Antibody-mediated Enhancement Research Articles

Zika virus T-cell based 704/DNA vaccine promotes protection from Zika virus infection in the absence of neutralizing antibodies.

Zika virus (ZIKV) and dengue virus (DENV) are closely related flaviviruses co-circulating in the same endemic areas. Infection can raise cross-reactive antibodies that can be either protective or increase risk of severe disease, depending on the infection sequence, DENV serotype and elapsed time between infection. On the contrast, T cell-mediated immunity against DENV and ZIKV is considered protective. Therefore, we have developed a T cell vaccine enriched in immunodominant T cell epitopes derived from ZIKV and evaluated its immunogenicity and efficacy against ZIKV and DENV infection. Mice were vaccinated using DNA vaccine platform using the tetrafunctional amphiphilic block copolymer 704. We show that vaccination of 2 different HLA class I transgenic mice with the ZIKV non-structural (NS) poly-epitope elicits T cell response against numerous ZIKV epitopes. Moreover, vaccination induces a significant protection against ZIKV infection, in the absence of neutralizing or enhancing antibodies against ZIKV. However, vaccination does not induce a significant protection against DENV2. In contrast, immunization with a DENV1-NS poly-epitope induces a significant protection against both DENV1 and DENV2, in the absence of humoral immunity. Taken together, we have shown that T-cell based vaccination could protect against multiple flavivirus infections and could overcome the complexity of antibody-mediated enhancement.

Complement C3 and marginal zone B cells promote IgG-mediated enhancement of RBC alloimmunization in mice.

Administration of anti-RhD immunoglobulin (Ig) to decrease maternal alloimmunization (antibody-mediated immune suppression [AMIS]) was a landmark clinical development. However, IgG has potent immune-stimulatory effects in other settings (antibody-mediated immune enhancement [AMIE]). The dominant thinking has been that IgG causes AMIS for antigens on RBCs but AMIE for soluble antigens. However, we have recently reported that IgG against RBC antigens can cause either AMIS or AMIE as a function of an IgG subclass. Recent advances in mechanistic understanding have demonstrated that RBC alloimmunization requires the IFN-α/-β receptor (IFNAR) and is inhibited by the complement C3 protein. Here, we demonstrate the opposite for AMIE of an RBC alloantigen (IFNAR is not required and C3 enhances). RBC clearance, C3 deposition, and antigen modulation all preceded AMIE, and both CD4+ T cells and marginal zone B cells were required. We detected no significant increase in antigen-specific germinal center B cells, consistent with other studies of RBC alloimmunization that show extrafollicular-like responses. To the best of our knowledge, these findings provide the first evidence of an RBC alloimmunization pathway which is IFNAR independent and C3 dependent, thus further advancing our understanding of RBCs as an immunogen and AMIE as a phenomenon.

Fusion of PspA to detoxified pneumolysin enhances pneumococcal vaccine coverage

Despite the implementation of conjugate vaccines in several countries, S. pneumoniae continues to pose a great burden worldwide, causing around 1 million annual deaths. Pneumococcal proteins have long been investigated as serotype-independent vaccines against this pathogen, with promising results. However, it is a consensus that one antigen alone will not be sufficient to provide long-term protection with wide coverage. Amongst the most well studied pneumococcal proteins are PspA and pneumolysin (Ply), two major virulence factors required by the bacterium for successful invasion of host tissues. PspA is highly immunogenic and protective, but it is structurally variable; pneumolysin is conserved among different pneumococci, but it is toxic to the host. To overcome these limitations, N-terminal PspA fragments have been genetically fused to non-toxic pneumolysin derivatives (PlD) to create PspA_PlD chimeras. Mouse immunization with these fusions confers protection against pneumococcal strains expressing heterologous PspAs, which correlates with antibody-induced complement C3 deposition on the surface of multiple pneumococcal strains. Analysis of mutant strains lacking PspA or Pneumolysin shows that both proteins contribute to the antibody-mediated enhancement in complement deposition induced by the fusion. These results expand previous data evaluating PspA_PlD and demonstrate that the fusion combines the protective traits of both proteins, inducing antibodies that efficiently promote complement deposition on multiple strains and cross-protection.

Global and cell type-specific immunological hallmarks of severe dengue progression identified via a systems immunology approach.

Severe dengue (SD) is a major cause of morbidity and mortality. To define dengue virus (DENV) target cells and immunological hallmarks of SD progression in children's blood, we integrated two single-cell approaches capturing cellular and viral elements: virus-inclusive single-cell RNA sequencing (viscRNA-Seq 2) and targeted proteomics with secretome analysis and functional assays. Beyond myeloid cells, in natural infection, B cells harbor replicating DENV capable of infecting permissive cells. Alterations in cell type abundance, gene and protein expression and secretion as well as cell-cell communications point towards increased immune cell migration and inflammation in SD progressors. Concurrently, antigen-presenting cells from SD progressors demonstrate intact uptake yet impaired interferon response and antigen processing and presentation signatures, which are partly modulated by DENV. Increased activation, regulation and exhaustion of effector responses and expansion of HLA-DR-expressing adaptive-like NK cells also characterize SD progressors. These findings reveal DENV target cells in human blood and provide insight into SD pathogenesis beyond antibody-mediated enhancement.

Novel B-Cell Epitopes of Non-Neutralizing Antibodies in the Receptor-Binding Domain of the SARS-CoV-2 S-Protein with Different Effects on the Severity of COVID-19.

Antibodies against the receptor-binding domain of the SARS-CoV-2 spike protein (RBD S-protein) contribute significantly to the humoral immune response during coronavirus infection (COVID-19) and after vaccination. The main focus of the studies of the RBD epitope composition is usually concentrated on the epitopes recognized by the virus-neutralizing antibodies. The role of antibodies that bind to RBD but do not neutralize SARS-CoV-2 remains unclear. In this study, immunochemical properties of the two mouse monoclonal antibodies (mAbs), RS17 and S11, against the RBD were examined. Both mAbs exhibited high affinity to RBD, but they did not neutralize the virus. The epitopes of these mAbs were mapped using phage display: the epitope recognized by the mAb RS17 is located at the N-terminal site of RBD (348-SVYAVNRKRIS-358); the mAb S11 epitope is inside the receptor-binding motif of RBD (452-YRLFRKSN-459). Three groups of sera were tested for presence of antibodies competing with the non-neutralizing mAbs S11 and RS17: (i) sera from the vaccinated healthy volunteers without history of COVID-19; (ii) sera from the persons who had a mild form of COVID-19; (iii) sera from the persons who had severe COVID-19. Antibodies competing with the mAb S11 were found in each group of sera with equal frequency, whereas presence of the antibodies competing with the mAb RS17 in the sera was significantly more frequent in the group of sera obtained from the patients recovered from severe COVID-19 indicating that such antibodies are associated with the severity of COVID-19. In conclusion, despite the clear significance of anti-RBD antibodies in the effective immune response against SARS-CoV-2, it is important to analyze their virus-neutralizing activity and to confirm absence of the antibody-mediated enhancement of infection by the anti-RBD antibodies.

Antigen copy number and antibody dose can determine the outcome of erythrocyte alloimmunization inducing either antibody-mediated immune suppression or enhancement in a murine model.

The administration of anti-D for the prevention of hemolytic disease of the fetus and newborn is one of the most successful clinical uses of the phenomenon of antibody-mediated immune suppression (AMIS). However, despite adequate prophylaxis, failures can still occur in the clinic and are poorly understood. Recently, the copy number of red blood cell (RBC) antigens has been shown to influence immunogenicity in the context of RBC alloimmunization; however, its influence on AMIS remains unexplored. RBCs expressing approximately 3,600 and approximately 12,400 copy numbers of surface-bound hen egg lysozyme (HEL), named respectively HELmed -RBCs and HELhi -RBCs, and selected doses of a polyclonal HEL-specific IgG were transfused into mice. Recipient HEL-specific IgM, IgG, and IgG subclass responses were evaluated by ELISA. Antigen copy number affected the antibody dose required for AMIS induction with higher antigen copy numbers requiring larger doses of antibody. For instance, 5μg of antibody caused AMIS for HELmed -RBCs but not HELhi -RBCs, while 20 μg induced significant suppression for both HEL-RBCs. Overall, increasing amounts of the AMIS-inducing antibody were associated with a more complete AMIS effect. In contrast, the lowest tested doses of the AMIS-inducing IgG led to evidence of enhancement at the IgM and IgG levels. The results demonstrate that the relationship between antigen copy number and antibody dose can influence the outcome of AMIS. Further, this work suggests that the same antibody preparation can induce both AMIS and enhancement but that the outcome may depend on the quantitative interrelationship of antigen-antibody binding.

Opsonizing antibodies mediated SARS-CoV-2 entry into monocytes leads to inflammation.

Opsonizing antibodies mediated SARS-CoV-2 entry into monocytes leads to inflammation.

Natural disease and evolution of an Amdoparvovirus endemic in striped skunks (Mephitis mephitis).

Striped skunks (Mephitis mephitis) densely populate the human-animal interface of suburbia throughout North America. Skunks share that habitat with numerous related mesocarnivores, where increased contact, competition for shared food and water sources and other stressors contribute to increased exposure and susceptibility to viral infection. The recently identified skunk amdoparvovirus (SKAV) has been detected at high prevalence in skunks and occasionally in mink, but its distribution in North America is unknown. To understand the impact of SKAV in striped skunks and the risk posed to related species, we investigated the geographic distribution of SKAV, analysed its genetic diversity and evolutionary dynamics and evaluated viral distribution in tissues of infected animals to identify possible mechanisms of transmission. SKAV was detected in 72.5% (37/51) skunks and was present at high rates at all locations tested across North America. Analysis of the complete genomic sequence of 29 strains showed a clear geographic segregation, frequent recombination and marked differences in the evolutionary dynamics of the major structural (VP2) and non-structural (NS1) proteins. NS1 was characterized by a higher variability and a higher percentage of positively selected codons. This could indicate that antibody-mediated enhancement of infection occurs in SKAV, an infection strategy that may be conserved across amdoparvoviruses. Finally, in situ hybridization revealed virus in epithelium of the gastrointestinal tract, urinary tract and skin, indicating that viral transmission could occur via oronasal, faecal and/or urinary secretions, as well as from skin and hair. The endemicity of SKAV over large geographic distances and its high genetic diversity suggest a long-term virus-host association. Persistent shedding and high environmental stability likely contribute to efficient viral spread, simultaneously offering opportunities for cross-species transmission with consequent risk to sympatric species, including domestic animals and wildlife.

Conformational dynamics and allosteric modulation of the SARS-CoV-2 spike.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects cells through binding to angiotensin-converting enzyme 2 (ACE2). This interaction is mediated by the receptor-binding domain (RBD) of the viral spike (S) glycoprotein. Structural and dynamic data have shown that S can adopt multiple conformations, which controls the exposure of the ACE2-binding site in the RBD. Here, using single-molecule Förster resonance energy transfer (smFRET) imaging, we report the effects of ACE2 and antibody binding on the conformational dynamics of S from the Wuhan-1 strain and in the presence of the D614G mutation. We find that D614G modulates the energetics of the RBD position in a manner similar to ACE2 binding. We also find that antibodies that target diverse epitopes, including those distal to the RBD, stabilize the RBD in a position competent for ACE2 binding. Parallel solution-based binding experiments using fluorescence correlation spectroscopy (FCS) indicate antibody-mediated enhancement of ACE2 binding. These findings inform on novel strategies for therapeutic antibody cocktails.

Impact of structural dynamics on biological functions of flaviviruses.

Flaviviruses comprise a number of mosquito- or tick-transmitted human pathogens of global public health importance. Advances in structural biology techniques have contributed substantially to our current understanding of the life cycle of these small enveloped RNA viruses and led to deep insights into details of virus assembly, maturation and cell entry. In addition to large-scale conformational changes and oligomeric rearrangements of envelope proteins during these processes, there is increasing evidence that smaller-scale protein dynamics (referred to as virus "breathing") can confer extra flexibility to these viruses for the fine-tuning of their interactions with the immune system and possibly with cellular factors they encounter in their complex ecological cycles in arthropod and vertebrate hosts. In this review, we discuss how work with tick-borne encephalitis virus has extended our view on flavivirus breathing, leading to the identification of a novel mechanism of antibody-mediated infection enhancement and demonstrating breathing intermediates of the envelope protein in the process of membrane fusion. These data are discussed in the context of other flaviviruses and the perspective of a potential role of virus breathing to cope with the requirements of adaptation and replication in evolutionarily very different hosts.

Decoding the Clinical and Laboratory Parameters of COVID-19 and Dengue Co-infection

Severe acute respiratory diseases caused by coronavirus disease 2019 (COVID-19) have caused infections around the world, and this disease has been declared a global pandemic by the World Health Organization. COVID-19 has severely impacted the world economy, and as it has multiple unnoticeable transmission routes, it can derail the health care system for a long time. Most states in India are affected by the COVID pandemic. As India is known for its seasonal infections such as dengue, leptospirosis, influenza, malaria, and enteric fever, it is expected that these infections may co-exist. Coinfection of these two viral infections causes challenges in diagnosis and treatment, especially in places with limited resources. Antibody-mediated enhancement of the immune response is a cause for concern in co-infection of COVID-19 and dengue. The present article discusses the clinical features, serological cross reactions, and antibody-dependent enhancement of COVID-19 coinfection with dengue infection.

ACE2 can act as the secondary receptor in the FcγR-dependent ADE of SARS-CoV-2 infection

SummaryIt is unknown whether antibody-mediated enhancement (ADE) contributes to the pathogenesis of COVID-19, and the conditions for ADE needs to be elucidated. We demonstrated that without inducing an ACE2-independent ADE on Raji cells, the neutralizing antibody CB6, a mouse anti-S1 serum and convalescent plasma, induced ADE on cells expressing FcγRIIA/CD32A and low levels of endogenous ACE2. ADE occurred at sub-neutralizing antibody concentrations, indicating that unneutralized S protein was required for ADE. The enhanced infectivity of 614G variant was higher than that of 614D wildtype in the presence of antibodies, further suggesting that ADE may be influenced by virus strains with different ACE2-binding affinity. Finally, knockdown of ACE2 or treatment with a fusion-inhibition peptide EK1C4 significantly reduced ADE. In conclusion, we identified an ADE mechanism mediated by neutralizing antibodies against SARS-CoV-2. ACE2 may act as a secondary receptor required for the antibody- and FcγR-mediated enhanced entry of SARS-CoV-2.

The SARS-CoV-2 Lambda variant exhibits enhanced infectivity and immune resistance.

SARS-CoV-2 Lambda, a variant of interest, has spread in some South American countries; however, its virological features and evolutionary traits remain unclear. In this study, we use pseudoviruses and reveal that the spike protein of the Lambda variant is more infectious than that of other variants due to the T76I and L452Q mutations. The RSYLTPGD246-253N mutation, a unique 7-amino acid deletion in the N-terminal domain of the Lambda spike protein, is responsible for evasion from neutralizing antibodies and further augments antibody-mediated enhancement of infection. Although this mutation generates a nascent N-linked glycosylation site, the additional N-linked glycan is dispensable for the virological property conferred by this mutation. Since the Lambda variant has dominantly spread according to the increasing frequency of the isolates harboring the RSYLTPGD246-253N mutation, our data suggest that the RSYLTPGD246-253N mutation is closely associated with the substantial spread of the Lambda variant in South America.

Dengue

Dengue is a mosquito-borne flavivirus infection, found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. There are four distinct dengue virus (DENV) serotypes, meaning that it is possible to be infected four times. While 75% of DENV infections are asymptomatic, 20% of result in mild to moderate disease (Dengue fever [DF]), and 5% can cause severe disease with activation of the coagulation system (Dengue hemorrhagic fever [DHF]), which is usually seen with subsequent DENV infections. Antibody-mediated disease enhancement (ADE) is a phenomenon that has been observed in various in vitro assays: low concentrations of cross-reacting antibodies from a previous DENV infection in a subsequent infection with another serotype do not neutralize DENV. Instead, they bind to the virus and attach to host cells; thus, enabling viral replication. ADE is one hypothesis proposed, among many, to explain sensitization to severe disease. There is no specific treatment for DENV. Early detection of disease progression and access to proper medical care lower fatality rates of DHF from about 2.5% to <1%. Severe dengue is a leading cause of serious illness and death in some Asian and Latin American countries. The global incidence of dengue has grown dramatically in recent decades. About half of the world's population is now at risk. There are an estimated 100–400 million infections each year. Dengue prevention and control relies on effective vector control measures. Sustained community involvement can improve vector control efforts substantially. There is one licensed dengue vaccine, CYD live attenuated tetravalent dengue vaccine (Dengvaxia®) developed by Sanofi Pasteur, which is approved for use in several dengue endemic countries for persons 9–45 years of age living in endemic areas who have had a previously documented dengue virus infection. Several other vaccines are in clinical development.

Overview of Pathogenesis, Diagnostics, and Therapeutics of Infectious Diseases: Dengue and Zika.

The emergence of more virulent SARS virus has made scientists look back at other so-called neglected diseases such as dengue, Zika, and chikungunya, etc. Until recently these neglected diseases have not received much attention for their control or elimination from society. Over the past decade several attempts to investigate the pathogenicity, diagnostic, and therapeutic strategies for flavivirus caused diseases have been made. Herein we have reviewed the progress made toward the detection and treatment of two diseases—dengue and Zika. The above flavivirus related pathogenesis is concerned with the host immune system and known to be mediated through various receptors along with antibody-mediated disease enhancement. Moreover, researchers have been progressing toward discovering new drugs and therapeutic methods that target various stages of the flavivirus life cycle to minimize the above caused mortality and morbidity. The available diagnostics are based on serological, small molecule detection systems and point-of-care sensing devices. In this work, we have reviewed the advancements made toward understanding the pathogenesis, diagnostics, and therapeutics of the viral diseases caused by dengue and Zika.

SARS-CoV-2 Neutralizing Antibodies for COVID-19 Prevention and Treatment.

Prophylactic and therapeutic drugs are urgently needed to combat coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Over the past year, SARS-CoV-2 neutralizing antibodies have been developed for preventive or therapeutic uses. While neutralizing antibodies target the spike protein, their neutralization potency and breadth vary according to recognition epitopes. Several potent SARS-CoV-2 antibodies have shown degrees of success in preclinical or clinical trials, and the US Food and Drug Administration has issued emergency use authorization for two neutralizing antibody cocktails.Nevertheless, antibody therapy for SARS-CoV-2 still faces potential challenges, including emerging viral variants of concern that have antibody-escape mutations and the potential for antibody-mediated enhancement of infection or inflammation. This review summarizes representative SARS-CoV-2 neutralizing antibodies that have been reported and discusses prospects and challenges for the development of the next generation of COVID-19 preventive or therapeutic antibodies.

Histomorphological patterns of regional lymph nodes in COVID-19 lungs.

BackgroundA dysregulated immune response is considered one of the major factors leading to severe COVID-19. Previously described mechanisms include the development of a cytokine storm, missing immunoglobulin class switch, antibody-mediated enhancement, and aberrant antigen presentation.ObjectivesTo understand the heterogeneity of immune response in COVID-19, a thorough investigation of histomorphological patterns in regional lymph nodes was performed.Materials and methodsLymph nodes from the cervical, mediastinal, and hilar regions were extracted from autopsies of patients with lethal COVID-19 (n = 20). Histomorphological characteristics, SARS-CoV‑2 qRT-PCR, and gene expression profiling on common genes involved in immunologic response were analyzed.ResultsLymph nodes displayed moderate to severe capillary stasis and edema, an increased presence of extrafollicular plasmablasts, mild to moderate plasmacytosis, a dominant population of CD8+ T‑cells, and CD11c/CD68+ histiocytosis with hemophagocytic activity. Out of 20 cases, 18 presented with hypoplastic or missing germinal centers with a decrease of follicular dendritic cells and follicular T‑helper cells. A positive viral load was detected by qRT-PCR in 14 of 20 cases, yet immunohistochemistry for SARS-CoV-2 N-antigen revealed positivity in sinus histiocytes of only one case. Gene expression analysis revealed an increased expression of STAT1, CD163, granzyme B, CD8A, MZB1, and PAK1, as well as CXCL9.ConclusionsTaken together, our findings imply a dysregulated immune response in lethal COVID-19. The absence/hypoplasia of germinal centers and increased presence of plasmablasts implies a transient B‑cell response, implying an impaired development of long-term immunity against SARS-CoV‑2 in such occasions.

No Evidence for Human Monocyte-Derived Macrophage Infection and Antibody-Mediated Enhancement of SARS-CoV-2 Infection.

Vaccines are essential to control the spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and to protect the vulnerable population. However, one safety concern of vaccination is the possible development of antibody-dependent enhancement (ADE) of SARS-CoV-2 infection. The potential infection of Fc receptor bearing cells such as macrophages, would support continued virus replication and inflammatory responses, and thereby potentially worsen the clinical outcome of COVID-19. Here we demonstrate that SARS-CoV-2 and SARS-CoV neither infect human monocyte-derived macrophages (hMDM) nor induce inflammatory cytokines in these cells, in sharp contrast to Middle East respiratory syndrome (MERS) coronavirus and the common cold human coronavirus 229E. Furthermore, serum from convalescent COVID-19 patients neither induced enhancement of SARS-CoV-2 infection nor innate immune response in hMDM. Although, hMDM expressed angiotensin-converting enzyme 2, no or very low levels of transmembrane protease serine 2 were found. These results support the view that ADE may not be involved in the immunopathological processes associated with COVID-19, however, more studies are necessary to understand the potential contribution of antibodies-virus complexes with other cells expressing FcR receptors.

Histomorphological patterns of regional lymph nodes in COVID-19 lungs

HintergrundEine dysregulierte Immunantwort, z. B. in der Form eines Zytokinsturmes, einer Störung des Immunglobulinklassenwechsels, eines sog. antikörpervermitteltem Enhancements oder einer aberranten Antigenpräsentation wurde bereits in schweren Krankheitsverläufen von COVID-19 beschrieben.Ziel der ArbeitZur Charakterisierung der COVID-19-Immunantwort wurde die Histomorphologie der Lymphknoten des pulmonalen Abflussgebietes untersucht.Material und MethodenRegionale Lymphknoten des pulmonalen Abflussgebiets wurden bei COVID-19-Autopsien asserviert (n = 20). Deren Histomorphologie, SARS-CoV-2-qRT-PCR sowie Genexpressionsanalysen von gängigen Genen der Immunantwort wurden berücksichtigt.ErgebnisseHistologisch zeigten sich ein mäßig- bis schwergradiges Ödem mit Kapillarostase, eine erhöhte Anzahl von extrafollikulären Plasmablasten, milde bis mäßige Plasmazytose, vermehrte CD8+-T-Zellen und CD11c/CD68+-Histiozyten mit Hämophagozytoseaktivität. Von 20 Fällen wiesen 18 hypoplastische oder fehlende Keimzentren sowie eine Verminderung der follikulären dendritischen Zellen und follikulären T‑Helferzellen auf. In 14 von 20 Fällen war der qRT-PCR-Nachweis von SARS-CoV‑2 positiv, jedoch zeigte sich nur bei einem einzigen Fall eine immunhistochemische Positivität für SARS-CoV-2-N-Antigene in Sinushistiozyten. In Genexpressionsanalysen war eine erhöhte Expression von STAT1, CD163, Granzym B, CD8A, MZB1 und PAK1, neben CXCL9 zu beobachten.DiskussionDie Befunde in den Lymphknoten deuten auf eine dysregulierte Immunantwort bei schweren COVID-19-Krankheitsverläufen hin. Insbesondere impliziert das Ausbleiben der Keimzentrumsreaktion und die vermehrte Präsenz von Plasmablasten eine nur transiente B‑Zellreaktion, welche die Entwicklung einer Langzeitimmunität infrage stellt.

ACE2 Can Act as the Secondary Receptor in the FcγR-Dependent ADE of SARS-CoV-2

Currently, it is not clear whether antibody-mediated enhancement (ADE) is involved in the pathogenesis of COVID-19, and the occurrence condition for ADE needs to be elucidated. We demonstrated that different from the reported RBD-targeting neutralizing antibody XG005 which elicits an ACE2-independent ADE on Raji cells, neutralizing antibody CB6, mouse anti-S1 serum and convalescent plasma could not elicit ADE on Raji cells; instead, they could elicit ADE on cells with FcγRIIA/CD32A expression and small amount of endogenous ACE2. ADE occurred at sub-neutralizing antibody concentrations, and the maximum induction concentration of ADE was correlated with IC50, implying that part of unneutralized S protein is essential for ADE. The enhanced infectivity of 614G variant was higher than that of 614D wildtype in the presence of antibodies, further indicating that ADE may be influenced by the virus strains with different ACE2 binding affinity and infectivity. ADE was proved to be FcγRII-dependent, and knockdown of ACE2 or the application of fusion-inhibition peptide EK1C4 significantly impaired ADE. In conclusion, our results identified a novel ADE mechanism for neutralizing antibodies against SARS-CoV-2. In certain circumstance, ACE2 may act as the secondary receptor in the antibody and FcγR-mediated enhanced entry of SARS-CoV-2.Funding: This work is supported by National Key R&D Program of China (2020YFA0707600), Natural Science Foundation of China (82170015), Medical and Health Science Technology Innovation Project of Chinese Academy of Medical Sciences (2020-I2M-2-014), Project of BRC-BC (Biomedical Translational Engineering Research Center of BUCT-CJFH) (XK2020-09), Natural Science Foundation of China (82041011/H0104 & 81800002/H0101); Chinese Academy of Medical Sciences (CAMS) Innovation Fund for Medical Sciences (CIFMS 2018-I2M-1-003 & 2020-I2M-CoV19-005).Declaration of Interests: The authors declare no competing interests.Ethics Approval Statement: The plasma from convalescent patients were collected 6 months after their discharge, with informed consent signed by every patient. The procedures were approved by the Ethics Committee in China- Japan Friendship Hospital (Beijing, China), and complied with all relevant ethical regulations regarding human research.