Antibody-dependent enhancement and SARS-CoV-2 vaccines and therapies

Expression of mammalian proteins for diagnostics and therapeutics: a review

BACKGROUND

Antibodies have proven to be remarkably successful for biomedical applications. They play important roles in epidemiology and medicine from diagnostics of diseases to therapeutics, treating diseases from incessant chronic diseases such as rheumatology to pandemic outbreaks. With no end in sight for the demand for antibody products, optimizations and new techniques must be expanded to accommodate this.

METHODS AND RESULTS

This review discusses optimizations and techniques for antibody production through choice of discovery platforms, expression systems, cell culture mediums, and other strategies to increase expression yield. Each system has its own merits and demerits, and the strategy chosen is critical in addressing various biological aspects.

CONCLUSIONS

There is still insufficient evidence to validate the efficacy of some of these techniques, and further research is needed to consolidate these industrial production systems. There is no doubt that more strategies, systems, and pipelines will contribute to enhance biopharmaceutical production.

Evolving understanding of antibody-dependent enhancement (ADE) of SARS-CoV-2

Since immune system and internal environment in vivo are large and complex, the interpretation of the observed immune effect from the perspective of a single immune cell or antibody seems a little feeble. Many studies have shown that specific antibodies against “ former” viruses have a reduced ability to neutralize “new” mutant strains. However, there is no comprehensive and clear view of whether there will be Antibody-dependent enhancement (ADE). We review the latest relevant studies, hoping to explain the ADE of SARS-CoV-2 infection sometimes observed in some patients.

Discovery and intranasal administration of a SARS-CoV-2 broadly acting neutralizing antibody with activity against multiple Omicron subvariants

BACKGROUND

The continual emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern, in particular the newly emerged Omicron (B.1.1.529) variant and its BA.X lineages, has rendered ineffective a number of previously FDA emergency use authorized SARS-CoV-2 neutralizing antibody therapies. Furthermore, those approved antibodies with neutralizing activity against Omicron BA.1 are reportedly ineffective against the subset of Omicron subvariants that contain a R346K substitution, BA.1.1, and the more recently emergent BA.2, demonstrating the continued need for discovery and characterization of candidate therapeutic antibodies with the breadth and potency of neutralizing activity required to treat newly diagnosed COVID-19 linked to recently emerged variants of concern.

METHODS

Following a campaign of antibody discovery based on the vaccination of Harbor H2L2 mice with defined SARS-CoV-2 spike domains, we have characterized the activity of a large collection of spike-binding antibodies and identified a lead neutralizing human IgG1 LALA antibody, STI-9167.

FINDINGS

STI-9167 has potent, broad-spectrum neutralizing activity against the current SARS-COV-2 variants of concern and retained activity against each of the tested Omicron subvariants in both pseudotype and live virus neutralization assays. Furthermore, STI-9167 nAb administered intranasally or intravenously provided protection against weight loss and reduced virus lung titers to levels below the limit of quantitation in Omicron-infected K18-hACE2 transgenic mice.

CONCLUSIONS

With this established activity profile, a cGMP cell line has been developed and used to produce cGMP drug product intended for intravenous or intranasal use in human clinical trials.

FUNDING

Funded by CRIPT (no. 75N93021R00014), DARPA (HR0011-19-2-0020), and NCI Seronet (U54CA260560).

Mathematical modeling the dynamics of SARS-CoV-2 infection with antibody-dependent enhancement

The advent and swift global spread of the novel coronavirus (COVID-19) transmitted by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have caused massive deaths and economic devastation worldwide. Antibody-dependent enhancement (ADE) is a common phenomenon in virology that directly affects the effectiveness of the vaccine, and there is no fully effective vaccine for diseases. In order to study the potential role of ADE on SARS-CoV-2 infection, we establish the SARS-CoV-2 infection dynamics model with ADE. The basic reproduction number is computed. We prove that when R 0 < 1 , the infection-free equilibrium is globally asymptotically stable, and the system is uniformly persistent when R 0 > 1 . We carry out the sensitivity analysis by the partial rank correlation coefficients and the extended version of the Fourier amplitude sensitivity test. Numerical simulations are implemented to illustrate the theoretical results. The potential impact of ADE on SARS-CoV-2 infection is also assessed. Our results show that ADE may accelerate SARS-CoV-2 infection. Furthermore, our findings suggest that increasing antibody titers can have the ability to control SARS-CoV-2 infection with ADE, but enhancing the neutralizing power of antibodies may be ineffective to control SARS-CoV-2 infection with ADE. Our study presumably contributes to a better understanding of the dynamics of SARS-CoV-2 infection with ADE.

Prefusion-specific antibody-derived peptides trivalently presented on DNA-nanoscaffolds as an innovative strategy against RSV entry

Human respiratory syncytial virus (RSV) is the primary cause of acute lower respiratory tract infections in children and the elderly worldwide, for which neither a vaccine nor an effective therapy is approved. The entry of RSV into the host cell is mediated by stepwise structural changes in the surface RSV fusion (RSV-F) glycoprotein. Recent progress in structural and functional studies of RSV-F glycoprotein revealed conformation-dependent neutralizing epitopes which have become attractive targets for vaccine and therapeutic development. As RSV-F is present on viral surface in a trimeric form, a trivalent binding interaction between a candidate fusion inhibitor and the respective epitopes on each of the three monomers is expected to prevent viral infection at higher potency than a monovalent or bivalent inhibitor. Here we demonstrate a novel RSV entry inhibitory approach by implementing a trimeric DNA nanostructure as a template to display up to three linear peptide moieties that simultaneously target an epitope on the surface of the prefusion RSV-F protein. In order to design synthetic binding peptides that can be coupled to the DNA nanostructure, the prefusion RSV-F-specific monoclonal antibody (D25) was selected. Complementarity-determining region 3 (CDR3) derived peptides underwent truncation and alanine-scanning mutagenesis analysis, followed by systematic sequence modifications using non-canonical amino acids. The most effective peptide candidate was used as a binding moiety to functionalize the DNA nanostructure. The designed DNA-peptide construct was able to block RSV infection on cells more efficiently than the monomeric peptides, however a more moderate reduction of viral load was observed in the lungs of infected mice upon intranasal application, likely due to dissociation or absorption of the underlying DNA structure by cells in the lungs. Taken together, our results point towards the inhibitory potential of a novel trimeric DNA-peptide based approach against RSV and open the possibility to apply this platform to target other viral infections.

The next frontier in vaccine design: blending immune correlates of protection into rational vaccine design

Despite the extraordinary speed and success in SARS-Cov-2 vaccine development, the emergence of variants of concern perplexed the vaccine development community. Neutralizing antibodies waned antibodies waned and were evaded by viral variants, despite the preservation of protection against severe disease and death across vaccinated populations. Similar to other vaccine design efforts, the lack of mechanistic correlates of immunity against Coronavirus Disease 2019, raised questions related to the need for vaccine redesign and boosting. Hence, our limited understanding of mechanistic correlates of immunity - across pathogens - remains a major obstacle in vaccine development. The identification and incorporation of mechanistic correlates of immunity are key to the accelerated design of highly impactful globally relevant vaccines. Systems-biology tools can be applied strategically to define a complete understanding of mechanistic correlates of immunity. Embedding immunological dissection and target immune profile identification, beyond canonical antibody binding and neutralization, may accelerate the design and success of durable protective vaccines.

Multivalent ACE2 engineering-A promising pathway for advanced coronavirus nanomedicine development

The spread of coronavirus diseases has resulted in a clarion call to develop potent drugs and vaccines even as different strains appear beyond human prediction. An initial step that is integral to the viral entry into host cells results from an active-targeted interaction of the viral spike (S) proteins and the cell surface receptor, called angiotensin-converting enzyme 2 (ACE2). Thus, engineered ACE2 has been an interesting decoy inhibitor against emerging coronavirus infestation. This article discusses promising innovative ACE2 engineering pathways for current and emerging coronavirus therapeutic development. First, we provide a brief discussion of some ACE2-associated human coronaviruses and their cell invasion mechanism. Then, we describe and contrast the individual spike proteins and ACE2 receptor interactions, highlighting crucial hotspots across the ACE2-associated coronaviruses. Lastly, we address the importance of multivalency in ACE2 nanomedicine engineering and discuss novel approaches to develop and achieve multivalent therapeutic outcomes. Beyond coronaviruses, these approaches will serve as a paradigm to develop new and improved treatment technologies against pathogens that use ACE2 receptor for invasion.

Spatial- and Valence-Matched Neutralizing DNA Nanostructure Blocks Wild-Type SARS-CoV-2 and Omicron Variant Infection

Natural ligand-receptor interactions that play pivotal roles in biological events are ideal models for design and assembly of artificial recognition molecules. Herein, aiming at the structural characteristics of the spike trimer and infection mechanism of SARS-CoV-2, we have designed a DNA framework-guided spatial-patterned neutralizing aptamer trimer for SARS-CoV-2 neutralization. The ∼5.8 nm tetrahedral DNA framework affords precise spatial organization and matched valence as four neutralizing aptamers (MATCH-4), which matches with nanometer precision the topmost surface of SARS-CoV-2 spike trimer, enhancing the interaction between MATCH-4 and spike trimer. Moreover, the DNA framework provides a dimensionally complementary nanoscale barrier to prevent the spike trimer-ACE2 interaction and the conformational transition, thereby inhibiting SARS-CoV-2-host cell fusion and infection. As a result, the spatial- and valence-matched MATCH-4 ensures improved binding affinity and neutralizing activity against SARS-CoV-2 and its varied mutant strains, particularly the current Omicron variant, that are evasive of the majority of existing neutralizing antibodies. In addition, because neutralizing aptamers specific to other targets can be evolved and assembled, the present design has the potential to inhibit other wide-range and emerging pathogens.

Theoretical Explanation for the Rarity of Antibody-Dependent Enhancement of Infection (ADE) in COVID-19

Global vaccination against the SARS-CoV-2 virus has proved to be highly effective. However, the possibility of antibody-dependent enhancement of infection (ADE) upon vaccination remains underinvestigated. Here, we aimed to theoretically determine conditions for the occurrence of ADE in COVID-19. We developed a series of mathematical models of antibody response: model Ab—a model of antibody formation; model Cv—a model of infection spread in the body; and a complete model, which combines the two others. The models describe experimental data on SARS-CoV and SARS-CoV-2 infections in humans and cell cultures, including viral load dynamics, seroconversion times and antibody concentration kinetics. The modelling revealed that a significant proportion of macrophages can become infected only if they bind antibodies with high probability. Thus, a high probability of macrophage infection and a sufficient amount of pre-existing antibodies are necessary for the development of ADE in SARS-CoV-2 infection. However, from the point of view of the dynamics of pneumocyte infection, the two cases where the body has a high concentration of preexisting antibodies and a high probability of macrophage infection and where there is a low concentration of antibodies in the body and no macrophage infection are indistinguishable. This conclusion could explain the lack of confirmed ADE cases for COVID-19.

Circulating multimeric immune complexes contribute to immunopathology in COVID-19

A dysregulated immune response with high levels of SARS-CoV-2 specific IgG antibodies characterizes patients with severe or critical COVID-19. Although a robust IgG response is considered to be protective, excessive triggering of activating Fc-gamma-receptors (FcγRs) could be detrimental and cause immunopathology. Here, we document excessive FcγRIIIA/CD16A activation in patients developing severe or critical COVID-19 but not in those with mild disease. We identify two independent ligands mediating extreme FcγRIIIA/CD16A activation. Soluble circulating IgG immune complexes (sICs) are detected in about 80% of patients with severe and critical COVID-19 at levels comparable to active systemic lupus erythematosus (SLE) disease. FcγRIIIA/CD16A activation is further enhanced by afucosylation of SARS-CoV-2 specific IgG. Utilizing cell-based reporter systems we provide evidence that sICs can be formed prior to a specific humoral response against SARS-CoV-2. Our data suggest a cycle of immunopathology driven by an early formation of sICs in predisposed patients. These findings suggest a reason for the seemingly paradoxical findings of high antiviral IgG responses and systemic immune dysregulation in severe COVID-19. The involvement of circulating sICs in the promotion of immunopathology in predisposed patients opens new possibilities for intervention strategies to mitigate critical COVID-19 progression.

During viral infections high levels of antibodies can form soluble immune complexes (sICs) with antigen and trigger Fcγ receptors (FcγR) leading to increased immunopathology. Here the authors measure FcγRs activation by sICs and consider how these may lead to excessive immunopathology during severe SARS-CoV-2 infection.

An albumin-angiotensin converting enzyme 2-based SARS-CoV-2 decoy with FcRn-driven half-life extension

The emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants and breakthrough infections despite available coronavirus disease 2019 (COVID-19) vaccines calls for antiviral therapeutics. The application of soluble angiotensin converting enzyme 2 (ACE2) as a SARS-CoV-2 decoy that reduces cell bound ACE2-mediated virus entry is limited by a short plasma half-life. This work presents a recombinant human albumin ACE2 genetic fusion (rHA-ACE2) to increase the plasma half-life by an FcRn-driven cellular recycling mechanism, investigated using a wild type (WT) albumin sequence and sequence engineered with null FcRn binding (NB). Binding of rHA-ACE2 fusions to SARS-CoV-2 spike protein subdomain 1 (S1) was demonstrated (WT-ACE2 K_D = 32.8 nM and NB-ACE2 K_D = 31.7 nM) using Bio-Layer Interferometry and dose-dependent in vitro inhibition of host cell infection of pseudotyped viruses displaying surface SARS-CoV-2 spike (S) protein. FcRn-mediated in vitro recycling was translated to a five times greater plasma half-life of WT-ACE2 (t_½ β = 13.5 h) than soluble ACE2 (t_½ β = 2.8 h) in humanised FcRn/albumin double transgenic mice. The rHA-ACE2-based SARS-CoV-2 decoy system exhibiting FcRn-driven circulatory half-life extension introduced in this work offers the potential to expand and improve the anti-COVID-19 anti-viral drug armoury.

Statement of significance

The COVID-19 pandemic has highlighted the need for rapid development of efficient antiviral therapeutics to combat SARS-CoV-2 and new mutants to lower morbidity and mortality in severe cases, and for people that are unable to receive a vaccine. Here we report a therapeutic albumin ACE2 fusion protein (rHA-ACE2), that can bind SARS-CoV-2 S protein decorated virus-like particles to inhibit viral infection, and exhibits extended in vivo half-life compared to ACE2 alone. Employing ACE2 as a binding decoy for the virus is expected to efficiently inhibit all SARS-CoV-2 mutants as they all rely on binding with endogenous ACE2 for viral cell entry and, therefore, rHA-ACE2 constitutes a versatile addition to the therapeutic arsenal for combatting COVID-19.

COVID-19 Convalescent Plasma and Clinical Trials: Understanding Conflicting Outcomes

Convalescent plasma (CP) recurs as a frontline treatment in epidemics because it is available as soon as there are survivors. The COVID-19 pandemic represented the first large-scale opportunity to shed light on the mechanisms of action, safety, and efficacy of CP using modern evidence-based medicine approaches. Studies ranging from observational case series to randomized controlled trials (RCTs) have reported highly variable efficacy results for COVID-19 CP (CCP), resulting in uncertainty. We analyzed variables associated with efficacy, such as clinical settings, disease severity, CCP SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) antibody levels and function, dose, timing of administration (variously defined as time from onset of symptoms, molecular diagnosis, diagnosis of pneumonia, or hospitalization, or by serostatus), outcomes (defined as hospitalization, requirement for ventilation, clinical improvement, or mortality), CCP provenance and time for collection, and criteria for efficacy. The conflicting trial results, along with both recent WHO guidelines discouraging CCP usage and the recent expansion of the FDA emergency use authorization (EUA) to include outpatient use of CCP, create confusion for both clinicians and patients about the appropriate use of CCP. A review of 30 available RCTs demonstrated that signals of efficacy (including reductions in mortality) were more likely if the CCP neutralizing titer was >160 and the time to randomization was less than 9 days. The emergence of the Omicron variant also reminds us of the benefits of polyclonal antibody therapies, especially as a bridge to the development and availability of more specific therapies.

Reevaluation of antibody-dependent enhancement of infection in anti-SARS-CoV-2 therapeutic antibodies and mRNA-vaccine antisera using FcR- and ACE2-positive cells

Many therapeutic antibodies (Abs) and mRNA vaccines, both targeting SARS-CoV-2 spike protein (S-protein), have been developed and approved in order to combat the ongoing COVID-19 pandemic. In consideration of these developments, a common concern has been the potential for Ab-dependent enhancement (ADE) of infection caused by inoculated or induced Abs. Although the preventive and therapeutic effects of these Abs are obvious, little attention has been paid to the influence of the remaining and dwindling anti-S-protein Abs in vivo. Here, we demonstrate that certain monoclonal Abs (mAbs) approved as therapeutic neutralizing anti-S-protein mAbs for human usage have the potential to cause ADE in a narrow range of Ab concentrations. Although sera collected from mRNA-vaccinated individuals exhibited neutralizing activity, some sera gradually exhibited dominance of ADE activity in a time-dependent manner. None of the sera examined exhibited neutralizing activity against infection with the Omicron strain. Rather, some ADE of Omicron infection was observed in some sera. These results suggest the possible emergence of adverse effects caused by these Abs in addition to the therapeutic or preventive effect.

Unbiased approach to identify and assess efficacy of human SARS-CoV-2 neutralizing antibodies

Coronavirus disease 2019 (COVID-19) continues to significantly impact the global population, thus countermeasure platforms that enable rapid development of therapeutics against variants of SARS-CoV-2 are essential. We report use of a phage display human antibody library approach to rapidly identify neutralizing antibodies (nAbs) against SARS-CoV-2. We demonstrate the binding and neutralization capability of two nAbs, STI-2020 and STI-5041, against the SARS-CoV-2 WA-1 strain as well as the Alpha and Beta variants. STI-2020 and STI-5041 were protective when administered intravenously or intranasally in the golden (Syrian) hamster model of COVID-19 challenged with the WA-1 strain or Beta variant. The ability to administer nAbs intravenously and intranasally may have important therapeutic implications and Phase 1 healthy subjects clinical trials are ongoing.

Contribution of Coronavirus-Specific Immunoglobulin G Responses to Complement Overactivation in Patients with Severe Coronavirus Disease 2019

BACKGROUND

Excessive complement activation has been implicated in the pathogenesis of coronavirus disease 2019 (COVID-19), but the mechanisms leading to this response remain unclear.

METHODS

We measured plasma levels of key complement markers, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA and antibodies against SARS-CoV-2 and seasonal human common cold coronaviruses (CCCs) in hospitalized patients with COVID-19 of moderate (n = 18) and critical severity (n = 37) and in healthy controls (n = 10).

RESULTS

We confirmed that complement activation is systemically increased in patients with COVID-19 and is associated with a worse disease outcome. We showed that plasma levels of C1q and circulating immune complexes were markedly increased in patients with severe COVID-19 and correlated with higher immunoglobulin (Ig) G titers, greater complement activation, and higher disease severity score. Additional analyses showed that the classical pathway was the main arm responsible for augmented complement activation in severe patients. In addition, we demonstrated that a rapid IgG response to SARS-CoV-2 and an anamnestic IgG response to the nucleoprotein of the CCCs were strongly correlated with circulating immune complex levels, complement activation, and disease severity.

CONCLUSIONS

These findings indicate that early, nonneutralizing IgG responses may play a key role in complement overactivation in severe COVID-19. Our work underscores the urgent need to develop therapeutic strategies to modify complement overactivation in patients with COVID-19.

A comprehensive review of BBV152 vaccine development, effectiveness, safety, challenges, and prospects

The world has responded to the COVID-19 pandemic with unprecedented speed and vigor in the mass vaccination campaigns, targeted to reduce COVID-19 severity and mortality, reduce the pressure on the healthcare system, re-open society, and reduction in disease mortality and morbidity. Here we review the preclinical and clinical development of BBV152, a whole virus inactivated vaccine and an important tool in the fight to control this pandemic. BBV152, formulated with a TLR7/8 agonist adjuvant generates a Th1-biased immune response that induces high neutralization efficacy against different SARS-CoV-2 variants of concern and robust long-term memory B- and T-cell responses. With seroconversion rates as high as 98.3% in vaccinated individuals, BBV152 shows 77.8% and 93.4% protection from symptomatic COVID-19 disease and severe symptomatic COVID-19 disease respectively. Studies in pediatric populations show superior immunogenicity (geometric mean titer ratio of 1.76 compared to an adult) with a seroconversion rate of >95%. The reactogenicity and safety profiles were comparable across all pediatric age groups between 2-18 yrs. as in adults. Like most approved vaccines, the BBV152 booster given 6 months after full vaccination, reverses a waning immunity, restores the neutralization efficacy, and shows synergy in a heterologous prime-boost study with about 3-fold or 300% increase in neutralization titers against multiple SARS-CoV-2 variants of concern. Based on the interim Phase III data, BBV152 received full authorization for adults and emergency use authorization for children from ages 6 to 18 years in India. It is also licensed for emergency use in 14 countries globally. Over 313 million vaccine doses have already been administered in India alone by April 18th, 2022.

Recombinant COVID-19 vaccine based on recombinant RBD/Nucleoprotein and saponin adjuvant induces long-lasting neutralizing antibodies and cellular immunity

SARS-CoV-2 has caused a global pandemic, infecting millions of people. An effective preventive vaccine against this virus is urgently needed. Here, we designed and developed a novel formulated recombinant receptor-binding domain (RBD) nucleocapsid (N) recombinant vaccine candidates. The RBD and N were separately expressed in E. coli and purified using column chromatography. The female Balb/c mice were immunized subcutaneously with the combination of purified RBD and N alone or formulated with saponin adjuvant in a two-week interval in three doses. Neutralization antibody (Nabs) titers against the SARS-CoV-2 were detected by a Surrogate Virus Neutralization (sVNT) Test. Also, total IgG and IgG1, and IgG2a isotypes and the balance of cytokines in the spleen (IFN-γ, Granzyme B, IL-4, and IL-12) were measured by ELISA. The percentages of CD4+ and CD8+ T cells were quantified by flow cytometry. The lymphoproliferative activity of restimulated spleen cells was also determined. The findings showed that the combination of RBD and N proteins formulated with saponin significantly promoted specific total IgG and neutralization antibodies, elicited robust specific lymphoproliferative and T cell response responses. Moreover, marked increase in CD4+ and CD8+ T cells were observed in the adjuvanted RBD and N vaccine group compared with other groups. The results suggest that the formulations are able to elicit a specific long-lasting mixed Th1/Th2 balanced immune response. Our data indicate the significance of the saponin-adjuvanted RBD/N vaccine in the design of SARS-CoV-2 vaccines and provide a rationale for the development of a protective long-lasting and strong vaccine.

SARS-CoV-2 mRNA-vaccine candidate; COReNAPCIN®, induces robust humoral and cellular immunity in mice and non-human primates

At the forefront of biopharmaceutical industry, the messenger RNA (mRNA) technology offers a flexible and scalable platform to address the urgent need for world-wide immunization in pandemic situations. This strategic powerful platform has recently been used to immunize millions of people proving both of safety and highest level of clinical efficacy against infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here we provide preclinical report of COReNAPCIN^®; a vaccine candidate against SARS-CoV-2 infection. COReNAPCIN^® is a nucleoside modified mRNA-based vaccine formulated in lipid nanoparticles (LNPs) for encoding the full-length prefusion stabilized SARS-CoV-2 spike glycoprotein on the cell surface. Vaccination of C57BL/6 and BALB/c mice and rhesus macaque with COReNAPCIN^® induced strong humoral responses with high titers of virus-binding and neutralizing antibodies. Upon vaccination, a robust SARS-CoV-2 specific cellular immunity was also observed in both mice and non-human primate models. Additionally, vaccination protected rhesus macaques from symptomatic SARS-CoV-2 infection and pathological damage to the lung upon challenging the animals with high viral loads of up to 2 × 10⁸ live viral particles. Overall, our data provide supporting evidence for COReNAPCIN^® as a potent vaccine candidate against SARS-CoV-2 infection for clinical studies.

Pathogen evolution during vaccination campaigns

Following the initiation of the unprecedented global vaccination campaign against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), attention has now turned to the potential impact of this large-scale intervention on the evolution of the virus. In this Essay, we summarize what is currently known about pathogen evolution in the context of immune priming (including vaccination) from research on other pathogen species, with an eye towards the future evolution of SARS-CoV-2.

Non-neutralizing antibodies: Deleterious or propitious during SARS-CoV-2 infection?

Antibody-dependent enhancement (ADE) is a complex phenomenon mediated by antibodies, frequently pre-existing non-neutralizing or sub-neutralizing antibodies. In the course of infectious diseases, ADE may be responsible for worsening the clinical course of the disease by increasing the virulence of pathogens (ADE of infection) or enhancing disease severity (ADE of disease). Here we reviewed the mechanisms thought to be behind the ADE phenomenon and its potential relationship with COVID-19 severity. Since the early COVID-19 epidemics, ADE has been mentioned as a possible mechanism involved in severe COVID-19 disease and, later, as a potential risk in the case of infection after vaccination. However, current data do not support its role in disease severity, both after infection and reinfection.

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.

Activating Fc Gamma Receptors and Viral Receptors Are Required for Antibody-Dependent Enhancement of Porcine Reproductive and Respiratory Syndrome Virus Infection

Simple Summary

Porcine reproductive and respiratory syndrome virus (PRRSV)-specific sub- or non-neutralizing antibodies promote the adhesion and internalization of the virion into host cells. This phenomenon is known as antibody-dependent enhancement (ADE) of PRRSV infection. It has long been accepted that Fc gamma receptors (FcγRs) are responsible for mediating ADE of virus infection. However, few researchers pay attention to the role of the virus receptors in the ADE of virus infection. In this study, we showed that activating FcγRs (FcγRI and FcγRIII) were responsible for mediating PRRSV-ADE infection. Simultaneously, we showed that the viral receptors (sialoadhesin and CD163) were involved in FcγR-mediated PRRSV-ADE infection. The extracellular domains 1-6 of sialoadhesin and the scavenger receptor cysteine-rich 5 domain of CD163 might play central roles in PRRSV-ADE infection. In conclusion, our studies indicated that activating FcγRs and virus receptors were required for PRRSV-ADE infection. Our findings should allow a more precise understanding of the structural basis for the mechanism of PRRSV-ADE infection, which would provide references for screening targets of novel PRRS vaccines or antiviral drugs against the PRRSV.

Abstract

Antibody-dependent enhancement (ADE) is an event in preexisting sub-, or non-neutralizing antibodies increasing the viral replication in its target cells. ADE is one crucial factor that intensifies porcine reproductive and respiratory syndrome virus (PRRSV) infection and results in PRRSV-persistent infection. Nevertheless, the exact mechanisms of PRRSV-ADE infection are poorly understood. In the current research, the results of the ADE assay showed that porcine immunoglobulin G (IgG) specific for the PRRSV significantly enhanced PRRSV proliferation in porcine alveolar macrophages (PAMs), suggesting that the ADE activity of PRRSV infection existed in pig anti-PRRSV IgG. The results of the RNA interference assay showed that knockdown of the Fc gamma receptor I (FcγRI) or FcγRIII gene significantly suppressed the ADE activity of PRRSV infection in PAMs, suggesting that FcγRI and FcγRIII were responsible for mediating PRRSV-ADE infection. In addition, the results of the antibody blocking assay showed that specific blocking of the Sn1, 2, 3, 4, 5, or 6 extracellular domain of the sialoadhesin (Sn) protein or selective blockade of the scavenger receptor cysteine-rich (SRCR) 5 domain of the CD163 molecule significantly repressed the ADE activity of PRRSV infection in PAMs, suggesting that Sn and CD163 were involved in FcγR-mediated PRRSV-ADE infection. The Sn1–6 domains of porcine Sn protein and the SRCR 5 domain of porcine CD163 molecule might play central roles in the ADE of PRRSV infection. In summary, our studies indicated that activating FcγRs (FcγRI and FcγRIII) and viral receptors (Sn and CD163) were required for ADE of PRRSV infection. Our findings provided a new insight into PRRSV infection that could be enhanced by FcγRs and PRRSV receptors-mediated PRRSV-antibody immune complexes (ICs), which would deepen our understanding of the mechanisms of PRRSV-persistent infection via the ADE pathway.

An ACE2-IgG4 Fc Fusion Protein Demonstrates Strong Binding to All Tested SARS-CoV-2 Variants and Reduced Lung Inflammation in Animal Models of SARS-CoV-2 and Influenza

Background:

The continued emergence of SARS-CoV-2 variants has caused concern that a constantly evolving virus will escape vaccines and antibody therapies. New approaches are needed.

Methods:

We created and manufactured an ACE2 extracellular domain (ECD) fragment Fc fusion drug candidate, G921, and engineered the compound for enhanced delivery of drug to peripheral tissues by minimizing the size of the ACE2 ECD and by incorporating an Fc domain to enhance transcytosis. G921 was assessed for binding, neutralization, in vivo anti-inflammatory effect, and pharmacokinetic profile.

Results:

G921 was expressed as an IgG4 Fc fusion protein presenting two ACE2 domains to ACE2 ligands while avoiding risk of infection via antibody-dependent enhancement. G921 strongly binds to the SARS-CoV-2 Wuhan-Hu-1 spike protein and demonstrates further diminished off rate to the spike protein from each of the currently identified variants of concern. G921 demonstrates ACE2 enzymatic activity comparable to positive control and binding to the neonatal Fc receptor (FcRn) without binding to low affinity Fc-gamma receptors (FcγRs). G921 is effective in a concentration-dependent manner in a focus reduction neutralization assay with EC₅₀=16.3±4.2 µg/mL without cytotoxicity in Vero E6 cells when tested at 200 µg/mL in an MTS cell proliferation assay. G921 demonstrates statistically significant reduction of lung inflammation in relevant models of both SARS-CoV-2 and influenza. The pharmacokinetic profile demonstrated dose-dependent exposure with a multi-day half-life in monkeys and rats.

Conclusion:

G921 data are consistent with both antiviral and anti-inflammatory modes of action. G921 is a novel approach for the prevention and treatment of COVID-19 and possible other diseases characterized by deficiency of ACE2.

Predicting Epitope Candidates for SARS-CoV-2

Epitopes are short amino acid sequences that define the antigen signature to which an antibody or T cell receptor binds. In light of the current pandemic, epitope analysis and prediction are paramount to improving serological testing and developing vaccines. In this paper, known epitope sequences from SARS-CoV, SARS-CoV-2, and other Coronaviridae were leveraged to identify additional antigen regions in 62K SARS-CoV-2 genomes. Additionally, we present epitope distribution across SARS-CoV-2 genomes, locate the most commonly found epitopes, and discuss where epitopes are located on proteins and how epitopes can be grouped into classes. The mutation density of different protein regions is presented using a big data approach. It was observed that there are 112 B cell and 279 T cell conserved epitopes between SARS-CoV-2 and SARS-CoV, with more diverse sequences found in Nucleoprotein and Spike glycoprotein.

Potent neutralizing anti-SARS-CoV-2 human antibodies cure infection with SARS-CoV-2 variants in hamster model

Treatment with neutralizing monoclonal antibodies (mAbs) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contributes to COVID-19 management. Unfortunately, SARS-CoV-2 variants escape several of these recently approved mAbs, highlighting the need for additional discovery and development. In a convalescent patient with COVID-19, we identified six mAbs, classified in four epitope groups, that potently neutralized SARS-CoV-2 D614G, beta, gamma, and delta infection in vitro, with three mAbs neutralizing omicron as well. In hamsters, mAbs 3E6 and 3B8 potently cured infection with SARS-CoV-2 Wuhan, beta, and delta when administered post-viral infection at 5 mg/kg. Even at 0.2 mg/kg, 3B8 still reduced viral titers. Intramuscular delivery of DNA-encoded 3B8 resulted in in vivo mAb production of median serum levels up to 90 μg/mL, and protected hamsters against delta infection. Overall, our data mark 3B8 as a promising candidate against COVID-19, and highlight advances in both the identification and gene-based delivery of potent human mAbs.

Antibodies against the SARS-CoV-2 S1-RBD cross-react with dengue virus and hinder dengue pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally since December 2019. Several studies reported that SARS-CoV-2 infections may produce false-positive reactions in dengue virus (DENV) serology tests and vice versa. However, it remains unclear whether SARS-CoV-2 and DENV cross-reactive antibodies provide cross-protection against each disease or promote disease severity. In this study, we confirmed that antibodies against the SARS-CoV-2 spike protein and its receptor-binding domain (S1-RBD) were significantly increased in dengue patients compared to normal controls. In addition, anti-S1-RBD IgG purified from S1-RBD hyperimmune rabbit sera could cross-react with both DENV envelope protein (E) and nonstructural protein 1 (NS1). The potential epitopes of DENV E and NS1 recognized by these antibodies were identified by a phage-displayed random peptide library. In addition, DENV infection and DENV NS1-induced endothelial hyperpermeability in vitro were inhibited in the presence of anti-S1-RBD IgG. Passive transfer anti-S1-RBD IgG into mice also reduced prolonged bleeding time and decreased NS1 seral level in DENV-infected mice. Lastly, COVID-19 patients’ sera showed neutralizing ability against dengue infection in vitro. Thus, our results suggest that the antigenic cross-reactivity between the SARS-CoV-2 S1-RBD and DENV can induce the production of anti-SARS-CoV-2 S1-RBD antibodies that cross-react with DENV which may hinder dengue pathogenesis.

Antibody-Dependent Enhancement: ″Evil″ Antibodies Favorable for Viral Infections

The pandemics caused by emerging viruses such as severe acute respiratory syndrome coronavirus 2 result in severe disruptions to public health. Vaccines and antibody drugs play essential roles in the control and prevention of emerging infectious diseases. However, in contrast with the neutralizing antibodies (NAbs), sub- or non-NAbs may facilitate the virus to enter the cells and enhance viral infection, which is termed antibody-dependent enhancement (ADE). The ADE of most virus infections is mediated by the Fc receptors (FcRs) expressed on the myeloid cells, while others are developed by other mechanisms, such as complement receptor-mediated ADE. In this review, we comprehensively analyzed the characteristics of the viruses inducing FcRs-mediated ADE and the new molecular mechanisms of ADE involved in the virus entry, immune response, and transcription modulation, which will provide insights into viral pathogenicity and the development of safer vaccines and effective antibody drugs against the emerging viruses inducing ADE.

Evaluation of immune evasion in SARS-CoV-2 Delta and Omicron variants

Emerging SARS-CoV-2 variants with higher transmissibility and immune escape remain a persistent threat across the globe. This is evident from the recent outbreaks of the Delta (B.1.617.2) and Omicron variants. These variants have originated from different continents and spread across the globe. In this study, we explored the genomic and structural basis of these variants for their lineage defining mutations of the spike protein through computational analysis, protein modeling, and molecular dynamic (MD) simulations. We further experimentally validated the importance of these deletion mutants for their immune escape using a pseudovirus-based neutralization assay, and an antibody (4A8) that binds directly to the spike protein's NTD. Delta variant with the deletion and mutations in the NTD revealed a better rigidity and reduced flexibility as compared to the wild-type spike protein (Wuhan isolate). Furthermore, computational studies of 4A8 monoclonal antibody (mAb) revealed a reduced binding of Delta variant compared to the wild-type strain. Similarly, the MD simulation data and virus neutralization assays revealed that the Omicron also exhibits immune escape, as antigenic beta-sheets appear to be disrupted. The results of the present study demonstrate the higher possibility of immune escape and thereby achieved better fitness advantages by the Delta and Omicron variants, which warrants further demonstrations through experimental evidences. Our study, based on in-silico computational modelling, simulations, and pseudovirus-based neutralization assay, highlighted and identified the probable mechanism through which the Delta and Omicron variants are more pathogenically evolved with higher transmissibility as compared to the wild-type strain.

High viral loads: what drives fatal cases of COVID-19 in vaccinees? - an autopsy study

The rate of SARS-CoV-2 infections in vaccinees has become a relevant serious issue. This study aimed to determine the causes of death, histological organ alteration, and viral spread in relation to demographic, clinical-pathological, viral variants, and vaccine types for deceased individuals with proven SARS-CoV-2 infection after vaccination who died between January and November 2021. Twenty-nine consecutively collected cases were analyzed and compared to 141 nonvaccinated control cases. Autopsies were performed on 16 partially and 13 fully vaccinated individuals. Most patients were elderly and suffered from several relevant comorbidities. Real-time RT-PCR (RT-qPCR) identified a significantly increased rate of generalized viral dissemination within organ systems in vaccinated cases versus nonvaccinated cases (45% vs. 16%, respectively; P = 0.008) mainly with Ct-values of higher than 25 in non-respiratory samples. However, vaccinated cases also showed high viral loads, reaching Ct-values below 10, especially in the upper airways and lungs. This was accompanied by high rates of pulmonal bacterial or mycotic superinfections and the occurrence of immunocompromising factors, such as malignancies, immunosuppressive drug intake, or decreased immunoglobulin levels. All these findings were particularly accentuated in partially vaccinated patients compared to fully vaccinated individuals. The virus dissemination observed in our case study may indicate that patients with an impaired immune system have a decreased ability to eliminate the virus. However, the potential role of antibody-dependent enhancement must also be ruled out in future studies. Fatal cases of COVID-19 in vaccinees were rare and often associated with severe comorbidities or other immunosuppressive conditions.

COVID-19 disease and autoimmune disorders: A mutual pathway

Coronavirus disease 2019 (COVID-19) is a real challenge for humanity with high morbidity and mortality. Despite being primarily a respiratory illness, COVID-19 can affect nearly every human body tissue, causing many diseases. After viral infection, the immune system can recognize the viral antigens presented by the immune cells. This immune response is usually controlled and terminated once the infection is aborted. Nevertheless, in some patients, the immune reaction becomes out of control with the development of autoimmune diseases. Several human tissue antigens showed a strong response with antibodies directed against many severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins, such as SARS-CoV-2 S, N, and autoimmune target proteins. The immunogenic effects of SARS-CoV-2 are due to the sizeable viral RNA molecules with interrupted transcription increasing the pool of epitopes with increased chances of molecular mimicry and interaction with the host immune system, the overlap between some viral and human peptides, the viral induced-tissue damage, and the robust and complex binding between sACE-2 and SARS-CoV-2 S protein. Consequently, COVID-19 and its vaccine may trigger the development of many autoimmune diseases in a predisposed patient. This review discusses the mutual relation between COVID-19 and autoimmune diseases, their interactive effects on each other, the role of the COVID-19 vaccine in triggering autoimmune diseases, the factors affecting the severity of COVID-19 in patients suffering from autoimmune diseases, and the different ways to minimize the risk of COVID-19 in patients with autoimmune diseases.

Engineered ACE2-Fc counters murine lethal SARS-CoV-2 infection through direct neutralization and Fc-effector activities

Soluble angiotensin-converting enzyme 2 (ACE2) constitutes an attractive antiviral capable of targeting a wide range of coronaviruses using ACE2 as their receptor. Using structure-guided approaches, we developed a series of bivalent ACE2-Fcs harboring functionally and structurally validated mutations that enhance severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor binding domain recognition by up to ~12-fold and remove angiotensin enzymatic activity. The lead variant M81 potently cross-neutralized SARS-CoV-2 variants of concern (VOCs), including Omicron, at subnanomolar half-maximal inhibitory concentration and was capable of robust Fc-effector functions, including antibody-dependent cellular cytotoxicity, phagocytosis, and complement deposition. When tested in a stringent K18-hACE2 mouse model, Fc-enhanced ACE2-Fc delayed death by 3 to 5 days or effectively resolved lethal SARS-CoV-2 infection in both prophylactic and therapeutic settings via the combined effects of neutralization and Fc-effector functions. These data add to the demonstrated utility of soluble ACE2 as a valuable SARS-CoV-2 antiviral and indicate that Fc-effector functions may constitute an important component of ACE2-Fc therapeutic activity.

SARS-CoV-2 spike and nucleocapsid proteins fail to activate human dendritic cells or γδ T cells

γδ T cells are thought to contribute to immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanisms by which they are activated by the virus are unknown. Using flow cytometry, we investigated if the two most abundant viral structural proteins, spike and nucleocapsid, can activate human γδ T cell subsets, directly or in the presence of dendritic cells (DC). Both proteins failed to induce interferon-γ production by Vδ1 or Vδ2 T cells within fresh mononuclear cells or lines of expanded γδ T cells generated from healthy donors, but the same proteins stimulated CD3⁺ cells from COVID-19 patients. The nucleocapsid protein stimulated interleukin-12 production by DC and downstream interferon-γ production by co-cultured Vδ1 and Vδ2 T cells, but protease digestion and use of an alternative nucleocapsid preparation indicated that this activity was due to contaminating non-protein material. Thus, SARS-CoV-2 spike and nucleocapsid proteins do not have stimulatory activity for DC or γδ T cells. We propose that γδ T cell activation in COVID-19 patients is mediated by immune recognition of viral RNA or other structural proteins by γδ T cells, or by other immune cells, such as DC, that produce γδ T cell-stimulatory ligands or cytokines.

Development of COVID-19 therapies: Nonclinical testing considerations

Therapies have been developed in the last couple of years to allow vaccination against, or treatment of patients with, COVID-19 using pathways such as Emergency Use Authorization (EUA) in the USA and Conditional Marketing Authorization (CMA) in the EU and UK. However, nonclinical studies were performed to allow such authorization and these were reviewed for 6 vaccines, 7 biological (monoclonal antibodies [mAbs]) and 4 small molecule therapies to examine whether the number and types of studies normally needed for regulatory agency authorization have been reduced. Results showed that the short answer is generally no. Thus, a battery of immunogenicity/efficacy or related pharmacology/biological activity studies showing utility against SARS-CoV-2 were performed as well as general toxicity studies across all 3 compound classes along with pharmacokinetic studies for mAbs and small molecules and, reproduction toxicity testing for vaccines and small molecules; additionally, genotoxicity testing occurred for small molecules. What was different from conventional, lengthy drug development, was that for vaccines and small molecules, leverage to existing platform technology or data available for other development programs, respectively, occurred. Recognition that mAbs can target the spike protein leading to neutralization allowed rapid development into clinical candidates.

Glycosylation and S-palmitoylation regulate SARS-CoV-2 spike protein intracellular trafficking

Post-translational modifications (PTMs), such as glycosylation and palmitoylation, are critical to protein folding, stability, intracellular trafficking, and function. Understanding regulation of PTMs of SARS-CoV-2 spike (S) protein could help the therapeutic drug design. Herein, the VSV vector was used to produce SARS-CoV-2 S pseudoviruses to examine the roles of the ⁶¹¹LYQD⁶¹⁴ and cysteine-rich motifs in S protein maturation and virus infectivity. Our results show that ⁶¹¹LY⁶¹² mutation alters S protein intracellular trafficking and reduces cell surface expression level. It also changes S protein glycosylation pattern and decreases pseudovirus infectivity. The S protein contains four cysteine-rich clusters with clusters I and II as the main palmitoylation sites. Mutations of clusters I and II disrupt S protein trafficking from ER-to-Golgi, suppress pseudovirus production, and reduce spike-mediated membrane fusion activity. Taken together, glycosylation and palmitoylation orchestrate the S protein maturation processing and are critical for S protein-mediated membrane fusion and infection.

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⁶¹¹LY⁶¹² mutation alters the glycosylation pattern of the SARS-CoV-2 S protein

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⁶¹¹LY⁶¹² mutation reduces S protein surface expression level

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Palmitoylation targets mature S protein to the Golgi and plasma membrane

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Palmitoylation is required for pseudovirus and SARS-CoV-2 production

The humoral response and antibodies against SARS-CoV-2 infection

Two and a half years into the COVID-19 pandemic, we have gained many insights into the human antibody response to the causative SARS-CoV-2 virus. In this Review, we summarize key observations of humoral immune responses in people with COVID-19, discuss key features of infection- and vaccine-induced neutralizing antibodies, and consider vaccine designs for inducing antibodies that are broadly protective against different variants of the SARS-CoV-2 virus.

Antibodies targeting conserved non-canonical antigens and endemic coronaviruses associate with favorable outcomes in severe COVID-19

While there have been extensive analyses characterizing cellular and humoral responses across the severity spectrum in COVID-19, outcome predictors within severe COVID-19 remain less comprehensively elucidated. Furthermore, properties of antibodies (Abs) directed against viral antigens beyond spike and their associations with disease outcomes remain poorly defined. We perform deep molecular profiling of Abs directed against a wide range of antigenic specificities in severe COVID-19 patients. The profiles included canonical (spike [S], receptor-binding domain [RBD], and nucleocapsid [N]) and non-canonical (orf3a, orf8, nsp3, nsp13, and membrane [M]) antigenic specificities. Notably, multivariate Ab profiles directed against canonical or non-canonical antigens are equally discriminative of survival in severe COVID-19. Intriguingly, pre-pandemic healthy controls have cross-reactive Abs directed against nsp13, a protein conserved across coronaviruses. Consistent with these findings, a model built on Ab profiles for endemic coronavirus antigens also predicts COVID-19 outcome. Our results suggest the importance of studying Abs targeting non-canonical severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and endemic coronavirus antigens in COVID-19.

Natural and genetically-modified animal models to investigate pulmonary and extrapulmonary manifestations of COVID-19

Coronavirus disease-19 (COVID-19), a pandemic caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), is a primarily respiratory tract disease. Suitable animal models for COVID-19 are required to study various aspects of pathogenesis, drug discovery, effective and safe vaccine development. Several laboratory animals including, non-human primates, hamsters, ferrets, transgenic mice, and zebrafish, have been used and proven their significance experimentally. Currently available animal models of SARS-CoV-2 can be broadly classified into two categories 1) natural animal models 2) genetically-modified that exhibit different degrees of susceptibility of SARS-CoV-2, tissue damage in respiratory and other organ systems. Not all the available animal models mimic COVID-19-like phenotype completely. Therefore, understanding various aspects of COVID-19 requires different animal models. In this review article, we provide an update on the immune response and clinical manifestations observed in naturally occurring and genetically-modified animals of COVID-19. We then review the transmission, viral replication, lung pathology, immunological aspects, and extrapulmonary phenotypes observed in various animal models. In the end, we put forth our perspective on the anticipated uses, disadvantages, and limitations of each type of animal model.

COVID-19 Vaccination Might Induce Postural Orthostatic Tachycardia Syndrome: A Case Report

We report a case of new-onset postural orthostatic tachycardia syndrome in a healthy 46-year-old female after a single dose of the BNT162b2 (Pfizer-BioNTech) SARS-CoV-2 vaccine. There have been three prior reports of new-onset postural orthostatic tachycardia syndrome after COVID-19 vaccination. Predominant symptoms noted included fatigue, brain fog, headache, sinus tachycardia, and dizziness. Management includes noninvasive therapies, behavioral approaches, and pharmacologic regimens. Here, the patient presented with fatigue, palpitations, dizziness, and presyncope, with symptoms beginning 7 days after vaccination. Presenting vitals included temperature within normal limits, inappropriate tachycardia, up to 120 beats per minute, blood pressure of 128/87 mm of mercury, and 100% saturation in room air. Her management included lifestyle changes, dietary supplements, and ivabradine. Further studies are needed to evaluate prevalence, etiology, and optimal management.

Antibodies to combat viral infections: development strategies and progress

Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections owing to characteristics such as their high specificity and their ability to enhance immune responses. Furthermore, antibody engineering can be used to strengthen effector function and prolong mAb half-life, and advances in structural biology have enabled the selection and optimization of potent neutralizing mAbs through identification of vulnerable regions in viral proteins, which can also be relevant for vaccine design. The COVID-19 pandemic has stimulated extensive efforts to develop neutralizing mAbs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with several mAbs now having received authorization for emergency use, providing not just an important component of strategies to combat COVID-19 but also a boost to efforts to harness mAbs in therapeutic and preventive settings for other infectious diseases. Here, we describe advances in antibody discovery and engineering that have led to the development of mAbs for use against infections caused by viruses including SARS-CoV-2, respiratory syncytial virus (RSV), Ebola virus (EBOV), human cytomegalovirus (HCMV) and influenza. We also discuss the rationale for moving from empirical to structure-guided strategies in vaccine development, based on identifying optimal candidate antigens and vulnerable regions within them that can be targeted by antibodies to result in a strong protective immune response.

Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections. This Review describes advances in antibody discovery and engineering that have led to the development of mAbs that target viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), respiratory syncytial virus and Ebola virus, and also considers the implications for vaccine development.

SARS-CoV-2-neutralising monoclonal antibodies to prevent COVID-19

BACKGROUND

Monoclonal antibodies (mAbs) are laboratory-produced molecules derived from the B cells of an infected host. They are being investigated as potential prophylaxis to prevent coronavirus disease 2019 (COVID-19).

OBJECTIVES

To assess the effects of SARS-CoV-2-neutralising mAbs, including mAb fragments, to prevent infection with SARS-CoV-2 causing COVID-19; and to maintain the currency of the evidence, using a living systematic review approach.

SEARCH METHODS

We searched the Cochrane COVID-19 Study Register, MEDLINE, Embase, and three other databases on 27 April 2022. We checked references, searched citations, and contacted study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that evaluated SARS-CoV-2-neutralising mAbs, including mAb fragments, alone or combined, versus an active comparator, placebo, or no intervention, for pre-exposure prophylaxis (PrEP) and postexposure prophylaxis (PEP) of COVID-19. We excluded studies of SARS-CoV-2-neutralising mAbs to treat COVID-19, as these are part of another review.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed search results, extracted data, and assessed risk of bias using Cochrane RoB 2. Prioritised outcomes were infection with SARS-CoV-2, development of clinical COVID-19 symptoms, all-cause mortality, admission to hospital, quality of life, adverse events (AEs), and serious adverse events (SAEs). We rated the certainty of evidence using GRADE.

MAIN RESULTS

We included four RCTs of 9749 participants who were previously uninfected and unvaccinated at baseline. Median age was 42 to 76 years. Around 20% to 77.5% of participants in the PrEP studies and 35% to 100% in the PEP studies had at least one risk factor for severe COVID-19. At baseline, 72.8% to 82.2% were SARS-CoV-2 antibody seronegative. We identified four ongoing studies, and two studies awaiting classification. Pre-exposure prophylaxis Tixagevimab/cilgavimab versus placebo One study evaluated tixagevimab/cilgavimab versus placebo in participants exposed to SARS-CoV-2 wild-type, Alpha, Beta, and Delta variant. About 39.3% of participants were censored for efficacy due to unblinding and 13.8% due to vaccination. Within six months, tixagevimab/cilgavimab probably decreases infection with SARS-CoV-2 (risk ratio (RR) 0.45, 95% confidence interval (CI) 0.29 to 0.70; 4685 participants; moderate-certainty evidence), decreases development of clinical COVID-19 symptoms (RR 0.18, 95% CI 0.09 to 0.35; 5172 participants; high-certainty evidence), and may decrease admission to hospital (RR 0.03, 95% CI 0 to 0.59; 5197 participants; low-certainty evidence). Tixagevimab/cilgavimab may result in little to no difference on mortality within six months, all-grade AEs, and SAEs (low-certainty evidence). Quality of life was not reported. Casirivimab/imdevimab versus placebo One study evaluated casirivimab/imdevimab versus placebo in participants who may have been exposed to SARS-CoV-2 wild-type, Alpha, and Delta variant. About 36.5% of participants opted for SARS-CoV-2 vaccination and had a mean of 66.1 days between last dose of intervention and vaccination. Within six months, casirivimab/imdevimab may decrease infection with SARS-CoV-2 (RR 0.01, 95% CI 0 to 0.14; 825 seronegative participants; low-certainty evidence) and may decrease development of clinical COVID-19 symptoms (RR 0.02, 95% CI 0 to 0.27; 969 participants; low-certainty evidence). We are uncertain whether casirivimab/imdevimab affects mortality regardless of the SARS-CoV-2 antibody serostatus. Casirivimab/imdevimab may increase all-grade AEs slightly (RR 1.14, 95% CI 0.98 to 1.31; 969 participants; low-certainty evidence). The evidence is very uncertain about the effects on grade 3 to 4 AEs and SAEs within six months. Admission to hospital and quality of life were not reported. Postexposure prophylaxis Bamlanivimab versus placebo One study evaluated bamlanivimab versus placebo in participants who may have been exposed to SARS-CoV-2 wild-type. Bamlanivimab probably decreases infection with SARS-CoV-2 versus placebo by day 29 (RR 0.76, 95% CI 0.59 to 0.98; 966 participants; moderate-certainty evidence), may result in little to no difference on all-cause mortality by day 60 (R 0.83, 95% CI 0.25 to 2.70; 966 participants; low-certainty evidence), may increase all-grade AEs by week eight (RR 1.12, 95% CI 0.86 to 1.46; 966 participants; low-certainty evidence), and may increase slightly SAEs (RR 1.46, 95% CI 0.73 to 2.91; 966 participants; low-certainty evidence). Development of clinical COVID-19 symptoms, admission to hospital within 30 days, and quality of life were not reported. Casirivimab/imdevimab versus placebo One study evaluated casirivimab/imdevimab versus placebo in participants who may have been exposed to SARS-CoV-2 wild-type, Alpha, and potentially, but less likely to Delta variant. Within 30 days, casirivimab/imdevimab decreases infection with SARS-CoV-2 (RR 0.34, 95% CI 0.23 to 0.48; 1505 participants; high-certainty evidence), development of clinical COVID-19 symptoms (broad-term definition) (RR 0.19, 95% CI 0.10 to 0.35; 1505 participants; high-certainty evidence), may result in little to no difference on mortality (RR 3.00, 95% CI 0.12 to 73.43; 1505 participants; low-certainty evidence), and may result in little to no difference in admission to hospital. Casirivimab/imdevimab may slightly decrease grade 3 to 4 AEs (RR 0.50, 95% CI 0.24 to 1.02; 2617 participants; low-certainty evidence), decreases all-grade AEs (RR 0.70, 95% CI 0.61 to 0.80; 2617 participants; high-certainty evidence), and may result in little to no difference on SAEs in participants regardless of SARS-CoV-2 antibody serostatus. Quality of life was not reported.

AUTHORS' CONCLUSIONS

For PrEP, there is a decrease in development of clinical COVID-19 symptoms (high certainty), infection with SARS-CoV-2 (moderate certainty), and admission to hospital (low certainty) with tixagevimab/cilgavimab. There is low certainty of a decrease in infection with SARS-CoV-2, and development of clinical COVID-19 symptoms; and a higher rate for all-grade AEs with casirivimab/imdevimab. For PEP, there is moderate certainty of a decrease in infection with SARS-CoV-2 and low certainty for a higher rate for all-grade AEs with bamlanivimab. There is high certainty of a decrease in infection with SARS-CoV-2, development of clinical COVID-19 symptoms, and a higher rate for all-grade AEs with casirivimab/imdevimab.   Although there is high-to-moderate certainty evidence for some outcomes, it is insufficient to draw meaningful conclusions. These findings only apply to people unvaccinated against COVID-19. They are only applicable to the variants prevailing during the study and not other variants (e.g. Omicron). In vitro, tixagevimab/cilgavimab is effective against Omicron, but there are no clinical data. Bamlanivimab and casirivimab/imdevimab are ineffective against Omicron in vitro. Further studies are needed and publication of four ongoing studies may resolve the uncertainties.

Seasonal coronaviruses and SARS-CoV-2: effects of preexisting immunity during the COVID-19 pandemic

Although the coronavirus disease 2019 (COVID-19) epidemic is still ongoing, vaccination rates are rising slowly and related treatments and drugs are being developed. At the same time, there is increasing evidence of preexisting immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in humans, mainly consisting of preexisting antibodies and immune cells (including T cells and B cells). The presence of these antibodies is mainly due to the seasonal prevalence of four common coronavirus types, especially OC43 and HKU1. The accumulated relevant evidence has suggested that the target of antibodies is mainly the S2 subunit of S protein, followed by evolutionary conservative regions such as the nucleocapsid (N) protein. Additionally, preexisting memory T and B cells are also present in the population. Preexisting antibodies can help the body protect against SARS-CoV-2 infection, reduce the severity of COVID-19, and rapidly increase the immune response post-infection. These multiple effects can directly affect disease progression and even the likelihood of death in certain individuals. Besides the positive effects, preexisting immunity may also have negative consequences, such as antibody-dependent enhancement (ADE) and original antigenic sin (OAS), the prevalence of which needs to be further established. In the future, more research should be focused on evaluating the role of preexisting immunity in COVID-19 outcomes, adopting appropriate policies and strategies for fighting the pandemic, and vaccine development that considers preexisting immunity.

Anti-SARS-CoV2 antibody-mediated cytokine release syndrome in a patient with acute promyelocytic leukemia

BACKGROUND

Passive immunization against SARS-CoV-2 limits viral burden and death from COVID-19; however, it poses a theoretical risk of disease exacerbation through antibody-dependent enhancement (ADE). ADE after anti-SARS-CoV2 antibody treatment has not been reported, and therefore the potential risk and promoting factors remain unknown.

CASE PRESENTATION

A 75-year-old female was admitted to the emergency room with recurrent, unexplained bruises and leukocytopenia, anemia, and thrombocytopenia. Evaluation of a bone marrow biopsy established the diagnosis of an acute promyelocytic leukemia (APL). SARS-CoV-2 RT-PCR testing of nasal and throat swabs on admission was negative. During the routine SARS-CoV-2 testing of inpatients, our patient tested positive for SARS-CoV-2 on day 14 after admission without typical COVID-19 symptoms. Due to disease- and therapy-related immunosuppression and advanced age conferring a high risk of progressing to severe COVID-19, casirivimab and imdevimab were administered as a preemptive approach. The patient developed immune activation and cytokine release syndrome (CRS) occurring within four hours of preemptive anti-SARS-CoV2 antibody (casirivimab/imdevimab) infusion. Immune activation and CRS were evidenced by a rapid increase in serum cytokines (IL-6, TNFα, IL-8, IL-10), acute respiratory insufficiency, and progressive acute respiratory distress syndrome.

DISCUSSION AND CONCLUSION

The temporal relationship between therapeutic antibody administration and the rapid laboratory, radiological, and clinical deterioration suggests that CRS was an antibody-related adverse event, potentially exacerbated by APL treatment-mediated differentiation of leukemic blasts and promyelocytes. This case highlights the need for careful assessment of life-threatening adverse events after passive SARS-CoV-2 immunization, especially in the clinical context of patients with complex immune and hematological landscapes.

[Development and Evaluation about "2nd-wave" COVID-19 Vaccines]

To tackle the pandemic of the novel coronavirus (severe acute respiratory syndrome coronavirus 2; SARS-CoV-2), the international society, including Japan, has been actively promoting vaccination for SARS-CoV-2. To effectively utilize these vaccines, clinical trials have been conducted to evaluate their safety and efficacy. For efficacy evaluation, prevention rate of symptomatic novel coronavirus infections (corona virus disease 2019; COVID-19) between placebo groups and investigational vaccine groups has been the key parameter to evaluate the novel COVID-19 vaccines. This approach is based on a consensus among international regulatory authorities. Compared to several months ago, the public vaccination campaign for COVID-19 has substantially progressed in many countries. This makes it difficult to conduct clinical trials, which have placebo control arms, anywhere in the world because of ethical problems in administering a placebo during a pandemic. Therefore, the new international consensus among regulatory authorities is that immunogenicity bridging studies between the new COVID-19 vaccines that are being developed and approved COVID-19 vaccines may be needed when placebo-controlled studies are no longer feasible. In the future, the number of unvaccinated people worldwide is expected significantly decrease; thus, the issue of how to evaluate additional immunization for those who have completed the initial immunization remains to be addressed. This would require new international convergence. The development of COVID-19 vaccines and their evaluation would have to be updated, considering the social situation and vaccine coverage.

Nonhuman primate models for evaluation of SARS-CoV-2 vaccines

INTRODUCTION

Evaluation of immunogenicity and efficacy in animal models provide critical data in vaccine development. Nonhuman primates (NHPs) have been used extensively in the evaluation of SARS-CoV-2 vaccines.

AREAS COVERED

A critical synthesis of SARS-CoV-2 vaccine development with a focus on challenge studies in NHPs is provided. The benefits and drawbacks of the NHP models are discussed. The citations were selected by the authors based on PubMed searches of the literature, summaries from national public health bodies, and press-release information provided by vaccine developers.

EXPERT OPINION

We identify several aspects of NHP models that limit their usefulness for vaccine-challenge studies and numerous variables that constrain comparisons across vaccine platforms. We propose that studies conducted in NHPs for vaccine development should use a standardized protocol and, where possible, be substituted with smaller animal models. This will ensure continued rapid progression of vaccines to clinical trials without compromising assessments of safety or efficacy.

Anti-coronavirus vaccines will not accelerate the transition of humanity to a non-pandemic period, but the pandemic will take fewer victims

The vaccination rate worldwide has reached enormous proportions, and it is likely that at least 75% of the world's population will be vaccinated. The controversy is that, while people aged 65 and older suffer a significantly higher mortality rate from COVID-19, plans are being made to vaccinate young people under the age of 20. Equally thorny is the question of vaccinating people who already have antibodies to SARS-CoV-2, as well as B and T memory cells, because they contracted and survived the virus. The possible consequences of large-scale vaccination are difficult to predict, when some people do not have access to the vaccine at all and others have already received 3 doses of the vaccine. SARS-CoV-2 will circulate through the human population forever and continue to mutate, as viruses do. Therefore, in the coming years, the need to develop and use effective vaccines and medicines for the prevention and treatment of COVID-19 will remain urgent in view of the high mortality rate from this disease. To date, three vaccine platforms have been most used: adenoviral vector, inactivated, and mRNA. There is some concern about the side effects that occur after vaccination. Whether modern anti-coronavirus vaccines can raise the safety threshold, only time will answer. It is obvious that the pandemic will end, but the virus will remain in the human population, leaving behind invaluable experience and tens of millions of victims. This article is based on search retrieves in research articles devoted to COVID-19 mainly published in 2020-2021 and examines the possible consequences of the worldwide vaccination against SARS-CoV-2 and suggests that, while anti-coronavirus vaccines will not magically transport humanity to a non-pandemic world, they may greatly reduce the number of victims of the pandemic and help us learn how to live with COVID-19.

IgG targeting distinct seasonal coronavirus- conserved SARS-CoV-2 spike subdomains correlates with differential COVID-19 disease outcomes

Despite SARS-CoV-2 being a "novel" virus, early detection of anti-spike IgG in severe COVID-19 patients may be caused by the amplification of humoral memory responses against seasonal coronaviruses. Here, we examine this phenomenon by characterizing anti-spike IgG responses in non-hospitalized convalescent individuals across a spectrum of COVID-19 severity. We observe that disease severity positively correlates with anti-spike IgG levels, IgG cross-reactivity against other betacoronaviruses (β-CoVs), and FcγR activation. Analysis of IgG targeting β-CoV-conserved and non-conserved immunodominant epitopes within the SARS-CoV-2 spike protein revealed epitope-specific relationships: IgG targeting the conserved heptad repeat (HR) 2 region significantly correlates with milder disease, while targeting the conserved S2'FP region correlates with more severe disease. Furthermore, a lower HR2-to-S2'FP IgG-binding ratio correlates with greater disease severity, with ICU-hospitalized COVID-19 patients showing the lowest HR2/S2'FP ratios. These findings suggest that HR2/S2'FP IgG profiles may predict disease severity and offer insight into protective versus deleterious humoral recall responses.