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

Antibody-dependent enhancement of SARS-CoV-2, the impact of variants and vaccination

This study characterized antibody-dependent enhancement (ADE) in serum samples from individuals exposed to SARS-CoV-2 via infection or vaccination and evaluated its association with SARS-CoV-2 variants (Wuhan and Omicron), MERS-CoV, and NL63. ADE assays were performed on sera from SARS-CoV-2-infected patients (n = 210) with varying disease severity and vaccinated individuals (n = 225) who received adenovirus vector, inactivated virus or mRNA vaccines. ADE was assessed using pseudoviruses (PVs) in BHK cells expressing FcgRIIa. Neutralizing antibody levels, total IgG, IgG subclasses, and complement activation were analyzed using ELISA and neutralization assays. ADE was observed in 6.2% of infection samples (primarily severe cases) and 5.3% of vaccinated samples (adenovirus-vector and inactivated virus groups). ADE-positive samples showed reduced neutralizing activity, while total IgG and IgG subclasses did not differ significantly between ADE-positive and negative samples. Complement activation was elevated in severe cases but did not correlate clearly with ADE. Notably, MERS-CoV PV induced ADE in a subset of infected samples, but no ADE was detected for NL63. ADE was observed in SARS-CoV-2-infected individuals, particularly in severe cases, and in those vaccinated with adenovirus-vector and inactivated virus vaccines, but not with mRNA vaccines. Cross-reactivity leading to ADE was detected for MERS-CoV but not for NL63. ADE was associated with reduced neutralizing antibody activity and elevated complement activation in severe infections, though the specific role of complement in ADE remains unclear. These findings highlight the need to investigate the mechanisms underlying ADE and its implications for vaccine design and post-infection immunity against respiratory viruses.

Efficacy and safety of SARS-CoV-2 neutralizing antibody, SCTA01, in high-risk outpatients diagnosed with COVID-19: A Phase II clinical trial

Background/Objective

The neutralizing monoclonal antibody against SARS-CoV-2 is regarded as one of the most effective therapies for COVID-19.: This study was a randomized, double-blinded, placebo-controlled Phase II trial conducted to evaluate the efficacy of neutralizing monoclonal antibody (SCTA01) in high-risk outpatients diagnosed with COVID-19.

Methods

The primary endpoint was the proportion of patients who experienced COVID-19-related hospitalization (defined as at least 24 h of acute care) or death (all causes) by Day 29.

Results

109 patients were randomly assigned to and received SCTA01 750 mg (n = 25), 1500 mg (n = 29), 3000 mg (n = 30), or placebo (n = 25). Only two experienced COVID-19-related hospitalization by Day 29, one from the 750 mg group and the other from the 3000 mg group. Statistical analysis revealed no significant differences in viral load reduction (p = 0.20) or symptom score reduction (p = 0.37) between the SCTA01 total and placebo groups. Additionally, the incidence of adverse events was comparable between the SCTA01 group (23.8 %) and the placebo group (24.0 %). Notably, no treatment-related serious adverse events (SAEs) were reported.

Conclusions

There was no significant difference in clinical outcome between SCTA01 and placebo in the treatment of high-risk outpatients diagnosed with COVID-19, and it was well tolerated.

CLINICAL TRIAL

The trial was registered at ClinicalTrial.gov (NCT04709328).

Fc-Modified Antibody in Hospitalized Severe COVID-19 Patients

Background: Hospitalized patients with severe COVID-19 are at high risk of clinical deterioration. Methods: A global, randomized, double-blinded, and placebo-controlled phase II trial that investigated the clinical efficacy of SCTA01, an Fc-modified monoclonal antibody, in patients hospitalized with severe COVID-19 during the Delta variant wave was performed. The primary outcome was time to clinical improvement up to Day 29. Secondary outcomes measured the all-cause mortality rate up to Day 29, time to SARS-CoV-2 RNA negativity up to Day 29, and the number of antibody-dependent enhancements. Results: From 27 March 2021, to 11 February 2022, 102 hospitalized adults with severe COVID-19 received a single intravenous infusion of SCTA01 15 mg/kg or 50 mg/kg or placebo in a 1:1:1 ratio. The median time to clinical improvement in the SCTA01 group was numerically shorter than that in the placebo group; however, the between group difference was statistically non-significant (SCTA01 15 mg/kg vs. placebo, HR 0.99, 95% CI 0.55-1.77, p = 0.742; SCTA01 50 mg/kg vs. placebo, HR 1.07, 95% CI 0.61-1.88, p = 0.095). The median time to achieve a negative SARS-CoV-2 status was shorter in the SCTA01 15 mg/kg group (14.0 days vs. 27.0 days) but not in the SCTA01 50 mg/kg group (28.0 days vs. 27.0 days) compared to the placebo group. Adverse events were comparable across all groups, and no treatment-related serious adverse event or antibody-dependent enhancement was reported. Conclusions: The Fc-modified antibody was safe but lacked significant clinical efficacy in vivo, likely due to the SARS-CoV-2 viral mutation.

Real-world assessment of reinfection with SARS-CoV-2: Implications for vaccines

BACKGROUND

There have been over 670 million confirmed cases of SARS-CoV-2 infection globally, resulting in over 6.87 million deaths. With approximately 0.1 %-6.8 % experiencing reinfection. This retrospective cohort study aimed to compare the risk of short-term circulatory and respiratory sequelae between SARS-CoV-2 reinfection and initial infection, and assess the impact of vaccination.

METHOD

Data from the TriNetX US Collaborative network (2020-2022) were used to create two cohorts based on reinfection status. The main outcome assessed were medical utilization, circulatory and respiratory symptoms, and circulatory and respiratory diseases. The Kaplan-Meier method was used to compare the risks between two cohorts. Four subgroup analyses (vaccination status, age, sex, race) and six sensitivity analyses (rigorous definition, modified exclusion criteria, treatment, different COVID-19 variants timeline, address survivorship bias, and E-value calculation) were also conducted.

RESULTS

The reinfection cohort showed a significant reduction in medical utilization [ Hazard ratio, HR: 0.867, (95 % confidence interval, CI:0.839-0.896) for hospitalization, 0.488 (0.418-0.570) for critical care services, and 0.476 (0.360-0.629) for mechanical ventilation], lower risk of circulatory diseases [ HR: 0.701 (95 % CI:0.637-0.772), 0.695 (0.583-0.829), 0.660 (0.605-0.719), 0.741 (0.644-0.854), 0.614 (0.535-0.705), and 0.758 (0.656-0.876) for ischemic heart disease, inflammatory heart disease, dysrhythmias, venous thromboembolism, other cardiac disorders, and cerebrovascular diseases, respectively], and lower risk of respiratory diseases such as pneumonia, other acute lower respiratory infections, asthma, and hypoxemia [HR: 0.302 (95 % CI: 0.273-0.333), 0.811 (0.686-0.958), 0.791 (0.735-0.850), and 0.392 (0.338-0.455), respectively]. The vaccinated reinfection cohort showed no significant differences in medical utilization, circulatory diseases, or respiratory conditions but had a higher risk of breathing abnormalities. breathing abnormalities [HR: 1.195 (95 % CI:1.087-1.313)].

CONCLUSIONS

The individuals who experienced reinfection exhibited milder short-term sequelae in the circulatory and respiratory systems. Vaccine administration protects against cardiovascular or respiratory systems.

HCoV-NL63 and HCoV-HKU1 seroprevalence and its relationship with the clinical features of COVID-19 patients from Villavicencio, Colombia

INTRODUCTION

Due to the cross-reactivity between SARS-CoV-2 and common human coronaviruses, previous infections with these viruses could contribute to serological or cellular cross-protection against severe COVID-19. However, protective immunity may not develop, or pre-existing immunity could increase COVID-19 severity.

OBJECTIVE

To determine the seroprevalence of IgG antibodies against HCoV-NL63 and HCoV-HKU1 and correlate previous exposure with COVID-19 signs in patients from Villavicencio.

MATERIALS AND METHODS

A cross-sectional retrospective study was conducted. ELISA technique was used to search for IgG antibodies against HCoV-NL3 and HCoV-HKU1 in patients with positive RT-qPCR results for SARS-CoV-2. Patients were grouped according to COVID-19 clinical characteristics in four groups: group 1: asymptomatic (n = 23); group 2: hospitalized (n = 24); group 3: intensive care units (n = 24), and group 4: dead (n = 22).

RESULTS

The overall seroprevalence of IgG antibodies against HCoV was 74.2% (n = 69; 95% CI: 65.3-83.1), with 66.7% of HCoV-NL63 (n = 62; 95% CI: 57,1-76,2), and 25.8% of HCoV-HKU1 (n = 24; 95% CI: 16,9-34,7). Based on crosstab analysis, prior exposure to HCoV-NL63 was associated with protection against severe COVID-19 (p = 0.042; adjusted OR = 0.159; 95% CI: 0.027-0.938), and previous coinfection of HCoV-NL63 and HCoVHKU1 was considered a positive association to severe COVID-19 (p = 0.048; adjusted OR = 16.704; 95% CI: 1.020 - 273.670).

CONCLUSION

To our knowledge, this is the first study addressing seroprevalence of HCoV IgG antibodies in Colombia and Latin America. Previous exposure to HCoV-NL63 could protect against severe COVID-19, whereas patients with underlying HCoV-NL63 and HCoVHKU1 coinfection could be hospitalized with severe signs of COVID-19.

Enhanced Assessment of Cross-Reactive Antigenic Determinants within the Spike Protein

Despite successful vaccination efforts, the emergence of new SARS-CoV-2 variants poses ongoing challenges to control COVID-19. Understanding humoral responses regarding SARS-CoV-2 infections and their impact is crucial for developing future vaccines that are effective worldwide. Here, we identified 41 immunodominant linear B-cell epitopes in its spike glycoprotein with an SPOT synthesis peptide array probed with a pool of serum from hospitalized COVID-19 patients. The bioinformatics showed a restricted set of epitopes unique to SARS-CoV-2 compared to other coronavirus family members. Potential crosstalk was also detected with Dengue virus (DENV), which was confirmed by screening individuals infected with DENV before the COVID-19 pandemic in a commercial ELISA for anti-SARS-CoV-2 antibodies. A high-resolution evaluation of antibody reactivity against peptides representing epitopes in the spike protein identified ten sequences in the NTD, RBD, and S2 domains. Functionally, antibody-dependent enhancement (ADE) in SARS-CoV-2 infections of monocytes was observed in vitro with pre-pandemic Dengue-positive sera. A significant increase in viral load was measured compared to that of the controls, with no detectable neutralization or considerable cell death, suggesting its role in viral entry. Cross-reactivity against peptides from spike proteins was observed for the pre-pandemic sera. This study highlights the importance of identifying specific epitopes generated during the humoral response to a pathogenic infection to understand the potential interplay of previous and future infections on diseases and their impact on vaccinations and immunodiagnostics.

Antibody-dependent enhancement (ADE) of SARS-CoV-2 in patients exposed to MERS-CoV and SARS-CoV-2 antigens

This study evaluated the potential for antibody-dependent enhancement (ADE) in serum samples from patients exposed to Middle East respiratory syndrome coronavirus (MERS-CoV). Furthermore, we evaluated the effect of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on ADE in individuals with a MERS infection history. We performed ADE assay in sera from MERS recovered and SARS-CoV-2-vaccinated individuals using BHK cells expressing FcgRIIa, SARS-CoV-2, and MERS-CoV pseudoviruses (PVs). Further, we analyzed the association of ADE to serum IgG levels and neutralization. Out of 16 MERS patients, nine demonstrated ADE against SARS-CoV-2 PV, however, none of the samples demonstrated ADE against MERS-CoV PV. Furthermore, out of the seven patients exposed to SARS-CoV-2 vaccination after MERS-CoV infection, only one patient (acutely infected with MERS-CoV) showed ADE for SARS-CoV-2 PV. Further analysis indicated that IgG1, IgG2, and IgG3 against SARS-CoV-2 S1 and RBD subunits, IgG1 and IgG2 against the MERS-CoV S1 subunit, and serum neutralizing activity were low in ADE-positive samples. In summary, samples from MERS-CoV-infected patients exhibited ADE against SARS-CoV-2 and was significantly associated with low levels of neutralizing antibodies. Subsequent exposure to SARS-CoV-2 vaccination resulted in diminished ADE activity while the PV neutralization assay demonstrated a broadly reactive antibody response in some patient samples.

Research progress in Fc-effector functions against SARS-CoV-2

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused more than 676 million cases in the global human population with approximately 7 million deaths and vaccination has been proved as the most effective countermeasure in reducing clinical complications and mortality rate of SARS-CoV-2 infection in people. However, the protective elements and correlation of protection induced by vaccination are still not completely understood. Various antibodies with multiple protective mechanisms can be induced simultaneously by vaccination in vivo, thereby complicating the identification and characterization of individual correlate of protection. Recently, an increasing body of observations suggests that antibody-induced Fc-effector functions play a crucial role in combating SARS-CoV-2 infections, including neutralizing antibodies-escaping variants. Here, we review the recent progress in understanding the impact of Fc-effector functions in broadly disarming SARS-CoV-2 infectivity and discuss various efforts in harnessing this conserved antibody function to develop an effective SARS-CoV-2 vaccine that can protect humans against infections by SARS-CoV-2 virus and its variants of concern.

Antibody escape, the risk of serotype formation, and rapid immune waning: Modeling the implications of SARS-CoV-2 immune evasion

As the COVID-19 pandemic progresses, widespread community transmission of SARS-CoV-2 has ushered in a volatile era of viral immune evasion rather than the much-heralded stability of "endemicity" or "herd immunity." At this point, an array of viral strains has rendered essentially all monoclonal antibody therapeutics obsolete and strongly undermined the impact of vaccinal immunity on SARS-CoV-2 transmission. In this work, we demonstrate that antibody escape resulting in evasion of pre-existing immunity is highly evolutionarily favored and likely to cause waves of short-term transmission. In the long-term, invading strains that induce weak cross-immunity against pre-existing strains may co-circulate with those pre-existing strains. This would result in the formation of serotypes that increase disease burden, complicate SARS-CoV-2 control, and raise the potential for increases in viral virulence. Less durable immunity does not drive positive selection as a trait, but such strains may transmit at high levels if they establish. Overall, our results draw attention to the importance of inter-strain cross-immunity as a driver of transmission trends and the importance of early immune evasion data to predict the trajectory of the pandemic.

Antibody-Dependent Enhancement with a Focus on SARS-CoV-2 and Anti-Glycan Antibodies

Antibody-dependent enhancement (ADE) is a phenomenon where virus-specific antibodies paradoxically cause enhanced viral replication and/or excessive immune responses, leading to infection exacerbation, tissue damage, and multiple organ failure. ADE has been observed in many viral infections and is supposed to complicate the course of COVID-19. However, the evidence is insufficient. Since no specific laboratory markers have been described, the prediction and confirmation of ADE are very challenging. The only possible predictor is the presence of already existing (after previous infection) antibodies that can bind to viral epitopes and promote the disease enhancement. At the same time, the virus-specific antibodies are also a part of immune response against a pathogen. These opposite effects of antibodies make ADE research controversial. The assignment of immunoglobulins to ADE-associated or virus neutralizing is based on their affinity, avidity, and content in blood. However, these criteria are not clearly defined. Another debatable issue (rather terminological, but no less important) is that in most publications about ADE, all immunoglobulins produced by the immune system against pathogens are qualified as pre-existing antibodies, thus ignoring the conventional use of this term for natural antibodies produced without any stimulation by pathogens. Anti-glycan antibodies (AGA) make up a significant part of the natural immunoglobulins pool, and there is some evidence of their antiviral effect, particularly in COVID-19. AGA have been shown to be involved in ADE in bacterial infections, but their role in the development of ADE in viral infections has not been studied. This review focuses on pros and cons for AGA as an ADE trigger. We also present the results of our pilot studies, suggesting that AGAs, which bind to complex epitopes (glycan plus something else in tight proximity), may be involved in the development of the ADE phenomenon.

Spotlight on contributory role of host immunogenetic profiling in SARS-CoV-2 infection: Susceptibility, severity, mortality, and vaccine effectiveness

BACKGROUND

The SARS-CoV-2 virus has spread continuously worldwide, characterized by various clinical symptoms. The immune system responds to SARS-CoV-2 infection by producing Abs and secreting cytokines. Recently, numerous studies have highlighted that immunogenetic factors perform a putative role in COVID-19 pathogenesis and implicate vaccination effectiveness.

AIM

This review summarizes the relevant articles and evaluates the significance of mutation and polymorphism in immune-related genes regarding susceptibility, severity, mortality, and vaccination effectiveness of COVID-19. Furthermore, the correlation between host immunogenetic and SARS-CoV-2 reinfection is discussed.

METHOD

A comprehensive search was conducted to identify relevant articles using five databases until January 2023, which resulted in 105 total articles.

KEY FINDINGS

Taken to gather this review summarized that: (a) there is a plausible correlation between immune-related genes and COVID-19 outcomes, (b) the HLAs, cytokines, chemokines, and other immune-related genes expression profiles can be a prognostic factor in COVID-19-infected patients, and (c) polymorphisms in immune-related genes have been associated with the effectiveness of vaccination.

SIGNIFICANCE

Regarding the importance of mutation and polymorphisms in immune-related genes in COVID-19 outcomes, modulating candidate genes is expected to help clinical decisions, patient outcomes management, and innovative therapeutic approach development. In addition, the manipulation of host immunogenetics is hypothesized to induce more robust cellular and humoral immune responses, effectively increase the efficacy of vaccines, and subsequently reduce the incidence rates of reinfection-associated COVID-19.

Pediatric multisystem inflammatory syndrome associated with COVID-19: Insights in pathogenesis and clinical management

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been a major challenge to be faced in recent years. While adults suffered the highest morbidity and mortality rates of coronavirus disease 2019, children were thought to be exclusively asymptomatic or to present with mild conditions. However, around April 2020, there was an outbreak of a new clinical syndrome related to SARS-CoV-2 in children - multisystemic inflammatory syndrome in children (MIS-C) - which comprises a severe and uncon-trolled hyperinflammatory response with multiorgan involvement. The Centers for Disease Control and Prevention considers a suspected case of MIS-C an individual aged < 21 years presenting with fever, high inflammatory markers levels, and evidence of clinically severe illness, with multisystem (> 2) organ involvement, no alternative plausible diagnoses, and positive for recent SARS-CoV-2 infection. Despite its severity, there are no definitive disease management guidelines for this condition. Conversely, the complex pathogenesis of MIS-C is still not completely understood, although it seems to rely upon immune dysregulation. Hence, in this study, we aim to bring together current evidence regarding the pathogenic mechanisms of MIS-C, clinical picture and management, in order to provide insights for clinical practice and implications for future research directions.

Are Measles-Mumps-Rubella (MMR) Antibodies Friends or Foes for Covid-19 Disease?

Many factors have been implicated in the pathogenesis and severity of COVID-19 pandemic. A wide variation in the susceptibility for SARS-CoV-2 infection among different population, gender and age has been observed. Multiple studies investigated the relationship between the antibody's titre of previously vaccinated individuals and the susceptibility of coronavirus infection, to find a rapid effective therapy for this pandemic. This study focused on the association between measles-mumps-rubella (MMR) antibodies titre and the severity of COVID-19 infection. We aimed to investigate the correlation between the antibody's titre of MMR and the SARS-CoV-2 infection susceptibility and disease severity, in a cohort of COVID-19 Egyptian patients, compared to a control group. MMR antibody titre was measured using enzyme Linked Immune Sorbent Assay; (ELISA) for 136 COVID-19 patients and 44 healthy individuals, as control group. There were high levels of measles and mumps antibodies titer in the deteriorating cases, which could not protect from SARS-CoV-2 infection. However, the rubella antibodies might protect from SARS-CoV-2 infection, but once the infection occurs, it may aggravate the risk of case deterioration. MMR antibodies could be used as a guideline for COVID-19 symptom-severity and, in turn, may be considered as an economic prognostic marker used for early protection from multiple autoimmune organ failure.

Evaluation of Anti-SARS-CoV-2 IgA Response in Tears of Vaccinated COVID-19 Subjects

Secretory IgA (sIgA), which may play an important role in the early defense against SARS-CoV-2 infection, were detected in the eye of COVID-19 patients. However, an evaluation of the sIgA response in the tears of vaccinated or non-vaccinated COVID-19 subjects is still lacking. Aimed at characterizing sIgA mucosal immunity in the eye, this study analyzed tear samples from 77 COVID-19 patients, including 63 vaccinated and 14 non-vaccinated subjects. The groups showed similar epidemiological features, but as expected, differences were observed in the percentage of asymptomatic/pauci-symptomatic subjects in the vaccinated vs. non-vaccinated cohort (46% and 29% of the total, respectively). Consistent with this, ocular sIgA values, evaluated by a specific quantitative ELISA assay, were remarkably different in vaccinated vs. non-vaccinated group for both frequency (69.8% vs. 57.1%, respectively) and titer (1372.3 U/mL vs. 143.7 U/mL, respectively; p = 0.01), which was significantly differently elevated depending on the type of administered vaccine. The data show for the first time significant differences of available vaccines to elicit sIgA response in the eye and suggest that quantitative tear-based sIgA tests may potentially serve as a rapid and easily accessible biomarker for the assessment of the development of a protective mucosal immunity toward SARS-CoV-2.

SARS-CoV-2 infection of phagocytic immune cells and COVID-19 pathology: Antibody-dependent as well as independent cell entry

Our review summarizes the evidence that COVID-19 can be complicated by SARS-CoV-2 infection of immune cells. This evidence is widespread and accumulating at an increasing rate. Research teams from around the world, studying primary and established cell cultures, animal models, and analyzing autopsy material from COVID-19 deceased patients, are seeing the same thing, namely that some immune cells are infected or capable of being infected with the virus. Human cells most vulnerable to infection include both professional phagocytes, such as monocytes, macrophages, and dendritic cells, as well as nonprofessional phagocytes, such as B-cells. Convincing evidence has accumulated to suggest that the virus can infect monocytes and macrophages, while data on infection of dendritic cells and B-cells are still scarce. Viral infection of immune cells can occur directly through cell receptors, but it can also be mediated or enhanced by antibodies through the Fc gamma receptors of phagocytic cells. Antibody-dependent enhancement (ADE) most likely occurs during the primary encounter with the pathogen through the first COVID-19 infection rather than during the second encounter, which is characteristic of ADE caused by other viruses. Highly fucosylated antibodies of vaccinees seems to be incapable of causing ADE, whereas afucosylated antibodies of persons with acute primary infection or convalescents are capable. SARS-CoV-2 entry into immune cells can lead to an abortive infection followed by host cell pyroptosis, and a massive inflammatory cascade. This scenario has the most experimental evidence. Other scenarios are also possible, for which the evidence base is not yet as extensive, namely productive infection of immune cells or trans-infection of other non-immune permissive cells. The chance of a latent infection cannot be ruled out either.

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.

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.