Monoclonal #antibodies from #COVID19 convalescent #patients target cryptic epitopes for broad #SARS-CoV-2 #neutralization

 

Significance

The rapid emergence of SARS-CoV-2 variants that efficiently spread and evade antibody-based treatments underscores the need for countermeasures that remain effective as the virus evolves. In this study, two human mAbs, TAU-1109 and TAU-2310, isolated from individuals who recovered from SARS-CoV-2 infection early in the pandemic, neutralize all tested variants of concern, including recent Omicron sublineages. Structural and functional analyses show that these antibodies recognize conserved, cryptic regions on the spike’s RBD and disable the virus by destabilizing the spike trimer and triggering premature loss of the S1 subunit, thereby preventing cell entry. These findings reveal a naturally occurring, broadly protective antibody mechanism and highlight conserved surfaces on the receptor-binding domain as promising blueprints for next-generation COVID-19 therapies and vaccines.

Abstract

The COVID-19 pandemic, which has resulted in over seven million global fatalities, poses a substantial threat to public health and precipitated a global economic crisis. Emerging variants of concern (VOCs) with enhanced transmissibility and improved immune evasion may compromise the efficacy of current antiviral and immunotherapies, necessitating comprehensive investigations into the immune response to SARS-CoV-2. The conformational dynamics of the receptor binding domain in SARS-CoV-2 spike and the presentation of neutralizing antibody epitopes influence viral transmission and infection rates. In this study, we have identified highly conserved non-receptor-binding motif epitopes for two potent monoclonal antibodies (mAbs), TAU-1109 and TAU-2310, isolated from convalescent human patients, which contribute to the broad neutralizing activity of these mAbs against all the circulating VOCs, including the recently emerged Omicron subvariants. We employed high-resolution structural data in conjunction with systematic biochemical investigation to elucidate the neutralization mechanism of TAU-1109 and TAU-2310. The mechanism involves antibody-mediated destabilization of the spike trimer, resulting in the premature shedding of the S1 subunit and rendering the spike incapable of mediating host cell entry. The identification of conserved cryptic epitopes in our study advances the mechanistic understanding of immune response against SARS-CoV-2, providing alternative avenues for the development of universal therapeutic antibodies and vaccines to combat COVID-19.

Source: 

Link: https://www.pnas.org/doi/abs/10.1073/pnas.2523864123?af=R

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Three decades of #discovery: An overview of #Hendra virus, the original #Henipavirus

 

Abstract

Hendra virus (HeV) emerged in Australia in 1994, causing a devastating outbreak among horses in Brisbane with spread to humans, resulting in one death. This nonsegmented, negative-stranded RNA virus belongs to the family Paramyxoviridae and represents the first zoonotic paramyxovirus isolated from bats. Flying foxes (genus Pteropus) serve as the natural reservoir, with all four mainland Australian species carrying antibodies with no apparent disease. HeV initiates infection by binding ephrin-B2 receptors on vascular endothelial cells, driving characteristic pathology involving vasculitis, thrombosis, and neurological complications. Horses are amplifying hosts, shedding virus abundantly in respiratory secretions and posing transmission risks to humans during invasive procedures. To date, seven confirmed human infections have been documented, with a 57% fatality rate, presenting as severe respiratory disease or progressive encephalitis. Two genetic variants are now recognized: the original HeV genotype 1 and the emerging HeV genotype 2, identified in limited equine cases. Recent surveillance of bat roosts revealed substantial viral diversity, with peak shedding occurring during winter—coinciding with equine spillover peaks. Prevention integrates multiple strategies: the licensed equine vaccine Equivac which provides One Health protection for both horses and human contacts; biosecurity measures including proper PPE; and habitat restoration to reduce nutritional stress in bat populations. Emerging therapeutics include monoclonal antibodies, with m102.4 showing cross-protective activity against both HeV and the closely related Nipah virus. No licensed human vaccines currently exist, though candidates are in development. Future prevention strategies increasingly recognize the importance of Indigenous-led conservation approaches alongside biomedical interventions. This review will focus on the history of HeV, virus replication and diversity, epidemiology, clinical manifestations, diagnosis, treatment, prevention, as well as ecological and interdisciplinary countermeasures.

Author summary

Hendra virus (HeV) was first detected in 1994, with two outbreaks occurring within 2 months of that year. One was the index outbreak in the Brisbane suburb of Hendra, and the other was retrospectively diagnosed in the following year. This review examines the discoveries that have been made in the 30 years since its discovery.

Source: 

Link: https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014138

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Porcine #influenza #mAbs to #H3, #H5, and #H7 hemagglutinins recognize H3 egg adapted site and target the HA stem

 

Abstract

Introduction

Monoclonal antibodies (mAbs) are critical tools for elucidating viral evolution, informing vaccine design, and developing antiviral therapeutics. Large-animal models, such as the pig, that closely mirror human immune responses are essential for understanding influenza immunity.

Methods

Pigs were either infected or sequentially immunized with influenza viruses and monoclonal antibodies directed against H3, H5, and H7 influenza virus haemagglutinins were isolated. Antibody specificity, breadth, epitope targeting (head versus stem), neutralizing capacity, and Fc-mediated activity were assessed across influenza subtypes.

Results

Pigs generated both strain-specific and broadly reactive mAbs targeting haemagglutinin head and stem epitopes. An H3-specific mAb (H3–57) selectively recognized the egg-adapted L194P mutation associated with reduced human vaccine effectiveness. H5 and H7 immunization induced neutralizing antibodies, including cross-group stem mAbs reactive with H1, H3, and H5 haemagglutinins. Fc-mediated activity correlated with antibody binding strength rather than epitope location.

Conclusions

These findings demonstrate that pigs mount antibody responses closely resembling those observed in humans, including recognition of conserved stem epitopes and adaptive head mutations. Porcine mAbs represent powerful new tools for dissecting influenza immunity, guiding vaccine design, and enhancing pandemic preparedness using a physiologically relevant large-animal model.

Source: 

Link: https://academic.oup.com/discovimmunology/article/5/1/kyag006/8503709

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Prophylactic and therapeutic efficacy of #monoclonal #antibodies against #H5N1 #influenza virus

 

Highlights

• mAbs could enhance our armamentarium against H5N1 in support of pandemic preparedness

• Several mAbs have shown prophylactic and therapeutic efficacy against H5N1 in animal models

• Anti-IAV mAbs that have advanced in clinical trials could be evaluated against H5N1

• Resistance emergence during mAb treatment was infrequent in pre- and clinical studies

Abstract

Highly pathogenic avian influenza H5N1 continues to pose a serious zoonotic and pandemic threat due to its increasing cross-species transmission and high virulence in humans. Despite the availability of vaccines and antivirals for seasonal influenza, effective prophylactic and treatment options for H5N1 remain limited. Herein we explore the potential action of monoclonal antibodies (mAbs) against H5N1, focusing on those with demonstrated efficacy in animal models. Most of these mAbs target conserved hemagglutinin epitopes and function as broad neutralizing fusion/entry inhibitors; notably, CR9114 targets both groups 1 and 2 influenza A strains as well as B lineages. Other mAbs prevent viral release by targeting neuraminidase, and those directed against the M2 ectodomain and nucleoprotein function through Fc receptor-mediated pathways. These mAbs have shown robust protection against lethal H5N1 challenge in mice, ferrets, and/or non-human primates. Compounds such as CR6261, MEDI8852, and TCN-032 have been evaluated in clinical trials for seasonal influenza, yielding encouraging safety and pharmacokinetics results and notably, no reported emergence of resistance. Despite these positive results their clinical development was prematurely discontinued. Integrating these highly effective mAbs into our H5N1 pandemic preparedness arsenal is a logical next step to provide a robust prophylactic and therapeutic option at the early stages of an outbreak. Future efforts must address regulatory and logistical barriers, invest in stockpiling and emergency use protocols, and support adaptive clinical trial frameworks to ensure rapid deployment when needed.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S0924857926000737?via%3Dihub

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Potent efficacy of an NA-targeting #antibody against a broad spectrum of #H5N1 #influenza viruses

 

Abstract

For nearly 30 years, Goose/Guangdong-derived highly pathogenic avian influenza H5N1 viruses have posed significant risks to economic stability, food security, and public health. Virus evolution has resulted in various clades, including the panzootic subclade 2.3.4.4b, recognized for its pandemic potential. Here we present the potent in vitro activity of FNI9, a pan-influenza NA-inhibiting monoclonal antibody, against a range of pseudoparticles with NA spanning decades of H5N1 virus evolution. FNI9 also shows strong prophylactic protection in female mice against lethal challenges with H5N1 from clade 1 and 2.3.4.4b. Cryo-EM and molecular dynamics analysis reveal that FNI9 binds to 7 highly conserved H5N1 NA residues (R118, E119, D151, E228, E278, R293, and R368). In silico evolutionary escape profiling and machine learning predict low escapability, high fitness costs, and minimal spread likelihood for viral mutations that evade FNI9 binding. These findings support FNI9 broad protection and underscore the NA role in future influenza vaccine design.

Source: 

Link: https://www.nature.com/articles/s41467-026-70036-8

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Re-infection with #SARS-CoV-2 is associated with increased #antibody breadth and potency against diverse #sarbecovirus strains

 

ABSTRACT

The ease with which emerging SARS-CoV-2 variants escape neutralizing antibodies limits the protection afforded by a prior exposure, be it infection or vaccination. While rare, broadly neutralizing antibodies with activity toward diverse sarbecoviruses have been detected in convalescent serum. Motivated by findings that plasma responses show increased neutralization breadth and potency with continued antigen exposure, we isolated monoclonal antibodies (mAbs) after a SARS-CoV-2 re-infection and compared them to those isolated 1 year prior, after the first breakthrough infection. Among clonal lineage members identified at both time points, mAbs from the later time point showed improved neutralization potency and breadth. One mAb isolated after re-infection, C68.490, targets a conserved region in the receptor binding domain and shows remarkable activity not only against SARS-CoV-2 variants, but also diverse sarbecoviruses from more distant clades present in animal reservoirs. These findings suggest that a focus on individuals with diverse and repeated antigen exposure could lead to the identification of antibodies with therapeutic utility not just toward current and future SARS-CoV-2 variants, but also distant sarbecoviruses in the event of a future spillover.

Source: 

Link: https://journals.asm.org/doi/full/10.1128/mbio.03612-25?af=R

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Functional and #antigenic constraints on the #Nipah virus #fusion protein

 

Abstract

Nipah virus is a highly pathogenic virus in the family Paramyxoviridae that utilizes two distinct surface glycoproteins to infect cells. The receptor-binding protein (RBP) binds host receptors whereas the fusion protein (F) merges viral and host membranes. Here, we use nonreplicative pseudoviruses to safely measure the effects of all F single amino acid residue mutations on its cell entry function and neutralization by monoclonal antibodies. We compare mutational tolerance in F with previous experimental measurements for RBP and show that F is much more functionally constrained than the RBP. We also identify mutationally intolerant sites on the F trimer surface and core that are critical for proper function, and describe mutations that are candidates for stabilizing F in the prefusion conformation for vaccine design. We quantify how F mutations affect neutralization by six monoclonal antibodies, and show that the magnitude of mutational effects on neutralization varies among antibodies. Our measurements of mutational effects on Nipah virus F predict the ability of the antibodies to neutralize the related Hendra virus. Overall, our work defines the functional and antigenic constraints on the F protein from an important zoonotic virus.

Source: 

Link: https://www.pnas.org/doi/abs/10.1073/pnas.2529505123?af=R

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Decoding #antibody response to #MERS-CoV in wild dromedary #camels

 

Significance

Middle East respiratory syndrome coronavirus (MERS-CoV) remains the most lethal human coronavirus, with continued zoonotic transmission from wild naturally infected dromedary camels, posing a persistent risk of spillover to humans. Despite this ongoing threat, no specific antiviral treatment has been approved. In this study, we characterize the antibody response to MERS-CoV in naturally infected dromedaries, the primary animal reservoir, and identify a panel of nanobodies (Nbs) exhibiting potent neutralizing activity. These Nbs recognize a previously unreported binding and neutralizing site on the virus spike receptor-binding domain (RBD). Their distinctive genetic, structural, and functional properties make them promising candidates for the development of effective and therapeutic interventions against MERS-CoV, as strongly advocated by global health authorities.

Abstract

Wild dromedary camels in the Arabian Peninsula and Africa have harbored antibodies against Middle East Respiratory Syndrome Coronavirus (MERS-CoV) for decades, predating zoonotic spillover to humans. However, the potency, specificity, and structural characteristics of these antibodies remain poorly understood. Here, we characterize the antibody responses of naturally infected wild dromedary camels in Tunisia, a MERS-CoV-endemic region. Plasma antibodies from nine camels exhibited variable neutralizing activity, generally increasing with age, and were largely autologous, with minimal cross-reactivity to SARS-CoV-1 or SARS-CoV-2. From a VHH antibody library derived from the peripheral blood mononuclear cells (PBMCs) of a single camel (D17), we identified 34 unique sequences with previously unreported germline origins and unusually long complementarity-determining region 3 (CDR3) sequences. Eight representative VHHs, expressed as human Fc fusions, displayed high-affinity binding to the MERS-CoV receptor-binding domain (RBD) and broad neutralization to RBD mutants (IC50: 1.05 to 9.55 ng/mL). Crystal structural analysis revealed distinct neutralization mechanisms: VHH-227 fully blocked DPP4 binding, achieving complete neutralization, while VHH-T71, with partial neutralization (~80%), targeted the RBD core subdomain. This study provides comprehensive characterization of wild dromedary antibody responses, identifying novel nanobodies (Nbs) with broad and potent neutralization to naturally occurring RBD mutants. These findings offer insights into camel immunity and highlight promising candidates for MERS-CoV prophylactic and therapeutic development.

Source: 

Link: https://www.pnas.org/doi/10.1073/pnas.2513716123

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Broadly neutralizing monoclonal #antibodies against #influenza A viruses: current #insights and future directions

 

Abstract

Monoclonal antibodies (mAbs) have become attractive tools for both the treatment and prevention of influenza A viruses due to their ability to target several viral components, which confers broad therapeutic potential. Advances in biotechnology, such as hybridoma technology, phage display technology, B cell immortalization, and artificial intelligence (Al)-driven antibody design, have significantly accelerated the development of effective mAbs. Clinical trials have shown that mAbs can improve clinical outcomes particularly in high-risk and immunocompromised populations by lowering viral loads and reducing disease severity. However, high production costs, the need for intravenous administration, and the risk of viral escape mutations are some of the obstacles to widespread clinical adoption. Post-marketing surveillance serves as a valuable source of information regarding safety, real-world effectiveness, and patterns of resistance. Broadly neutralizing antibodies (bnAbs), particularly those directed against conserved regions of the virus’s surface proteins, such as hemagglutinin (HA) and neuraminidase (NA), have demonstrated efficacy against antigenic drift-derived variants. Nevertheless, the emergence of escape mutants underscores the need for careful monitoring of mAb candidates and combination therapy. Monitoring genomic shifts requires a careful focus on the targeted regions affected by combination therapy. Challenges in accessibility are compounded by financial barriers, emphasizing the importance of large-scale production and alternative delivery methods, such as inhaled mAbs. To ensure that future mAb-based therapies for influenza A are both effective and accessible, it is critical to integrate resistance surveillance tools, monitoring AI, and advanced computational modeling in therapeutic strategies. This comprehensive review discusses the potential of mAbs to enhance influenza A treatment by offering precise and adaptable alternatives to traditional antivirals. It also examines recent technological advances, clinical performance, and scalability that may redefine future therapeutic strategies.

Source: 

Link: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1738181/full

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#mRNA-delivered neutralizing #antibodies confer protection against #SARS-CoV-2 in animal #models

 

ABSTRACT

Monoclonal antibodies represent potent biological countermeasures against a wide range of human diseases; however, their clinical application and widespread use are limited by the high cost and complexity of antibody production and manufacturing. The mRNA-lipid nanoparticle (mRNA-LNP) platform offers a versatile strategy for vaccine development and protein-replacement therapies. Since the COVID-19 pandemic, a number of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-neutralizing antibodies have been identified, with several granted emergency use authorization for patients. Here, we report the design and generation of mRNA-LNPs encoding two SARS-CoV-2-neutralizing antibodies, 76E1 and LY1404, which, respectively, target the spike protein’s fusion peptide (FP) and receptor-binding domain (RBD). We demonstrated that a single intramuscular administration of these mRNA-LNPs in mice resulted in robust antibody production that sustained in circulation for 7–14 days. Furthermore, we evaluated protective effects of these mRNA-delivered antibodies in animal models and showed that a single IM dose of mRNA-LNPs encoding LY1404 or 76E1 conferred significant protection against multiple SARS-CoV-2 variants, including Omicron BQ.1 and Delta, in mice and hamsters. Collectively, these findings highlight the potential of mRNA-based antibody delivery for rapid prevention or treatment of pathogenic infections.

Source: 

Link: https://journals.asm.org/doi/full/10.1128/jvi.01897-25?af=R

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An ultrapotent #human #antibody neutralizes all maturation states of #Zika virus

 

Significance

Zika virus causes microcephaly in fetuses and no vaccines or therapeutics currently exist against it. Mature and immature flavivirus particles are infectious. Here, we showed the cryoelectron microscopy (cryoEM) structures of an ultrapotent A9E human antibody, complexed with both mature (mZIKV) and immature (immZIKV) Zika virus, and the antibody neutralization mechanism. One important characteristic is that Fab A9E can distort both mZIKV and ImmZIKV particle structures. Additionally, Fab A9E or IgG A9E LALA mutant can abolish or reduce the overall infection to myeloid cells when added to other infection enhancing antibody DV62.5:immZIKV complexes. Thus, antibody A9E represents a promising potential prophylactic and therapeutic candidate, as it is effective against all maturation states of Zika virus.

Abstract

Zika virus (ZIKV), a flavivirus, causes a range of clinical complications including microcephaly in human fetuses. Currently, there is no treatment or vaccine. Different maturation states (mature and immature forms) of flavivirus particles have been observed to be released from infected cells and are infectious. To understand how an ultrapotent human antibody (HMAb) A9E can neutralize these Zika particles, we determined the cryoEM structures of the A9E Fab fragment complexed with mature (mZIKV) and immature (immZIKV) ZIKV to 2.8Å and 7.5Å, respectively. A9E binds to an epitope spanning Domain I (EDI), EDIII, and their linker in an E protein protomer in both immZIKV and mZIKV particles. A9E generally inhibited prior to or during virus attachment to cells, via virus aggregation, distortion of virus particles and inhibition of receptor binding. ImmZIKV is particularly sensitive to structural distortion by Fab A9E. The primary mode of infection used by ImmZIKV is via antibody-dependent enhancement of infection (ADE)—the formation of virus complex with nonneutralizing or subneutralizing concentrations of antibodies, that leads to enhanced infection of Fcγ positive myeloid cells. IgG A9E, by itself displays poor ADE activity. When IgG LALA mutant or Fab A9E is added to other enhancing antibody (DV62.5):virus complexes, they can strongly reduce the overall ADE activity. This is likely due to their ability to distort virus particle structure, suggesting that HMAb A9E could be a potential prophylactic and therapeutic candidate against all maturation states of ZIKV.

Source: 

Link: https://www.pnas.org/doi/abs/10.1073/pnas.2502522122?af=R

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#Human monoclonal #antibodies that target clade 2.3.4.4b #H5N1 hemagglutinin

 

Abstract

The highly pathogenic avian influenza H5N1 virus clade 2.3.4.4b has been spreading globally since 2022, causing mortality and morbidity in domestic and wild birds, as well as in mammals, which underscores its potential to cause a pandemic. Here, we generate a panel of anti-hemagglutinin (HA) human monoclonal antibodies (mAbs) against the H5 protein of clade 2.3.4.4b. To develop human chimeric antibodies, H2L2 Harbor Mice®, which express human immunoglobulin germline genes, were immunized with H5 and N1 recombinant proteins from A/mallard/New York/22-008760-007- original/2022 H5N1 virus. Through hybridoma technology, sixteen fully human mAbs are generated, most of which show cross-reactivity against H5 proteins from different clade 2.3.4.4 virus variants. Fourteen out of the sixteen mAbs neutralize the virus in vitro. The mAbs with the strongest hemagglutination inhibition activity also demonstrate greater neutralizing capacity and show increased protective effects in vivo when administered prophylactically or therapeutically in a murine H5N1 challenge model. Using cryo-electron microscopy, we identify a cross-clonotype conserved motif that bound a hydrophobic groove on the head domain of H5 HA. Akin to mAbs against severe acute respiratory syndrome coronavirus 2 during the coronavirus 2019 pandemic, these mAbs could serve as treatments in case of a widespread H5N1 epidemic or pandemic.

Source: 

Link: https://www.nature.com/articles/s41467-025-66829-y

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Direct #airway delivery of a humanized anti - #H7N9 neutralizing #antibody broadly protects against divergent #H7 #influenza viruses in the mouse model

 

ABSTRACT

Passive administration of broadly neutralizing anti-influenza monoclonal antibodies (mAbs) before or after virus infection can prevent or alleviate disease. Unlike seasonal influenza, infection with zoonotic avian influenza viruses can lead to acute respiratory distress syndrome and high mortality in humans. Respiratory tract-targeting antibody delivery appears to be more clinically relevant and effective for zoonotic influenza treatment. In this study, the efficacy of an anti-H7N9 murine mAb 4B7 and its humanized form (chi4B7) against H7 subtype influenza viruses administered through the intranasal route was investigated in mice. 4B7 recognizes critical residues in the vestigial esterase domain and receptor-binding sites in the hemagglutinin of H7N9 virus. The antibody had cross-H7 binding, hemagglutination inhibition, and neutralizing activities. In particular, the dose of 4B7 required for prophylactic protection against H7N9 infection was significantly reduced in mice treated locally (intranasal) compared with those treated systemically (intraperitoneal). Intranasal delivery of the antibody also enhanced therapeutic efficacy against H7N9 infection compared to intraperitoneal administration. Chi4B7 generated by grafting the variable regions onto the human IgG1 backbone sustained cross-reactivity with different H7 viruses of the parental murine antibody. Airway-delivered chi4B7 provided broad prophylactic and therapeutic protection against divergent H7 viruses in mice. Moreover, intranasal administration of chi4B7 had a long effective prophylaxis window against H7N9 infection. Our results suggest that airway delivery of the humanized anti-H7 antibody is a favorable approach for broad-spectrum prophylaxis and therapy against the H7 subtype influenza.

Source: 

Link: https://journals.asm.org/doi/10.1128/jvi.01327-25

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#Evolution of #antibody cross-reactivity to #influenza #H5N1 #neuraminidase from an N2-specific germline

 

Highlights

• Human antibody HB420 cross-reacts with neuraminidases from H3N2 and H5N1

• HB420 engages the neuraminidase active site via a single Asp residue

• Germline HB420 is N2 specific but gains reactivity to N1 through somatic mutation

• HB420 provides in vivo protection against both H3N2 and H5N1

Summary

The ongoing spread of highly pathogenic avian influenza H5N1 clade 2.3.4.4b virus in animals and its occasional spillover to humans have raised concerns about a potential H5N1 pandemic. Although recent studies have shown that pre-existing human antibodies can recognize H5N1 neuraminidase, the molecular basis of how this cross-reactivity develops remains poorly understood. In this study, we used a phage display antibody library derived from 245 healthy donors to isolate an antibody, HB420, that cross-reacts with neuraminidases of human H3N2 and avian H5N1 clade 2.3.4.4b viruses and confers protection in vivo. Cryogenic electron microscopy analysis reveals that HB420 targets the neuraminidase active site by mimicking sialic acid binding through a single Asp residue. Furthermore, the inferred germline of HB420 is N2 specific but acquires cross-reactivity to H5N1 neuraminidase through somatic hypermutation. Overall, our findings provide insights into how neuraminidase antibody evolves breadth, which has important implications for the development of broadly protective influenza vaccines.

Source: Cell Host & Microbe, https://www.cell.com/cell-host-microbe/abstract/S1931-3128(25)00381-6?rss=yes

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Structural basis for a potent #human neutralizing #antibody targeting a conserved epitope on the #H7 #hemagglutinin head

 

Significance

The high-resolution cryo-EM structure indicates that the human antibody 6Y13 binds strongly to a conserved pan-H7 epitope on the hemagglutinin head, distinct from the receptor-binding site and lateral patch. However, 6Y13 can broadly neutralize H7 viruses, fully protect H7N9-infected mice, and potently block receptor binding through mechanisms, independent of Fc-mediated steric hindrance.

Abstract

Zoonotic H7N9 avian influenza virus infection remains a global concern because of its pandemic potential. Therefore, developing effective antibodies and vaccines against H7N9 is vital for preventing and controlling major outbreaks. Here, we isolated a human VH3-30 gene-encoded antibody, designated 6Y13, from a survivor of H7N9 infection. This antibody recognized the hemagglutinins (HAs) of the representative H7 subtype zoonotic viruses spanning two decades of antigenic evolution and potently neutralized epidemic H7N9 viruses in vitro. Moreover, 6Y13 conferred complete protection in mice against lethal H7N9 challenge in both prophylactic and therapeutic experiments. Structural analysis by cryoelectron microscopy indicated that 6Y13 binds to a unique conserved site on the HA head, distinct from the receptor-binding site and lateral patch. Nevertheless, 6Y13 efficiently blocked viral receptor binding without interfering with HA receptor binding, independent of Fc-mediated steric hindrance. Our findings provide a promising therapeutic candidate against pan-H7 subtype viruses and are beneficial for the design of H7 subtype influenza vaccine immunogens.

Source: Proceedings of the National Academy of Sciences of the United States of America, https://www.pnas.org/doi/10.1073/pnas.2503008122

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#Evolution of #antibody cross-reactivity to #influenza #H5N1 #neuraminidase from an N2-specific germline

 

Highlights

• Human antibody HB420 cross-reacts with neuraminidases from H3N2 and H5N1

• HB420 engages the neuraminidase active site via a single Asp residue

• Germline HB420 is N2 specific but gains reactivity to N1 through somatic mutation

• HB420 provides in vivo protection against both H3N2 and H5N1

Summary

The ongoing spread of highly pathogenic avian influenza H5N1 clade 2.3.4.4b virus in animals and its occasional spillover to humans have raised concerns about a potential H5N1 pandemic. Although recent studies have shown that pre-existing human antibodies can recognize H5N1 neuraminidase, the molecular basis of how this cross-reactivity develops remains poorly understood. In this study, we used a phage display antibody library derived from 245 healthy donors to isolate an antibody, HB420, that cross-reacts with neuraminidases of human H3N2 and avian H5N1 clade 2.3.4.4b viruses and confers protection in vivo. Cryogenic electron microscopy analysis reveals that HB420 targets the neuraminidase active site by mimicking sialic acid binding through a single Asp residue. Furthermore, the inferred germline of HB420 is N2 specific but acquires cross-reactivity to H5N1 neuraminidase through somatic hypermutation. Overall, our findings provide insights into how neuraminidase antibody evolves breadth, which has important implications for the development of broadly protective influenza vaccines.

Source: Cell Host & Microbe, https://www.sciencedirect.com/science/article/pii/S1931312825003816?via%3Dihub

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Cross-neutralizing and potent #human monoclonal #antibodies against historical and emerging #H5Nx #influenza viruses

Abstract

Highly pathogenic avian influenza H5Nx viruses are an emerging threat for global health, especially clade 2.3.4.4b H5N1 virus which causes panzootic infections. Here we describe the isolation and characterization of broadly cross-neutralizing monoclonal antibodies (mAbs) against diverse H5Nx viruses from individuals who received a monovalent H5N1 vaccine 15 years ago. By screening over 500 mAbs, we identified 5 mAbs that neutralized the majority of H5 clades including 2.3.4.4b and target three distinct conserved epitopes within the HA globular head. Cryo-electron microscopy structures of these mAbs in complex with HA, deep mutational scanning and neutralization escape studies define the sites of vulnerability of H5 HA. These mAbs mediated stronger prophylactic protection against clade 2.3.4.4b H5N1 infection in mice than the best-in-class mAb targeting the HA stem. Our study identified several highly potent broadly neutralizing H5 mAbs from humans that either alone or in combination provide a pragmatic pandemic preparedness option against the threat of panzootic H5N1 influenza.

Source: Nature Microbiology, https://www.nature.com/articles/s41564-025-02137-x

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#Childhood immunological #imprinting of cross-subtype #antibodies targeting the hemagglutinin head domain of #influenza viruses

 

Abstract

Influenza virus cross-subtype antibodies targeting the hemagglutinin (HA) head are rare. Here, we found that a large proportion of monoclonal antibodies (mAbs) isolated from individuals immunized with the 2021-22 seasonal influenza vaccine bound to an epitope on the HA head of both the H1N1 vaccine strain and H3N2 strains from the mid-1990s. These H1/H3 cross-reactive antibodies were also found in polyclonal sera, but only in samples from individuals born in the 1990s. Ferrets sequentially exposed to an H3N2 virus from the 1990s and a contemporary seasonal influenza vaccine produced the same type of H1/H3 cross-reactive antibodies. We found evidence that H1N1 viruses are currently evolving within the human population to abrogate the binding of these antibodies. Together, our study demonstrates how prior influenza virus exposures can influence the specificity of antibodies elicited by entirely different influenza virus subtypes, and how viruses evolve to escape these types of antibodies.

Competing Interest Statement

S.E.H. is a co-inventor on patents that describe the use of nucleoside-modified mRNA as a vaccine platform. S.E.H reports receiving consulting fees from Sanofi, Pfizer, Lumen, Novavax, and Merck. S.D.B. has consulted for Regeneron, Sanofi, Novartis, Genentech, Visterra, and Janssen on topics unrelated to this study, is a scientific co-founder of Immunera Inc., and owns stock in AbCellera Biologics Inc.

Funding Statement

This project has been funded with Federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under Contract No. 75N93021C00015 (S.E.H., S.D.B., I.A.W., A.B.W., S.S.L., E.T.M.).

Source: MedRxIV, https://www.medrxiv.org/content/10.1101/2025.09.24.25335646v1

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Broadly #Sarbecovirus-Neutralizing #Antibodies Induced by Ancestral #SARS-CoV-2 #Infection

 

Abstract

The COVID-19 pandemic, driven by SARS-CoV-2, continues to challenge global health due to emerging variants and the potential risk posed by related sarbecoviruses. Neutralizing antibodies targeting the spike (S) glycoprotein, particularly the receptor-binding domain (RBD), play a crucial role in viral neutralization and vaccine design. Although broadly neutralizing anti-RBD antibodies have been identified, the nature of cross-reactive humoral responses induced by natural infection with ancestral SARS-CoV-2 strains remains incompletely understood. Here, we isolated 105 S-specific monoclonal antibodies (mAbs) from individuals recovered from prototype SARS-CoV-2 infection. Of these, 30 mAbs cross-recognized SARS-CoV-1, including 25 RBD-directed mAbs, of which 12 displayed cross-neutralizing activity against both viruses. Among them, mAb 12C2 potently neutralized SARS-CoV-1 and multiple SARS-CoV-2 variants, likely through mechanisms that include inhibition of membrane fusion and potential destabilization of the S trimer. Cryo-electron microscopy revealed that 12C2 engages the outer face of the RBD, overlapping with the epitope recognized by the broadly neutralizing antibody S309 derived from SARS-CoV-1 convalescent. Collectively, these findings demonstrate that ancestral SARS-CoV-2 infection can elicit robust cross-neutralizing antibody responses and provide valuable insights for the design of broadly protective antibodies and vaccines.

Source: Viruses, https://www.mdpi.com/1999-4915/17/10/1285

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Non-neutralizing #antibodies to #influenza A #matrix-protein-2-ectodomain are broadly effective #therapeutics and resistant to viral escape mutations

 

Abstract

Influenza A viruses remain a global health threat, yet no universal antibody therapy exists. Clinical programs have centered on neutralizing mAbs, only to be thwarted by strain specificity and rapid viral escape. We instead engineered three non-neutralizing IgG2a mAbs that target distinct, overlapping epitopes within the conserved N terminus of the M2 ectodomain (M2e). Combined at low dose, this “triple M2e-mAb” confers robust prophylactic and therapeutic protection in mice challenged with diverse human and zoonotic IAV strains, including highly pathogenic variants. Therapeutic efficacy depends on Fc-mediated effector activity via FcγRI, FcγRIII, and FcγRIV, rather than in vitro neutralization. Serial passaging in triple M2e-mAb–treated immunocompetent and immunodeficient hosts failed to generate viral escape mutants. Our findings redefine the influenza-specific antibody therapeutic design and support Fc-optimized, non-neutralizing M2e-mAbs as a broadly effective, mutation-resistant, off-the-shelve therapy with direct relevance to human pandemic preparedness.

Source: Science Advances, https://www.science.org/doi/10.1126/sciadv.adx3505

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