Antibody-dependent enhancement of Ebola virus infection

Molecular insights into the Ebola virus life cycle

Ebola virus and other orthoebolaviruses cause severe haemorrhagic fevers in humans, with very high case fatality rates. Their non-segmented single-stranded RNA genome encodes only seven structural proteins and a small number of non-structural proteins to facilitate the virus life cycle. The basics of this life cycle are well established, but recent advances have substantially increased our understanding of its molecular details, including the viral and host factors involved. Here we provide a comprehensive overview of our current knowledge of the molecular details of the orthoebolavirus life cycle, with a special focus on proviral host factors. We discuss the multistep entry process, viral RNA synthesis in specialized phase-separated intracellular compartments called inclusion bodies, the expression of viral proteins and ultimately the assembly of new virus particles and their release at the cell surface. In doing so, we integrate recent studies into the increasingly detailed model that has developed for these fundamental aspects of orthoebolavirus biology.

A Review: Understanding Molecular Mechanisms of Antibody-Dependent Enhancement in Viral Infections

Antibody Dependent Enhancement (ADE) of an infection has been of interest in the investigation of many viruses. It is associated with the severity of the infection. ADE is mediated by non-neutralizing antibodies, antibodies at sub-neutralizing concentrations, or cross-reactive non-neutralizing antibodies. Treatments like plasma therapy, B cell immunizations, and antibody therapies may trigger ADE. It is seen as an impediment to vaccine development as well. In viruses including the Dengue virus (DENV), severe acute respiratory syndrome (SARS) virus, Middle East respiratory syndrome (MERS) virus, human immunodeficiency virus (HIV), Ebola virus, Zika virus, and influenza virus, the likely mechanisms of ADE are postulated and described. ADE improves the likelihood of productively infecting cells that are expressing the complement receptor or the Fc receptor (FcR) rather than the viral receptors. ADE occurs when the FcR, particularly the Fc gamma receptor, and/or complement system, particularly Complement 1q (C1q), allow the entry of the virus-antibody complex into the cell. Moreover, ADE alters the innate immune pathways to escape from lysis, promoting viral replication inside the cell that produces viral particles. This review discusses the involvement of FcR and the downstream immunomodulatory pathways in ADE, the complement system, and innate antiviral signaling pathways modification in ADE and its impact on facilitating viral replication. Additionally, we have outlined the modes of ADE in the cases of different viruses reported until now.

Dengue virus infection - a review of pathogenesis, vaccines, diagnosis and therapy

The transmission of dengue virus (DENV) from an infected Aedes mosquito to a human, causes illness ranging from mild dengue fever to fatal dengue shock syndrome. The similar conserved structure and sequence among distinct DENV serotypes or different flaviviruses has resulted in the occurrence of cross reaction followed by antibody-dependent enhancement (ADE). Thus far, the vaccine which can provide effective protection against infection by different DENV serotypes remains the biggest hurdle to overcome. Therefore, deep investigation is crucial for the potent and effective therapeutic drugs development. In addition, the cross-reactivity of flaviviruses that leads to false diagnosis in clinical settings could result to delay proper intervention management. Thus, the accurate diagnostic with high specificity and sensitivity is highly required to provide prompt diagnosis in respect to render early treatment for DENV infected individuals. In this review, the recent development of neutralizing antibodies, antiviral agents, and vaccine candidates in therapeutic platform for DENV infection will be discussed. Moreover, the discovery of antigenic cryptic epitopes, principle of molecular mimicry, and application of single-chain or single-domain antibodies towards DENV will also be presented.

Filoviruses: Innate Immunity, Inflammatory Cell Death, and Cytokines

Filoviruses are a group of single-stranded negative sense RNA viruses. The most well-known filoviruses that affect humans are ebolaviruses and marburgviruses. During infection, they can cause life-threatening symptoms such as inflammation, tissue damage, and hemorrhagic fever, with case fatality rates as high as 90%. The innate immune system is the first line of defense against pathogenic insults such as filoviruses. Pattern recognition receptors (PRRs), including toll-like receptors, retinoic acid-inducible gene-I-like receptors, C-type lectin receptors, AIM2-like receptors, and NOD-like receptors, detect pathogens and activate downstream signaling to induce the production of proinflammatory cytokines and interferons, alert the surrounding cells to the threat, and clear infected and damaged cells through innate immune cell death. However, filoviruses can modulate the host inflammatory response and innate immune cell death, causing an aberrant immune reaction. Here, we discuss how the innate immune system senses invading filoviruses and how these deadly pathogens interfere with the immune response. Furthermore, we highlight the experimental difficulties of studying filoviruses as well as the current state of filovirus-targeting therapeutics.

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.

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.

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.

Structural Dynamics of the SARS-CoV-2 Spike Protein: A 2-Year Retrospective Analysis of SARS-CoV-2 Variants (from Alpha to Omicron) Reveals an Early Divergence between Conserved and Variable Epitopes

We analyzed the epitope evolution of the spike protein in 1,860,489 SARS-CoV-2 genomes. The structural dynamics of these epitopes was determined by molecular modeling approaches. The D614G mutation, selected in the first months of the pandemic, is still present in currently circulating SARS-CoV-2 strains. This mutation facilitates the conformational change leading to the demasking of the ACE2 binding domain. D614G also abrogated the binding of facilitating antibodies to a linear epitope common to SARS-CoV-1 and SARS-CoV-2. The main neutralizing epitope of the N-terminal domain (NTD) of the spike protein showed extensive structural variability in SARS-CoV-2 variants, especially Delta and Omicron. This epitope is located on the flat surface of the NTD, a large electropositive area which binds to electronegatively charged lipid rafts of host cells. A facilitating epitope located on the lower part of the NTD appeared to be highly conserved among most SARS-CoV-2 variants, which may represent a risk of antibody-dependent enhancement (ADE). Overall, this retrospective analysis revealed an early divergence between conserved (facilitating) and variable (neutralizing) epitopes of the spike protein. These data aid in the designing of new antiviral strategies that could help to control COVID-19 infection by mimicking neutralizing antibodies or by blocking facilitating antibodies.

Evaluation of Antibody-Dependent Fc-Mediated Viral Entry, as Compared With Neutralization, in SARS-CoV-2 Infection

Fc-mediated virus entry has been observed for many viruses, but the characterization of this activity in convalescent plasma against SARS-CoV-2 Variants of Concern (VOC) is undefined. In this study, we evaluated Fc-mediated viral entry (FVE) on FcγRIIa-expressing HEK293 cells in the presence of SARS-CoV-2 convalescent plasma and compared it with SARS-CoV-2 pseudovirus neutralization using ACE2-expressing HEK293 cells. The plasma were collected early in the pandemic from 39 individuals. We observed both neutralization and FVE against the infecting Washington SARS-CoV-2 strain for 31% of plasmas, neutralization, but not FVE for 61% of plasmas, and no neutralization or FVE for 8% of plasmas. Neutralization titer correlated significantly with the plasma dilution at which maximum FVE was observed, indicating Fc-mediated uptake peaked as neutralization potency waned. While total Spike-specific plasma IgG levels were similar between plasma that mediated FVE and those that did not, Spike-specific plasma IgM levels were significantly higher in plasma that did not mediate FVE. Plasma neutralization titers against the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1) and Delta (B.1.617.2) VOC were significantly lower than titers against the Washington strain, while plasma FVE activity against the VOC was either higher or similar. This is the first report to demonstrate a functional shift in convalescent plasma antibodies from neutralizing and FVE-mediating against the earlier Washington strain, to an activity mediating only FVE and no neutralization activity against the emerging VOC, specifically the Beta (B.1.351) and Gamma (P.1) VOC. It will be important to determine the in vivo relevance of these findings.

Complement-Mediated Neutralisation Identified in Ebola Virus Disease Survivor Plasma: Implications for Protection and Pathogenesis

The 2013-2016 Ebola virus (EBOV) epidemic in West Africa was unprecedented in case numbers and fatalities, and sporadic outbreaks continue to arise. Antibodies to the EBOV glycoprotein (GP) are strongly associated with survival and their use in immunotherapy is often initially based on their performance in neutralisation assays. Other immune effector functions also contribute to EBOV protection but are more complex to measure. Their interactions with the complement system in particular are comparatively under-researched and commonly excluded from cellular immunoassays. Using EBOV convalescent plasma samples from the 2013-2016 epidemic, we investigated antibody and complement-mediated neutralisation and how these interactions can influence immunity in response to EBOV-GP and its secreted form (EBOV-sGP). We defined two cohorts: one with low-neutralising titres in relation to EBOV-GP IgG titres (LN cohort) and the other with a direct linear relationship between neutralisation and EBOV-GP IgG titres (N cohort). Using flow cytometry antibody-dependent complement deposition (ADCD) assays, we found that the LN cohort was equally efficient at mediating ADCD in response to the EBOV-GP but was significantly lower in response to the EBOV-sGP, compared to the N cohort. Using wild-type EBOV neutralisation assays with a cohort of the LN plasma, we observed a significant increase in neutralisation associated with the addition of pooled human plasma as a source of complement. Flow cytometry ADCD was also applied using the GP of the highly virulent Sudan virus (SUDV) of the Sudan ebolavirus species. There are no licensed vaccines or therapeutics against SUDV and it overlaps in endemicity with EBOV. We found that the LN plasma was significantly less efficient at cross-reacting and mediating ADCD. Overall, we found a differential response in ADCD between LN and N plasma in response to various Ebolavirus glycoproteins, and that these interactions could significantly improve EBOV neutralisation for selected LN plasma samples. Preservation of the complement system in immunoassays could augment our understanding of neutralisation and thus protection against infection.

Multiple Routes of Antibody-Dependent Enhancement of SARS-CoV-2 Infection

Antibody-dependent enhancement (ADE) of infection is generally known for many viruses. A potential risk of ADE in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has also been discussed since the beginning of the coronavirus disease 2019 (COVID-19) pandemic; however, clinical evidence of the presence of antibodies with ADE potential is limited. Here, we show that ADE antibodies are produced by SARS-CoV-2 infection and the ADE process can be mediated by at least two different host factors, Fcγ receptor (FcγR) and complement component C1q. Of 89 serum samples collected from acute or convalescent COVID-19 patients, 62.9% were found to be positive for SARS-CoV-2-specific IgG. FcγR- and/or C1q-mediated ADE were detected in 50% of the IgG-positive sera, whereas most of them showed neutralizing activity in the absence of FcγR and C1q. Importantly, ADE antibodies were found in 41.4% of the acute COVID-19 patients. Neutralizing activity was also detected in most of the IgG-positive sera, but it was counteracted by ADE in subneutralizing conditions in the presence of FcγR or C1q. Although the clinical importance of ADE needs to be further investigated with larger numbers of COVID-19 patient samples, our data suggest that SARS-CoV-2 utilizes multiple mechanisms of ADE. C1q-mediated ADE may particularly have a clinical impact since C1q is present at high concentrations in plasma and its receptors are ubiquitously expressed on the surfaces of many types of cells, including respiratory epithelial cells, which SARS-CoV-2 primarily infects.

IMPORTANCE Potential risks of antibody-dependent enhancement (ADE) in the coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been discussed and the proposed mechanism mostly depends on the Fc gamma receptor (FcγR). However, since FcγRs are exclusively expressed on immune cells, which are not primary targets of SARS-CoV-2, the clinical importance of ADE of SARS-CoV-2 infection remains controversial. Our study demonstrates that SARS-CoV-2 infection induces antibodies that increase SARS-CoV-2 infection through another ADE mechanism in which complement component C1q mediates the enhancement. Although neutralizing activity was also detected in the serum samples, it was counteracted by ADE in the presence of FcγR or C1q. Considering the ubiquity of C1q and its cellular receptors, C1q-mediated ADE may more likely occur in respiratory epithelial cells, which SARS-CoV-2 primarily infects. Our data highlight the importance of careful monitoring of the antibody properties in COVID-19 convalescent and vaccinated individuals.

Neutralizing Antibodies and Antibody-Dependent Enhancement in COVID-19: A Perspective

Antibody-dependent enhancement (ADE) is an alternative route of viral entry in the susceptible host cell. In this process, antiviral antibodies enhance the entry access of virus in the cells via interaction with the complement or Fc receptors leading to the worsening of infection. SARS-CoV-2 variants pose a general concern for the efficacy of neutralizing antibodies that may fail to neutralize infection, raising the possibility of a more severe form of COVID-19. Data from various studies on respiratory viruses raise the speculation that antibodies elicited against SARS-CoV-2 and during COVID-19 recovery could potentially exacerbate the infection through ADE at sub-neutralizing concentrations; this may contribute to disease pathogenesis. It is, therefore, of utmost importance to study the effectiveness of the anti-SARS-CoV-2 antibodies in COVID-19-infected subjects. Theoretically, ADE remains a general concern for the efficacy of antibodies elicited during infection, most notably in convalescent plasma therapy and in response to vaccines where it could be counterproductive.

Vaccine-Associated Enhanced Disease and Pathogenic Human Coronaviruses

Vaccine-associated enhanced disease (VAED) is a difficult phenomenon to define and can be confused with vaccine failure. Using studies on respiratory syncytial virus (RSV) vaccination and dengue virus infection, we highlight known and theoretical mechanisms of VAED, including antibody-dependent enhancement (ADE), antibody-enhanced disease (AED) and Th2-mediated pathology. We also critically review the literature surrounding this phenomenon in pathogenic human coronaviruses, including MERS-CoV, SARS-CoV-1 and SARS-CoV-2. Poor quality histopathological data and a lack of consistency in defining severe pathology and VAED in preclinical studies of MERS-CoV and SARS-CoV-1 vaccines in particular make it difficult to interrogate potential cases of VAED. Fortuitously, there have been only few reports of mild VAED in SARS-CoV-2 vaccination in preclinical models and no observations in their clinical use. We describe the problem areas and discuss methods to improve the characterisation of VAED in the future.

An Ebola, Neisseria and Trypanosoma human protein interaction census reveals a conserved human protein cluster targeted by various human pathogens

Filovirus ebolavirus (ZE; Zaire ebolavirus, Bundibugyo ebolavirus), Neisseria meningitidis (NM), and Trypanosoma brucei (Tb) are serious infectious pathogens, spanning viruses, bacteria and protists and all may target the blood and central nervous system during their life cycle. NM and Tb are extracellular pathogens while ZE is obligatory intracellular, targetting immune privileged sites. By using interactomics and comparative evolutionary analysis we studied whether conserved human proteins are targeted by these pathogens. We examined 2797 unique pathogen-targeted human proteins. The information derived from orthology searches of experimentally validated protein-protein interactions (PPIs) resulted both in unique and shared PPIs for each pathogen. Comparing and analyzing conserved and pathogen-specific infection pathways for NM, TB and ZE, we identified human proteins predicted to be targeted in at least two of the compared host-pathogen networks. However, four proteins were common to all three host-pathogen interactomes: the elongation factor 1-alpha 1 (EEF1A1), the SWI/SNF complex subunit SMARCC2 (matrix-associated actin-dependent regulator of chromatin subfamily C), the dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit 1 (RPN1), and the tubulin beta-5 chain (TUBB). These four human proteins all are also involved in cytoskeleton and its regulation and are often addressed by various human pathogens. Specifically, we found (i) 56 human pathogenic bacteria and viruses that target these four proteins, (ii) the well researched new pandemic pathogen SARS-CoV-2 targets two of these four human proteins and (iii) nine human pathogenic fungi (yet another evolutionary distant organism group) target three of the conserved proteins by 130 high confidence interactions.

Efficacy of a live attenuated highly pathogenic PRRSV vaccine against a NADC30-like strain challenge: implications for ADE of PRRSV

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) infection can cause severe reproductive failure in sows and respiratory distress in pigs of all ages, leading to major economic losses. To date, there are still no effective strategies to prevent and control PRRSV. Antibody-dependent enhancement (ADE), a phenomenon in which preexisting non-neutralizing antibodies or sub-neutralizing antibodies facilitate virus entry and replication, may be a significant obstacle in the development of effective vaccines for many viruses, including PRRSV. However, the contribution of ADE to PRRSV infection remains controversial, especially in vivo. Whether attenuated PRRSV vaccines prevent or worsen subsequent disease in pigs infected by novel PRRSV strains requires more research. In the present study, in vivo experiments were conducted to evaluate ADE under different immune statuses, which were produced by waiting different lengths of time after vaccination with a commercially available attenuated highly pathogenic PRRSV (HP-PRRSV) vaccine (JXA1-R) before challenging the pigs with a novel heterologous NADC30-like strain.

RESULTS

Piglets that were vaccinated before being challenged with PRRSV exhibited lower mortality rates, lower body temperatures, higher bodyweight gain, and lower viremia. These results demonstrate that vaccination with JXA1-R alleviated the clinical signs of PRRSV infection in all vaccinated groups.

CONCLUSIONS

The obtained data indicate that the attenuated vaccine test here provided partial protection against the NADC30-like strain HNhx. No signs of enhanced PRRSV infection were observed under the applied experimental conditions. Our results provide some insight into the molecular mechanisms underlying vaccine-induced protection or enhancement in PRRSV.

Human Coronaviruses: Counteracting the Damage by Storm

Over the past 18 years, three highly pathogenic human (h) coronaviruses (CoVs) have caused severe outbreaks, the most recent causative agent, SARS-CoV-2, being the first to cause a pandemic. Although much progress has been made since the COVID-19 pandemic started, much about SARS-CoV-2 and its disease, COVID-19, is still poorly understood. The highly pathogenic hCoVs differ in some respects, but also share some similarities in clinical presentation, the risk factors associated with severe disease, and the characteristic immunopathology associated with the progression to severe disease. This review aims to highlight these overlapping aspects of the highly pathogenic hCoVs-SARS-CoV, MERS-CoV, and SARS-CoV-2-briefly discussing the importance of an appropriately regulated immune response; how the immune response to these highly pathogenic hCoVs might be dysregulated through interferon (IFN) inhibition, antibody-dependent enhancement (ADE), and long non-coding RNA (lncRNA); and how these could link to the ensuing cytokine storm. The treatment approaches to highly pathogenic hCoV infections are discussed and it is suggested that a greater focus be placed on T-cell vaccines that elicit a cell-mediated immune response, using rapamycin as a potential agent to improve vaccine responses in the elderly and obese, and the potential of stapled peptides as antiviral agents.

Adjunctive treatment with high-titre convalescent plasma in severely and critically ill COVID-19 patients - a safe but futile intervention. A comparative cohort study

Background

Convalescent plasma (CP) containing antibodies derived from coronavirus disease 2019 (COVID-19) survivors has been proposed as a promising therapeutic option for severe COVID-19.

Methods

In our intensive care unit (ICU), 55 patients (46 male, median age 61 years) with PCR-confirmed COVID-19 (35 = 63.6% on mechanical ventilation, 7 = 14.5% on high-flow nasal oxygen, 12 = 20% on non-invasive ventilation, 1 = 1.8% without respiratory support) were treated with high-titre CP (200 mL per dose, range 1–6 doses, median 3 doses per patient, minimum titre > 1:100, Wantai test). 139 COVID-19 patients treated in the same ICU who did not receive CP served as control group. In 27 patients, the effect of CP on the individual levels of SARS-CoV-2 IgG antibodies was assessed by ELISA in serum sample pairs collected before and after CP transfusion.

Results

The first CP dose was administered at a median of 8 days after symptom onset. 13 patients in the plasma cohort died (28-day mortality 24.1%), compared to 42 (30.2%) in the cohort who did not receive CP (p = 0.5, Pearson Chi-squared test). Out of the 27 individuals investigated for the presence of IgG antibodies, 8 did not have detectable IgG levels before the first CP transfusion. In this subpopulation, 3 patients (37.5%) died. Not a single confirmed adverse reaction to CP was noted.

Conclusions

While adjunctive treatment with CP for severe and life-threatening COVID-19 was a very safe intervention, we did not observe any effect on mortality.

An Engineered Receptor-Binding Domain Improves the Immunogenicity of Multivalent SARS-CoV-2 Vaccines

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein mediates viral entry into cells expressing angiotensin-converting enzyme 2 (ACE2). The S protein engages ACE2 through its receptor-binding domain (RBD), an independently folded 197-amino-acid fragment of the 1,273-amino-acid S-protein protomer. The RBD is the primary SARS-CoV-2 neutralizing epitope and a critical target of any SARS-CoV-2 vaccine. Here, we show that this RBD conjugated to each of two carrier proteins elicited more potent neutralizing responses in immunized rodents than did a similarly conjugated proline-stabilized S-protein ectodomain. Nonetheless, the native RBD is expressed inefficiently, limiting its usefulness as a vaccine antigen. However, we show that an RBD engineered with four novel glycosylation sites (gRBD) is expressed markedly more efficiently and generates a more potent neutralizing responses as a DNA vaccine antigen than the wild-type RBD or the full-length S protein, especially when fused to multivalent carriers, such as a Helicobacter pylori ferritin 24-mer. Further, gRBD is more immunogenic than the wild-type RBD when administered as a subunit protein vaccine. Our data suggest that multivalent gRBD antigens can reduce costs and doses, and improve the immunogenicity, of all major classes of SARS-CoV-2 vaccines.IMPORTANCE All available vaccines for coronavirus disease 2019 (COVID-19) express or deliver the full-length SARS-CoV-2 spike (S) protein. We show that this antigen is not optimal, consistent with observations that the vast majority of the neutralizing response to the virus is focused on the S-protein receptor-binding domain (RBD). However, this RBD is not expressed well as an independent domain, especially when expressed as a fusion protein with a multivalent scaffold. We therefore engineered a more highly expressed form of the SARS-CoV-2 RBD by introducing four glycosylation sites into a face of the RBD normally occluded in the full S protein. We show that this engineered protein, gRBD, is more immunogenic than the wild-type RBD or the full-length S protein in both genetic and protein-delivered vaccines.

Convalescent Plasma Transfusion for the Treatment of COVID-19 in Adults: A Global Perspective

More than one year into the novel coronavirus disease 2019 (COVID-19) pandemic, healthcare systems across the world continue to be overwhelmed with soaring daily cases. The treatment spectrum primarily includes ventilation support augmented with repurposed drugs and/or convalescent plasma transfusion (CPT) from recovered COVID-19 patients. Despite vaccine variants being recently developed and administered in several countries, challenges in global supply chain logistics limit their timely availability to the wider world population, particularly in developing countries. Given the measured success of conventional CPT in treating several infections over the past decade, recent studies have reported its effectiveness in decreasing the duration and severity of COVID-19 symptoms. In this review, we conduct a literature search of published studies investigating the use of CPT to treat COVID-19 patients from January 2020 to January 2021. The literature search identified 181 records of which 39 were included in this review. A random-effects model was used to aggregate data across studies, and mortality rates of 17 vs. 32% were estimated for the CPT and control patient groups, respectively, with an odds ratio (OR) of 0.49. The findings indicate that CPT shows potential in reducing the severity and duration of COVID-19 symptoms. However, early intervention (preferably within 3 days), recruitment of donors, and plasma potency introduce major challenges for its scaled-up implementation. Given the low number of existing randomized clinical trials (RCTs, four with a total of 319 patients), unanticipated risks to CPT recipients are highlighted and discussed. Nevertheless, CPT remains a promising COVID-19 therapeutic option that merits internationally coordinated RCTs to achieve a scientific risk-benefit consensus.

Antibodies Against Pseudomonas aeruginosa Alkaline Protease Directly Enhance Disruption of Neutrophil Extracellular Traps Mediated by This Enzyme

Extracellular traps released by neutrophils (NETs) are essential for the clearance of Pseudomonas aeruginosa. Alkaline protease (AprA) secreted by P. aeruginosa negatively correlates with clinical improvement. Moreover, anti-AprA in patients with cystic fibrosis (CF) can help identify patients with aggressive forms of chronic infection. However, the mechanism underlying the clinical outcomes remains unclear. We demonstrated that aprA deficiency in P. aeruginosa decreased the bacterial burden and reduced lung infection. AprA degraded NET components in vitro and in vivo but did not affect NET formation. Importantly, antibodies induced by AprA acted as an agonist and directly enhanced the degrading activities of AprA. Moreover, antisera from patients with P. aeruginosa infection exhibited antibody-dependent enhancement (ADE) similar to that of the antibodies we prepared. Our further investigations showed that the interaction between AprA and the specific antibodies might make the enzyme active sites better exposed, and subsequently enhance the recognition of substrates and accelerate the degradation. Our findings revealed that AprA secreted by P. aeruginosa may aggravate infection by destroying formed NETs, an effect that was further enhanced by its antibodies.

Early control of viral load by favipiravir promotes survival to Ebola virus challenge and prevents cytokine storm in non-human primates

Ebola virus has been responsible for two major epidemics over the last several years and there has been a strong effort to find potential treatments that can improve the disease outcome. Antiviral favipiravir was thus tested on non-human primates infected with Ebola virus. Half of the treated animals survived the Ebola virus challenge, whereas the infection was fully lethal for the untreated ones. Moreover, the treated animals that did not survive died later than the controls. We evaluated the hematological, virological, biochemical, and immunological parameters of the animals and performed proteomic analysis at various timepoints of the disease. The viral load strongly correlated with dysregulation of the biological functions involved in pathogenesis, notably the inflammatory response, hemostatic functions, and response to stress. Thus, the management of viral replication in Ebola virus disease is of crucial importance in preventing the immunopathogenic disorders and septic-like shock syndrome generally observed in Ebola virus-infected patients.

Ebola virus was responsible for several epidemics in the recent years and is now considered as a major public health concern in Central and West African countries. We and others demonstrated that pathogenic events observed during Ebola virus disease are linked to a deleterious immune response. However, the mechanisms implicated are not fully understood. Here, we studied immune responses depending on the viral loads observed in infected cynomolgus monkeys. An antiviral treatment allowed the reduction of viral load in some animals and we observed that these animals did not experience deleterious immune response and the loss of hemostasis. The release of pathogen-associated molecular patterns may thus be limited by the inhibition of viral replication, avoiding the overstimulation of the immune system and consequently the pathogenic events observed in Ebola virus disease.

AI Aided Design of Epitope-Based Vaccine for the Induction of Cellular Immune Responses Against SARS-CoV-2

The heavy burden imposed by the COVID-19 pandemic on our society triggered the race toward the development of therapies or preventive strategies. Among these, antibodies and vaccines are particularly attractive because of their high specificity, low probability of drug-drug interaction, and potentially long-standing protective effects. While the threat at hand justifies the pace of research, the implementation of therapeutic strategies cannot be exempted from safety considerations. There are several potential adverse events reported after the vaccination or antibody therapy, but two are of utmost importance: antibody-dependent enhancement (ADE) and cytokine storm syndrome (CSS). On the other hand, the depletion or exhaustion of T-cells has been reported to be associated with worse prognosis in COVID-19 patients. This observation suggests a potential role of vaccines eliciting cellular immunity, which might simultaneously limit the risk of ADE and CSS. Such risk was proposed to be associated with FcR-induced activation of proinflammatory macrophages (M1) by Fu et al. (2020) and Iwasaki and Yang (2020). All aspects of the newly developed vaccine (including the route of administration, delivery system, and adjuvant selection) may affect its effectiveness and safety. In this work we use a novel in silico approach (based on AI and bioinformatics methods) developed to support the design of epitope-based vaccines. We evaluated the capabilities of our method for predicting the immunogenicity of epitopes. Next, the results of our approach were compared with other vaccine-design strategies reported in the literature. The risk of immuno-toxicity was also assessed. The analysis of epitope conservation among other Coronaviridae was carried out in order to facilitate the selection of peptides shared across different SARS-CoV-2 strains and which might be conserved in emerging zootic coronavirus strains. Finally, the potential applicability of the selected epitopes for the development of a vaccine eliciting cellular immunity for COVID-19 was discussed, highlighting the benefits and challenges of such an approach.

Convalescent plasma and hyperimmune globulin therapy in COVID-19

Introduction: Severe acute respiratory syndrome causing coronavirus SARS-CoV-2 (coronavirus disease 2019 (COVID-19)) has recently resulted in the recent global pandemic. As convalescent plasma (CP) therapy has been used with success in several viral infections before, it has become a treatment of choice. Medical literature is reviewed for randomized controlled studies using convalescent plasma therapy.Areas covered: More than one type of neutralizing antibody against a specific microorganism may be found in both CP and hyperimmune globulins. To give a standard titer of a specific neutralizing antibody to a patient, a reliable antibody titration assay should be developed. It is challenging to test the efficacy of the CP and HIG therapies with double-blind studies. There is a difficulty in the standardization of the CP and HIG study groups, as patients use various additional therapies. Different amounts and titers of CP and HIG and different titers of CP are used in patients. This review discusses the current knowledge on CP and HIG therapies used in COVID-19 disease.Expert opinion: The immune response to COVID-19 have diverse characteristics. The antibody produced after COVID-19 disease and vaccination is short-lived. Thus, CP should be an alternative especially in patients with lymphopenia and primary/secondary antibody deficiency.

Cellular and Humoral Immune Responses in Covid-19 and Immunotherapeutic Approaches

Coronavirus disease 2019 (Covid-19), caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can range in severity from asymptomatic to severe/critical disease. SARS-CoV-2 uses angiotensin-converting enzyme 2 to infect cells leading to a strong inflammatory response, which is most profound in patients who progress to severe Covid-19. Recent studies have begun to unravel some of the differences in the innate and adaptive immune response to SARS-CoV-2 in patients with different degrees of disease severity. These studies have attributed the severe form of Covid-19 to a dysfunctional innate immune response, such as a delayed and/or deficient type I interferon response, coupled with an exaggerated and/or a dysfunctional adaptive immunity. Differences in T-cell (including CD4+ T-cells, CD8+ T-cells, T follicular helper cells, γδ-T-cells, and regulatory T-cells) and B-cell (transitional cells, double-negative 2 cells, antibody-secreting cells) responses have been identified in patients with severe disease compared to mild cases. Moreover, differences in the kinetic/titer of neutralizing antibody responses have been described in severe disease, which may be confounded by antibody-dependent enhancement. Importantly, the presence of preexisting autoantibodies against type I interferon has been described as a major cause of severe/critical disease. Additionally, priorVaccine and multiple vaccine exposure, trained innate immunity, cross-reactive immunity, and serological immune imprinting may all contribute towards disease severity and outcome. Several therapeutic and preventative approaches have been under intense investigations; these include vaccines (three of which have passed Phase 3 clinical trials), therapeutic antibodies, and immunosuppressants.

A potent neutralizing nanobody against SARS-CoV-2 with inhaled delivery potential

The coronavirus disease 2019 (COVID‐19) pandemic has become a serious burden on global public health. Although therapeutic drugs against COVID‐19 have been used in many countries, their efficacy is still limited. We here reported nanobody (Nb) phage display libraries derived from four camels immunized with the SARS‐CoV‐2 spike receptor‐binding domain (RBD), from which 381 Nbs were identified to recognize SARS‐CoV‐2‐RBD. Furthermore, seven Nbs were shown to block interaction of human angiotensin‐converting enzyme 2 (ACE2) with SARS‐CoV‐2‐RBD variants and two Nbs blocked the interaction of human ACE2 with bat‐SL‐CoV‐WIV1‐RBD and SARS‐CoV‐1‐RBD. Among these candidates, Nb11‐59 exhibited the highest activity against authentic SARS‐CoV‐2 with 50% neutralizing dose (ND₅₀) of 0.55 μg/ml. Nb11‐59 can be produced on large scale in Pichia pastoris, with 20 g/L titer and 99.36% purity. It also showed good stability profile, and nebulization did not impact its stability. Overall, Nb11‐59 might be a promising prophylactic and therapeutic molecule against COVID‐19, especially through inhalation delivery.

Learning from the past: development of safe and effective COVID-19 vaccines

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has elicited an equally rapid response aiming to develop a COVID-19 vaccine. These efforts are encouraging; however, comprehensive efficacy and safety evaluations are essential in the development of a vaccine, and we can learn from previous vaccine development campaigns. In this Perspective, we summarize examples of vaccine-associated disease enhancement in the history of developing vaccines against respiratory syncytial virus, dengue virus, SARS-CoV and Middle East respiratory syndrome coronavirus, which highlight the importance of a robust safety and efficacy profile, and present recommendations for preclinical and clinical evaluation of COVID-19 vaccine candidates as well as for vaccine design and optimization.

Potential impact of individual exposure histories to endemic human coronaviruses on age-dependent severity of COVID-19

BACKGROUND

Cross-reactivity to SARS-CoV-2 from exposure to endemic human coronaviruses (eHCoV) is gaining increasing attention as a possible driver of both protection against infection and COVID-19 severity. Here we explore the potential role of cross-reactivity induced by eHCoVs on age-specific COVID-19 severity in a mathematical model of eHCoV and SARS-CoV-2 transmission.

METHODS

We use an individual-based model, calibrated to prior knowledge of eHCoV dynamics, to fully track individual histories of exposure to eHCoVs. We also model the emergent dynamics of SARS-CoV-2 and the risk of hospitalisation upon infection.

RESULTS

We hypothesise that primary exposure with any eHCoV confers temporary cross-protection against severe SARS-CoV-2 infection, while life-long re-exposure to the same eHCoV diminishes cross-protection, and increases the potential for disease severity. We show numerically that our proposed mechanism can explain age patterns of COVID-19 hospitalisation in EU/EEA countries and the UK. We further show that some of the observed variation in health care capacity and testing efforts is compatible with country-specific differences in hospitalisation rates under this model.

CONCLUSIONS

This study provides a "proof of possibility" for certain biological and epidemiological mechanisms that could potentially drive COVID-19-related variation across age groups. Our findings call for further research on the role of cross-reactivity to eHCoVs and highlight data interpretation challenges arising from health care capacity and SARS-CoV-2 testing.

Prevention and treatment of COVID-19: Focus on interferons, chloroquine/hydroxychloroquine, azithromycin, and vaccine

The ongoing pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has drawn the attention of researchers and clinicians from several disciplines and sectors who are trying to find durable solutions both at preventive and treatment levels. To date, there is no approved effective treatment or vaccine available to control the coronavirus disease-2019 (COVID-19). The preliminary in vitro studies on viral infection models showed potential antiviral activities of type I and III interferons (IFNs), chloroquine (CQ)/hydroxychloroquine (HCQ), and azithromycin (AZM); however, the clinical studies on COVID-19 patients treated with CQ/HCQ and AZM led to controversies in different regions due to their adverse side effects, as well as their combined treatment could prolong the QT interval. Interestingly, the treatment with type I IFNs showed encouraging results. Moreover, the different preliminary reports of COVID-19 candidate vaccines showcase promising results by inducing the production of a high level of neutralizing antibodies (NAbs) and specific T cell-mediated immune response in almost all participants. The present review aims to summarize and analyze the recent progress evidence concerning the use of IFNs, CQ/HCQ, and AZM for the treatment of COVID-19. The available data on immunization options to prevent the COVID-19 are also analyzed with the aim to present the promising options which could be investigated in future for sustainable control of the pandemic.

Antibody dependent enhancement: Unavoidable problems in vaccine development

In some cases, antibodies can enhance virus entry and replication in cells. This phenomenon is called antibody-dependent infection enhancement (ADE). ADE not only promotes the virus to be recognized by the target cell and enters the target cell, but also affects the signal transmission in the target cell. Early formalin-inactivated virus vaccines such as aluminum adjuvants (RSV and measles) have been shown to induce ADE. Although there is no direct evidence that there is ADE in COVID-19, this potential risk is a huge challenge for prevention and vaccine development. This article focuses on the virus-induced ADE phenomenon and its molecular mechanism. It also summarizes various attempts in vaccine research and development to eliminate the ADE phenomenon, and proposes to avoid ADE in vaccine development from the perspective of antigens and adjuvants.

Current Understanding of the Pathogenesis of Dengue Virus Infection

The pathogenesis of dengue virus infection is attributed to complex interplay between virus, host genes and host immune response. Host factors such as antibody-dependent enhancement (ADE), memory cross-reactive T cells, anti-DENV NS1 antibodies, autoimmunity as well as genetic factors are major determinants of disease susceptibility. NS1 protein and anti-DENV NS1 antibodies were believed to be responsible for pathogenesis of severe dengue. The cytokine response of cross-reactive CD4+ T cells might be altered by the sequential infection with different DENV serotypes, leading to further elevation of pro-inflammatory cytokines contributing a detrimental immune response. Fcγ receptor-mediated antibody-dependent enhancement (ADE) results in release of cytokines from immune cells leading to vascular endothelial cell dysfunction and increased vascular permeability. Genomic variation of dengue virus and subgenomic flavivirus RNA (sfRNA) suppressing host immune response are viral determinants of disease severity. Dengue infection can lead to the generation of autoantibodies against DENV NS1antigen, DENV prM, and E proteins, which can cross-react with several self-antigens such as plasminogen, integrin, and platelet cells. Apart from viral factors, several host genetic factors and gene polymorphisms also have a role to play in pathogenesis of DENV infection. This review article highlights the various factors responsible for the pathogenesis of dengue and also highlights the recent advances in the field related to biomarkers which can be used in future for predicting severe disease outcome.

Enhancement of infectivity of insect cell-derived La Crosse Virus by human serum

Given the dual life cycle of arboviruses in insect and animal hosts and the importance of serum factors as a first line antiviral defense, we have examined the outcome of interactions between the arbovirus La Crosse Virus (LACV) and human serum. To mimic the life cycle between species, we used LACV derived from insect (I-LACV) and human keratinocyte (HaCaT) cells. Incubation of I-LACV with normal human serum did not result in neutralization, but instead stabilized I-LACV virions and enhanced the amount of infectious virus. Enhanced infectivity was also seen with heat-inactivated serum devoid of complement activity and with serum from a range of animals including mouse, ferret, and non-human primates. Depletion of antibodies from serum resulted in loss of enhancement of infectivity and sucrose gradient sedimentation assays showed IgG co-sedimenting with I-LACV particles. In agreement with our results with I-LACV, HaCaT-derived LACV was not neutralized by complement or antibodies in normal human serum. However, in contrast to I-LACV, HaCaT-derived LACV infectivity was stable when incubated alone and treatment with serum did not enhance infectivity. Our results indicate that LACV derived from insect cells differs substantially from virus derived from human cells, with I-LACV being dependent on serum factors to enhance infectivity. These findings suggest that understanding differential composition of insect versus animal cell-derived LACV may form the foundation for potential new antiviral approaches.

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

Antibody-based drugs and vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are being expedited through preclinical and clinical development. Data from the study of SARS-CoV and other respiratory viruses suggest that anti-SARS-CoV-2 antibodies could exacerbate COVID-19 through antibody-dependent enhancement (ADE). Previous respiratory syncytial virus and dengue virus vaccine studies revealed human clinical safety risks related to ADE, resulting in failed vaccine trials. Here, we describe key ADE mechanisms and discuss mitigation strategies for SARS-CoV-2 vaccines and therapies in development. We also outline recently published data to evaluate the risks and opportunities for antibody-based protection against SARS-CoV-2.

Convalescent Plasma: The Relay Baton in the Race for Coronavirus Disease 2019 Treatment

Coronavirus disease 2019 (COVID-19) is a pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Most infected people have mild or moderate symptoms and recover without the need for extensive treatment. However, for seriously ill patients, no specific treatments are currently available. Convalescent plasma therapy (CPT), a passive immunotherapy, involves infusing plasma from recovered people into actively infected people, and is thought to be a specific intervention to improve outcome in patients with severe COVID-19. The presumed mechanism involves neutralizing antibodies and antibody dependent cytotoxicity/phagocytosis. Previous CPT trials showed an effect in SARS and pilot studies suggest CPT is an effective and safe strategy for seriously ill COVID-19 patients. CPT is currently being tested in large randomized clinical trials. Herein, we critically review the mechanism, applications and the challenges for CPT in the treatment of severe COVID-19, paving the way toward vaccine and immunotherapy development.

Convalescent Plasma Therapy for COVID-19: State of the Art

Convalescent plasma (CP) therapy has been used since the early 1900s to treat emerging infectious diseases; its efficacy was later associated with the evidence that polyclonal neutralizing antibodies can reduce the duration of viremia. Recent large outbreaks of viral diseases for which effective antivirals or vaccines are still lacking has renewed the interest in CP as a life-saving treatment. The ongoing COVID-19 pandemic has led to the scaling up of CP therapy to unprecedented levels. Compared with historical usage, pathogen reduction technologies have now added an extra layer of safety to the use of CP, and new manufacturing approaches are being explored. This review summarizes historical settings of application, with a focus on betacoronaviruses, and surveys current approaches for donor selection and CP collection, pooling technologies, pathogen inactivation systems, and banking of CP. We additionally list the ongoing registered clinical trials for CP throughout the world and discuss the trial results published thus far.

A complement component C1q-mediated mechanism of antibody-dependent enhancement of Ebola virus infection

Besides the common Fc receptor (FcR)-mediated mechanism of antibody-dependent enhancement (ADE), Ebola virus (EBOV) is known to utilize the complement component C1q for ADE of infection. This mechanism is FcR-independent and mediated by cross-linking of virus-antibody-C1q complexes to cell surface C1q receptors, leading to enhanced viral entry into cells. Using confocal microscopy, we found that virus-like particles (VLPs) consisting of EBOV glycoprotein, nucleoprotein, and matrix protein attached to the surface of human kidney 293 cells more efficiently in the presence of an ADE monoclonal antibody and C1q than with the antibody or C1q alone, and that there was no significant difference in the efficiency of VLP uptake into endosomes between the C1q-mediated ADE and non-ADE entry. Accordingly, both ADE and non-ADE infection were similarly decreased by inhibitors of the signaling pathways known to be required for endocytosis. These results suggest that C1q-mediated ADE of EBOV infection is simply caused by increased attachment of virus particles to the cell surface, which is distinct from the mechanism of FcR-mediated ADE requiring intracellular signaling to promote phagocytosis/macropinocytosis.

Principles Learned from the International Race to Develop a Safe and Effective COVID-19 Vaccine

Vaccines against COVID-19 have the potential to protect people before they are exposed to the infective form of the virus. However, because of the involvement of pathogenic immune processes in many severe presentations of COVID-19, eliciting an immune response with a vaccine must strike a delicate balance to achieve viral clearance without also inducing immune-mediated harm. This Outlook synthesizes current laboratory findings to define which parts of the immune system help with recovery from and protection against the virus and which can lead to adverse outcomes. To inform our understanding, we analyze research about the immune mechanisms implicated in SARS-CoV, from the 2003 outbreak, and SARS-CoV-2, the virus causing COVID-19. The impact of how innate immunity, humoral immunity, and cell-mediated immunity play a role in a harmful versus helpful response is discussed, establishing principles to guide the development and evaluation of a safe but effective COVID-19 vaccine. The principles derived include (i) targeting the appropriate specificity and effector function of the humoral response, (ii) eliciting a T cell response, especially a cytotoxic T cell response, to achieve safe, yet effective, immune protection from COVID-19, and (iii) monitoring for the possibility of acute lung injury during SARS-CoV-2 infection post-vaccination in preclinical and clinical studies. These principles can not only guide efforts toward a safe and effective COVID-19 vaccine, but also the development of effective vaccines for viral pandemics to come.

The role of IgG Fc receptors in antibody-dependent enhancement

Antibody-dependent enhancement (ADE) is a mechanism by which the pathogenesis of certain viral infections is enhanced in the presence of sub-neutralizing or cross-reactive non-neutralizing antiviral antibodies. In vitro modelling of ADE has attributed enhanced pathogenesis to Fcγ receptor (FcγR)-mediated viral entry, rather than canonical viral receptor-mediated entry. However, the putative FcγR-dependent mechanisms of ADE overlap with the role of these receptors in mediating antiviral protection in various viral infections, necessitating a detailed understanding of how this diverse family of receptors functions in protection and pathogenesis. Here, we discuss the diversity of immune responses mediated upon FcγR engagement and review the available experimental evidence supporting the role of FcγRs in antiviral protection and pathogenesis through ADE. We explore FcγR engagement in the context of a range of different viral infections, including dengue virus and SARS-CoV, and consider ADE in the context of the ongoing SARS-CoV-2 pandemic.

Antibody-dependent enhancement (ADE) has been described as a mechanism that contributes to the pathogenesis of dengue virus infection. Limited evidence also suggests that it can also occur in other viral infections. Here, the authors explore the history of the ADE phenomenon, discuss the diversity of Fc effector functions and consider its potential relevance in the context of SARS-CoV-2 infection.

Mast cell degranulation and histamine release during A/H5N1 influenza infection in influenza-sensitized mice

Here we evaluate the role of mast cells in infection with influenza A/H5N1 virus in immunized mice. CBA mice were immunized intramuscularly with formalin-inactivated A/Vietnam/1194/2004 (H5N1)NIBRG-14 (H5N1). Serum samples were obtained on days 7, 12, 14, 21 after immunization. At day 14, the mice were infected intranasally with the A/Indonesia/5/2005 (H5N1)IDCDC-RG2 (H5N1) influenza virus with half of the animals receiving a mixture of the antihistamines. 67% of the vaccinated mice were protected from the lethality compared to 43% in the PBS-immunized group. Administration of antihistamines increased survival up to 85%–95%. Immunohistochemical examination using CD117 staining of the lungs demonstrated a larger quantity of activated mast cells after infection of immunized mice compared to mock-immunized mice. This was correlated to increased histamine level in the lungs and blood. Our experimental results suggest the involvement of mast cells and the histamine they produce in the pathogenesis of influenza infection in case of incomplete formation of the immune response to vaccination and mismatch of the vaccine and infection influenza viruses.

Efficacy of Plasmapheresis and Immunoglobulin Replacement Therapy (IVIG) on Patients with COVID-19

Since the rapidly evolving outbreak of COVID-19, several empirical therapeutic options have been recommended including the use of antivirals, steroids, and vaccines. According to recent observations about different modalities in treatment of patients infected with COVID-19, plasmapheresis and intravenous immunoglobulin (IVIg) have been reported to be an effective empirical therapeutic option to control the infection. In this review, we aimed to provide an overview on the possible application of plasmapheresis and intravenous immunoglobulin in patients with COVID-19.

Viral Evasion of the Complement System and Its Importance for Vaccines and Therapeutics

The complement system is a key component of innate immunity which readily responds to invading microorganisms. Activation of the complement system typically occurs via three main pathways and can induce various antimicrobial effects, including: neutralization of pathogens, regulation of inflammatory responses, promotion of chemotaxis, and enhancement of the adaptive immune response. These can be vital host responses to protect against acute, chronic, and recurrent viral infections. Consequently, many viruses (including dengue virus, West Nile virus and Nipah virus) have evolved mechanisms for evasion or dysregulation of the complement system to enhance viral infectivity and even exacerbate disease symptoms. The complement system has multifaceted roles in both innate and adaptive immunity, with both intracellular and extracellular functions, that can be relevant to all stages of viral infection. A better understanding of this virus-host interplay and its contribution to pathogenesis has previously led to: the identification of genetic factors which influence viral infection and disease outcome, the development of novel antivirals, and the production of safer, more effective vaccines. This review will discuss the antiviral effects of the complement system against numerous viruses, the mechanisms employed by these viruses to then evade or manipulate this system, and how these interactions have informed vaccine/therapeutic development. Where relevant, conflicting findings and current research gaps are highlighted to aid future developments in virology and immunology, with potential applications to the current COVID-19 pandemic.

Potential benefits, mechanisms, and uncertainties of convalescent plasma therapy for COVID-19

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China led to a public health emergency of international concern, putting all health organizations on high alert in the beginning of 2020. Corona virus disease 2019 (COVID-19) is highly infectious and has resulted in thousands of deaths which exceeded that of the SARS coronavirus (SARS-CoV) outbreak back in 2002 and 2003 in China. Besides, the number of diagnosed patients, patients who are suspected to have contracted the disease, and deaths are increasing worldwide. Unfortunately, effective drugs and vaccines to combat SARS-CoV-2 are still lacking. Convalescent plasma, a seemingly successful treatment for COVID-19 patients, proved to be of huge value in terms of saving severely ill patients. This review introduces the reported effects, potential mechanisms, and future uncertainties of convalescent plasma therapy in the treatment of COVID-19 patients, in the hopes that it will provide useful information for relevant physicians and researchers.

Understanding SARS-CoV-2-Mediated Inflammatory Responses: From Mechanisms to Potential Therapeutic Tools

Currently there is no effective antiviral therapy for SARS-CoV-2 infection, which frequently leads to fatal inflammatory responses and acute lung injury. Here, we discuss the various mechanisms of SARS-CoV-mediated inflammation. We also assume that SARS-CoV-2 likely shares similar inflammatory responses. Potential therapeutic tools to reduce SARS-CoV-2-induced inflammatory responses include various methods to block FcR activation. In the absence of a proven clinical FcR blocker, the use of intravenous immunoglobulin to block FcR activation may be a viable option for the urgent treatment of pulmonary inflammation to prevent severe lung injury. Such treatment may also be combined with systemic anti-inflammatory drugs or corticosteroids. However, these strategies, as proposed here, remain to be clinically tested for effectiveness.

Impact of immune enhancement on Covid-19 polyclonal hyperimmune globulin therapy and vaccine development

The pandemic spread of a novel coronavirus - SARS coronavirus-2 (SARS-CoV-2) as a cause of acute respiratory illness, named Covid-19, is placing the healthcare systems of many countries under unprecedented stress. Global economies are also spiraling towards a recession in fear of this new life-threatening disease. Vaccines that prevent SARS-CoV-2 infection and therapeutics that reduces the risk of severe Covid-19 are thus urgently needed. A rapid method to derive antiviral treatment for Covid-19 is the use of convalescent plasma derived hyperimmune globulin. However, both hyperimmune globulin and vaccine development face a common hurdle - the risk of antibody-mediated disease enhancement. The goal of this review is to examine the body of evidence supporting the hypothesis of immune enhancement that could be pertinent to Covid-19. We also discuss how this risk could be mitigated so that both hyperimmune globulin and vaccines could be rapidly translated to overcome the current global health crisis.

Molecular Mechanism for Antibody-Dependent Enhancement of Coronavirus Entry

Antibody-dependent enhancement (ADE) of viral entry has been a major concern for epidemiology, vaccine development, and antibody-based drug therapy. However, the molecular mechanism behind ADE is still elusive. Coronavirus spike protein mediates viral entry into cells by first binding to a receptor on the host cell surface and then fusing viral and host membranes. In this study, we investigated how a neutralizing monoclonal antibody (MAb), which targets the receptor-binding domain (RBD) of Middle East respiratory syndrome (MERS) coronavirus spike, mediates viral entry using pseudovirus entry and biochemical assays. Our results showed that MAb binds to the virus surface spike, allowing it to undergo conformational changes and become prone to proteolytic activation. Meanwhile, MAb binds to cell surface IgG Fc receptor, guiding viral entry through canonical viral-receptor-dependent pathways. Our data suggest that the antibody/Fc-receptor complex functionally mimics viral receptor in mediating viral entry. Moreover, we characterized MAb dosages in viral-receptor-dependent, Fc-receptor-dependent, and both-receptors-dependent viral entry pathways, delineating guidelines on MAb usages in treating viral infections. Our study reveals a novel molecular mechanism for antibody-enhanced viral entry and can guide future vaccination and antiviral strategies.IMPORTANCE Antibody-dependent enhancement (ADE) of viral entry has been observed for many viruses. It was shown that antibodies target one serotype of viruses but only subneutralize another, leading to ADE of the latter viruses. Here we identify a novel mechanism for ADE: a neutralizing antibody binds to the surface spike protein of coronaviruses like a viral receptor, triggers a conformational change of the spike, and mediates viral entry into IgG Fc receptor-expressing cells through canonical viral-receptor-dependent pathways. We further evaluated how antibody dosages impacted viral entry into cells expressing viral receptor, Fc receptor, or both receptors. This study reveals complex roles of antibodies in viral entry and can guide future vaccine design and antibody-based drug therapy.

Molecular Mechanism for Antibody-Dependent Enhancement of Coronavirus Entry

Antibody-dependent enhancement (ADE) of viral entry has been observed for many viruses. It was shown that antibodies target one serotype of viruses but only subneutralize another, leading to ADE of the latter viruses. Here we identify a novel mechanism for ADE: a neutralizing antibody binds to the surface spike protein of coronaviruses like a viral receptor, triggers a conformational change of the spike, and mediates viral entry into IgG Fc receptor-expressing cells through canonical viral-receptor-dependent pathways. We further evaluated how antibody dosages impacted viral entry into cells expressing viral receptor, Fc receptor, or both receptors. This study reveals complex roles of antibodies in viral entry and can guide future vaccine design and antibody-based drug therapy.

Antibody-dependent enhancement (ADE) of viral entry has been a major concern for epidemiology, vaccine development, and antibody-based drug therapy. However, the molecular mechanism behind ADE is still elusive. Coronavirus spike protein mediates viral entry into cells by first binding to a receptor on the host cell surface and then fusing viral and host membranes. In this study, we investigated how a neutralizing monoclonal antibody (MAb), which targets the receptor-binding domain (RBD) of Middle East respiratory syndrome (MERS) coronavirus spike, mediates viral entry using pseudovirus entry and biochemical assays. Our results showed that MAb binds to the virus surface spike, allowing it to undergo conformational changes and become prone to proteolytic activation. Meanwhile, MAb binds to cell surface IgG Fc receptor, guiding viral entry through canonical viral-receptor-dependent pathways. Our data suggest that the antibody/Fc-receptor complex functionally mimics viral receptor in mediating viral entry. Moreover, we characterized MAb dosages in viral-receptor-dependent, Fc-receptor-dependent, and both-receptors-dependent viral entry pathways, delineating guidelines on MAb usages in treating viral infections. Our study reveals a novel molecular mechanism for antibody-enhanced viral entry and can guide future vaccination and antiviral strategies.

IMPORTANCE Antibody-dependent enhancement (ADE) of viral entry has been observed for many viruses. It was shown that antibodies target one serotype of viruses but only subneutralize another, leading to ADE of the latter viruses. Here we identify a novel mechanism for ADE: a neutralizing antibody binds to the surface spike protein of coronaviruses like a viral receptor, triggers a conformational change of the spike, and mediates viral entry into IgG Fc receptor-expressing cells through canonical viral-receptor-dependent pathways. We further evaluated how antibody dosages impacted viral entry into cells expressing viral receptor, Fc receptor, or both receptors. This study reveals complex roles of antibodies in viral entry and can guide future vaccine design and antibody-based drug therapy.

MVA Vectored Vaccines Encoding Rift Valley Fever Virus Glycoproteins Protect Mice against Lethal Challenge in the Absence of Neutralizing Antibody Responses

In vitro neutralizing antibodies have been often correlated with protection against Rift Valley fever virus (RVFV) infection. We have reported previously that a single inoculation of sucrose-purified modified vaccinia Ankara (MVA) encoding RVFV glycoproteins (rMVAGnGc) was sufficient to induce a protective immune response in mice after a lethal RVFV challenge. Protection was related to the presence of glycoprotein specific CD8+ cells, with a low-level detection of in vitro neutralizing antibodies. In this work we extended those observations aimed to explore the role of humoral responses after MVA vaccination and to study the contribution of each glycoprotein antigen to the protective efficacy. Thus, we tested the efficacy and immune responses in BALB/c mice of recombinant MVA viruses expressing either glycoprotein Gn (rMVAGn) or Gc (rMVAGc). In the absence of serum neutralizing antibodies, our data strongly suggest that protection of vaccinated mice upon the RVFV challenge can be achieved by the activation of cellular responses mainly directed against Gc epitopes. The involvement of cellular immunity was stressed by the fact that protection of mice was strain dependent. Furthermore, our data suggest that the rMVA based single dose vaccination elicits suboptimal humoral immune responses against Gn antigen since disease in mice was exacerbated upon virus challenge in the presence of rMVAGnGc or rMVAGn immune serum. Thus, Gc-specific cellular immunity could be an important component in the protection after the challenge observed in BALB/c mice, contributing to the elimination of infected cells reducing morbidity and mortality and counteracting the deleterious effect of a subneutralizing antibody immune response.