Therapeutic antibodies, targeting the SARS-CoV-2 spike N-terminal domain, protect lethally infected K18-hACE2 mice

Synergistic effect of two human-like monoclonal antibodies confers protection against orthopoxvirus infection

The eradication of smallpox was officially declared by the WHO in 1980, leading to discontinuation of the vaccination campaign against the virus. Consequently, immunity against smallpox and related orthopoxviruses like Monkeypox virus gradually declines, highlighting the need for efficient countermeasures not only for the prevention, but also for the treatment of already exposed individuals. We have recently developed human-like monoclonal antibodies (mAbs) from vaccinia virus-immunized non-human primates. Two mAbs, MV33 and EV42, targeting the two infectious forms of the virus, were selected for in vivo evaluation, based on their in vitro neutralization potency. A single dose of either MV33 or EV42 administered three days post-infection (dpi) to BALB/c female mice provides full protection against lethal ectromelia virus challenge. Importantly, a combination of both mAbs confers full protection even when provided five dpi. Whole-body bioimaging and viral load analysis reveal that combination of the two mAbs allows for faster and more efficient clearance of the virus from target organs compared to either MV33 or EV42 separately. The combined mAbs treatment further confers post-exposure protection against the currently circulating Monkeypox virus in Cast/EiJ female mice, highlighting their therapeutic potential against other orthopoxviruses.

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

A comprehensive review on immunogen and immune-response proteins of SARS-CoV-2 and their applications in prevention, diagnosis, and treatment of COVID-19

Exposure to severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2) prompts humoral immune responses in the human body. As the auxiliary diagnosis of a current infection, the existence of viral proteins can be checked from specific antibodies (Abs) induced by immunogenic viral proteins. For people with a weakened immune system, Ab treatment can help neutralize viral antigens to resist and treat the disease. On the other hand, highly immunogenic viral proteins can serve as effective markers for detecting prior infections. Additionally, the identification of viral particles or the presence of antibodies may help establish an immune defense against the virus. These immunogenic proteins rather than SARS-CoV-2 can be given to uninfected people as a vaccination to improve their coping ability against COVID-19 through the generation of memory plasma cells. In this work, we review immunogenic and immune-response proteins derived from SARS-CoV-2 with regard to their classification, origin, and diverse applications (e.g., prevention (vaccine development), diagnostic testing, and treatment (via neutralizing Abs)). Finally, advanced immunization strategies against COVID-19 are discussed along with the contemporary circumstances and future challenges.

Passive antibody therapy in emerging infectious diseases

The epidemic of corona virus disease 2019 (COVID-19) caused by severe acute respiratory syndrome Coronavirus 2 and its variants of concern (VOCs) has been ongoing for over 3 years. Antibody therapies encompassing convalescent plasma, hyperimmunoglobulin, and neutralizing monoclonal antibodies (mAbs) applied in passive immunotherapy have yielded positive outcomes and played a crucial role in the early COVID-19 treatment. In this review, the development path, action mechanism, clinical research results, challenges, and safety profile associated with the use of COVID-19 convalescent plasma, hyperimmunoglobulin, and mAbs were summarized. In addition, the prospects of applying antibody therapy against VOCs was assessed, offering insights into the coping strategies for facing new infectious disease outbreaks.

Challenges of SARS-CoV-2 genomic surveillance in India during low positivity rate scenario

Being the second most populous country in the world, India presents valuable lessons for the world about dealing with the SARS-CoV-2 pandemic. From this perspective, we attempted a retrospective evaluation of India's SARS-CoV-2 genomic surveillance strategy and also gave some recommendations for undertaking effective genomic surveillance. The dynamics of the COVID-19 pandemic are continuously evolving, and there is a dire need to modulate the genomic surveillance strategy accordingly. The pandemic is now settling towards a low positivity rate scenario, so it is required to revise the practices and policies formulated for a high positivity rate scenario. The perspective also recommends adopting a decentralised approach for SARS-CoV-2 genomic surveillance with a focus on optimising the workflow of SARS-CoV-2 genomic surveillance to ensure early detection of emerging variants, especially in the low positivity rate scenario. The perspective emphasises a key observation that the SARS-CoV-2 genomic surveillance is an important mitigation effort during the pandemic, the guards of such mitigation efforts should not be lowered during the low positivity rate scenario. We attempt to highlight the limitations faced by the Indian healthcare administration during the SARS-CoV-2 genomic surveillance and, simultaneously, suggest policy interventions derived from our first-hand experience, which may be implementable in a vast, populated country like India.

Broadly neutralizing antibodies to SARS-CoV-2 and other human coronaviruses

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a recently emerged pathogenic human coronavirus that belongs to the sarbecovirus lineage of the genus Betacoronavirus. The ancestor strain has evolved into a number of variants of concern, with the Omicron variant of concern now having many distinct sublineages. The ongoing COVID-19 pandemic caused by SARS-CoV-2 has caused serious damage to public health and the global economy, and one strategy to combat COVID-19 has been the development of broadly neutralizing antibodies for prophylactic and therapeutic use. Many are in preclinical and clinical development, and a few have been approved for emergency use. Here we summarize neutralizing antibodies that target four key regions within the SARS-CoV-2 spike (S) protein, namely the N-terminal domain and the receptor-binding domain in the S1 subunit, and the stem helix region and the fusion peptide region in the S2 subunit. Understanding the characteristics of these broadly neutralizing antibodies will accelerate the development of new antibody therapeutics and provide guidance for the rational design of next-generation vaccines.

Novel skewed usage of B-cell receptors in COVID-19 patients with various clinical presentations

B cell-mediated immune responses play important roles in controlling SARS-CoV infection. Here, we performed the single-cell B cell receptor sequencing (scBCR-seq) of the PBMC samples from eleven healthy controls, five asymptomatic subjects and 33 symptomatic COVID-19 patients with various clinical presentations, and subsequently analyzed the abundance and diversity of the BCR repertoires in different groups, respectively. We revealed the skewed usage of the IGHV, IGLV and IGKV genes and identified a number of heavy or light chain VDJ gene pairs and combinational preference in each group, such as IGKV3-7 and IGKV2-24 enriched in the asymptomatic subjects, whereas IGHV3-13, IGHV3-23-IGHJ4, IGHV1-18-IGLV3-19, IGHV1-18-IGLV3-21, and IGHV1-18-IGLV3-25 enriched in the recovery patients with severe diseases. We also observed the differential expression of IGHV3-23 in various B cell clusters by analysis of the scRNA-seq data. Additional dock analysis indicated that IGHV3-13 could bind to the spike protein of SARS-CoV-2. These findings may advance our understanding of the humoral immune responses in COVID-19 patients and help develop novel vaccine candidates as well as therapeutical antibodies against SASR-CoV-2 infections.

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.

DNA aptamers inhibit SARS-CoV-2 spike-protein binding to hACE2 by an RBD- independent or dependent approach

Objective: Nobody knows when the COVID-19 pandemic will end or when and where the next coronavirus will outbreak. Therefore, it is still necessary to develop SARS-CoV-2 inhibitors for different variants or even the new coronavirus. Since SARS-CoV-2 uses its surface spike-protein to recognize hACE2, mediating its entry into cells, ligands that can specifically recognize the spike-protein have the potential to prevent infection. Methods: We have recently discovered DNA aptamers against the S2-domain of the WT spike-protein by exploiting the selection process called SELEX. After optimization, among all candidates, the aptamer S2A2C1 has the shortest sequence and the best binding affinity toward the S2-protein. More importantly, the S2A2C1 aptamer does not bind to the RBD of the spike-protein, but it efficiently blocks the spike-protein/hACE2 interaction, suggesting an RBD-independent inhibition approach. To further improve its performance, we conjugated the S2A2C1 aptamer with a reported anti-RBD aptamer, S1B6C3, using various linkers and constructed hetero-bivalent fusion aptamers. Binding affinities of mono and fusion aptamers against the spike-proteins were measured. The inhibition efficacies of mono and fusion aptamers to prevent the hACE2/spike-protein interaction were determined using ELISA. Results: Anti-spike-protein aptamers, including S2A2C1 and S1B6C3-A5-S2A2C1, maintained high binding affinity toward the WT, Delta, and Omicron spike-proteins and high inhibition efficacies to prevent them from binding to hACE2, rendering them well-suited as diagnostic and therapeutic molecular tools to target SARS-CoV-2 and its variants. Conclusions: Overall, we discovered the anti-S2 aptamer, S2A2C1, which inhibits the hACE2/spike-protein interaction via an RBD-independent approach. The anti-S2 and anti-RBD aptamers were conjugated to obtain the fusion aptamer, S1B6C3-A5-S2A2C1, which recognizes the spike-protein by an RBD-dependent approach. Our strategies, which discovered aptamer inhibitors targeting the highly conserved S2-protein, as well as the design of fusion aptamers, can be used to target new coronaviruses as they emerge.

Potent human broadly SARS-CoV-2-neutralizing IgA and IgG antibodies effective against Omicron BA.1 and BA.2

Memory B-cell and antibody responses to the SARS-CoV-2 spike protein contribute to long-term immune protection against severe COVID-19, which can also be prevented by antibody-based interventions. Here, wide SARS-CoV-2 immunoprofiling in Wuhan COVID-19 convalescents combining serological, cellular, and monoclonal antibody explorations revealed humoral immunity coordination. Detailed characterization of a hundred SARS-CoV-2 spike memory B-cell monoclonal antibodies uncovered diversity in their repertoire and antiviral functions. The latter were influenced by the targeted spike region with strong Fc-dependent effectors to the S2 subunit and potent neutralizers to the receptor-binding domain. Amongst those, Cv2.1169 and Cv2.3194 antibodies cross-neutralized SARS-CoV-2 variants of concern, including Omicron BA.1 and BA.2. Cv2.1169, isolated from a mucosa-derived IgA memory B cell demonstrated potency boost as IgA dimers and therapeutic efficacy as IgG antibodies in animal models. Structural data provided mechanistic clues to Cv2.1169 potency and breadth. Thus, potent broadly neutralizing IgA antibodies elicited in mucosal tissues can stem SARS-CoV-2 infection, and Cv2.1169 and Cv2.3194 are prime candidates for COVID-19 prevention and treatment.

A combination of potently neutralizing monoclonal antibodies isolated from an Indian convalescent donor protects against the SARS-CoV-2 Delta variant

Although efficacious vaccines have significantly reduced the morbidity and mortality of COVID-19, there remains an unmet medical need for treatment options, which monoclonal antibodies (mAbs) can potentially fill. This unmet need is exacerbated by the emergence and spread of SARS-CoV-2 variants of concern (VOCs) that have shown some resistance to vaccine responses. Here we report the isolation of five neutralizing mAbs from an Indian convalescent donor, out of which two (THSC20.HVTR04 and THSC20.HVTR26) showed potent neutralization of SARS-CoV-2 VOCs at picomolar concentrations, including the Delta variant (B.1.617.2). One of these (THSC20.HVTR26) also retained activity against the Omicron variant. These two mAbs target non-overlapping epitopes on the receptor-binding domain (RBD) of the spike protein and prevent virus attachment to its host receptor, human angiotensin converting enzyme-2 (hACE2). Furthermore, the mAb cocktail demonstrated protection against the Delta variant at low antibody doses when passively administered in the K18 hACE2 transgenic mice model, highlighting their potential as a cocktail for prophylactic and therapeutic applications. Developing the capacity to rapidly discover and develop mAbs effective against highly transmissible pathogens like coronaviruses at a local level, especially in a low- and middle-income country (LMIC) such as India, will enable prompt responses to future pandemics as an important component of global pandemic preparedness.

Optimization of Anti-SARS-CoV-2 Neutralizing Antibody Therapies: Roadmap to Improve Clinical Effectiveness and Implementation

One of the major breakthroughs to combat the current Coronavirus Disease 2019 (COVID-19) pandemic has been the development of highly effective vaccines against the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Still, alternatives are needed for individuals who are at high risk of developing severe COVID-19 and are not protected by vaccination. Monoclonal antibodies against the spike protein of SARS-CoV-2 have been shown to be effective as prophylaxis and treatment against COVID-19. However, the emergence of variants of concern (VOCs) challenges the efficacy of antibody therapies. This review describes the neutralization resistance of the clinically-approved monoclonal antibody therapies against the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P1), Delta (B.1.617.2), and the Omicron (B.1.1.529) variants. To guide the development of monoclonal antibody therapies and to anticipate on the continuous evolution of SARS-CoV-2, we highlight different strategies to broaden the antibody activity by targeting more conserved epitopes and/or simultaneously targeting multiple sites of vulnerability of the virus. This review further describes the contribution of antibody Fc effector functions to optimize the antibody efficacy. In addition, the main route of SARS-CoV-2 antibody administration is currently intravenously and dictates a monthly injection when used as prophylactic. Therefore, we discusses the concept of long-acting antibodies (LAABs) and non-intravenously routes of antibody administration in order to broaden the clinical applicability of antibody therapies.

Immunodominant Linear B-Cell Epitopes of SARS-CoV-2 Spike, Identified by Sera from K18-hACE2 Mice Infected with the WT or Variant Viruses

SARS-CoV-2 surface spike protein mediates the viral entry into the host cell and represents the primary immunological target of COVID-19 vaccines as well as post-exposure immunotherapy. Establishment of the highly immunogenic B-cell epitope profile of SARS-CoV-2 proteins in general, and that of the spike protein in particular, may contribute to the development of sensitive diagnostic tools and identification of vaccine` candidate targets. In the current study, the anti-viral antibody response in transgenic K18-hACE-2 mice was examined by implementing an immunodominant epitope mapping approach of the SARS-CoV-2 spike. Serum samples for probing an epitope array covering the entire spike protein were collected from mice following infection with the original SARS-CoV-2 strain as well as the B.1.1.7 Alpha and B.1.351 Beta genetic variants of concern. The analysis resulted in distinction of six linear epitopes common to the humoral response against all virus variants inspected at a frequency of more than 20% of the serum samples. Finally, the universality of the response was probed by cross-protective in vitro experiments using plaque-reducing neutralization tests. The data presented here has important implications for prediction of the efficacy of immune countermeasures against emerging SARS-CoV-2 variants.

Induction of Innate Immune Response by TLR3 Agonist Protects Mice against SARS-CoV-2 Infection

SARS-CoV-2, a member of the coronavirus family, is the causative agent of the COVID-19 pandemic. Currently, there is still an urgent need in developing an efficient therapeutic intervention. In this study, we aimed at evaluating the therapeutic effect of a single intranasal treatment of the TLR3/MDA5 synthetic agonist Poly(I:C) against a lethal dose of SARS-CoV-2 in K18-hACE2 transgenic mice. We demonstrate here that early Poly(I:C) treatment acts synergistically with SARS-CoV-2 to induce an intense, immediate and transient upregulation of innate immunity-related genes in lungs. This effect is accompanied by viral load reduction, lung and brain cytokine storms prevention and increased levels of macrophages and NK cells, resulting in 83% mice survival, concomitantly with long-term immunization. Thus, priming the lung innate immunity by Poly(I:C) or alike may provide an immediate, efficient and safe protective measure against SARS-CoV-2 infection.

Monoclonal antibodies for COVID-19 therapy and SARS-CoV-2 detection

The coronavirus disease 2019 (COVID-19) pandemic is an exceptional public health crisis that demands the timely creation of new therapeutics and viral detection. Owing to their high specificity and reliability, monoclonal antibodies (mAbs) have emerged as powerful tools to treat and detect numerous diseases. Hence, many researchers have begun to urgently develop Ab-based kits for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Ab drugs for use as COVID-19 therapeutic agents. The detailed structure of the SARS-CoV-2 spike protein is known, and since this protein is key for viral infection, its receptor-binding domain (RBD) has become a major target for therapeutic Ab development. Because SARS-CoV-2 is an RNA virus with a high mutation rate, especially under the selective pressure of aggressively deployed prophylactic vaccines and neutralizing Abs, the use of Ab cocktails is expected to be an important strategy for effective COVID-19 treatment. Moreover, SARS-CoV-2 infection may stimulate an overactive immune response, resulting in a cytokine storm that drives severe disease progression. Abs to combat cytokine storms have also been under intense development as treatments for COVID-19. In addition to their use as drugs, Abs are currently being utilized in SARS-CoV-2 detection tests, including antigen and immunoglobulin tests. Such Ab-based detection tests are crucial surveillance tools that can be used to prevent the spread of COVID-19. Herein, we highlight some key points regarding mAb-based detection tests and treatments for the COVID-19 pandemic.

Characterization of antibody-antigen interactions using biolayer interferometry

This protocol describes the use of a biolayer interferometry platform for assessing antibody-antigen interactions. The protocol focuses on affinity determination and epitope binning, although the system can be utilized for measuring any protein-protein interaction. Readings are collected in real time, allowing the use of unlabeled molecules, and data can thus be obtained in a fast and easy manner. Experiments should be carefully designed, taking into consideration the tested interaction, available sensors, and suitable controls. For complete details on the use and execution of this protocol, please refer to Noy-Porat et al. (2021).

Animal models for SARS-CoV-2 infection and pathology

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiology of coronavirus disease 2019 (COVID-19) pandemic. Current variants including Alpha, Beta, Gamma, Delta, and Lambda increase the capacity of infection and transmission of SARS-CoV-2, which might disable the in-used therapies and vaccines. The COVID-19 has now put an enormous strain on health care system all over the world. Therefore, the development of animal models that can capture characteristics and immune responses observed in COVID-19 patients is urgently needed. Appropriate models could accelerate the testing of therapeutic drugs and vaccines against SARS-CoV-2. In this review, we aim to summarize the current animal models for SARS-CoV-2 infection, including mice, hamsters, nonhuman primates, and ferrets, and discuss the details of transmission, pathology, and immunology induced by SARS-CoV-2 in these animal models. We hope this could throw light to the increased usefulness in fundamental studies of COVID-19 and the preclinical analysis of vaccines and therapeutic agents.

Fc-Independent Protection from SARS-CoV-2 Infection by Recombinant Human Monoclonal Antibodies

The use of passively-administered neutralizing antibodies is a promising approach for the prevention and treatment of SARS-CoV-2 infection. Antibody-mediated protection may involve immune system recruitment through Fc-dependent activation of effector cells and the complement system. However, the role of Fc-mediated functions in the efficacious in-vivo neutralization of SARS-CoV-2 is not yet clear, and it is of high importance to delineate the role this process plays in antibody-mediated protection. Toward this aim, we have chosen two highly potent SARS-CoV-2 neutralizing human monoclonal antibodies, MD65 and BLN1 that target distinct domains of the spike (RBD and NTD, respectively). The Fc of these antibodies was engineered to include the triple mutation N297G/S298G/T299A that eliminates glycosylation and the binding to FcγR and to the complement system activator C1q. As expected, the virus neutralization activity (in-vitro) of the engineered antibodies was retained. To study the role of Fc-mediated functions, the protective activity of these antibodies was tested against lethal SARS-CoV-2 infection of K18-hACE2 transgenic mice, when treatment was initiated either before or two days post-exposure. Antibody treatment with both Fc-variants similarly rescued the mice from death reduced viral load and prevented signs of morbidity. Taken together, this work provides important insight regarding the contribution of Fc-effector functions in MD65 and BLN1 antibody-mediated protection, which should aid in the future design of effective antibody-based therapies.

In Vivo Electroporation of Plasmid DNA: A Promising Strategy for Rapid, Inexpensive, and Flexible Delivery of Anti-Viral Monoclonal Antibodies

Since the first approval of monoclonal antibodies by the United States Food and Drug Administration (FDA) in 1986, therapeutic antibodies have become one of the predominant classes of drugs in oncology and immunology. Despite their natural function in contributing to antiviral immunity, antibodies as drugs have only more recently been thought of as tools for combating infectious diseases. Passive immunization, or the delivery of the products of an immune response, offers near-immediate protection, unlike the active immune processes triggered by traditional vaccines, which rely on the time it takes for the host's immune system to develop an effective defense. This rapid onset of protection is particularly well suited to containing outbreaks of emerging viral diseases. Despite these positive attributes, the high cost associated with antibody manufacture and the need for a cold chain for storage and transport limit their deployment on a global scale, especially in areas with limited resources. The in vivo transfer of nucleic acid-based technologies encoding optimized therapeutic antibodies transform the body into a bioreactor for rapid and sustained production of biologics and hold great promise for circumventing the obstacles faced by the traditional delivery of antibodies. In this review, we provide an overview of the different antibody delivery strategies that are currently being developed, with particular emphasis on in vivo transfection of naked plasmid DNA facilitated by electroporation.

Neutralizing antibodies for the prevention and treatment of COVID-19

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) initiates the infection process by binding to the viral cellular receptor angiotensin-converting enzyme 2 through the receptor-binding domain (RBD) in the S1 subunit of the viral spike (S) protein. This event is followed by virus-cell membrane fusion mediated by the S2 subunit, which allows virus entry into the host cell. Therefore, the SARS-CoV-2 S protein is a key therapeutic target, and prevention and treatment of coronavirus disease 2019 (COVID-19) have focused on the development of neutralizing monoclonal antibodies (nAbs) that target this protein. In this review, we summarize the nAbs targeting SARS-CoV-2 proteins that have been developed to date, with a focus on the N-terminal domain and RBD of the S protein. We also describe the roles that binding affinity, neutralizing activity, and protection provided by these nAbs play in the prevention and treatment of COVID-19 and discuss the potential to improve nAb efficiency against multiple SARS-CoV-2 variants. This review provides important information for the development of effective nAbs with broad-spectrum activity against current and future SARS-CoV-2 strains.

Live imaging of SARS-CoV-2 infection in mice reveals that neutralizing antibodies require Fc function for optimal efficacy

Neutralizing antibodies (NAbs) are effective in treating COVID-19, but the mechanism of immune protection is not fully understood. Here, we applied live bioluminescence imaging (BLI) to monitor the real-time effects of NAb treatment during prophylaxis and therapy of K18-hACE2 mice intranasally infected with SARS-CoV-2-nanoluciferase. Real-time imaging revealed that the virus spread sequentially from the nasal cavity to the lungs in mice and thereafter systemically to various organs including the brain, culminating in death. Highly potent NAbs from a COVID-19 convalescent subject prevented, and also effectively resolved, established infection when administered within three days. In addition to direct neutralization, depletion studies indicated that Fc effector interactions of NAbs with monocytes, neutrophils, and natural killer cells were required to effectively dampen inflammatory responses and limit immunopathology. Our study highlights that both Fab and Fc effector functions of NAbs are essential for optimal in vivo efficacy against SARS-CoV-2.

The neutralization potency of anti-SARS-CoV-2 therapeutic human monoclonal antibodies is retained against viral variants

A wide range of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing monoclonal antibodies (mAbs) have been reported, most of which target the spike glycoprotein. Therapeutic implementation of these antibodies has been challenged by emerging SARS-CoV-2 variants harboring mutated spike versions. Consequently, re-assessment of previously identified mAbs is of high priority. Four previously selected mAbs targeting non-overlapping epitopes are now evaluated for binding potency to mutated RBD versions, reported to mediate escape from antibody neutralization. In vitro neutralization potencies of these mAbs, and two NTD-specific mAbs, are evaluated against two frequent SARS-CoV-2 variants of concern, the B.1.1.7 Alpha and the B.1.351 Beta. Furthermore, we demonstrate therapeutic potential of three selected mAbs by treatment of K18-human angiotensin-converting enzyme 2 (hACE2) transgenic mice 2 days post-infection with each virus variant. Thus, despite the accumulation of spike mutations, the highly potent MD65 and BL6 mAbs retain their ability to bind the prevalent viral mutants, effectively protecting against B.1.1.7 and B.1.351 variants.

Homologous and heterologous serological response to the N-terminal domain of SARS-CoV-2 in humans and mice

The increasing numbers of infected cases of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses serious threats to public health and the global economy. Most SARS-CoV-2 neutralizing antibodies target the receptor binding domain (RBD) and some the N-terminal domain (NTD) of the spike protein, which is the major antigen of SARS-CoV-2. While the antibody response to RBD has been extensively characterized, the antigenicity and immunogenicity of the NTD protein are less well studied. Using 227 plasma samples from COVID-19 patients, we showed that SARS-CoV-2 NTD-specific antibodies could be induced during infection. As compared to the results of SARS-CoV-2 RBD, the serological response of SARS-CoV-2 NTD is less cross-reactive with SARS-CoV, a pandemic strain that was identified in 2003. Furthermore, neutralizing antibodies are rarely elicited in a mice model when NTD is used as an immunogen. We subsequently demonstrate that NTD has an altered antigenicity when expressed alone. Overall, our results suggest that while NTD offers a supplementary strategy for serology testing, it may not be suitable as an immunogen for vaccine development.

Sensitive Immunodetection of Severe Acute Respiratory Syndrome Coronavirus 2 Variants of Concern 501Y.V2 and 501Y.V1

Emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants may influence the effectiveness of existing laboratory diagnostics. In the current study we determined whether the British (20I/501Y.V1) and South African (20H/501Y.V2) SARS-CoV-2 variants of concern are detected with an in-house S1-based antigen detection assay, analyzing spiked pools of quantitative reverse-transcription polymerase chain reaction-negative nasopharyngeal swab specimens. The assay, combining 4 monoclonal antibodies, allowed sensitive detection of both the wild type and the variants of concern, despite accumulation of several mutations in the variants' S1 region-results suggesting that this combination, targeting distinct epitopes, enables both specificity and the universality.

Neutralizing Monoclonal Anti-SARS-CoV-2 Antibodies Isolated from Immunized Rabbits Define Novel Vulnerable Spike-Protein Epitope

Monoclonal antibodies represent an important avenue for COVID-19 therapy and are routinely used for rapid and accessible diagnosis of SARS-CoV-2 infection. The recent emergence of SARS-CoV-2 genetic variants emphasized the need to enlarge the repertoire of antibodies that target diverse epitopes, the combination of which may improve immune-diagnostics, augment the efficiency of the immunotherapy and prevent selection of escape-mutants. Antigen-specific controlled immunization of experimental animals may elicit antibody repertoires that significantly differ from those generated in the context of the immune response mounted in the course of disease. Accordingly, rabbits were immunized by several recombinant antigens representing distinct domains of the viral spike protein and monoclonal antibodies were isolated from single cells obtained by cell sorting. Characterization of a panel of successfully isolated anti-receptor binding domain (RBD) and anti-N-terminal domain (NTD) antibodies demonstrated that they exhibit high specificity and affinity profiles. Anti-RBD antibodies revealing significant neutralizing potency against SARS-CoV-2 in vitro were found to target at least three distinct epitopes. Epitope mapping established that two of these antibodies recognized a novel epitope located on the surface of the RBD. We suggest that the antibodies isolated in this study are useful for designing SARS-CoV-2 diagnosis and therapy approaches.