Rapid selection of P323L in the SARS-CoV-2 polymerase (NSP12) in humans and non-human primate models and confers a large plaque phenotype (preprint)

The mutational landscape of SARS-CoV-2 varies at both the dominant viral genome sequence and minor genomic variant population. An early change associated with transmissibility was the D614G substitution in the spike protein. This appeared to be accompanied by a P323L substitution in the viral polymerase (NSP12), but this latter change was not under strong selective pressure. Investigation of P323L/D614G changes in the human population showed rapid emergence during the containment phase and early surge phase of wave 1 in the UK. This rapid substitution was from minor genomic variants to become part of the dominant viral genome sequence. A rapid emergence of 323L but not 614G was observed in a non-human primate model of COVID-19 using a starting virus with P323 and D614 in the dominant genome sequence and 323L and 614G in the minor variant population. In cell culture, a recombinant virus with 323L in NSP12 had a larger plaque size than the same recombinant virus with P323. These data suggest that it may be possible to predict the emergence of a new variant based on tracking the distribution and frequency of minor variant genomes at a population level, rather than just focusing on providing information on the dominant viral genome sequence e.g., consensus level reporting. The ability to predict an emerging variant of SARS-CoV-2 in the global landscape may aid in the evaluation of medical countermeasures and non-pharmaceutical interventions.

Identification and quantification of SARS-CoV-2 leader subgenomic mRNA gene junctions in nasopharyngeal samples shows phasic transcription in animal models of COVID-19 and aberrant pattens in humans (preprint)

Introduction: SARS-CoV-2 has a complex strategy for the transcription of viral subgenomic mRNAs (sgmRNAs), which are targets for nucleic acid diagnostics. Each of these sgRNAs has a unique 5 sequence, the leader-transcriptional regulatory sequence gene junction (leader-TRS-junction), that can be identified using sequencing. Results: High resolution sequencing has been used to investigate the biology of SARS-CoV-2 and the host response in cell culture models and from clinical samples. LeTRS, a bioinformatics tool, was developed to identify leader-TRS-junctions and be used as a proxy to quantify sgmRNAs for understanding virus biology. This was tested on published datasets and clinical samples from patients and longitudinal samples from animal models with COVID-19. Discussion: LeTRS identified known leader-TRS-junctions and identified novel species that were common across different species. The data indicated multi-phasic abundance of sgmRNAs in two different animal models, with spikes in sgmRNA abundance reflected in human samples, and therefore has implications for transmission models and nucleic acid-based diagnostics.

Intranasal type I interferon treatment is beneficial only when administered before clinical signs onset in the SARS-CoV-2 hamster model (preprint)

Impaired type I interferons (IFNs) production or signaling have been associated with severe COVID-19, further promoting the evaluation of recombinant type I IFNs as therapeutics against SARS-CoV-2 infection. In the Syrian hamster model, we show that intranasal administration of IFN- starting one day pre-infection or one day post-infection limited weight loss and decreased viral lung titers. By contrast, intranasal administration of IFN- starting at the onset of symptoms three days post-infection had no impact on the clinical course of SARS-CoV-2 infection. Our results provide evidence that early type I IFN treatments are beneficial, while late interventions are ineffective, although not associated with signs of enhanced disease.

Changes in SARS-CoV-2 before the peak in each country, producing unique variants. (preprint)

The second and third waves of coronavirus disease 2019 (COVID-19) have caused problems worldwide. Those are often thought to have resulted from people's carelessness or people not following restrictions, but in reality, the cause remains unclear. Here, using an objective analytical method, we present the changes in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing COVID-19 over time. The virus has mutated in three major directions, with three groups remaining to date. The basic structure of the groups was completed by April and shared across all continents. However, the virus continued to mutate independently in each country after the borders were closed. In particular, the virus mutated before the occurrence of a second or third peak. It seems that the mutations conferred higher infectivity to the virus, because of which the virus overcame previously effective protections. Currently, each country may possess such a unique stronger variant, which may cause another peak in other countries. These viruses could also serve as sources of mutations by exchanging parts of the genome. Such mutations could create a variant with superior infectivity.

The SARS-CoV-2 spike protein disrupts the cooperative function of human cardiac pericytes - endothelial cells through CD147 receptor-mediated signalling: a potential non-infective mechanism of COVID-19 microvascular disease (preprint)

Background: Severe coronavirus disease 2019 (COVID-19) manifests as a life-threatening microvascular syndrome. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses primarily the capsid spike (S) protein to engage with its receptors and infect host cells. To date, it is still not known if the S protein alone, without the other viral elements, is able to trigger vascular cell signalling and provoke cell dysfunction. Methods: We investigated the effects of the recombinant, stabilised S protein on primary human cardiac pericytes (PCs) signalling and function. Endpoints included cell viability, proliferation, migration, cooperation with endothelial cells (ECs) in angiogenesis assays, and release of pro-inflammatory cytokines. Adopting a blocking strategy against the S protein receptors ACE2 and CD147, we explored which receptor mediates the S protein signalling in PCs. Findings: We show, for the first time, that the recombinant S protein alone elicits functional alterations in cardiac PCs. This was documented as: (1) increased migration, (2) reduced ability to support EC network formation on Matrigel, (3) secretion of pro-inflammatory molecules typically involved in the cytokine storm; and (4) production of pro-apoptotic factors responsible for EC death. Furthermore, the S protein stimulates the phosphorylation/activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) through the CD147 receptor, but not ACE2, in cardiac PCs. Accordingly, the neutralization of CD147, using a blocking antibody, prevented the activation of ERK1/2 and partially rescued the PC function in the presence of the S protein. Interpretation: Our findings suggest the new, intriguing hypothesis that the S protein may elicit vascular cell dysfunction, potentially amplifying, or perpetuating, the damage caused by the whole coronavirus. This mechanism may have clinical and therapeutic implication.

Immunological and pathological outcomes of SARS-CoV-2 challenge after formalin-inactivated vaccine immunisation of ferrets and rhesus macaques (preprint)

There is an urgent requirement for safe and effective vaccines to prevent novel coronavirus disease (COVID-19) caused by SARS-CoV-2. A concern for the development of new viral vaccines is the potential to induce vaccine-enhanced disease (VED). This was reported in several preclinical studies with both SARS-CoV-1 and MERS vaccines but has not been reported with SARS-CoV-2 vaccines. We have used ferret and rhesus macaques challenged with SARS-CoV-2 to assess the potential for VED in animals vaccinated with formaldehyde-inactivated SARS-CoV-2 (FIV) formulated with Alhydrogel, compared to a negative control vaccine in ferrets or unvaccinated macaques. We showed no evidence of enhanced disease in ferrets or rhesus macaques given FIV except for mild transient enhanced disease seen at seven days post infection in ferrets. This increased lung pathology was observed early in the infection (day 7) but was resolved by day 15. We also demonstrate that formaldehyde treatment of SARS-CoV-2 reduces exposure of the spike receptor binding domain providing a mechanistic explanation for suboptimal immunity.

Cetylpyridinium chloride-containing mouthwashes reduce in vitro SARS-CoV-2 infectivity (preprint)

Oral mouthwashes decrease the infectivity of several respiratory viruses including SARS-CoV-2. However, the precise agents with antiviral activity present in these oral rinses and their exact mechanism of action remain unknown. Here we show that Cetylpyridinium chloride (CPC), a quaternary ammonium compound present in many oral mouthwashes, reduces SARS-CoV-2 infectivity by inhibiting viral fusion with target cells. We also found that CPC and CPC-containing mouth rinses decreased a thousand times the infectivity of SARS-CoV-2 in vitro, while the corresponding vehicles had no effect. CPC-containing mouth rinses could represent a cost-effective measure to reduce SARS-CoV-2 infectivity in saliva, aiding to reduce viral transmission from infected individuals.

From infection to immunity: understanding the response to SARS-CoV2 through in-silico modeling (preprint)

Background: Immune system conditions of the patient is a key factor in COVID-19 infection survival. A growing number of studies have focused on immunological determinants to develop better biomarkers for therapies. Aim: The dynamics of the insurgence of immunity is at the core of the both SARS-CoV-2 vaccine development and therapies. This paper addresses a fundamental question in the management of the infection: can we describe the insurgence (and the span) of immunity in COVID-19? The in-silico model developed here answers this question at individual (personalized) and population levels. We simulate the immune response to SARS-CoV-2 and analyze the impact of infecting viral load, affinity to the ACE2 receptor and age in the artificially infected population on the course of the disease. Methods: We use a stochastic agent-based immune simulation platform to construct a virtual cohort of infected individuals with age-dependent varying degree of immune competence. We use a parameter setting to reproduce known inter-patient variability and general epidemiological statistics. Results: We reproduce in-silico a number of clinical observations and we identify critical factors in the statistical evolution of the infection. In particular we evidence the importance of the humoral response over the cytotoxic response and find that the antibody titers measured after day 25 from the infection is a prognostic factor for determining the clinical outcome of the infection. Our modeling framework uses COVID-19 infection to demonstrate the actionable effectiveness of simulating the immune response at individual and population levels. The model developed is able to explain and interpret observed patterns of infection and makes verifiable temporal predictions. Within the limitations imposed by the simulated environment, this work proposes in a quantitative way that the great variability observed in the patient outcomes in real life can be the mere result of subtle variability in the infecting viral load and immune competence in the population. In this work we i) show the power of model predictions, ii) identify the clinical end points that could be more suitable for computational modeling of COVID-19 immune response, iii) define the resolution and amount of data required to empower this class of models for translational medicine purposes and, iv) we exemplify how computational modeling of immune response provides an important light to discuss hypothesis and design new experiments.

Binding strength and hydrogen bond numbers between Covid-19 RBD and HVR of antibody (preprint)

The global battle against the Covid-19 pandemic relies strongly on the human defence of antibody, which is assumed to bind the Receptor Binding Domain of the antigen with its Hypervariable Region. Due to the similarity to other viruses such as SARS, however, our understanding of the antibody-virus interaction has been limited to the genomic sequencing, which poses serious challenges to the containment, vaccine exploration and rapid serum testing. Based on the physical/chemical nature of the interaction, infrared spectroscopy was employed to reveal the binding disparity, when unusual temperature dependence was discovered from the 1550cm 1 absorption band, attributed to the hydrogen bonds by carboxyl/amino groups, binding the SARS-CoV-2 spike protein and closely resembled SARS-CoV-2 or SARS-CoV-1 antibodies. The infrared absorption intensity, associated with the number of hydrogen bonds, was found to increase sharply between 27C and 31C, with the relative absorbance matches at 37C the hydrogen bonding numbers of the two antibody types (19 vs 12). As a result, the specificity of the SARS-CoV-2 antibody will be more conclusive beyond 31C, instead of at the usual room temperature of 20C - 25C, when the vaccine research and antibody diagnosis would likely be undermined.

Predicting COVID-19 cases with unknown homogeneous or heterogeneous resistance to infectivity (preprint)

This article constructs a restricted infection rate inverse binomial-based approach to predict COVID-19 cases after a family gathering. The traditional inverse binomial (IB) model is unqualified to match the reality of COVID-19, because the data contradicts the models requirement that variance should be greater than expected value. A refined version of the IB model is a necessity to predict COVID-19 cases after family gatherings. Our refined version of an IB model is more appropriate and versatile, as it accommodates all potential data scenarios: equal, lesser, or greater variance than expected value. Application of the approach is based on a restricted infectivity rate and methodology on Fan et al.s COVID-19 data, which exhibits two clusters of infectivity. Cluster 1 has a smaller number of primary cases and exhibits larger variance than the expected cases with a negative correlation of 28%, implying that the number of secondary cases is lesser when the number of primary cases increases and vice versa. The traditional inverse binomial (IB) model is appropriate for Cluster 1. The probability of contracting COVID-19 is estimated to be 0.13 among the primary, but is 0.75 among the secondary in Cluster 1, with a wider gap. Conversely, Cluster 2, exhibits smaller variance than the expected cases with a correlation of 79%, implying the number of primary and secondary cases increase or decrease together. Cluster 2 disqualifies the traditional IB model and demands its refined version. Probability of contracting COVID-19 is estimated to be 0.74 among the primary, but is 0.72 among the secondary in Cluster 2, with a narrower gap. The models ability to estimate the communitys health system memory for future policies to be developed is an asset of this approach. The current hazard level to be infected with COVID-19 among the primary and secondary groups are estimable and interpretable. Author SummaryCurrent statistical models are not able to accurately predict disease infection spread in the COVID-19 pandemic. We have applied a widely-used inverse binomial method to predict rates of infection after small gatherings, going from primary (original) cases to secondary (later) cases after family gatherings or social events, using the data from the Wuhan and Gansu provinces in China, where the virus first spread. The advantages of the proposed approach include that the models ability to estimate the communitys health system memory for future policies to be developed, as such policies might reduce COVIDs spread if not its control. In our approach, as demonstrated, the current hazard level of becoming infected with COVID-19 and the odds of contracting COVID-19 among the primary in comparison to the secondary groups are estimable and interpretable. We hope the proposed approach will be used in future epidemics.

In vitro characterization of engineered red blood cells as potent viral traps against HIV-1 and SARS-CoV-2 (preprint)

Engineered red blood cells (RBCs) expressing viral receptors could be used therapeutically as viral traps as RBCs lack nuclei and other organelles required for viral replication. Here we show that the combination of a powerful erythroid-specific expression system and transgene codon optimization yields high expression levels of the HIV-1 receptors CD4 and CCR5, as well as a CD4-glycophorin A (CD4-GpA) fusion protein on enucleated RBCs. Engineered RBCs expressing CD4 and CCR5 were efficiently infected by HIV-1, but CD4 or CD4-GpA expression in the absence of CCR5 was sufficient to potently neutralize HIV-1 in vitro. To facilitate continuous large-scale production of engineered RBCs, we generated erythroblast cell lines stably expressing CD4-GpA or ACE2-GpA fusion proteins, which produced potent RBC viral traps against HIV-1 and SARS-CoV-2. Our results suggest that this approach warrants further investigation as a potential treatment against viral infections.

A recombinant protein SARS-CoV-2 candidate vaccine elicits high-titer neutralizing antibodies in macaques. (preprint)

Vaccines that generate robust and long-lived protective immunity against SARS-CoV-2 infection are urgently required. We assessed the potential of vaccine candidates based on the SARS-CoV-2 spike in cynomolgus macaques (M. fascicularis) by examining their ability to generate spike binding antibodies with neutralizing activity. Antigens were derived from two distinct regions of the spike S1 subunit, either the N-terminal domain (NTD) or an extended C-terminal domain containing the receptor-binding domain (RBD) and were fused to the human IgG1 Fc domain. Three groups of 2 animals each were immunized with either each antigen, alone or in combination. The development of antibody responses was evaluated through 20 weeks post-immunization. A robust IgG response to the spike protein was detected as early as 2 weeks after immunization with either protein and was maintained for over 20 weeks. Sera from animals immunized with antigens derived from the RBD were able to prevent binding of soluble spike proteins to the ACE2 receptor, shown by in vitro binding assays, while sera from animals immunized with the NTD alone lacked this activity. Crucially, sera from animals immunized with the RBD but not the NTD had potent neutralizing activity against SARS-CoV-2 pseudotyped virus, with titers in excess of 10,000, greatly exceeding that typically found in convalescent humans. Neutralizing activity persisted for more than 20 weeks. These data support the utility of spike subunit-based antigens as a vaccine for use in humans.

In vitro measurements of protein-protein interactions show that antibody affinity governs the inhibition of SARS-CoV-2 spike/ACE2 binding in convalescent serum (preprint)

The humoral immune response plays a key role in suppressing the pathogenesis of SARS-CoV-2. The molecular determinants underlying the neutralization of the virus remain, however, incompletely understood. Here, we show that the ability of antibodies to disrupt the binding of the viral spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor on the cell, the key molecular event initiating SARS-CoV-2 entry into host cells, is controlled by the affinity of these antibodies to the viral antigen. By using microfluidic antibody-affinity profiling, we were able to quantify the serum-antibody mediated inhibition of ACE2-spike binding in two SARS-CoV-2 seropositive individuals. Measurements to determine the affinity, concentration, and neutralization potential of antibodies were performed directly in human serum. Using this approach, we demonstrate that the level of inhibition in both samples can be quantitatively described using the binding energies of the binary interactions between the ACE2 receptor and the spike protein, and the spike protein and the neutralizing antibody. These experiments represent a new type of in-solution receptor binding competition assay, which has further potential areas of application ranging from decisions on donor selection for convalescent plasma therapy, to identification of lead candidates in therapeutic antibody development, and vaccine development.

Evidence of a dysregulated Vitamin D pathway in SARS-CoV-2 infected patient's lung cells (preprint)

Although a defective vitamin D pathway has been widely suspected to be associated in SARS-CoV-2 pathobiology, the status of the vitamin D pathway and vitamin D-modulated genes in lung cells of patients infected with SARS-CoV-2 remains unknown. To understand the significance of the vitamin D pathway in SARS-CoV-2 pathobiology, computational approaches were applied to transcriptomic datasets from bronchoalveolar lavage fluid (BALF) cells of such patients or healthy individuals. Levels of vitamin D receptor, retinoid X receptor, and CYP27A1 in BALF cells of patients infected with SARS-CoV-2 were found to be reduced. Additionally, 107 differentially expressed, predominantly downregulated genes modulated by vitamin D were identified in transcriptomic datasets from patient's cells. Further analysis of differentially expressed genes provided eight novel genes with a conserved motif with vitamin D-responsive elements, implying the role of both direct and indirect mechanisms of gene expression by the dysregulated vitamin D pathway in SARS-CoV-2-infected cells. Network analysis of differentially expressed vitamin D-modulated genes identified pathways in the immune system, NF-KB;cytokine signaling, and cell cycle regulation as top predicted pathways that might be affected in the cells of such patients. In brief, the results provided computational evidence to implicate a dysregulated vitamin D pathway in the pathobiology of SARS-CoV-2 infection.

pH and Receptor Induced Confirmational Changes- Implications Towards S1 Dissociation of SARS-CoV2 Spike Glycoprotein (preprint)

Viruses, being obligate intracellular parasites, must first attach themselves and gain entry into host cells. Viral fusion machinery is the central player in the viral attachment process in almost every viral disease. Viruses have incorporated an array of efficient fusion proteins on their surfaces to bind efficiently to host cell receptors. They make use of the host proteolytic enzymes to rearrange their surface protein(s) into the form which facilitates their binding to host-cell membrane proteins and subsequently, fusion. This stage of viral entry is very critical and has many therapeutic implications. The current global pandemic of COVID-19 has sparked severe health crisis and economic shutdowns. SARS-CoV2, the etiological agent of the disease has led to millions of deaths and brought the scientific community together in an attempt to understand the mechanisms of SARS-CoV2 pathogenesis and mortality. Like other viral fusion machinery, CoV2 spike (S) glycoprotein- 'The Demogorgon' poses the same questions about viral-host cell fusion. The intermediate stages of S protein-mediated viral fusion are unclear owing to the lack of structural insights and concrete biochemical evidence. The mechanism of conformational transition is still unclear. S protein binding and fusion with host cell receptors, Eg., angiotensin-converting enzyme-2 (ACE2) is accompanied by cleavage of S1/S2 subunits. To track the key events of viral-host cell fusion, we have identified (in silico) that low pH-induced conformational change and ACE-2 binding events promote S1 dissociation. Deciphering key mechanistic insights of SARS-CoV2 fusion will further our understanding of other class- I fusion proteins.

Mutation Landscape of SARS COV2 in Africa (preprint)

COVID-19 disease has had a relatively less severe impact in Africa. To understand the role of SARS CoV2 mutations on COVID-19 disease in Africa, we analysed 282 complete nucleotide sequences from African isolates deposited in the NCBI Virus Database. Sequences were aligned against the prototype Wuhan sequence (GenBank accession: NC_045512.2) in BWA v. 0.7.17. SAM and BAM files were created, sorted and indexed in SAMtools v. 1.10 and marked for duplicates using Picard v. 2.23.4. Variants were called with mpileup in BCFtools v. 1.11. Phylograms were created using Mr. Bayes v 3.2.6. A total of 2,349 single nucleotide polymorphism (SNP) profiles across 294 sites were identified. Clades associated with severe disease in the United States, France, Italy, and Brazil had low frequencies in Africa (L84S=2.5%, L3606F=1.4%, L3606F/V378I/=0.35, G251V=2%). Sub Saharan Africa (SSA) accounted for only 3% of P323L and 4% of Q57H mutations in Africa. Comparatively low infections in SSA were attributed to the low frequency of the D614G clade in earlier samples (25% vs 67% global). Higher disease burden occurred in countries with higher D614G frequencies (Egypt=98%, Morocco=90%, Tunisia=52%, South Africa) with D614G as the first confirmed case. V367F, D364Y, V483A and G476S mutations associated with efficient ACE2 receptor binding and severe disease were not observed in Africa. 95% of all RdRp mutations were deaminations leading to CpG depletion and possible attenuation of virulence. More genomic and experimental studies are needed to increase our understanding of the temporal evolution of the virus in Africa, clarify our findings, and reveal hot spots that may undermine successful therapeutic and vaccine interventions.