Systematical assessment of the impact of single spike mutations of SARS-CoV-2 Omicron sub-variants on the neutralization capacity of post-vaccination sera (preprint)

The evolution of novel SARS-CoV-2 variants significantly affects vaccine effectiveness. While these effects can only be studied retrospectively, neutralizing antibody titers are most used as correlates of protection. However, studies assessing neutralizing antibody titers often show heterogeneous data. To address this, we investigated assay variance and identified virus infection time and dose as factors affecting assay robustness. We next measured neutralization against Omicron sub-variants in cohorts with hybrid or vaccine induced immunity, identifying a gradient of immune escape potential. To evaluate the effect of individual mutations on this immune escape potential of Omicron variants, we systematically assessed the effect of each individual mutation specific to Omicron BA.1, BA.2, BA.2.12.1, and BA.4/5. We cloned a library of pseudo-viruses expressing spikes with single point mutations, and subjected it to pooled sera from vaccinated hosts, thereby identifying multiple mutations that independently affect neutralization potency. These data might help to predict antigenic features of novel viral variants carrying these mutations and support the development of broad monoclonal antibodies.

Persicamidine – Außergewöhnliche Sesquarterpenoide mit potenter antiviraler Bioaktivität gegen Coronaviren

Eine neue Substanzfamilie von ungewöhnlichen Sesquarterpenoiden (Persicamidine A–E) mit hoher antiviraler Aktivität wurde aus einem kürzlich entdeckten Aktinobakterien‐Stamm (Kibdelosporangium persicum sp. nov.) isoliert, welcher aus einem Wüstenhabitat im Iran stammt. Umfangreiche NMR‐Analysen entlarvten ein hexazyklisches Terpenoidmolekül mit einer modifizierten Zuckereinheit auf einer Seite und einer höchst ungewöhnlichen Isoharnstoffeinheit, die mit der Terpenoidstruktur verbunden ist. Die Strukturen der fünf Derivate unterschieden sich ausschließlich durch die Aminoalkyl‐Seitenkette, die an die Isoharnstoffeinheit gebunden ist. Die Persicamidine A–E zeigten eine starke Aktivität gegen hCoV‐229E‐ und SARS‐CoV‐2‐Viren im nanomolaren Bereich bei gleichzeitig sehr guten Selektivitätsindizes. Dies macht die Persicamidine zu vielversprechenden Ausgangsverbindungen für die Arzneimittelentwicklung.

TMPRSS2 is essential for SARS-CoV-2 Beta and Omicron infection (preprint)

The COVID-19 pandemic remains a global health threat and novel antiviral strategies are urgently needed. SARS-CoV-2 employs the cellular serine protease TMPRSS2 for entry into lung cells and TMPRSS2 inhibitors are being developed for COVID-19 therapy. However, the SARS-CoV-2 Omicron variant, which currently dominates the pandemic, prefers the endo/lysosomal cysteine protease cathepsin L over TMPRSS2 for cell entry, raising doubts whether TMPRSS2 inhibitors would be suitable for treatment of patients infected with the Omicron variant. Nevertheless, the contribution of TMPRSS2 to spread of SARS-CoV-2 in the infected host is largely unclear. Here, we show that loss of TMPRSS2 strongly reduced the replication of the Beta variant in nose, trachea and lung of C57BL mice and protected the animals from weight loss and disease. Infection of mice with the Omicron variant did not cause disease, as expected, but again TMPRSS2 was essential for ef-ficient viral spread in the upper and lower respiratory tract. These results identify a key role of TMPRSS2 in SARS-CoV-2 Beta and Omicron infection and highlight TMPRSS2 as an attractive target for antiviral intervention.

Long-term immune protection against SARS-CoV-2 escape variants upon a single vaccination with murine cytomegalovirus expressing the spike protein (preprint)

Vaccines are central to controlling the coronavirus disease 2019 (COVID-19) pandemic but the durability of protection is limited for currently approved COVID-19 vaccines. Further, the emergence of variants of concern (VoCs) that evade immune recognition has reduced vaccine effectiveness, compounding the problem. Here, we show that a single dose of a murine cytomegalovirus (MCMV)-based vaccine, which expresses the spike (S) protein of the virus circulating early in the pandemic (MCMVS), protects highly susceptible K18-hACE2 mice from clinical symptoms and death upon challenge with a lethal dose of D614G SARS-CoV-2. Moreover, MCMVS vaccination controlled two immune-evading VoCs, the Beta (B.1.135) and the Omicron (BA.1) variants in BALB/c mice, and S-specific immunity was maintained for at least 5 months after immunization, where neutralizing titers against all tested VoCs were higher at 5-months than at 1-month post-vaccination. Thus, cytomegalovirus (CMV)-based vector vaccines might allow for long-term protection against COVID-19.

Pharmacological modulators of epithelial immunity uncovered by synthetic genetic tracing of SARS-CoV-2 infection responses (preprint)

Epithelial immune responses govern tissue homeostasis and offer drug targets against maladaptation. Here, we report a framework to generate drug discovery-ready reporters of cellular responses to viral infection. We reverse engineered epithelial cell responses to SARS- CoV-2, the viral agent fueling the ongoing COVID-19 pandemic and designed synthetic transcriptional reporters whose molecular logic comprises interferon-a/b/g-, and NF-kB pathways. Such regulatory potential reflected single-cell data from experimental models to severe COVID-19 patient epithelial cells infected by SARS-CoV-2. SARS-CoV-2, type-I interferons, and RIG-I drive reporter activation. Live-cell-image-based phenotypic drug screens identified JAK inhibitors and DNA damage inducers as antagonistic modulators of epithelial cell response to interferons, RIG-I stimulation, and SARS-CoV-2. Synergistic or antagonistic modulation of the reporter by drugs underscored their similar mechanism of action. Thus, this study describes a tool for dissecting antiviral responses to infection and sterile cues, and a rapid approach to other emerging viruses of public health concern in order to discover rational drug combinations.

ORFeome Phage Display Reveals a Major Immunogenic Epitope on the S2 Subdomain of SARS-Cov-2 Spike Protein (preprint)

The development of antibody therapies against SARS-CoV-2 remains a challenging task during the ongoing COVID-19 pandemic. All approved therapeutic antibodies are directed against the receptor binding domain (RBD) of Spike and lost neutralization efficacy against continuously emerging SARS-CoV-2 variants, which especially mutate in the RBD region. Previously, phage display has been used to identify epitopes of antibody responses against several diseases. Such epitopes have been applied to design vaccines or neutralizing antibodies. Here, we constructed an ORFeome phage display library for the SARS-CoV-2 genome. Open reading frames (ORFs) representing the SARS-CoV-2 genome were displayed on the surface of phage particles in order to identify enriched immunogenic epitopes from COVID-19 patients. Library quality was assessed by both, NGS and epitope mapping of a monoclonal antibody with known binding site. The most prominent epitope captured represented parts of Spike´s fusion peptide (FP). It is associated with the cell entry mechanism of SARS-CoV-2 into the host cell and the serine protease TMPRSS2 cleaves Spike within this sequence. Blocking of this mechanism could be a potential target for non-RBD binding therapeutic anti-SARS-CoV-2 antibodies. As mutations within the FP amino acid sequence were rather rare among SARS-CoV-2 variants so far, this may be an advantage in the fight against future virus variants.

Diminished neutralization responses towards SARS-CoV-2 Omicron VoC after mRNA or vector-based COVID-19 vaccinations (preprint)

Background: SARS-CoV-2 variants accumulating immune escape mutations provide a significant risk to vaccine-induced protection. The novel variant of concern Omicron (B.1.1.529) has to date the largest number of amino acid alterations in its Spike protein. Thus, it may efficiently escape recognition by neutralizing antibodies, allowing breakthrough infections in convalescent and vaccinated individuals. Aims: We analysed neutralization activity after vaccination with all mRNA-, vector- or heterologous immunization schemes currently available in Europe at peak response and in a longitudinal follow-up with BNT162b2 vaccinees to define immune escape potential of the Omicron VoC. Methods: We tested sera by in vitro neutralization assay towards SARS-CoV-2 B.1, Omicron, Beta and Delta pseudotypes Results: All vaccines apart from Ad26.CoV2.S showed high levels of responder rates (93.3-100%) towards SARS-CoV-2 wild-type, but some reductions in neutralizing Beta and Delta VoC pseudotypes. The novel Omicron variant had the biggest impact, both in terms of response rates and neutralization titres among responders. Only mRNA-1273 showed a 100% response rate to Omicron and induced the highest titres of neutralizing antibodies, followed by heterologous prime-boost approaches. Homologous BNT162b2 vaccination or vector-based formulations with AZD1222 or Ad26.CoV2.S performed less well with peak responder rates of 33%, 50% and 9%, respectively. However, Omicron responder rates in BNT162b2 recipients were maintained in our six month longitudinal follow-up and even slightly increased to 47%, indicating cross-protection against Omicron is maintained over time. Conclusions: Overall, our data strongly argues for urgent booster doses in individuals who were previously vaccinated with BNT162b2, or a vector-based immunization scheme.

A third vaccination with a single T cell epitope protects against SARS-CoV-2 infection in the absence of neutralizing antibodies (preprint)

Understanding the mechanisms and impact of booster vaccinations can facilitate decisions on vaccination programmes. This study shows that three doses of the same synthetic peptide vaccine eliciting an exclusive CD8+ T cell response against one SARS-CoV-2 Spike epitope protected all mice against lethal SARS-CoV-2 infection in the K18-hACE2 transgenic mouse model in the absence of neutralizing antibodies, while only a second vaccination with this T cell vaccine was insufficient to provide protection. The third vaccine dose of the single T cell epitope peptide resulted in superior generation of effector-memory T cells in the circulation and tissue-resident memory T (TRM) cells, and these tertiary vaccine-specific CD8+ T cells were characterized by enhanced polyfunctional cytokine production. Moreover, fate mapping showed that a substantial fraction of the tertiary effector-memory CD8+ T cells developed from remigrated TRM cells. Thus, repeated booster vaccinations quantitatively and qualitatively improve the CD8+ T cell response leading to protection against otherwise lethal SARS-CoV-2 infection.

Human serum from SARS-CoV-2 vaccinated and COVID-19 patients shows reduced binding to the RBD of SARS-CoV-2 Omicron variant in comparison to the original Wuhan strain and the Beta and Delta variants (preprint)

Background The ongoing COVID-19 pandemic is caused by the beta coronavirus SARS-CoV-2. COVID-19 manifests itself from mild or even asymptomatic infections to severe forms of life-threatening pneumonia. At the end of November 2021, yet another novel SARS-CoV-2 variant named B.1.1.529 or Omicron was discovered and classified as a variant of concern (VoC) by the WHO. Omicron shows significantly more mutations in the amino acid (aa) sequence of its spike protein than any previous variant, with the majority of those concentrated in the receptor binding domain (RBD). In this work, the binding of the Omicron RBD to the human ACE2 receptor was experimentally analyzed in comparison to the original Wuhan SARS-CoV-2 virus, and the Beta and Delta variants. Moreover, we compared the ability of human sera from COVID-19 convalescent donors and persons fully vaccinated with BNT162b2 (Corminaty) or Ad26.COV2.S (Janssen COVID-19 vaccine) as well as individuals who had boost vaccine doses with BNT162b2 or mRNA-1273 (Spikevax) to bind the different RBDs variants. Methods The Omicron RBD with 15 aa mutations compared to the original Wuhan strain was produced baculovirus-free in insect cells. Binding of the produced Omicron RBD to hACE was analyzed by ELISA. Sera from 27 COVID-19 patients, of whom 21 were fully vaccinated and 16 booster recipients were titrated on the original Wuhan strain, Beta, Delta and Omicron RBD and compared to the first WHO International Standard for anti-SARS-CoV-2 immunoglobulin (human) using the original Wuhan strain as reference. Results The Omicron RBD showed a slightly reduced binding to ACE2 compared to the other RBDs. The serum of COVID-19 patients, BNT162b2 vaccinated and boost vaccinated persons showed a reduced binding to Omicron RBD in comparison to the original Wuhan strain, Beta und Delta RBDs. In this assay, the boost vaccination did not improve the RBD binding when compared to the BNT162b2 fully vaccinated group. The RBD binding of the Ad26.COV2.S serum group was lower at all compared to the other groups. Conclusions The reduced binding of human sera to Omicron RBD provides first hints that the current vaccinations using BNT162b2, mRNA-1273 and Ad26.COV2.S may be less efficient in preventing infections with the Omicron variant.

MCMV based vaccine vectors expressing full-length viral proteins provide long-term humoral immune protection upon a single-shot vaccination (preprint)

Global pandemics by influenza or coronaviruses cause severe disruptions to the public health and lead to severe morbidity and mortality. Vaccines against these pathogens remain a medical need. CMV (cytomegalovirus) is a β-herpesvirus that induces uniquely robust immune responses, where outstandingly large populations of antigen-specific CD8+ T cells are maintained for a lifetime. Hence, CMV has been proposed and investigated as a novel vaccine vector expressing antigenic peptides or proteins to elicit protective cellular immune responses against numerous pathogens. We generated two recombinant murine CMV (MCMV) vaccine vectors expressing the hemagglutinin (HA) of influenza A virus (MCMVHA) or the spike protein of the severe acute respiratory syndrome coronavirus 2 (MCMVS). A single shot of MCMVs expressing either viral protein induced potent neutralizing antibody responses, which strengthened over time. Importantly, MCMVHA vaccinated mice were protected from illness following challenge with the influenza virus, and we excluded that this protection was due to effects of memory T cells. Conclusively, we show here that MCMV vectors do not only induce long-term cellular immunity, but also humoral responses that provide long-term immune protection against clinically relevant respiratory pathogens.

Revealing the host antiviral protein ZAP-S as an inhibitor of SARS-CoV-2 programmed ribosomal frameshifting (preprint)

Programmed ribosomal frameshifting (PRF) is a fundamental gene expression event in many viruses including SARS-CoV-2, which allows production of essential structural and replicative enzymes from an alternative reading frame. Despite the importance of PRF for the viral life cycle, it is still largely unknown how and to what extent cellular factors alter mechanical properties of frameshifting RNA molecules and thereby impact virulence. This prompted us to comprehensively dissect the interplay between the host proteome and the SARS-CoV-2 frameshift element. Here, we reveal that zinc-finger antiviral protein (ZAP-S) is a direct and specific regulator of PRF in SARS-CoV-2 infected cells. ZAP-S overexpression strongly impairs frameshifting and viral replication. Using in vitro ensemble and single-molecule techniques, we further demonstrate that ZAP-S directly interacts with the SARS-CoV-2 RNA and ribosomes and interferes with the folding of the frameshift RNA. Together these data illuminate ZAP-S as de novo host-encoded specific inhibitor of SARS-CoV-2 frameshifting and expand our understanding of RNA-based gene regulation.

Antiviral activity of influenza A virus defective interfering particles against SARS-CoV-2 replication in vitro through stimulation of innate immunity (preprint)

SARS-CoV-2 causing COVID-19 emerged in late 2019 and resulted in a devastating pandemic. Although the first approved vaccines were already administered by the end of 2020, worldwide vaccine availability is still limited. Moreover, immune escape variants of the virus are emerging against which the current vaccines may confer only limited protection. Further, existing antivirals and treatment options against COVID-19 only show limited efficacy. Influenza A virus (IAV) defective interfering particles (DIPs) were previously proposed not only for antiviral treatment of the influenza disease but also for pan-specific treatment of interferon (IFN)-sensitive respiratory virus infections. To investigate the applicability of IAV DIPs as an antiviral for the treatment of COVID-19, we conducted in vitro co-infection experiments with cell culture-derived DIPs and the IFN-sensitive SARS-CoV-2 in human lung cells. We show that treatment with IAV DIPs leads to complete abrogation of SARS-CoV-2 replication. Moreover, this inhibitory effect was dependent on janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling. Further, our results suggest boosting of IFN-induced antiviral activity by IAV DIPs as a major contributor in suppressing SARS-CoV-2 replication. Thus, we propose IAV DIPs as an effective antiviral agent for treatment of COVID-19, and potentially also for suppressing the replication of new variants of SARS-CoV-2.

A SARS-CoV-2 Neutralizing Antibody Selected from COVID-19 Patients by Phage Display is Binding to the ACE2-RBD Interface and is Tolerant to Known RBD Mutations (preprint)

The novel betacoranavirus SARS-CoV-2 causes a form of severe pneumonia disease, termed COVID-19 (coronavirus disease 2019). Recombinant human antibodies are proven potent neutralizers of viruses and can block the interaction of viral surface proteins with their host receptors. To develop neutralizing anti-SARS-CoV-2 antibodies, antibody gene libraries from convalescent COVID-19 patients were constructed and recombinant antibody fragments (scFv) against the receptor binding domain (RBD) of the S1 subunit of the viral spike (S) protein were selected by phage display. The selected antibodies were produced in the scFv-Fc format and 30 showed more than 80% inhibition of spike (S1-S2) binding to cells expressing ACE2, assessed by flow cytometry screening assay. The majority of these inhibiting antibodies are derived from the VH3-66 V-gene. The antibody STE90-C11 showed an IC50 of 0.56 nM in a plaque-based live SARS-CoV-2 neutralization assay. The crystal structure of STE90-C11 in complex with SARS-CoV-2-RBD was solved at 2.0 Å resolution showing that the antibody binds at the same region as ACE2 to RBD. In contrast to other published anti-SARS-CoV-2 antibodies, the binding of STE90-C11 is not blocked by known RBD mutations, endowing our antibody with higher intrinsic resistance to those possible escape mutants.Funding: We kindly acknowledge the financial support of MWK Niedersachsen (14-76103-184CORONA-2/20) for antibody generation. We also acknowledge support of the European Union for the ATAC (“antibody therapy against corona”, Horizon 2020 number 101003650) consortium.Conflict of Interest: The authors declare a conflict of interest. F.B., D.M.,N.L., S.S., P.A.H., R.B., M.R., K.T.S.,K.D.R.R., S.Z.-E., M.B., V.F., S.T.,M.S. and M.H. are inventors on a patent application on blocking antibodies against SARS-CoV-2. A.H., A.F. and T.S. are officers of CORAT Therapeutics GmbH, a company founded by YUMAB GmbH for the clinical and regulatory development of STE90-C11 (COR-101). A.F., T.S., S.D. and M.H. are shareholders of YUMAB GmbH.Ethical Approval: Approval number, FV-2020-02. Approved by the TU BraunschweigInstitute for Psychology.

A SARS-CoV-2 neutralizing antibody selected from COVID-19 patients by phage display is binding to the ACE2-RBD interface and is tolerant to known RBD mutations (preprint)

The novel betacoranavirus SARS-CoV-2 causes a form of severe pneumonia disease, termed COVID-19 (coronavirus disease 2019). Recombinant human antibodies are proven potent neutralizers of viruses and can block the interaction of viral surface proteins with their host receptors. To develop neutralizing anti-SARS-CoV-2 antibodies, antibody gene libraries from convalescent COVID-19 patients were constructed and recombinant antibody fragments (scFv) against the receptor binding domain (RBD) of the S1 subunit of the viral spike (S) protein were selected by phage display. The selected antibodies were produced in the scFv-Fc format and 30 showed more than 80% inhibition of spike (S1-S2) binding to cells expressing ACE2, assessed by flow cytometry screening assay. The majority of these inhibiting antibodies are derived from the VH3-66 V-gene. The antibody STE90-C11 showed an IC50 of 0.56 nM in a plaque-based live SARS-CoV-2 neutralization assay. The crystal structure of STE90-C11 in complex with SARS-CoV-2-RBD was solved at 2.0 A resolution showing that the antibody binds at the same region as ACE2 to RBD. In contrast to other published anti-SARS-CoV-2 antibodies, the binding of STE90-C11 is not blocked by known RBD mutations, endowing our antibody with higher intrinsic resistance to those possible escape mutants.

Consistent and High-Frequency Identification of an Intra-Sample Genetic Variant of SARS-CoV-2 with Elevated Fusogenic Properties (preprint)

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a genome comprised of a ~30K nucleotides non-segmented, positive single-stranded RNA. Although its RNA-dependent RNA polymerase exhibits exonuclease proofreading activity, viral sequence diversity can be induced by replication errors and host factors. These variations can be observed in the population of viral sequences isolated from infected host cells and are not necessarily reflected in the genome of transmitted founder viruses. We profiled intra-sample genetic diversity of SARS-CoV-2 variants using 15,289 high-throughput sequencing datasets from infected individuals and infected cell lines. Most of the genetic variations observed, including C->U and G->U, were consistent with errors due to heat-induced DNA damage during sample processing, and/or sequencing protocols. Despite high mutational background, we confidently identified intra-variable positions recurrent in the samples analyzed, including several positions at the end of the gene encoding the viral S protein. Notably, most of the samples possesses a C->A missense mutation resulting in the S protein lacking the last 20 amino acids (S{Delta}20). Here we demonstrate that S{Delta}20 exhibits increased cell-to-cell fusion and syncytia formations. Our findings are suggestive of the consistent emergence of high-frequency viral quasispecies that are not horizontally transmitted but involved in intra-host infection and spread. Author summaryThe severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated disease, COVID-19, has caused significant worldwide mortality and unprecedented economic burden. Here we studied the intra-host genetic diversity of SARS-CoV-2 genomes and identified a high-frequency and recurrent non-sense mutation yielding a truncated form of the viral spike protein, in both human COVID-19 samples and in cell culture experiments. Through the use of a functional assay, we observed that this truncated spike protein displays an elevated fusogenic potential and forms syncytia. Given the high frequency at which this mutation independently arises across various samples, it can be hypothesized that this deletion mutation provides a selective advantage to viral replication and may also have a role in pathogenesis in humans.

SARS-CoV-2 in Brazil: analysis of molecular variance and genetic diversity in viral haplotypes found in the states of Rio de Janeiro, Sao Paulo, Parana and Tocantins (preprint)

In this work, 18 sequences of the SARS-CoV-2 virus were used, from four Brazilian states (Rio de Janeiro, Sao Paulo, Parana and Tocantins) with 09, 04, 04, 8 and 01 haplotypes, respectively, with lengths ranging from 234 to 29,903 bp. All sequences were publicly available on the National Biotechnology Information Center (NCBI) platform and were previously aligned with the MEGA X software, where all gaps and ambiguous sites were extracted for the construction of the phylogenetic tree. Of the 301 sites analyzed, 68% varied, 131 of which were parsimonium-informative sites. Phylogenetic analyses revealed the presence of two distinct subgroups, corroborated by the high FST (80%). The high degree of polymorphism found among these samples helped to establish a clear pattern of non-genetic structuring, based on the time of divergence between the groups. All molecular variance estimators confirmed that there was no consensus in the conservation of the studied sequences, also indicating a high variation for the protein products of the virus. In a highly miscegenational and diverse population such as the Brazilian population, this observation draws our attention to the need for an urgent increase in public health actions, awareness strategies, hygiene and distancing practices and not the other way around.

SARS-CoV-2 D614 and G614 spike variants impair neuronal synapses and exhibit differential fusion ability (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes Coronavirus disease 2019 (COVID-19) exhibits two major variants based on mutations of its spike protein, i.e., the D614 prototype and G614 variant. Although neurological symptoms have been frequently reported in patients, it is still unclear whether SARS-CoV-2 impairs neuronal activity or function. Here, we show that expression of both D614 and G614 spike proteins is sufficient to induce phenotypes of impaired neuronal morphology, including defective dendritic spines and shortened dendritic length. Using spike protein-specific monoclonal antibodies, we found that D614 and G614 spike proteins show differential S1/S2 cleavage and cell fusion efficiency. Our findings provide an explanation for higher transmission of the G614 variant and the neurological manifestations observed in COVID-19 patients.

Identification of low micromolar SARS-CoV-2 Mpro inhibitors from hits identified by in silico screens (preprint)

Mpro, also known as 3CLpro, is the main protease of the SARS-CoV-2 coronavirus and, as such, is essential for the viral life cycle. Two studies have each screened and ranked in silico more than one billion chemical compounds in an effort to identify putative inhibitors of Mpro. More than five hundred of the seven thousand top-ranking hits were synthesized by an external supplier and examined with respect to their activity in two biochemical assays: a protease activity assay and a thermal shift assay. Two clusters of chemical compounds with Mpro inhibitory activity were identified. An additional five hundred molecules, analogues of the compounds in the two clusters described above, were also synthesized and characterized in vitro. The study of the analogues revealed that the compounds of the first cluster acted by denaturing Mpro and might denature other proteins as well. In contrast, the compounds of the second cluster targeted Mpro with much greater specificity and enhanced its melting temperature, consistent with the formation of stable Mpro-inhibitor complexes. The most active compounds of the second cluster exhibited IC50 values between 4 and 7 M and their chemical structure suggests that they could serve as leads for the development of potent Mpro inhibitors.

SARS-CoV-2 Quasispecies Mediate Rapid Virus Evolution and Adaptation (preprint)

The pandemic spread of SARS-CoV-2 and the resulting global healthcare emergency warrants a better understanding of its biology.The potential of SARS-CoV-2 evolution to create novel dangerous variants remain underexplored. Thus, we passaged SARS-CoV-2 in defined conditions and determined its genomic adaptation dynamics. We demonstrate the presence of remarkably stable SARS-CoV-2 quasispecies. We further show that the quasispecies nature of the virus population ensured rapid adaptation of the spike PRRARS motif upon passaging in Vero cells. On the other hand, SARS-CoV-2 replication in TMPRSS2 expressing cells led to a reverse mutation at the same site. We observed the emergence of novel mutations in envelope protein upon virus culture in Calu-3 and Caco-2 cells. Finally, we show that the heparan sulfate-binding motif (PRRARS) of the SARS-CoV-2 S protein acted as a determinant of negative growth selection. Overall, our research has far-reaching implications for development of antiviral strategies, suggesting viral quasispecies may facilitate rapid emergence of escape mutants under selection pressure, such as the treatment with antivirals against SARS-CoV-2.