce the risk of SARS-CoV-2 infection. This study provided supporting evidences for the real-world effectiveness and safety of the nasal spray A8G6 among high-risk close contacts in the post-exposure prevention of COVID-19 during the Omicron BA.5.2 wave in China. This is the first proof of concept of using nasal spray neutralizing antibody for the prevention of viral infection. It implicates that the promising efficacy of the nasal spray A8G6 makes it possible for the fast-acting prevention in future COVID-19 waves.

A cocktail containing two synergetic antibodies broadly neutralizes SARS-CoV-2 and its variants including Omicron BA.1 and BA.2 (preprint)

Neutralizing antibodies (NAbs) can prevent and treat infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, continuously emerging variants, such as Omicron, have significantly reduced the potency of most known NAbs. The selection of NAbs with broad neutralizing activities and the identification of conserved critical epitopes are still urgently needed. Here, we identified an extremely potent antibody (55A8) by single B-cell sorting from convalescent SARS-CoV-2-infected patients that recognized the receptor-binding domain (RBD) in the SARS-CoV-2 spike (S) protein. 55A8 could bind to wild-type SARS-CoV-2, Omicron BA.1 and Omicron BA.2 simultaneously with 58G6, a NAb previously identified by our group. Importantly, an antibody cocktail containing 55A8 and 58G6 (2-cocktail) showed synergetic neutralizing activity with a half-maximal inhibitory concentration (IC50) in the picomolar range in vitro and prophylactic efficacy in hamsters challenged with Omicron (BA.1) through intranasal delivery at an extraordinarily low dosage (25 g of each antibody daily) at 3 days post-infection. Structural analysis by cryo-electron microscopy (cryo-EM) revealed that 55A8 is a Class III NAb that recognizes a highly conserved epitope. It could block angiotensin-converting enzyme 2 (ACE2) binding to the RBD in the S protein trimer via steric hindrance. The epitopes in the RBD recognized by 55A8 and 58G6 were found to be different and complementary, which could explain the synergetic mechanism of these two NAbs. Our findings not only provide a potential antibody cocktail for clinical use against infection with current SARS-CoV-2 strains and future variants but also identify critical epitope information for the development of better antiviral agents.

Extensive neutralization against SARS-CoV-2 variants elicited by Omicron-specific subunit vaccine booster (preprint)

With the development of COVID-19, even though increased global vaccination coverage, a super variant of SARS-CoV-2, Omicron, carrying a great number of mutations, has been verified its strong capacity of immune escape. An increased risk of SARS-CoV-2 reinfection or breakthrough infection should be concerned. We analyzed the humoral immune response of Omicron breakthrough infection and found its cross-neutralization against VOCs. We established mouse models to verify whether Omicron-specific RBD subunit boost immune response by immunizing Omicron-RBD recombinant proteins. The results suggest that an additional boost vaccination with Omicron-RBD protein could increase humoral immune response against both WT and current VOCs.

Immunomolecular Assay Based on Selective Virion Capture by Spike Antibody and Viral Nucleic Acid Amplification for Detecting Intact SARS-CoV-2 Particles (preprint)

Background: Effective therapeutics and vaccines for coronavirus disease 2019 (COVID-19) are currently lacking because of the mutation and immune escape of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Based on the propagation characteristics of SARS-CoV-2, rapid and accurate detection of complete virions from clinical samples and the environment is critical for assessing infection risk and containing further COVID-19 outbreaks. However, currently applicable methods cannot achieve large-scale clinical application because of factors such as the high viral load, cumbersome virus isolation steps, demanding environmental conditions, and long experimental periods. In this study, we developed an immunomolecular detection method combining capture of the viral spike glycoprotein with monoclonal antibodies and nucleic acid amplification via quantitative reverse transcription PCR to rapidly and accurately detect complete virions. Results: : After constructing a novel pseudovirus, screening for specific antibodies, and optimizing the detection parameters, the assay achieved a limit of detection of 9 × 10 2 transduction units/mL of viral titer with high confidence (~95%) and excellent stability against human serum and common virus/pseudovirus. The coefficients of variation were 1.0–2.0% for intra-assay and inter-assay analyses, respectively. Compared with reverse transcription-PCR, the immunomolecular method more accurately quantified complete virions. SARS-CoV-2/pseudovirus was more stable on plastic and paper than on aluminum and copper in the detection of SARS-CoV-2 pseudovirus under different conditions, and complete virions were detected up to 96 h after they were applied to these surfaces (except for copper), although the titer of the virions was greatly reduced. Conclusions: : Convenient, inexpensive, and accurate complete virus detection can be applied in many fields, such as monitoring the infectivity of convalescent and post-discharge patients and assessing high-risk environments (isolation rooms, operating rooms, patient living environments, and cold chain logistics). This method can also be used to detect intact virions such as those of hepatitis B and C viruses, human immunodeficiency virus, influenza, and the partial pulmonary virus, which may further improve the accuracy of diagnoses and facilitate individualized and precise treatments.

Characterization of SARS-CoV-2 variants B.1.617.1 (Kappa), B.1.617.2 (Delta) and B.1.618 on cell entry, host range, and sensitivity to convalescent plasma and ACE2 decoy receptor (preprint)

Recently, highly transmissible SARS-CoV-2 variants B.1.617.1 (Kappa), B.1.617.2 (Delta) and B.1.618 were identified in India with mutations within the spike proteins. The spike protein of Kappa contains four mutations E154K, L452R, E484Q and P681R, and Delta contains L452R, T478K and P681R, while B.1.618 spike harbors mutations {Delta}145-146 and E484K. However, it remains unknown whether these variants have altered in their entry efficiency, host tropism, and sensitivity to neutralizing antibodies as well as entry inhibitors. In this study, we found that Kappa, Delta or B.1.618 spike uses human ACE2 with no or slightly increased efficiency, while gains a significantly increased binding affinity with mouse, marmoset and koala ACE2 orthologs, which exhibits limited binding with WT spike. Furthermore, the P618R mutation leads to enhanced spike cleavage, which could facilitate viral entry. In addition, Kappa, Delta and B.1.618 exhibits a reduced sensitivity to neutralization by convalescent sera owning to the mutation of E484Q, T478K, {Delta}145-146 or E484K, but remains sensitive to entry inhibitors-ACE2-lg decoy receptor. Collectively, our study revealed that enhanced human and mouse ACE2 receptor engagement, increased spike cleavage and reduced sensitivity to neutralization antibodies of Kappa, Delta and B.1.618 may contribute to the rapid spread of these variants and expanded host range. Furthermore, our result also highlighted that ACE2-lg could be developed as broad-spectrum antiviral strategy against SARS-CoV-2 variants.

Mutation Y453F in the spike protein of SARS-CoV-2 enhances interaction with the mink ACE2 receptor for host adaption (preprint)

COVID-19 patients transmitted SARS-CoV-2 to minks in the Netherlands in April 2020. Subsequently, the mink-associated virus (miSARS-CoV-2) spilled back over into humans. Genetic sequences of the miSARS-CoV-2 identified a new genetic variant known as "Cluster 5" that contained mutations in the spike protein. However, the functional properties of these "Cluster 5" mutations have not been well established. In this study, we found that the Y453F mutation located in the RBD domain of miSARS-CoV-2 is an adaptive mutation that enhances binding to mink ACE2 and other orthologs of Mustela species without compromising, and even enhancing, its ability to utilize human ACE2 as a receptor for entry. Structural analysis suggested that despite the similarity in the overall binding mode of SARS-CoV-2 RBD to human and mink ACE2, Y34 of mink ACE2 was better suited to interact with a Phe rather than a Tyr at position 453 of the viral RBD due to less steric clash and tighter hydrophobic-driven interaction. Additionally, the Y453F spike exhibited resistance to convalescent serum, posing a risk for vaccine development. Thus, our study suggests that since the initial transmission from humans, SARS-CoV-2 evolved to adapt to the mink host, leading to widespread circulation among minks while still retaining its ability to efficiently utilize human ACE2 for entry, thus allowing for transmission of the miSARS-CoV-2 back into humans. These findings underscore the importance of active surveillance of SARS-CoV-2 evolution in Mustela species and other susceptible hosts in order to prevent future outbreaks.

Reduced neutralization of SARS-CoV-2 B.1.617 variant by inactivated and RBD-subunit vaccine (preprint)

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The Spike protein that mediates coronavirus entry into host cells is a major target for COVID-19 vaccines and antibody therapeutics. However, multiple variants of SARS-CoV-2 have emerged, which may potentially compromise vaccine effectiveness. Using a pseudovirus-based assay, we evaluated SARS-CoV-2 cell entry mediated by the viral Spike B.1.617 and B.1.1.7 variants. We also compared the neutralization ability of monoclonal antibodies from convalescent sera and neutralizing antibodies (NAbs) elicited by CoronaVac (inactivated vaccine) and ZF2001 (RBD-subunit vaccine) against B.1.617 and B.1.1.7 variants. Our results showed that, compared to D614G and B.1.1.7 variants, B.1.617 shows enhanced viral entry and membrane fusion, as well as more resistant to antibody neutralization. These findings have important implications for understanding viral infectivity and for immunization policy against SARS-CoV-2 variants.

Ultrapotent SARS-CoV-2 neutralizing antibodies with protective efficacy against newly emerged mutational variants (preprint)

Accumulating mutations in the SARS-CoV-2 Spike (S) protein can increase the possibility of immune escape, challenging the present COVID-19 prophylaxis and clinical interventions. Here, 3 receptor binding domain (RBD) specific monoclonal antibodies (mAbs), 58G6, 510A5 and 13G9, with high neutralizing potency blocking authentic SARS-CoV-2 virus displayed remarkable efficacy against authentic B.1.351 virus. Each of these 3 mAbs in combination with one neutralizing Ab recognizing non-competing epitope exhibited synergistic effect against authentic SARS-CoV-2 virus. Surprisingly, structural analysis revealed that 58G6 and 13G9, encoded by the IGHV1-58 and the IGKV3-20 germline genes, both recognized the steric region S470-495 on the RBD, overlapping the E484K mutation presented in B.1.351. Also, 58G6 directly bound to another region S450-458 in the RBD. Significantly, 58G6 and 510A5 both demonstrated prophylactic efficacy against authentic SARS-CoV-2 and B.1.351 viruses in the transgenic mice expressing human ACE2 (hACE2), protecting weight loss and reducing virus loads. These 2 ultrapotent neutralizing Abs can be promising candidates to fulfill the urgent needs for the prolonged COVID-19 pandemic.

CCR1 regulatory variants linked to pulmonary macrophage recruitment in severe COVID-19 (preprint)

Genome-wide association studies have identified 3p21.31 as the main risk locus for severe symptoms and hospitalization in COVID-19 patients. To elucidate the mechanistic basis of this genetic association, we performed a comprehensive epigenomic dissection of the 3p21.31 locus. Our analyses pinpoint activating variants in regulatory regions of the chemokine receptor-encoding CCR1 gene as potentially pathogenic by enhancing infiltration of monocytes and macrophages into the lungs of patients with severe COVID-19.

Exploring the natural origins of SARS-CoV-2 (preprint)

The lack of an identifiable intermediate host species for the proximal animal ancestor of SARS-CoV-2 and the distance (~1500 km) from Wuhan to Yunnan province, where the closest evolutionary related coronaviruses circulating in horseshoe bats have been identified, is fueling speculation on the natural origins of SARS-CoV-2. Here we analyse SARS-CoV-2's related horseshoe bat and pangolin Sarbecoviruses and confirm Rhinolophus affinis continues to be the likely reservoir species as its host range extends across Central and Southern China. This would explain the bat Sarbecovirus recombinants in the West and East China, trafficked pangolin infections and bat Sarbecovirus recombinants linked to Southern China. Recent ecological disturbances as a result of changes in meat consumption could then explain SARS-CoV-2 transmission to humans through direct or indirect contact with the reservoir wildlife, and subsequent emergence towards Hubei in Central China. The only way, however, of finding the animal progenitor of SARS-CoV-2 as well as the whereabouts of its close relatives, very likely capable of posing a similar threat of emergence in the human population and other animals, will be by increasing the intensity of our sampling.

Emerging SARS-CoV-2 variants reduce neutralization sensitivity to convalescent sera and monoclonal antibodies (preprint)

SARS-CoV-2 Spike-specific antibodies contribute the majority of the neutralizing activity in most convalescent human sera. Two SARS-CoV-2 variants, N501Y.V1 (also known as B.1.1.7 lineage or VOC-202012/01) and N501Y.V2 (B.1.351 lineage), reported from the United Kingdom and South Africa, contain several mutations in the receptor binding domain of Spike and are of particular concern. To address the infectivity and neutralization escape phenotypes potentially caused by these mutations, we used SARS-CoV-2 pseudovirus system to compare the viral infectivity, as well as the neutralization activities of convalescent sera and monoclonal antibodies (mAbs) against SARS-CoV-2 variants. Our results showed that N501Y Variant 1 and Variant 2 increase viral infectivity compared to the reference strain (wild-type, WT) in vitro. At 8 months after symptom onset, 17 serum samples of 20 participants (85%) retaining titers of ID50 >40 against WT pseudovirus, whereas the NAb titers of 8 samples (40%) and 18 samples (90%) decreased below the threshold against N501Y.V1 and N501Y.V2, respectively. In addition, both N501Y Variant 1 and Variant 2 reduced neutralization sensitivity to most (6/8) mAbs tested, while N501Y.V2 even abrogated neutralizing activity of two mAbs. Taken together the results suggest that N501Y.V1 and N501Y.V2 reduce neutralization sensitivity to some convalescent sera and mAbs.

Host metabolite-cytokine correlation landscape in SARS-CoV-2 infection (preprint)

The systemic cytokine release syndrome (CRS) is a major cause of the multi-organ injury and fatal outcome induced by SARS-CoV-2 infection in severe COVID-19 patients. It has been well-known that metabolism plays a role in modulating the immune responses in infectious diseases. Yet, how the host metabolism correlates with CRS in COVID-19 patients and how the perturbed metabolites affect the cytokine release remains unclear. Here, we performed both metabolomics and cytokine/chemokine profiling on serum samples from the same cohort of healthy controls, mild and severe COVID-19 patients and delineated the global metabolic and immune response landscape along disease progression. Intriguingly, the correlation analysis revealed the tight link between metabolites and proinflammatory cytokines and chemokines, such as IL-6, M-CSF, IL-1α, IL-1β, implying the potential regulatory role of arginine metabolism, tryptophan metabolism, and purine metabolism in hyperinflammation. Importantly, we demonstrated that targeting metabolism markedly modulated the proinflammatory cytokines release by PBMCs isolated from SARS-CoV-2-infected rhesus macaques ex vivo. Beyond providing a comprehensive resource of metabolism and immunology data of SARS-CoV-2 infection, our study showed that metabolic alterations can be potentially exploited to develop novel strategy for the treatment of fatal CRS in COVID-19.

A rapid and efficient screening system for neutralizing antibodies and its application for SARS-CoV-2 (preprint)

After the epidemic of COVID-19, neutralizing antibodies (NAbs) against SARS-CoV-2 has been developed for the preventative and therapeutic purposes. However, few methodologies are reported in detail on how to rapidly and efficiently generate NAbs of interest. Here, we present a strategically optimized screening method for NAbs, which has enabled us to obtain SARS-CoV-2 receptor-binding domain (RBD) specific monoclonal Abs within 4 days, followed by additional 2 days to evaluate their neutralizing activities. Using this method, we obtained 198 specific Abs against SARS-CoV-2 RBD from the blood samples of COVID-19 convalescent patients, and 96 of them showed neutralizing activity. At least 20% of these NAbs exhibited high neutralizing potency. The top 2 NAbs showed the half-maximal inhibitory concentration (IC50) to block authentic SARS-CoV-2 at 9.88 and 11.13 ng/ml, respectively. Altogether, our study provides a fundamental methodology for discovering NAbs with potential preventative and therapeutic value for emerging infectious diseases.

A key linear epitope for a potent neutralizing antibody to SARS-CoV-2 S-RBD (preprint)

The spread of SARS-CoV-2 confers a serious threat to the public health without effective intervention strategies1-3. Its variant carrying mutated Spike (S) protein D614G (SD614G) has become the most prevalent form in the current global pandemic4,5. We have identified a large panel of potential neutralizing antibodies (NAbs) targeting the receptor-binding domain (RBD) of SARS-CoV-2 S6. Here, we focused on the top 20 potential NAbs for the mechanism study. Of them, the top 4 NAbs could individually neutralize both authentic SARS-CoV-2 and SD614G pseudovirus efficiently. Our epitope mapping revealed that 16/20 potent NAbs overlapped the same steric epitope. Excitingly, we found that one of these potent NAbs (58G6) exclusively bound to a linear epitope on S-RBD (termed as 58G6e), and the interaction of 58G6e and the recombinant ACE2 could be blocked by 58G6. We confirmed that 58G6e represented a key site of vulnerability on S-RBD and it could positively react with COVID-19 convalescent patients plasma. We are the first, as far as we know, to provide direct evidences of a linear epitope that can be recognized by a potent NAb against SARS-CoV-2 S-RBD. This study paves the way for the applications of these NAbs and the potential safe and effective vaccine design.

Molecular Characterization, Phylogenetic and Variation Analyzes of SARS-CoV-2 strains in Turkey (preprint)

IntroductionWe present the sequence analysis for 47 complete genomes for SARS-CoV-2 isolates on Turkish patients. To identify their genetic similarity, phylogenetic analysis was performed by comparing the worldwide SARS-CoV-2 sequences, selected from GISAID, to the complete genomes from Turkish isolates. In addition, we focused on the variation analysis to show the mutations on SARS-CoV-2 genomes. MethodsIllumina MiSeq platform was used for sequencing the libraries. The raw reads were aligned to the known SARS-CoV-2 genome (GenBank: MN908947.3) using the Burrows-Wheeler aligner (v.0.7.1). The phylogenetic tree was constructer using Phylip v.3.6 with Neighbor-Joining and composite likelihood method. The variants were detected by using Genome Analysis Toolkit-HaplotypeCaller v.3.8.0 and were inspected on GenomeBrowse v2.1.2. ResultsAll viral genome sequences of our isolates was located in lineage B under the different clusters such as B.1 (n=3), B.1.1 (n=28), and B.1.9 (n=16). According to the GISAID nomenclature, all our complete genomes were placed in G, GR and GH clades. Five hundred forty-nine total and 53 unique variants were detected. All 47 genomes exhibited different kinds of variants. The distinct variants consist of 274 missense, 225 synonymous, and 50 non-coding alleles. ConclusionThe results indicated that the SARS-CoV-2 sequences of our isolates have great similarity with all Turkish and European sequences. Further studies should be performed for better comparison of strains, after more complete genome sequences will be released. We also believe that collecting and sharing any data about SARS-CoV-2 virus and COVID-19 will be effective and may help the related studies.

A comparative survey of betacoronavirus strain molecular dynamics identifies key ACE2 binding sites (preprint)

Comparative functional analysis of the binding interactions between various betacoronavirus strains and their potential human target proteins, such as ACE1, ACE2 and CD26, is critical to our future understanding and combating of COVID-19. Here, employing large replicate sets of GPU accelerated molecular dynamics simulations, we statistically compare atom fluctuations of the known human target proteins in both the presence and absence of different strains of the viral receptor binding domain (RBD) of the S spike glycoprotein. We identify a common interaction site between the N-terminal helices of ACE2 and the viral RBD in all strains (hCoV-OC43, hCoV-HKU1, MERS-CoV, SARS-CoV1, and SARS-CoV-2) and a second more dynamically complex RBD interaction site involving the ACE2 amino acid sites K353, Q325, and a novel motif, AAQPFLL (386-392) in the more recent cross-species spillovers (i.e. absent in hCoV-OC43). We use computational mutagenesis to further confirm the functional relevance of these sites. We propose a "one touch/two touch" model of viral evolution potentially involved in functionally facilitating binding interactions in zoonotic spillovers. We also observe these two touch sites governing RBD binding activity in simulations on hybrid models of the suspected viral progenitor, batCoV-HKU4, interacting with both the human SARS target, ACE2, and the human MERS target, CD26. Lastly, we confirm that the presence of a common hypertension drug (lisinopril) within the target site of SARS-CoV-2 bound models of ACE1 and ACE2 acts to enhance the RBD interactions at the same key sites in our proposed model. In the near future, we recommend that our comparative computational analysis identifying these key viral RBD-ACE2 binding interactions be supplemented with comparative studies of site-directed mutagenesis in order to screen for current and future coronavirus strains at high risk of zoonotic transmission to humans. STATEMENT OF SIGNIFICANCEWe generated structural models of the spike glycoprotein receptor binding domain from recent and past betacoronavirus outbreak strains aligned to the angiotensin 1 converting enzyme 2 protein, the primary target protein of the SARS-CoV-2 virus causing COVID 19. We then statistically compared computer simulated molecular dynamics of viral bound and unbound versions of each model to identify locations where interactions with each viral strain have dampened the atom fluctuations during viral binding. We demonstrate that all known strains of betacoronavirus are strongly interactive with the N-terminal helix region of ACE2. We also identify a more complex viral interaction with three novel sites that associates with more recent and deadly SARS strains, and also a bat progenitor strain HKU4.

What if we perceive SARS-CoV-2 genomes as documents? Topic modelling using Latent Dirichlet Allocation to identify mutation signatures and classify SARS-CoV-2 genomes (preprint)

Topic modeling is frequently employed for discovering structures (or patterns) in a corpus of documents. Its utility in text-mining and document retrieval tasks in various fields of scientific research is rather well known. An unsupervised machine learning approach, Latent Dirichlet Allocation (LDA) has particularly been utilized for identifying latent (or hidden) topics in document collections and for deciphering the words that define one or more topics using a generative statistical model. Here we describe how SARS-CoV-2 genomic mutation profiles can be structured into a Bag of Words to enable identification of signatures (topics) and their probabilistic distribution across various genomes using LDA. Topic models were generated using ~47000 novel corona virus genomes (considered as documents), leading to identification of 16 amino acid mutation signatures and 18 nucleotide mutation signatures (equivalent to topics) in the corpus of chosen genomes through coherence optimization. The document assumption for genomes also helped in identification of contextual nucleotide mutation signatures in the form of conventional N-grams (e.g. bi-grams and tri-grams). We validated the signatures obtained using LDA driven method against the previously reported recurrent mutations and phylogenetic clades for genomes. Additionally, we report the geographical distribution of the identified mutation signatures in SARS-CoV-2 genomes on the global map. Use of the non-phylogenetic albeit classical approaches like topic modeling and other data centric pattern mining algorithms is therefore proposed for supplementing the efforts towards understanding the genomic diversity of the evolving SARS-CoV-2 genomes (and other pathogens/microbes).

A rapid and efficient screening system for neutralizing antibodies and its application for the discovery of potent neutralizing antibodies to SARS-CoV-2 S-RBD (preprint)

Neutralizing antibodies (Abs) have been considered as promising therapeutics for the prevention and treatment of pathogens. After the outbreak of COVID-19, potent neutralizing Abs to SARS-CoV-2 were promptly developed, and a few of those neutralizing Abs are being tested in clinical studies. However, there were few methodologies detailly reported on how to rapidly and efficiently generate neutralizing Abs of interest. Here, we present a strategically optimized method for precisive screening of neutralizing monoclonal antibodies (mAbs), which enabled us to identify SARS-CoV-2 receptor-binding domain (RBD) specific Abs within 4 days, followed by another 2 days for neutralization activity evaluation. By applying the screening system, we obtained 198 Abs against the RBD of SARS-CoV-2. Excitingly, we found that approximately 50% (96/198) of them were candidate neutralizing Abs in a preliminary screening of SARS-CoV-2 pseudovirus and 20 of these 96 neutralizing Abs were confirmed with high potency. Furthermore, 2 mAbs with the highest neutralizing potency were identified to block authentic SARS-CoV-2 with the half-maximal inhibitory concentration (IC50) at concentrations of 9.88 ng/ml and 11.13 ng/ml. In this report, we demonstrated that the optimized neutralizing Abs screening system is useful for the rapid and efficient discovery of potent neutralizing Abs against SARS-CoV-2. Our study provides a methodology for the generation of preventive and therapeutic antibody drugs for emerging infectious diseases.

Susceptibility of raccoon dogs for experimental SARS-CoV-2 infection (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in China at the end of 2019, and became pandemic. The zoonotic virus most likely originated from bats, but definite intermediate hosts have not yet been identified. Raccoon dogs (Nyctereutes procyonoides) are kept for fur production, in particular in China, and were suspected as potential intermediate host for both SARS-CoV6 and SARS-CoV2. Here we demonstrate susceptibility of raccoon dogs for SARS-CoV-2 infection after intranasal inoculation and transmission to direct contact animals. Rapid, high level virus shedding, in combination with minor clinical signs and pathohistological changes, seroconversion and absence of viral adaptation highlight the role of raccoon dogs as a potential intermediate host. The results are highly relevant for control strategies and emphasize the risk that raccoon dogs may represent a potential SARS-CoV-2 reservoir. Our results support the establishment of adequate surveillance and risk mitigation strategies for kept and wild raccoon dogs. Article Summary LineRaccoon dogs are susceptible to and efficiently transmit SARS-CoV2 and may serve as intermediate host