Human monoclonal antibodies against highly conserved HR1 and HR2 domains of the SARS-CoV spike protein are more broadly neutralizing

Broad sarbecovirus neutralization by combined memory B cell antibodies to ancestral SARS-CoV-2

Antibodies play a pivotal role in protecting from SARS-CoV-2 infection, but their efficacy is challenged by the continuous emergence of viral variants. In this study, we describe two broadly neutralizing antibodies cloned from the memory B cells of a single convalescent individual after infection with ancestral SARS-CoV-2. Cv2.3194, a resilient class 1 anti-RBD antibody, remains active against Omicron sub-variants up to BA.2.86. Cv2.3132, a near pan-Sarbecovirus neutralizer, targets the heptad repeat 2 membrane proximal region. When combined, Cv2.3194 and Cv2.3132 form a complementary SARS-CoV-2 neutralizing antibody cocktail exhibiting a local dose-dependent synergy. Thus, remarkably robust neutralizing memory B cell antibodies elicited in response to ancestral SARS-CoV-2 infection can withstand viral evolution and immune escape. The cooperative effect of such antibody combination may confer a certain level of protection against the latest SARS-CoV-2 variants.

Empowering SARS-CoV-2 variant neutralization with a bifunctional antibody engineered with tandem heptad repeat 2 peptides

With the global pandemic and the continuous mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the need for effective and broadly neutralizing treatments has become increasingly urgent. This study introduces a novel strategy that targets two aspects simultaneously, using bifunctional antibodies to inhibit both the attachment of SARS-CoV-2 to host cell membranes and viral fusion. We developed pioneering IgG4-(HR2)4 bifunctional antibodies by creating immunoglobulin G4-based and phage display-derived human monoclonal antibodies (mAbs) that specifically bind to the SARS-CoV-2 receptor-binding domain, engineered with four heptad repeat 2 (HR2) peptides. Our in vitro experiments demonstrate the superior neutralization efficacy of these engineered antibodies against various SARS-CoV-2 variants, ranging from original SARS-CoV-2 strain to the recently emerged Omicron variants, as well as SARS-CoV, outperforming the parental mAb. Notably, intravenous monotherapy with the bifunctional antibody neutralizes a SARS-CoV-2 variant in a murine model without causing significant toxicity. In summary, this study unveils the significant potential of HR2 peptide-driven bifunctional antibodies as a potent and versatile strategy for mitigating SARS-CoV-2 infections. This approach offers a promising avenue for rapid development and management in the face of the continuously evolving SARS-CoV-2 variants, holding substantial promise for pandemic control.

DNA origami vaccine (DoriVac) nanoparticles improve both humoral and cellular immune responses to infectious diseases

Current SARS-CoV-2 vaccines have demonstrated robust induction of neutralizing antibodies and CD4+ T cell activation, however CD8+ responses are variable, and the duration of immunity and protection against variants are limited. Here we repurposed our DNA origami vaccine platform, DoriVac, for targeting infectious viruses, namely SARS-CoV-2, HIV, and Ebola. The DNA origami nanoparticle, conjugated with infectious-disease-specific HR2 peptides, which act as highly conserved antigens, and CpG adjuvant at precise nanoscale spacing, induced neutralizing antibodies, Th1 CD4+ T cells, and CD8+ T cells in naïve mice, with significant improvement over a bolus control. Pre-clinical studies using lymph-node-on-a-chip systems validated that DoriVac, when conjugated with antigenic peptides or proteins, induced promising cellular immune responses in human cells. These results suggest that DoriVac holds potential as a versatile, modular vaccine platform, capable of inducing both humoral and cellular immunities. The programmability of this platform underscores its potential utility in addressing future pandemics.

Computational design of scFv anti-receptor binding domain of SARS-CoV-2 spike protein based on antibody S230 anti-SARS-CoV-1

Developing therapeutics such as neutralizing antibodies targeting the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is essential to halt the Covid-19 infection. However, antibody production is expensive and relatively inaccessible to many low-income countries. Therefore, a more efficient and smaller antibody fragment, such as a single-chain variable fragment (scFv), derived from a known neutralizing antibody structure, is of interest due to the lower cost of recombinant protein production and the ability to tailor scFvs against circulating viruses. In this study, we used computational design to create an scFv based on the structure of a known neutralizing antibody, S230, for SARS-CoV-1. By analyzing the interaction of S230 with the RBD of both SARS-CoV-1 and SARS-CoV-2, five mutations were introduced to improve the binding of the scFv to the RBD of SARS-CoV-2. These mutations were Ser32Thr, Trp99Val, Asn57Val, Lys65Glu, and Tyr106Ile. Molecular dynamics simulations were used to evaluate the stability and affinity of the designed scFv. Our results showed that the designed scFv improved binding to the RBD of SARS-CoV-2 compared to the original S230, as indicated by principal component analysis, distance analysis, and MM/GBSA interaction energy. Furthermore, a positive result in a spot test lateral flow assay of the expressed scFv against the RBD indicated that the mutations did not alter the protein's structure. The designed scFv showed a negative result when tested against human serum albumin as a negative control, indicating reasonable specificity. We hope that this study will be useful in designing a specific and low-cost therapeutic agent, particularly during early outbreaks when information on neutralizing antibodies is limited.Communicated by Ramaswamy H. Sarma.

Current Status and Perspectives of Therapeutic Antibodies Targeting the Spike Protein S2 Subunit against SARS-CoV-2

The global coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has devastated public health and the global economy. New variants are continually emerging because of amino acid mutations within the SARS-CoV-2 spike protein. Existing neutralizing antibodies (nAbs) that target the receptor-binding domain (RBD) within the spike protein have been shown to have reduced neutralizing activity against these variants. In particular, the recently expanding omicron subvariants BQ 1.1 and XBB are resistant to nAbs approved for emergency use by the United States Food and Drug Administration. Therefore, it is essential to develop broad nAbs to combat emerging variants. In contrast to the massive accumulation of mutations within the RBD, the S2 subunit remains highly conserved among variants. Therefore, nAbs targeting the S2 region may provide effective cross-protection against novel SARS-CoV-2 variants. Here, we provide a detailed summary of nAbs targeting the S2 subunit: the fusion peptide, stem helix, and heptad repeats 1 and 2. In addition, we provide prospects to solve problems such as the weak neutralizing potency of nAbs targeting the S2 subunit.

Experimental Identification of Cross-Reacting IgG Hotspots to Predict Existing Immunity Evasion of SARS-CoV-2 Variants by a New Biotechnological Application of Phage Display

Multiple pathogens are competing against the human immune response, leading to outbreaks that are increasingly difficult to control. For example, the SARS-CoV-2 virus continually evolves, giving rise to new variants. The ability to evade the immune system is a crucial factor contributing to the spread of these variants within the human population. With the continuous emergence of new variants, it is challenging to comprehend all the possible combinations of previous infections, various vaccination types, and potential exposure to new variants in an individual patient. Rather than conducting variant-to-variant comparisons, an efficient approach could involve identifying key protein regions associated with the immune evasion of existing immunity against the virus. In this study, we propose a new biotechnological application of bacteriophages, the phage display platform for experimental identification of regions (linear epitopes) that may function as cross-reacting IgG hotspots in SARS-CoV-2 structural proteins. A total of 34,949 epitopes derived from genomes of all SARS-CoV-2 variants deposited prior to our library design were tested in a single assay. Cross-reacting IgG hotspots are protein regions frequently recognized by cross-reacting antibodies in many variants. The assay facilitated the one-step identification of immunogenic regions of proteins that effectively induced specific IgG in SARS-CoV-2-infected patients. We identified four regions demonstrating both significant immunogenicity and the activity of a cross-reacting IgG hotspot in protein S (located at NTD, RBD, HR1, and HR2/TM domains) and two such regions in protein N (at 197-280 and 358-419 aa positions). This novel method for identifying cross-reacting IgG hotspots holds promise for informing vaccine design and serological diagnostics for COVID-19 and other infectious diseases.

Strategies for the development and approval of COVID-19 vaccines and therapeutics in the post-pandemic period

The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in significant casualties and put immense strain on public health systems worldwide, leading to economic recession and social unrest. In response, various prevention and control strategies have been implemented globally, including vaccine and drug development and the promotion of preventive measures. Implementing these strategies has effectively curbed the transmission of the virus, reduced infection rates, and gradually restored normal social and economic activities. However, the mutations of SARS-CoV-2 have led to inevitable infections and reinfections, and the number of deaths continues to rise. Therefore, there is still a need to improve existing prevention and control strategies, mainly focusing on developing novel vaccines and drugs, expediting medical authorization processes, and keeping epidemic surveillance. These measures are crucial to combat the Coronavirus disease (COVID-19) pandemic and achieve sustained, long-term prevention, management, and disease control. Here, we summarized the characteristics of existing COVID-19 vaccines and drugs and suggested potential future directions for their development. Furthermore, we discussed the COVID-19-related policies implemented over the past years and presented some strategies for the future.

Mapping immunological and host receptor binding determinants of SARS-CoV spike protein utilizing the Qubevirus platform

The motifs involved in tropism and immunological interactions of SARS-CoV spike (S) protein were investigated utilizing the Qubevirus platform. We showed that separately, 14 overlapping peptide fragments representing the S protein (F1-14 of 100 residues each) could be inserted into the C terminus of A1 on recombinant Qubevirus without affecting its viability. Additionally, recombinant phage expression resulted in the surface exposure of different engineered fragments in an accessible manner. The F6 from S425-525 was found to contain the binding determinant of the recombinant human angiotensin-converting enzyme 2, with the shortest active binding motif situated between residues S437-492. Upstream, another fragment, F7, containing an overlapping portion of F6 would not bind to recombinant human angiotensin-converting enzyme 2, confirming that a contiguous stretch of residues could adopt the appropriate structural orientation of F6 as an insertion within the Qubevirus. The F6 (S441-460) and other inserts, including F7/F8 (S601-620) and F10 (S781-800), were demonstrated to contain important immunological determinants through recognition and binding of S protein specific (anti-S) antibodies. An engineered chimeric insert bearing the fusion of all three anti-S reactive epitopes improved substantially the recognition and binding to their cognate antibodies. These results provide insights into humoral immune relevant epitopes and tropism characteristics of the S protein with implications for the development of subunit vaccines or other biologics against SARS-CoV.

Circularized Nanodiscs for Multivalent Mosaic Display of SARS-CoV-2 Spike Protein Antigens

The emergence of vaccine-evading SARS-CoV-2 variants urges the need for vaccines that elicit broadly neutralizing antibodies (bnAbs). Here, we assess covalently circularized nanodiscs decorated with recombinant SARS-CoV-2 spike glycoproteins from several variants for eliciting bnAbs with vaccination. Cobalt porphyrin-phospholipid (CoPoP) was incorporated into the nanodisc to allow for anchoring and functional orientation of spike trimers on the nanodisc surface through their His-tag. Monophosphoryl-lipid (MPLA) and QS-21 were incorporated as immunostimulatory adjuvants to enhance vaccine responses. Following optimization of nanodisc assembly, spike proteins were effectively displayed on the surface of the nanodiscs and maintained their conformational capacity for binding with human angiotensin-converting enzyme 2 (hACE2) as verified using electron microscopy and slot blot assay, respectively. Six different formulations were prepared where they contained mono antigens; four from the year 2020 (WT, Beta, Lambda, and Delta) and two from the year 2021 (Omicron BA.1 and BA.2). Additionally, we prepared a mosaic nanodisc displaying the four spike proteins from year 2020. Intramuscular vaccination of CD-1 female mice with the mosaic nanodisc induced antibody responses that not only neutralized matched pseudo-typed viruses, but also neutralized mismatched pseudo-typed viruses corresponding to later variants from year 2021 (Omicron BA.1 and BA.2). Interestingly, sera from mosaic-immunized mice did not effectively inhibit Omicron spike binding to human ACE-2, suggesting that some of the elicited antibodies were directed towards conserved neutralizing epitopes outside the receptor binding domain. Our results show that mosaic nanodisc vaccine displaying spike proteins from 2020 can elicit broadly neutralizing antibodies that can neutralize mismatched viruses from a following year, thus decreasing immune evasion of new emerging variants and enhancing healthcare preparedness.

Mapping immunological and host receptor binding determinants of SARS-CoV spike protein utilizing the Qubevirus platform

The motifs involved in tropism and immunological interactions of SARS-CoV spike (S) protein were investigated utilizing the Qubevirus platform. We showed that separately, 14 overlapping peptide fragments representing the S protein (F1-14 of 100 residues each) could be inserted into the C-terminus of A1 on recombinant Qubevirus without affecting its viability. Additionally, recombinant phage expression resulted in the surface exposure of different engineered fragments in an accessible manner. The F6 from S 425-525 , was found to contain the binding determinant of the recombinant human angiotensin converting enzyme 2 (rhACE2), with the shortest active binding motif situated between residues S 437-492 . Upstream, another fragment, F7, containing an overlapping portion of F6 would not bind to rhACE2, confirming not just only that residues were linear but equally also the appropriate structural orientation of F6 upon the Qubevirus. The F6 (S 441-460 ) and other inserts, including F7/F8 (S 601-620 ) and F10 (S 781-800 ), were demonstrated to contain important immunological determinants through recognition and binding of S protein specific (anti-S) antibodies. An engineered chimeric insert bearing the fusion of all three anti-S reactive epitopes, improved substantially the recognition and binding to their cognate antibodies. These results provide insights into humoral immune relevant epitopes and tropism characteristics of the S protein with implications for the development of subunit vaccines or other biologics against SARS-CoV.

Significance

Mapping epitopes within the receptor binding domains of viruses which are essential for viral tropism is critical for developing antiviral agents and subunit vaccines. In this study we have engineered the surface of Qubevirus to display a peptide library derived from the SARS-CoV S protein. In biopanning with S protein antibodies, we have identified three peptide fragments (EP1, EP2 and EP3) which reacted selectively with antibodies specific to the S protein. We demonstrated that all recombinant phage displayed peptide fragments both individually and as chimera exposed important immunological epitopes to their cognate antibodies. A peptide fragment F6 situated at S 425-525 , was found containing the binding determinant of the recombinant human angiotensin converting enzyme 2 (rhACE2), with the shortest active binding motif situated between residues S 437-492 . The platform is rapidly to identify epitopes and receptor binding sites within viral receptors found in target host cell. Thus, this platform holds great significance.

Severe COVID-19: Drugs and Clinical Trials

By January of 2023, the COVID-19 pandemic had led to a reported total of 6,700,883 deaths and 662,631,114 cases worldwide. To date, there have been no effective therapies or standardized treatment schemes for this disease; therefore, the search for effective prophylactic and therapeutic strategies is a primary goal that must be addressed. This review aims to provide an analysis of the most efficient and promising therapies and drugs for the prevention and treatment of severe COVID-19, comparing their degree of success, scope, and limitations, with the aim of providing support to health professionals in choosing the best pharmacological approach. An investigation of the most promising and effective treatments against COVID-19 that are currently available was carried out by employing search terms including "Convalescent plasma therapy in COVID-19" or "Viral polymerase inhibitors" and "COVID-19" in the Clinicaltrials.gov and PubMed databases. From the current perspective and with the information available from the various clinical trials assessing the efficacy of different therapeutic options, we conclude that it is necessary to standardize certain variables-such as the viral clearance time, biomarkers associated with severity, hospital stay, requirement of invasive mechanical ventilation, and mortality rate-in order to facilitate verification of the efficacy of such treatments and to better assess the repeatability of the most effective and promising results.

Antitarget, Anti-SARS-CoV-2 Leads, Drugs, and the Drug Discovery-Genetics Alliance Perspective

The most advanced antiviral molecules addressing major SARS-CoV-2 targets (Main protease, Spike protein, and RNA polymerase), compared with proteins of other human pathogenic coronaviruses, may have a short-lasting clinical efficacy. Accumulating knowledge on the mechanisms underlying the target structural basis, its mutational progression, and the related biological significance to virus replication allows envisaging the development of better-targeted therapies in the context of COVID-19 epidemic and future coronavirus outbreaks. The identification of evolutionary patterns based solely on sequence information analysis for those targets can provide meaningful insights into the molecular basis of host-pathogen interactions and adaptation, leading to drug resistance phenomena. Herein, we will explore how the study of observed and predicted mutations may offer valuable suggestions for the application of the so-called "synthetic lethal" strategy to SARS-CoV-2 Main protease and Spike protein. The synergy between genetics evidence and drug discovery may prioritize the development of novel long-lasting antiviral agents.

Nanobodies against SARS-CoV-2 reduced virus load in the brain of challenged mice and neutralized Wuhan, Delta and Omicron Variants

In this work, we developed llama-derived nanobodies (Nbs) directed to the receptor binding domain (RBD) and other domains of the Spike (S) protein of SARS-CoV-2. Nanobodies were selected after the biopanning of two VHH-libraries, one of which was generated after the immunization of a llama (lama glama) with the bovine coronavirus (BCoV) Mebus, and another with the full-length pre-fused locked S protein (S-2P) and the RBD from the SARS-CoV-2 Wuhan strain (WT). Most of the neutralizing Nbs selected with either RBD or S-2P from SARS-CoV-2 were directed to RBD and were able to block S-2P/ACE2 interaction. Three Nbs recognized the N-terminal domain (NTD) of the S-2P protein as measured by competition with biliverdin, while some non-neutralizing Nbs recognize epitopes in the S2 domain. One Nb from the BCoV immune library was directed to RBD but was non-neutralizing. Intranasal administration of Nbs induced protection ranging from 40% to 80% against COVID-19 death in k18-hACE2 mice challenged with the WT strain. Interestingly, protection was not only associated with a significant reduction of virus replication in nasal turbinates and lungs, but also with a reduction of virus load in the brain. Employing pseudovirus neutralization assays, we were able to identify Nbs with neutralizing capacity against the Alpha, Beta, Delta and Omicron variants. Furthermore, cocktails of different Nbs performed better than individual Nbs to neutralize two Omicron variants (B.1.529 and BA.2). Altogether, the data suggest these Nbs can potentially be used as a cocktail for intranasal treatment to prevent or treat COVID-19 encephalitis, or modified for prophylactic administration to fight this disease.

Towards Quantum-Chemical Level Calculations of SARS-CoV-2 Spike Protein Variants of Concern by First Principles Density Functional Theory

The spike protein (S-protein) is a crucial part of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with its many domains responsible for binding, fusion, and host cell entry. In this review we use the density functional theory (DFT) calculations to analyze the atomic-scale interactions and investigate the consequences of mutations in S-protein domains. We specifically describe the key amino acids and functions of each domain, which are essential for structural stability as well as recognition and fusion processes with the host cell; in addition, we speculate on how mutations affect these properties. Such unprecedented large-scale ab initio calculations, with up to 5000 atoms in the system, are based on the novel concept of amino acid-amino acid-bond pair unit (AABPU) that allows for an alternative description of proteins, providing valuable information on partial charge, interatomic bonding and hydrogen bond (HB) formation. In general, our results show that the S-protein mutations for different variants foster an increased positive partial charge, alter the interatomic interactions, and disrupt the HB networks. We conclude by outlining a roadmap for future computational research of biomolecular virus-related systems.

SARS-CoV-2 variant evasion of monoclonal antibodies based on in vitro studies

Monoclonal antibodies (mAbs) offer a treatment option for individuals with severe COVID-19 and are especially important in high-risk individuals where vaccination is not an option. Given the importance of understanding the evolution of resistance to mAbs by SARS-CoV-2, we reviewed the available in vitro neutralization data for mAbs against live variants and viral constructs containing spike mutations of interest. Unfortunately, evasion of mAb-induced protection is being reported with new SARS-CoV-2 variants. The magnitude of neutralization reduction varied greatly among mAb-variant pairs. For example, sotrovimab retained its neutralization capacity against Omicron BA.1 but showed reduced efficacy against BA.2, BA.4 and BA.5, and BA.2.12.1. At present, only bebtelovimab has been reported to retain its efficacy against all SARS-CoV-2 variants considered here. Resistance to mAb neutralization was dominated by the action of epitope single amino acid substitutions in the spike protein. Although not all observed epitope mutations result in increased mAb evasion, amino acid substitutions at non-epitope positions and combinations of mutations also contribute to evasion of neutralization. This Review highlights the implications for the rational design of viral genomic surveillance and factors to consider for the development of novel mAb therapies.

Enhanced recombination among Omicron subvariants of SARS-CoV-2 contributes to viral immune escape

Genetic recombination is an important driver of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolution, which requires the coinfection of a single host cell with different SARS-CoV-2 strains. To understand the emergence and prevalence of recombinant SARS-CoV-2 lineages through time and space, we analyzed SARS-CoV-2 genome sequences collected from November 2019 to July 2022. We observed an extraordinary increase in the emergence of SARS-CoV-2 recombinant lineages during the Omicron wave, particularly in Northern America and Europe. This phenomenon was independent of the sequencing frequency or genetic diversity of circulating SARS-CoV-2 strains. The recombination breakpoints were more prevalent in the 3'-untranslated region of the viral genome. Importantly, we noted the enrichment of certain amino acids in the Spike protein of recombinant lineages, which have been reported to confer immune escape from neutralizing antibodies and increase angiotensin-converting enzyme 2 receptor binding in some cases. We also observed I42V amino acid change genetically fixated in the NSP14 of the Omicron lineage, which needs further characterization for its potential role in enhanced recombination. Overall, we report the important and timely observation of accelerated recombination in the currently circulating SARS-CoV-2 Omicron variants and explore their potential contribution to viral fitness, particularly immune escape.

Recombinant Protein Vaccines against Human Betacoronaviruses: Strategies, Approaches and Progress

Betacoronaviruses have already troubled humanity more than once. In 2002-2003 and 2012, the SARS-CoV and MERS-CoV, respectively, caused outbreaks of respiratory syndromes with a fatal outcome. The spread of the SARS-CoV-2 coronavirus has become a pandemic. These three coronaviruses belong to the genus Betacoronavirus and have a zoonotic origin. The emergence of new coronavirus infections in the future cannot be ruled out, and vaccination is the main way to prevent the spread of the infection. Previous experience in the development of vaccines against SARS and MERS has helped to develop a number of vaccines against SARS-CoV-2 in a fairly short time. Among them, there are quite a few recombinant protein vaccines, which seem to be very promising in terms of safety, minimization of side effects, storage and transportation conditions. The problem of developing a universal betacoronavirus vaccine is also still relevant. Here, we summarize the information on the designing of vaccines based on recombinant proteins against highly pathogenic human betacoronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2.

Clinical Application of Antibody Immunity Against SARS-CoV-2: Comprehensive Review on Immunoassay and Immunotherapy

The current COVID-19 global pandemic poses immense challenges to global health, largely due to the difficulty to detect infection in the early stages of the disease, as well as the current lack of effective antiviral therapy. Research and understanding of the human immune system can provide important theoretical and technical support for the clinical diagnosis and treatment of COVID-19, the clinical implementations of which include immunoassays and immunotherapy, which play a crucial role in the fight against the pandemic. This review consolidates the current scientific evidence for immunoassay, which includes multiple methods of detecting antigen and antibody against SARS-CoV-2. We compared the characteristics, advantages and disadvantages, and clinical applications of these three detection techniques. In addition to detecting viral infections, knowledge on the body's immunity against the virus is desirable; thus, the immunotherapy-based neutralizing antibody (nAb) detection methods were discussed. We also gave a brief introduction to the new immunoassay technology such as biosensing. This was followed by an in-depth and extensive review on a variety of immunotherapy methods. It includes convalescent plasma therapy, neutralizing antibody-based treatments targeting different regions of SARS-CoV-2, immunotherapy targeted on the host cell including inhibiting the host cell receptor and cytokine storm, as well as cocktail antibodies, cross-neutralizing antibodies, and immunotherapy based on cross-reactivity between viral epitopes and autoepitopes and autoantibody. Despite the development of various immunological testing methods and antibody therapies, the current global situation of COVID-19 is still tense. We need more efficient detection methods and more reliable antibody therapies. The up-to-date knowledge on therapeutic strategies will likely help clinicians worldwide to protect patients from life-threatening viral infections.

Is the Stalk of the SARS-CoV-2 Spike Protein Druggable?

The spike protein is key to SARS-CoV-2 high infectivity because it facilitates the receptor binding domain (RBD) encounter with ACE2. As targeting subunit S1 has not yet delivered an ACE2-binding inhibitor, we have assessed the druggability of the conserved segment of the spike protein stalk within subunit S2 by means of an integrated computational approach that combines the molecular docking of an optimized library of fragments with high-throughput molecular dynamics simulations. The high propensity of the spike protein to mutate in key regions that are responsible for the recognition of the human angiotensin-converting enzyme 2 (hACE2) or for the recognition of antibodies, has made subunit S1 of the spike protein difficult to target. Despite the inherent flexibility of the stalk region, our results suggest two hidden interhelical binding sites, whose accessibility is only partially hampered by glycan residues.

Novel chimeric proteins mimicking SARS-CoV-2 spike epitopes with broad inhibitory activity

SARS-CoV-2 spike (S) protein mediates virus attachment to the cells and fusion between viral and cell membranes. Membrane fusion is driven by mutual interaction between the highly conserved heptad-repeat regions 1 and 2 (HR1 and HR2) of the S2 subunit of the spike. For this reason, these S2 regions are interesting therapeutic targets for COVID-19. Although HR1 and HR2 have been described as transiently exposed during the fusion process, no significant antibody responses against these S2 regions have been reported. Here we designed chimeric proteins that imitate highly stable HR1 helical trimers and strongly bind to HR2. The proteins have broad inhibitory activity against WT B.1 and BA.1 viruses. Sera from COVID-19 convalescent donors showed significant levels of reactive antibodies (IgG and IgA) against the HR1 mimetic proteins, whereas these antibody responses were absent in sera from uninfected donors. Moreover, both inhibitory activity and antigenicity of the proteins correlate positively with their structural stability but not with the number of amino acid changes in their HR1 sequences, indicating a conformational and conserved nature of the involved epitopes. Our results reveal previously undetected spike epitopes that may guide the design of new robust COVID-19 vaccines and therapies.

Sinopharm's BBIBP-CorV Vaccine and ChAdOx1 nCoV-19 Vaccine Are Associated with a Comparable Immune Response against SARS-CoV-2

Coronavirus disease 2019 (COVID-19) has affected millions of people worldwide. During the early stages of vaccination in Egypt, the ChAdOx1 nCoV-19 and BBIBP-CorV vaccines were the most distributed. The aim of this study was to compare the immune responses and short-term efficacies of these two vaccines. We recruited adults who received two doses of either vaccine. Samples were collected after the first dose of ChAdOx1 nCoV-1 and after the second dose of both vaccines. Antibodies against SARS-CoV-2 antigens were measured using LABScreen™ COVID Plus kits, and cell-mediated immune responses were assessed using flow cytometry. Of the 109 recruited subjects, 60 (55%) received the ChAdOx1 nCoV-19 vaccine, and the remainder received the BBIBP-CorV vaccine. The total antibody level did not significantly differ between the two groups. The level of the anti-spike subunit 2 (S2) antibody was significantly higher in the ChAdOx1 nCoV-19 group. The percentages of both total T cells and B cells were unaffected by the type of vaccination. However, the ChAdOx1 nCoV-1 vaccine was significantly associated with a higher percentage of CD8+ cells. The vaccines did not significantly differ in the number or severity of infections postvaccination. None of the participants were admitted to the hospital or died of COVID-19 infection. In conclusion, the BBIBP-CorV vaccine is associated with an immune response and protection against infection that is comparable to that of the ChAdOx1 nCoV-1 vaccine. Follow-up is needed to study the long-term protective effects of both vaccines. Inactivated vaccines are easier to manufacture in developing countries and their limited side effects may lead to better economic benefits by limiting the number of absences from work.

Preclinical study of a DNA vaccine targeting SARS-CoV-2

To fight against the worldwide COVID-19 pandemic, the development of an effective and safe vaccine against SARS-CoV-2 is required. As potential pandemic vaccines, DNA/RNA vaccines, viral vector vaccines and protein-based vaccines have been rapidly developed to prevent pandemic spread worldwide. In this study, we designed plasmid DNA vaccine targeting the SARS-CoV-2 Spike glycoprotein (S protein) as pandemic vaccine, and the humoral, cellular, and functional immune responses were characterized to support proceeding to initial human clinical trials. After intramuscular injection of DNA vaccine encoding S protein with alum adjuvant (three times at 2-week intervals), the humoral immunoreaction, as assessed by anti-S protein or anti-receptor-binding domain (RBD) antibody titers, and the cellular immunoreaction, as assessed by antigen-induced IFNγ expression, were up-regulated. In IgG subclass analysis, IgG2b was induced as the main subclass. Based on these analyses, DNA vaccine with alum adjuvant preferentially induced Th1-type T cell polarization. We confirmed the neutralizing action of DNA vaccine-induced antibodies by a binding assay of RBD recombinant protein with angiotensin-converting enzyme 2 (ACE2), a receptor of SARS-CoV-2, and neutralization assays using pseudo-virus, and live SARS-CoV-2. Further B cell epitope mapping analysis using a peptide array showed that most vaccine-induced antibodies recognized the S2 and RBD subunits. Finally, DNA vaccine protected hamsters from SARS-CoV-2 infection. In conclusion, DNA vaccine targeting the spike glycoprotein of SARS-CoV-2 might be an effective and safe approach to combat the COVID-19 pandemic.

Monoclonal antibodies: a remedial approach to prevent SARS-CoV-2 infection

SARS-CoV-2, the newly emerged virus of the Coronaviridae family is causing havoc worldwide. The novel coronavirus 2019 was first reported in Wuhan, China marked as the third highly infectious pathogenic virus of the twenty-first century. The typical manifestations of COVID-19 include cough, sore throat, fever, fatigue, loss of sense of taste and difficulties in breathing. Large numbers of SARS-CoV-2 infected patients have mild to moderate symptoms, however severe and life-threatening cases occur in about 5-10% of infections with an approximately 2% mortality rate. For the treatment of SARS-CoV-2, the use of neutralizing monoclonal antibodies (mAbs) could be one approach. The receptor binding domain (RBD) and N-terminal domain (NTD) situated on the peak of the spike protein (S-Protein) of SARS-CoV-2 are immunogenic in nature, therefore, can be targeted by neutralizing monoclonal antibodies. Several bioinformatics approaches highlight the identification of novel SARS-CoV-2 epitopes which can be targeted for the development of COVID-19 therapeutics. Here we present a summary of neutralizing mAbs isolated from COVID-19 infected patients which are anticipated to be a better therapeutic alternative against SARS-CoV-2. However, provided the vast escalation of the disease worldwide affecting people from all strata, affording expensive mAb therapy will not be feasible. Hence other strategies are also being employed to find suitable vaccine candidates and antivirals against SARS-CoV-2 that can be made easily available to the population.

Antibody-mediated immunity to SARS-CoV-2 spike

Despite effective spike-based vaccines and monoclonal antibodies, the SARS-CoV-2 pandemic continues more than two and a half years post-onset. Relentless investigation has outlined a causative dynamic between host-derived antibodies and reciprocal viral subversion. Integration of this paradigm into the architecture of next generation antiviral strategies, predicated on a foundational understanding of the virology and immunology of SARS-CoV-2, will be critical for success. This review aims to serve as a primer on the immunity endowed by antibodies targeting SARS-CoV-2 spike protein through a structural perspective. We begin by introducing the structure and function of spike, polyclonal immunity to SARS-CoV-2 spike, and the emergence of major SARS-CoV-2 variants that evade immunity. The remainder of the article comprises an in-depth dissection of all major epitopes on SARS-CoV-2 spike in molecular detail, with emphasis on the origins, neutralizing potency, mechanisms of action, cross-reactivity, and variant resistance of representative monoclonal antibodies to each epitope.

SARS-CoV-2 S2-targeted vaccination elicits broadly neutralizing antibodies

Several variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have emerged during the current coronavirus disease 2019 (COVID-19) pandemic. Although antibody cross-reactivity with the spike glycoproteins (S) of diverse coronaviruses, including endemic common cold coronaviruses (HCoVs), has been documented, it remains unclear whether such antibody responses, typically targeting the conserved S2 subunit, contribute to protection when induced by infection or through vaccination. Using a mouse model, we found that prior HCoV-OC43 S-targeted immunity primes neutralizing antibody responses to otherwise subimmunogenic SARS-CoV-2 S exposure and promotes S2-targeting antibody responses. Moreover, vaccination with SARS-CoV-2 S2 elicited antibodies in mice that neutralized diverse animal and human alphacoronaviruses and betacoronaviruses in vitro and provided a degree of protection against SARS-CoV-2 challenge in vivo. Last, in mice with a history of SARS-CoV-2 Wuhan-based S vaccination, further S2 vaccination induced broader neutralizing antibody response than booster Wuhan S vaccination, suggesting that it may prevent repertoire focusing caused by repeated homologous vaccination. These data establish the protective value of an S2-targeting vaccine and support the notion that S2 vaccination may better prepare the immune system to respond to the changing nature of the S1 subunit in SARS-CoV-2 variants of concern, as well as to future coronavirus zoonoses.

Recombinant Protein Technology in the Challenging Era of Coronaviruses

Coronaviruses have caused devastation in both human and animal populations, affecting both health and the economy. Amidst the emergence and re-emergence of coronaviruses, humans need to surmount the health and economic threat of coronaviruses through science and evidence-based approaches. One of these approaches is through biotechnology, particularly the heterologous production of biopharmaceutical proteins. This review article briefly describes the genome, general virion morphology, and key structural proteins of different coronaviruses affecting animals and humans. In addition, this review paper also presents the different systems in recombinant protein technology such as bacteria, yeasts, plants, mammalian cells, and insect/insect cells systems used to express key structural proteins in the development of countermeasures such as diagnostics, prophylaxis, and therapeutics in the challenging era of coronaviruses.

Nanodisc-Mediated Conversion of Virustatic Antiviral Antibody to Disrupt Virus Envelope in Infected Cells

Many antibody-based antivirals, including broadly neutralizing antibodies (bnAbs) against various influenza virus strains, suffer from limited potency. A booster of the antiviral activity of an antibody is expected to facilitate development of antiviral therapeutics. In this study, a nanodisc (ND), a discoidal lipid bilayer encircled by membrane scaffold proteins, is engineered to provide virucidal properties to antibodies, thereby augmenting their antiviral activity. NDs carrying the Fc-binding peptide sequence form an antibody-ND complex (ANC), which can co-endocytose into cells infected with influenza virus. ANC efficiently inhibits endosome escape of viral RNA by dual complimentary mode of action. While the antibody moiety in an ANC inhibits hemagglutinin-mediated membrane fusion, its ND moiety destroys the viral envelope using free hemagglutinins that are not captured by antibodies. Providing virus-infected host cells with the ability to self-eliminate by the synergistic effect of ANC components dramatically amplifies the antiviral efficacy of a bnAb against influenza virus. When the efficacy of ANC is assessed in mouse models, administration of ANCs dramatically reduces morbidity and mortality compared to bnAb alone. This study is the first to demonstrate the novel nanoparticle ANC and its role in combating viral infections, suggesting that ANC is a versatile platform applicable to various viruses.

Neutralizing monoclonal antibodies against highly pathogenic coronaviruses

The pandemic of Coronavirus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome 2 coronavirus (SARS-CoV-2) is a continuing worldwide threat to human health and social economy. Historically, SARS-CoV-2 follows SARS and MERS as the third coronavirus spreading across borders and continents, but far more dangerous with long-lasting symptomatic consequences. The current situation is strong evidence that coronaviruses will continue to be pathogens of consequence in the future, thus calling for the development of neutralizing antibody-based prophylactics and therapeutics for prevention and treatment of COVID-19 and other human coronavirus diseases. This review summarized the progresses of developing neutralizing monoclonal antibodies against infection of SARS-CoV-2, SARS-CoV, and MERS-CoV, and discussed their potential applications in prevention and treatment of COVID-19 and other human coronavirus diseases.

Vaccine Candidate Against COVID-19 Based on Structurally Modified Plant Virus as an Adjuvant

A recombinant vaccine candidate has been developed based on the major coronaviruses’ antigen (S protein) fragments and a novel adjuvant—spherical particles (SPs) formed during tobacco mosaic virus thermal remodeling. The receptor-binding domain and the highly conserved antigenic fragments of the S2 protein subunit were chosen for the design of recombinant coronavirus antigens. The set of three antigens (Co1, CoF, and PE) was developed and used to create a vaccine candidate composed of antigens and SPs (SPs + 3AG). Recognition of SPs + 3AG compositions by commercially available antibodies against spike proteins of SARS-CoV and SARS-CoV-2 was confirmed. The immunogenicity testing of these compositions in a mouse model showed that SPs improved immune response to the CoF and PE antigens. Total IgG titers against both proteins were 9–16 times higher than those to SPs. Neutralizing activity against SARS-CoV-2 in serum samples collected from hamsters immunized with the SPs + 3AG was demonstrated.

Neutralizing Monoclonal Antibodies Inhibit SARS-CoV-2 Infection through Blocking Membrane Fusion

Most of SARS-CoV-2 neutralizing antibodies (nAbs) targeted the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein. However, mutations at RBD sequences found in the emerging SARS-CoV-2 variants greatly reduced the effectiveness of nAbs. Here we showed that four nAbs, S2-4D, S2-5D, S2-8D, and S2-4A, which recognized a conserved epitope in the S2 subunit of the S protein, can inhibit SARS-CoV-2 infection through blocking the S protein-mediated membrane fusion. Notably, these four nAbs exhibited broadly neutralizing activity against SARS-CoV-2 Alpha, Gamma, Delta, and Epsilon variants. Antisera collected from mice immunized with the identified epitope peptides of these four nAbs also exhibited potent virus neutralizing activity. Discovery of the S2-specific nAbs and their unique antigenic epitopes paves a new path for development of COVID-19 therapeutics and vaccines.

IMPORTANCE The spike (S) protein on the surface of SARS-CoV-2 mediates receptor binding and virus-host cell membrane fusion during virus entry. Many neutralizing antibodies (nAbs), which targeted the receptor binding domain (RBD) of S protein, lost the neutralizing activity against the newly emerging SARS-CoV-2 variants with sequence mutations at the RBD. In contrast, the nAb against the highly conserved S2 subunit, which plays the key role in virus–host cell membrane fusion, was poorly discovered. We showed that four S2-specific nAbs, S2-4D, S2-5D, S2-8D, and S2-4A, inhibited SARS-CoV-2 infection through blocking the S protein-mediated membrane fusion. These nAbs exhibited broadly neutralizing activity against Alpha, Gamma, Delta, and Epsilon variants. Antisera induced by the identified epitope peptides also possessed potent neutralizing activity. This work not only unveiled the S2-specific nAbs but also discovered an immunodominant epitope in the S2 subunit that can be rationally designed as the broad-spectrum vaccine against the SARS-like coronaviruses.

Rapid identification of neutralizing antibodies against SARS-CoV-2 variants by mRNA display

The increasing prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with the ability to escape existing humoral protection conferred by previous infection and/or immunization necessitates the discovery of broadly reactive neutralizing antibodies (nAbs). Utilizing mRNA display, we identify a set of antibodies against SARS-CoV-2 spike (S) proteins and characterize the structures of nAbs that recognize epitopes in the S1 subunit of the S glycoprotein. These structural studies reveal distinct binding modes for several antibodies, including the targeting of rare cryptic epitopes in the receptor-binding domain (RBD) of S that interact with angiotensin-converting enzyme 2 (ACE2) to initiate infection, as well as the S1 subdomain 1. Further, we engineer a potent ACE2-blocking nAb to sustain binding to S RBD with the E484K and L452R substitutions found in multiple SARS-CoV-2 variants. We demonstrate that mRNA display is an approach for the rapid identification of nAbs that can be used in combination to combat emerging SARS-CoV-2 variants.

Highly feasible immunoprotective multicistronic SARS-CoV-2 vaccine candidate blending novel eukaryotic expression and Salmonella bactofection

Introduction

The emergence of SARS-CoV-2 variants has raised concerns on future vaccine efficacy as most vaccines target only the spike protein. Hence, vaccines targeting multiple SARS-CoV-2 proteins will offer broader protection and improve our preparedness to combat the pandemic.

Objectives

The study aimed to develop a novel vaccine strategy by combining a eukaryotic vector expressing multiple SARS-CoV-2 genes and Salmonella-mediated in vivo DNA delivery.

Methods

The eukaryotic vector was designed to function as a DNA-launched RNA replicon in a self-replicating and self-amplifying mRNA mechanism. By exploiting the self-cleaving peptide, P2A, we fused four SARS-CoV-2 targets, including receptor-binding domain (RBD), heptad repeat domain (HR), membrane protein (M) and epitopes of nsp13, in a single open reading frame. Western blot and immunofluorescence assays were used to determine protein expression. In mice, the vaccine's safety and immunogenicity were investigated.

Results

Western blot analysis revealed co-expression all four proteins from the vaccine construct, confirming the efficiency of Salmonella-mediated gene delivery and protein expression. The vaccine candidate was safe and elicited robust antigen-specific antibody titers in mice, and a recall response from splenocytes revealed induction of strong cell-mediated immunity. Flow cytometry demonstrated an increase in sub-populations of CD4+ and CD8+ T cells with the highest CD4+ and CD8+ T cells recorded for HR and RBD, respectively. Overall, humoral and cellular immune response data suggested the induction of both Th1 and Th2 immunity with polarization towards an antiviral Th1 response. We recorded a potent SARS-CoV-2 neutralizing antibody titers in the immunized mice sera.

Conclusions

The Salmonella bactofection ensured optimum in vivo gene delivery, and through a P2A-enabled efficient multicistronic expression, the vaccine candidate elicited potent anti-SARS-CoV-2 immune responses. These findings provide important insight into development of an effective multivalent vaccine to combat SARS-CoV-2 and its variants.

Diagnostic performance of two serological assays for the detection of SARS-CoV-2 specific antibodies: surveillance after vaccination

Massive vaccination programs are being carried out to limit the SARS-CoV-2 pandemic that started in December 2019. Serological tests are of major importance as an indicator of circulation of the virus and to assess how vaccine-induced immunity progresses.

An Enzyme-Linked Immunosorbent Assay (ELISA) and a Lateral Flow Assay (LFA) have been developed based on the SARS-CoV-2 recombinant Receptor Binding Domain (RBD) and the combination of Spike and Nucleoprotein, respectively. The validation with 1272 serum samples by comparison with INgezim COVID 19 DR showed good diagnostic performance (sensitivity: 93.2%-97.2%; specificity: 98.3%-99.3%) for detection of previous contact with SARS-CoV-2. Moreover, according to our results, these assays can help in the serosurveillance during and after vaccination, by detecting the humoral immune response as soon as 15 days postvaccination and identifying low-respondents. Hence, these tests could play a key role in the progression to a COVID-19 free world, helping to adjust future vaccination protocols.

Essentials of COVID-19 and treatment approaches

The coronavirus family is as old as the 1930s when it first showed symptoms in chicken. The virus thereafter kept evolving and it has significantly taken over a large percentage of people worldwide in the form of this new pandemic. As of the present day, there is no treatment available for coronavirus disease 2019 (COVID-19) (caused by the severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]), although supportive therapy and preventive measures have shown a tremendous control rate among certain patients. Drugs like remdesivir, camostat, nafamostat, ritonavir/lopinavir, several monoclonal antibodies, and CPs are in their early phases of trials. There are approved by the WHO under an emergency use authorization program. Favipiravir has entered its phase 3 clinical trial and is supported by evidence to show no or less adverse effects in patients infected with SARS-CoV-2. Vaccine development is accelerating its pace, and vaccines will probably become available by the end of the year 2020.

Highly synergistic combinations of nanobodies that target SARS-CoV-2 and are resistant to escape

The emergence of SARS-CoV-2 variants threatens current vaccines and therapeutic antibodies and urgently demands powerful new therapeutics that can resist viral escape. We therefore generated a large nanobody repertoire to saturate the distinct and highly conserved available epitope space of SARS-CoV-2 spike, including the S1 receptor binding domain, N-terminal domain, and the S2 subunit, to identify new nanobody binding sites that may reflect novel mechanisms of viral neutralization. Structural mapping and functional assays show that indeed these highly stable monovalent nanobodies potently inhibit SARS-CoV-2 infection, display numerous neutralization mechanisms, are effective against emerging variants of concern, and are resistant to mutational escape. Rational combinations of these nanobodies that bind to distinct sites within and between spike subunits exhibit extraordinary synergy and suggest multiple tailored therapeutic and prophylactic strategies.

Nanovesicles derived from bispecific CAR-T cells targeting the spike protein of SARS-CoV-2 for treating COVID-19

BACKGROUND

Considering the threat of the COVID-19 pandemic, caused by SARS-CoV-2, there is an urgent need to develop effective treatments. At present, neutralizing antibodies and small-molecule drugs such as remdesivir, the most promising compound to treat this infection, have attracted considerable attention. However, some potential problems need to be concerned including viral resistance to antibody-mediated neutralization caused by selective pressure from a single antibody treatment, the unexpected antibody-dependent enhancement (ADE) effect, and the toxic effect of small-molecule drugs.

RESULTS

Here, we constructed a type of programmed nanovesicle (NV) derived from bispecific CAR-T cells that express two single-chain fragment variables (scFv), named CR3022 and B38, to target SARS-CoV-2. Nanovesicles that express both CR3022 and B38 (CR3022/B38 NVs) have a stronger ability to neutralize Spike-pseudovirus infectivity than nanovesicles that express either CR3022 or B38 alone. Notably, the co-expression of CR3022 and B38, which target different epitopes of spike protein, could reduce the incidence of viral resistance. Moreover, the lack of Fc fragments on the surface of CR3022/B38 NVs could prevent ADE effects. Furthermore, the specific binding ability to SARS-CoV-2 spike protein and the drug loading capacity of CR3022/B38 NVs can facilitate targeted delivery of remdesiver to 293 T cells overexpressing spike protein. These results suggest that CR3022/B38 NVs have the potential ability to target antiviral drugs to the main site of viral infection, thereby enhancing the antiviral ability by inhibiting intracellular viral replication and reducing adverse drug reactions.

CONCLUSIONS

In summary, we demonstrate that nanovesicles derived from CAR-T cells targeting the spike protein of SARS-COV-2 have the ability to neutralize Spike-pseudotyped virus and target antiviral drugs. This novel therapeutic approach may help to solve the dilemma faced by neutralizing antibodies and small-molecule drugs in the treatment of COVID-19.

Evaluation of spike protein antigens for SARS-CoV-2 serology

BACKGROUND

Spike protein domains are being used in various serology-based assays to detect prior exposure to SARS-CoV-2 virus. However, there has been limited comparison of antibody titers against various spike protein antigens among COVID-19 infected patients.

METHODS

We compared four spike proteins (RBD, S1, S2 and a stabilized spike trimer (ST)) representing commonly used antigens for their reactivity to human IgG antibodies using indirect ELISA in serum from COVID-19 patients and pre-2020 samples. ST ELISA was also compared against the EUROIMMUN IgG ELISA test. Further, we estimated time appropriate IgG and IgA seropositivity rates in COVID-19 patients using a panel of sera samples collected longitudinally from the day of onset of symptoms (DOS).

RESULTS

Among the four spike antigens tested, the ST demonstrated the highest sensitivity (86.2 %; 95 % CI: 77.8-91.7 %), while all four antigens showed high specificity to COVID-19 sera (94.7-96.8 %). 13.8 % (13/94) of the samples did not show seroconversion in any of the four antigen-based assays. In a double-blinded head-to-head comparison, ST based IgG ELISA displayed a better sensitivity (87.5 %, 95 % CI: 76.4-93.8 %) than the EUROIMMUN IgG ELISA (67.9 %, 95 % CI: 54.8-78.6 %). Further, in ST-based assays, we found 48 % and 50 % seroconversion in the first six days (from DOS) for IgG and IgA antibodies, respectively, which increased to 84 % (IgG) and 85 % (IgA) for samples collected ≥22 days from DOS.

CONCLUSIONS

Comparison of spike antigens demonstrates that spike trimer protein is a superior option as an ELISA antigen for COVID-19 serology.

Rapid Identification of Neutralizing Antibodies against SARS-CoV-2 Variants by mRNA Display

The increasing prevalence of SARS-CoV-2 variants with the ability to escape existing humoral protection conferred by previous infection and/or immunization necessitates the discovery of broadly-reactive neutralizing antibodies (nAbs). Utilizing mRNA display, we identified a set of antibodies against SARS-CoV-2 spike (S) proteins and characterized the structures of nAbs that recognized epitopes in the S1 subunit of the S glycoprotein. These structural studies revealed distinct binding modes for several antibodies, including targeting of rare cryptic epitopes in the receptor-binding domain (RBD) of S that interacts with angiotensin- converting enzyme 2 (ACE2) to initiate infection, as well as the S1 subdomain 1. A potent ACE2-blocking nAb was further engineered to sustain binding to S RBD with the E484K and L452R substitutions found in multiple SARS-CoV-2 variants. We demonstrate that mRNA display is a promising approach for the rapid identification of nAbs that can be used in combination to combat emerging SARS-CoV-2 variants.

Broad betacoronavirus neutralization by a stem helix-specific human antibody

The spillovers of betacoronaviruses in humans and the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants highlight the need for broad coronavirus countermeasures. We describe five monoclonal antibodies (mAbs) cross-reacting with the stem helix of multiple betacoronavirus spike glycoproteins isolated from COVID-19 convalescent individuals. Using structural and functional studies, we show that the mAb with the greatest breadth (S2P6) neutralizes pseudotyped viruses from three different subgenera through the inhibition of membrane fusion, and we delineate the molecular basis for its cross-reactivity. S2P6 reduces viral burden in hamsters challenged with SARS-CoV-2 through viral neutralization and Fc-mediated effector functions. Stem helix antibodies are rare, oftentimes of narrow specificity, and can acquire neutralization breadth through somatic mutations. These data provide a framework for structure-guided design of pan-betacoronavirus vaccines eliciting broad protection.

Treatment and prevention strategies for the COVID 19 pandemic: A review of immunotherapeutic approaches for neutralizing SARS-CoV-2

Researchers from the world over are working to create prophylactic and therapeutic interventions to combat the COVID-19 global healthcare crisis. The current therapeutic options against the COVID-19 include repurposed drugs aimed at targets other than virus-specific proteins. Antibody-based therapeutics carry a lot of promise, and there are several of these candidates for COVID-19 treatment currently being investigated in the preclinical and clinical research stages around the world. The viral spike protein (S protein) appears to be the main target of antibody development candidates, with the majority being monoclonal antibodies. Several antibody candidates targeting the SARS-CoV-2 S protein include LY-CoV555, REGN-COV2, JS016, TY027, CT-P59, BRII-196, BRII-198 and SCTA01. These neutralizing antibodies will treat COVID-19 and possibly future coronavirus infections. Future studies should focus on effective immune-therapeutics and immunomodulators with the purpose of developing specific, affordable, and cost-effective prophylactic and treatment regimens to fight the COVID-19 globally.

Fusion Peptide of SARS-CoV-2 Spike Rearranges into a Wedge Inserted in Bilayered Micelles

The receptor binding and proteolysis of Spike of SARS-CoV-2 release its S2 subunit to rearrange and catalyze viral-cell fusion. This deploys the fusion peptide for insertion into the cell membranes targeted. We show that this fusion peptide transforms from intrinsic disorder in solution into a wedge-shaped structure inserted in bilayered micelles, according to chemical shifts, 15N NMR relaxation, and NOEs. The globular fold of three helices contrasts the open, extended forms of this region observed in the electron density of compact prefusion states. In the hydrophobic, narrow end of the wedge, helices 1 and 2 contact the fatty acyl chains of phospholipids, according to NOEs and proximity to a nitroxide spin label deep in the membrane mimic. The polar end of the wedge may engage and displace lipid head groups and bind Ca2+ ions for membrane fusion. Polar helix 3 protrudes from the bilayer where it might be accessible to antibodies.

SARS coronavirus outbreaks past and present-a comparative analysis of SARS-CoV-2 and its predecessors

The Coronavirus Disease 2019 (COVID-19), a pneumonic disease caused by the SARS Coronavirus 2 (SARS-CoV-2), is the 7th Coronavirus to have successfully infected and caused an outbreak in humans. Genome comparisons have shown that previous isolates, the SARS-related coronavirus (SARSr-CoV), including the SARS-CoV are closely related, yet different in disease manifestation. Several explanations were suggested for the undetermined origin of SARS-CoV-2, in particular, bats, avian and Malayan pangolins as reservoir hosts, owing to the high genetic similarity. The general morphology and structure of all these viral isolates overlap with analogous disease symptoms such as fever, dry cough, fatigue, dyspnoea and headache, very similar to the current SARS-CoV-2. Chest CT scans for SARS-CoV-2, SARS-CoV and MERS-CoV reveal pulmonary lesions, bilateral ground-glass opacities, and segmental consolidation in the lungs, a common pathological trait. With greatly overlapping similarities among the previous coronavirus, the SARS-CoV, it becomes interesting to observe marked differences in disease severity of the SARS-CoV-2 thereby imparting it the ability to rapidly transmit, exhibit greater stability, bypass innate host defences, and increasingly adapt to their new host thereby resulting in the current pandemic. The most recent B.1.1.7, B.1.351 and P.1 variants of SARS-CoV-2, highlight the fact that changes in amino acids in the Spike protein can contribute to enhanced infection and transmission efficiency. This review covers a comparative analysis of previous coronavirus outbreaks and highlights the differences and similarities among different coronaviruses, including the most recent isolates that have evolved to become easily transmissible with higher replication efficiency in humans.

SARS-CoV-2 Spike Protein Extrapolation for COVID Diagnosis and Vaccine Development

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) led to coronavirus disease 2019 (COVID-19) pandemic affecting nearly 71.2 million humans in more than 191 countries, with more than 1.6 million mortalities as of 12 December, 2020. The spike glycoprotein (S-protein), anchored onto the virus envelope, is the trimer of S-protein comprised of S1 and S2 domains which interacts with host cell receptors and facilitates virus-cell membrane fusion. The S1 domain comprises of a receptor binding domain (RBD) possessing an N-terminal domain and two subdomains (SD1 and SD2). Certain regions of S-protein of SARS-CoV-2 such as S2 domain and fragment of the RBD remain conserved despite the high selection pressure. These conserved regions of the S-protein are extrapolated as the potential target for developing molecular diagnostic techniques. Further, the S-protein acts as an antigenic target for different serological assay platforms for the diagnosis of COVID-19. Virus-specific IgM and IgG antibodies can be used to detect viral proteins in ELISA and lateral flow immunoassays. The S-protein of SARS-CoV-2 has very high sequence similarity to SARS-CoV-1, and the monoclonal antibodies (mAbs) against SARS-CoV-1 cross-react with S-protein of SARS-CoV-2 and neutralize its activity. Furthermore, in vitro studies have demonstrated that polyclonal antibodies targeted against the RBD of S-protein of SARS-CoV-1 can neutralize SARS-CoV-2 thus inhibiting its infectivity in permissive cell lines. Research on coronaviral S-proteins paves the way for the development of vaccines that may prevent SARS-CoV-2 infection and alleviate the current global coronavirus pandemic. However, specific neutralizing mAbs against SARS-CoV-2 are in clinical development. Therefore, neutralizing antibodies targeting SARS-CoV-2 S-protein are promising specific antiviral therapeutics for pre-and post-exposure prophylaxis and treatment of SARS-CoV-2 infection. We hereby review the approaches taken by researchers across the world to use spike gene and S-glycoprotein for the development of effective diagnostics, vaccines and therapeutics against SARA-CoV-2 infection the COVID-19 pandemic.

COVID-19 versus SARS: A comparative review

The two genetically similar severe acute respiratory syndrome coronaviruses, SARS-CoV-1 and SARS-CoV-2, have each been responsible for global epidemics of vastly different scales. Although both viruses arose from similar origins, they quickly diverged due to differences in their transmission dynamics and spectrum of clinical presentations. The potential involvement of multiple organs systems, including the respiratory, cardiac, gastrointestinal and neurological, during infection necessitates a comprehensive understanding of the clinical pathogenesis of each virus. The management of COVID-19, initially modelled after SARS and other respiratory illnesses, has continued to evolve as we accumulate more knowledge and experience during the pandemic, as well as develop new therapeutics and vaccines. The impact of these two coronaviruses has been profound for our health care and public health systems, and we hope that the lessons learned will not only bring the current pandemic under control, but also prevent and reduce the impact of future pandemics.

Advances in Neutralization Assays for SARS‐CoV‐2

The coronavirus disease 2019 (COVID‐19) pandemic has triggered a global health emergency and brought disaster to humans. Tremendous efforts have been made to control the pandemic, among which neutralizing antibodies (NAbs) are of specific interest to researchers. Neutralizing antibodies are generated within weeks after infection or immunization and can protect cells from virus intrusion and confer protective immunity to cells. Thus, production of NAbs is considered as a main goal for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) vaccines and NAbs may be used for patient treatment in the form of monoclonal antibodies. Neutralization assays are capable of quantitatively detecting NAbs against SARS‐CoV‐2, allowing to explore the relationship between the level of NAbs and the severity of the disease, and may predict the possibility of re‐infection in COVID‐19 patients. They can also be used to test the effects of monoclonal antibodies, convalescent plasma and vaccines. At present, wild‐type virus neutralization assay remains the gold standard for measuring Nabs, while pseudovirus neutralization assays, Surrogate virus neutralization test (sVNT) and high‐throughput versions of neutralization assays are popular alternatives with their own advantages and disadvantages. In this review article, we summarize the characteristics and recent progress of SARS‐CoV‐2 neutralization assays. Special attention is given to the current limitations of various neutralization assays so as to promote new possible strategies with NAbs by which rapid SARS‐CoV‐2 serological diagnosis and antiviral screening in the future will be achieved.

SARS coronavirus outbreaks past and present-a comparative analysis of SARS-CoV-2 and its predecessors

The Coronavirus Disease 2019 (COVID-19), a pneumonic disease caused by the SARS Coronavirus 2 (SARS-CoV-2), is the 7th Coronavirus to have successfully infected and caused an outbreak in humans. Genome comparisons have shown that previous isolates, the SARS-related coronavirus (SARSr-CoV), including the SARS-CoV are closely related, yet different in disease manifestation. Several explanations were suggested for the undetermined origin of SARS-CoV-2, in particular, bats, avian and Malayan pangolins as reservoir hosts, owing to the high genetic similarity. The general morphology and structure of all these viral isolates overlap with analogous disease symptoms such as fever, dry cough, fatigue, dyspnoea and headache, very similar to the current SARS-CoV-2. Chest CT scans for SARS-CoV-2, SARS-CoV and MERS-CoV reveal pulmonary lesions, bilateral ground-glass opacities, and segmental consolidation in the lungs, a common pathological trait. With greatly overlapping similarities among the previous coronavirus, the SARS-CoV, it becomes interesting to observe marked differences in disease severity of the SARS-CoV-2 thereby imparting it the ability to rapidly transmit, exhibit greater stability, bypass innate host defences, and increasingly adapt to their new host thereby resulting in the current pandemic. The most recent B.1.1.7, B.1.351 and P.1 variants of SARS-CoV-2, highlight the fact that changes in amino acids in the Spike protein can contribute to enhanced infection and transmission efficiency. This review covers a comparative analysis of previous coronavirus outbreaks and highlights the differences and similarities among different coronaviruses, including the most recent isolates that have evolved to become easily transmissible with higher replication efficiency in humans.

Structural basis for broad coronavirus neutralization

Three highly pathogenic β-coronaviruses have crossed the animal-to-human species barrier in the past two decades: SARS-CoV, MERS-CoV and SARS-CoV-2. To evaluate the possibility of identifying antibodies with broad neutralizing activity, we isolated a monoclonal antibody, termed B6, that cross-reacts with eight β-coronavirus spike glycoproteins, including all five human-infecting β-coronaviruses. B6 broadly neutralizes entry of pseudotyped viruses from lineages A and C, but not from lineage B, and the latter includes SARS-CoV and SARS-CoV-2. Cryo-EM, X-ray crystallography and membrane fusion assays reveal that B6 binds to a conserved cryptic epitope located in the fusion machinery. The data indicate that antibody binding sterically interferes with the spike conformational changes leading to membrane fusion. Our data provide a structural framework explaining B6 cross-reactivity with β-coronaviruses from three lineages, along with a proof of concept for antibody-mediated broad coronavirus neutralization elicited through vaccination. This study unveils an unexpected target for next-generation structure-guided design of a pan-β-coronavirus vaccine.

An overview of some potential immunotherapeutic options against COVID-19

After the advent of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) in the late 2019, the resulting severe and pernicious syndrome (COVID-19) immediately was deployed all around the world. To date, despite relentless efforts to control the disease by drug repurposing, there is no approved specific therapy for COVID-19. Given the role of innate and acquired immune components in the control and elimination of viral infections and inflammatory mutilations during SARS-CoV2 pathogenesis, immunotherapeutic strategies appear to be beneficent. Passive immunotherapies such as convalescent plasma, which has received much attention especially in severe cases, as well as suppressing inflammatory cytokines, interferon administration, inhibition of kinases and complement cascade, virus neutralization with key engineered products, cell-based therapies, immunomodulators and anti-inflammatory drugs are among the key immunotherapeutic approaches to deal with COVID-19, which is discussed in this review. Also, details of leading COVID-19 vaccine candidates as the most potent immunotherapy have been provided. However, despite salient improvements, there is still a lack of completely assured vaccines for universal application. Therefore, adopting proper immunotherapies according to the cytokine pattern and involved immune responses, alongside engineered biologics specially ACE2-Fc to curb SARS-CoV2 infection until achieving a tailored vaccine is probably the best strategy to better manage this pandemic. Therefore, gaining knowledge about the mechanism of action, potential targets, as well as the effectiveness of immune-based approaches to confront COVID-19 in the form of a well-ordered review study is highly momentous.

Heterologous humoral immunity to human and zoonotic coronaviruses: Aiming for the achilles heel

Coronaviruses are evolutionarily successful RNA viruses, common to multiple avian, amphibian and mammalian hosts. Despite their ubiquity and potential impact, knowledge of host immunity to coronaviruses remains incomplete, partly owing to the lack of overt pathogenicity of endemic human coronaviruses (HCoVs), which typically cause common colds. However, the need for deeper understanding became pressing with the zoonotic introduction of three novel coronaviruses in the past two decades, causing severe acute respiratory syndromes in humans, and the unfolding pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This renewed interest not only triggered the discovery of two of the four HCoVs, but also uncovered substantial cellular and humoral cross-reactivity with shared or related coronaviral antigens. Here, we review the evidence for cross-reactive B cell memory elicited by HCoVs and its potential impact on the puzzlingly variable outcome of SARS-CoV-2 infection. The available data indicate targeting of highly conserved regions primarily in the S2 subunits of the spike glycoproteins of HCoVs and SARS-CoV-2 by cross-reactive B cells and antibodies. Rare monoclonal antibodies reactive with conserved S2 epitopes and with potent virus neutralising activity have been cloned, underscoring the potential functional relevance of cross-reactivity. We discuss B cell and antibody cross-reactivity in the broader context of heterologous humoral immunity to coronaviruses, as well as the limits of protective immune memory against homologous re-infection. Given the bidirectional nature of cross-reactivity, the unprecedented current vaccination campaign against SARS-CoV-2 is expected to impact HCoVs, as well as future zoonotic coronaviruses attempting to cross the species barrier. However, emerging SARS-CoV-2 variants with resistance to neutralisation by vaccine-induced antibodies highlight a need for targeting more constrained, less mutable parts of the spike. The delineation of such cross-reactive areas, which humoral immunity can be trained to attack, may offer the key to permanently shifting the balance of our interaction with current and future coronaviruses in our favour.

Potent Molecular Feature-based Neutralizing Monoclonal Antibodies as Promising Therapeutics Against SARS-CoV-2 Infection

The 2019-2020 winter was marked by the emergence of a new coronavirus (SARS-CoV-2) related disease (COVID-19), which started in Wuhan, China. Its high human-to-human transmission ability led to a worldwide spread within few weeks and has caused substantial human loss. Mechanical antiviral control approach, drug repositioning, and use of COVID-19 convalescent plasmas (CPs) were the first line strategies utilized to mitigate the viral spread, yet insufficient. The urgent need to contain this deadly pandemic has led searchers and pharmaceutical companies to develop vaccines. However, not all vaccines manufactured are safe. Besides, an alternative and effective treatment option for such an infectious disease would include pure anti-viral neutralizing monoclonal antibodies (NmAbs), which can block the virus at specific molecular targets from entering cells by inhibiting virus-cell structural complex formation, with more safety and efficiency than the CP. Indeed, there is a lot of molecular evidence about the protector effect and the use of molecular feature-based NmAbs as promising therapeutics to contain COVID-19. Thus, from the scientific publication database screening, we here retrieved antibody-related papers and summarized the repertory of characterized NmAbs against SARS-CoV-2, their molecular neutralization mechanisms, and their immunotherapeutic pros and cons. About 500 anti-SARS-CoV-2 NmAbs, characterized through competitive binding assays and neutralization efficacy, were reported at the writing time (January 2021). All NmAbs bind respectively to SARS-CoV-2 S and exhibit high molecular neutralizing effects against wild-type and/or pseudotyped virus. Overall, we defined six NmAb groups blocking SARS-CoV-2 through different molecular neutralization mechanisms, from which five potential neutralization sites on SARS-CoV-2 S protein are described. Therefore, more efforts are needed to develop NmAbs-based cocktails to mitigate COVID-19.