A broadly protective human monoclonal antibody targeting the sialidase activity of influenza A and B virus neuraminidases

Identification of a seasonal influenza vaccine-induced broadly protective neuraminidase antibody

Seasonal influenza viruses cause significant global illness and death annually, and the potential spillover of avian H5N1 poses a serious pandemic threat. Traditional influenza vaccines target the variable hemagglutinin (HA) protein, necessitating annual vaccine updates, while the slower-evolving neuraminidase (NA) presents a promising target for broader protection. We investigated the breadth of anti-NA B cell responses to seasonal influenza vaccination in humans. We screened plasmablast-derived monoclonal antibodies (mAbs) from three donors, identifying 11 clonally distinct NA mAbs from 268 vaccine-specific mAbs. Among these, mAb-297 showed exceptionally broad NA inhibition, effectively protecting mice against lethal doses of influenza A and B viruses, including H5N1. We show that mAb-297 targets a common binding motif in the conserved NA active site. Our findings show that while B cell responses against NA following conventional, egg-derived influenza vaccines are rare, inducing broadly protective NA antibodies through such vaccination remains feasible, highlighting the importance of improving NA immunogens to develop a more broadly protective influenza vaccine.

Fluorescence-barcoded cell lines stably expressing membrane-anchored influenza neuraminidases

The discovery of broadly protective antibodies to the influenza virus neuraminidase (NA) has raised interest in NA as a vaccine target. However, recombinant, solubilized tetrameric NA ectodomains are often challenging to express and isolate, hindering the study of anti-NA humoral responses. To address this obstacle, we established a panel of 22 non-adherent cell lines stably expressing native, historical N1, N2, N3, N9, and NB NAs anchored on the cell surface. The cell lines are barcoded with fluorescent proteins, enabling high-throughput, 16-plex analyses of antibody binding with commonly available flow cytometers. The cell lines were at least as efficient as a Luminex multiplex binding assay at identifying NA antibodies from a library of unselected clonal IgGs derived from human memory B cells. The cell lines were also useful for measuring the magnitude and breadth of the serum antibody response elicited by experimental infection of rhesus macaques with influenza virus. The membrane-anchored NAs are catalytically active and are compatible with established sialidase activity assays. NA-expressing K530 cell lines therefore represent a useful tool for studying NA immunity and evaluating influenza vaccine efficacy.

A monoclonal anti-hemagglutinin stem antibody modified with zanamivir protects against both influenza A and B viruses

Influenza remains a significant public health threat. Both monoclonal antibodies and small-molecule inhibitors can target the influenza surface glycoproteins hemagglutinin (HA) or neuraminidase (NA) for prevention and treatment of influenza. Here, we combine the strengths of anti-influenza antibodies and small molecules by site-specific conjugation of the NA inhibitor zanamivir to MEDI8852, an HA-specific fully human monoclonal antibody. MEDI8852 targets the conserved stem region of HA and inhibits HA-mediated fusion of the viral and host cell membranes. Elimination of virus-infected cells involves Fcγ receptor-mediated effector functions. The efficacy of MEDI8852 is limited to influenza A viruses. Zanamivir, on the other hand, binds to the active site of NA in both influenza A and B viruses to inhibit NA activity and virus release. However, because of its small size, zanamivir has a short half-life and requires repeated dosing at high concentrations. We produced a MEDI8852-zanamivir antibody-drug conjugate (ADC) that engages Fc-mediated effector functions and benefits from neonatal Fc receptor (FcRn)-mediated recycling. The MEDI8852-zanamivir conjugate extends the circulatory half-life of zanamivir, targets both influenza HA and NA, and shows enhanced antibody-dependent cellular cytotoxicity (ADCC) compared to MEDI8852 alone. The MEDI8852-zanamivir conjugate protected mice from a lethal (10 × LD50) challenge with influenza A and B viruses at a dose similar to that required for broadly neutralizing anti-NA antibodies, with the added advantage of simultaneously targeting NA (influenza A and B) and HA (influenza A).

How to manage antivirals in critically ill patients with influenza?

BACKGROUND

Influenza is a significant cause of morbidity and mortality, particularly in critically ill patients. The availability of effective antiviral therapies is pivotal in mitigating the severity and complications associated with influenza.

OBJECTIVES

This review evaluates the antivirals available for the treatment of severe influenza in critically ill patients, focusing on the strength of recommendations and levels of evidence derived from clinical trials, observational studies, and guidelines. The aim is to provide clinicians with evidence-based insights to optimize antiviral strategies in the intensive care unit setting.

SOURCES

A comprehensive literature search was conducted using PubMed, Embase, and Cochrane Library databases for studies published up to January 2025. Keywords included "antiviral therapy," "influenza," "critically ill patients," "oseltamivir," "peramivir," "zanamivir," "lanimavir," "baloxavir," and "favipiravir." Additional references were identified from the bibliographies of relevant articles.

CONTENT

The following topics are covered: antivirals available for treating influenza and evidence supporting their use in critically ill patients, pharmacokinetic issues of enteral oseltamivir administration in critically ill patients, and neuraminidase inhibitors resistance.

IMPLICATIONS

Neuraminidase inhibitors constitute the vast majority of antivirals currently prescribed for influenza. The most commonly prescribed neuraminidase inhibitor to date is oseltamivir. Although its efficacy in nonsevere cases of influenza is well established, the evidence for its efficacy in critically ill patients is based on less robust studies, as no randomized controlled trials have been conducted in this population. Limited data on oseltamivir pharmacokinetics is available in critically ill patients. The selection of A(H1N1)pdm09 resistant variants to oseltamivir is particularly problematic in critically ill patients hospitalized in intensive care units. Data on other antivirals, such as neuraminidase inhibitors (i.e. zanamivir, peramivir and laninamivir) or baloxavir marboxil in critically ill patients are scarce. Further research is needed to develop new drugs and assess their efficacy in critically ill patients and to better assess the effect of oseltamivir in this population.

Drug-Fc conjugate CD388 targets influenza virus neuraminidase and is broadly protective in mice

The ability of influenza virus to undergo rapid antigenic shift to elude humoral immunity highlights the need for effective broad-spectrum influenza antivirals for treatment, prophylaxis and pandemic preparedness. Strategies providing durable, universal influenza protection in healthy and high-risk populations are urgently needed. Here we describe the design and preclinical characterization of CD388, a first-in-class antiviral drug-Fc conjugate (DFC), in mice and cynomolgus macaques. CD388 comprises a multivalent conjugate of the influenza virus neuraminidase inhibitor zanamivir, linked to a CH1-Fc hybrid domain of human IgG1 engineered for extended half-life. CD388 improves the antiviral activity of zanamivir, demonstrating potent, universal activity across influenza A and B viruses, including high pathogenicity and neuraminidase inhibitor resistant strains, a low potential for resistance development and potent efficacy in lethal mouse infection models. These results suggest that CD388 has the potential for universal prevention of influenza A and B in healthy and high-risk populations.

Rapid Quantification of Neuraminidase Activity by MALDI-TOF MS via On-Target Labeling of Its Substrate and Product

Neuraminidase (NA) is a kind of glycoside hydrolase enzyme, functioning to remove terminal sialic acid (Sia) from glycans which are located on the cell surface. NA plays an essential role in cell interactions with ligands, microbes, and other cells during physiological and pathological processes. Additionally, NA is a major target for developing anti-influenza drugs and influenza vaccines. Herein, a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) based method to quantify NA activity is demonstrated for the first time. A reactive matrix 2-hydrazinoquinoline (2-HQ) is used to on-target label the natural substrate (3-sialyllactose, 3'-SL) and its enzymatic product (Sia). The derivatization enhances the ionization efficiency of 3'-SL and Sia, especially in negative ion detection mode. Moreover, the lactose ion signals and noise are significantly suppressed. Consequently, NA activity in influenza vaccines has been successfully quantified by comparing the relative intensity of 2-HQ derivatized Sia and 3'-SL in the absence of an additional internal standard. Moreover, the inhibition efficiencies of NA inhibitors have also been measured. Due to its operating simplicity, high-throughput capacity, and quantification accuracy, the proposed method has potential to be applied for the detection of different kinds of NA activity to reveal the role of NA in immunity, vaccine, and infection processes.

Antiviral strategies against influenza virus: an update on approved and innovative therapeutic approaches

Influenza viruses still represent a great concern for Public Health by causing yearly seasonal epidemics and occasionally worldwide pandemics. Moreover, spillover events at the animal-human interface are becoming more frequent nowadays, also involving animal species not previously found as reservoirs. To restrict the effects of influenza virus epidemics, especially in at-risk population, and to prepare a drug arsenal for possible future pandemics, researchers worldwide have been working on the development of antiviral strategies since the 80's of the last century. One of the main obstacles is the considerable genomic variability of influenza viruses, which constantly poses the issues of drug-resistance emergence and immune evasion. This review summarizes the approved therapeutics for clinical management of influenza, promising new anti-flu compounds and monoclonal antibodies currently undergoing clinical evaluation, and molecules with efficacy against influenza virus in preclinical studies. Moreover, we discuss some innovative anti-influenza therapeutic approaches such as combination therapies and targeted protein degradation. Given the limited number of drugs approved for influenza treatment, there is a still strong need for novel potent anti-influenza drugs endowed with a high barrier to drug resistance and broad-spectrum activity against influenza viruses of animal origin that may be responsible of future large outbreaks and pandemics.

Pre-exposure antibody prophylaxis protects macaques from severe influenza

Influenza virus pandemics and seasonal epidemics have claimed countless lives. Recurrent zoonotic spillovers of influenza viruses with pandemic potential underscore the need for effective countermeasures. In this study, we show that pre-exposure prophylaxis with broadly neutralizing antibody (bnAb) MEDI8852 is highly effective in protecting cynomolgus macaques from severe disease caused by aerosolized highly pathogenic avian influenza H5N1 virus infection. Protection was antibody dose-dependent yet independent of Fc-mediated effector functions at the dose tested. Macaques receiving MEDI8852 at 10 milligrams per kilogram or higher had negligible impairment of respiratory function after infection, whereas control animals were not protected from severe disease and fatality. Given the breadth of MEDI8852 and other bnAbs, we anticipate that protection from unforeseen pandemic influenza A viruses is achievable.

Identification of a broad-inhibition influenza neuraminidase antibody from pre-existing memory B cells

Identifying broadly reactive B precursor cells and conserved epitopes is crucial for developing a universal flu vaccine. In this study, using influenza neuraminidase (NA) mutant probes, we find that human pre-existing NA-specific memory B cells (MBCs) account for ∼0.25% of total MBCs, which are heterogeneous and dominated by class-unswitched MBCs. In addition, we identify three NA broad-inhibition monoclonal antibodies (mAbs) (BImAbs) that block the activity of NA derived from different influenza strains, including the recent cow H5N1. The cryoelectron microscopy (cryo-EM) structure shows that the BImAb targets the conserved NA enzymatic pocket and a separate epitope in the neighboring NA monomer. Furthermore, the NA BImAbs protect mice from the lethal challenge of the human pandemic H1N1 and H5N1. Our work demonstrates that the NA broad-inhibition precursor MBCs exist in healthy adults and could be targeted by the NA-based universal flu vaccine.

Fluorescence-barcoded cell lines stably expressing membrane-anchored influenza neuraminidases

The discovery of broadly protective antibodies to the influenza virus neuraminidase (NA) has raised interest in NA as a vaccine target. However, recombinant, solubilized tetrameric NA ectodomains are often challenging to express and isolate, hindering the study of anti-NA humoral responses. To address this obstacle, we established a panel of 22 non-adherent cell lines stably expressing native, historical N1, N2, N3, N9, and NB NAs anchored on the cell surface. The cell lines are barcoded with fluorescent proteins, enabling high-throughput, 16-plex analyses of antibody binding with commonly available flow cytometers. The cell lines were at least as efficient as a Luminex multiplex binding assay at identifying NA antibodies from a library of unselected clonal IgGs derived from human memory B cells. The membrane-anchored NAs are catalytically active and are compatible with established small-molecule catalytic activity assays. NA-expressing K530 cell lines therefore represent a useful tool for studying NA immunity and evaluating influenza vaccine efficacy.

Structural Convergence and Water-Mediated Substrate Mimicry Enable Broad Neuraminidase Inhibition by Human Antibodies

Influenza has been responsible for multiple global pandemics and seasonal epidemics and claimed millions of lives. The imminent threat of a panzootic outbreak of avian influenza H5N1 virus underscores the urgent need for pandemic preparedness and effective countermeasures, including monoclonal antibodies (mAbs). Here, we characterize human mAbs that target the highly conserved catalytic site of viral neuraminidase (NA), termed NCS mAbs, and the molecular basis of their broad specificity. Cross-reactive NA-specific B cells were isolated by using stabilized NA probes of non-circulating subtypes. We found that NCS mAbs recognized multiple NAs of influenza A as well as influenza B NAs and conferred prophylactic protections in mice against H1N1, H5N1, and influenza B viruses. Cryo-electron microscopy structures of two NCS mAbs revealed that they rely on structural mimicry of sialic acid, the substrate of NA, by coordinating not only amino acid side chains but also water molecules, enabling inhibition of NA activity across multiple influenza A and B viruses, including avian influenza H5N1 clade 2.3.4.4b viruses. Our results provide a molecular basis for the broad reactivity and inhibitory activity of NCS mAbs targeting the catalytic site of NA through substrate mimicry.

Broad-Spectrum Engineered Multivalent Nanobodies Against SARS-CoV-1/2

SARS-CoV-2 Omicron sublineages escape most preclinical/clinical neutralizing antibodies in development, suggesting that previously employed antibody screening strategies are not well suited to counteract the rapid mutation of SARS-CoV-2. Therefore, there is an urgent need to screen better broad-spectrum neutralizing antibody. In this study, a comprehensive approach to design broad-spectrum inhibitors against both SARS-CoV-1 and SARS-CoV-2 by leveraging the structural diversity of nanobodies is proposed. This includes the de novo design of a fully human nanobody library and the camel immunization-based nanobody library, both targeting conserved epitopes, as well as the development of multivalent nanobodies that bind nonoverlapping epitopes. The results show that trivale B11-E8-F3, three nanobodies joined tandemly in trivalent form, have the broadest spectrum and efficient neutralization activity, which spans from SARS-CoV-1 to SARS-CoV-2 variants. It is also demonstrated that B11-E8-F3 has a very prominent preventive and some therapeutic effect in animal models of three authentic viruses. Therefore, B11-E8-F3 has an outstanding advantage in preventing SARS-CoV-1/SARS-CoV-2 infections, especially in immunocompromised populations or elderly people with high-risk comorbidities.

A recombinant N2 neuraminidase-based CpG 1018® adjuvanted vaccine provides protection against challenge with heterologous influenza viruses in mice and hamsters

Recombinant influenza virus neuraminidase (NA) is a promising broadly protective influenza vaccine candidate. However, the recombinant protein alone is not sufficient to induce durable and protective immune responses and requires the coadministration of immunostimulatory molecules. Here, we evaluated the immunogenicity and cross-protective potential of a recombinant influenza virus N2 neuraminidase vaccine construct, adjuvanted with a toll-like receptor 9 (TLR9) agonist (CpG 1018® adjuvant), and alum. The combination of CpG 1018 adjuvant and alum induced a balanced and robust humoral and T-cellular immune response against the NA, which provided protection and reduced morbidity against homologous and heterologous viral challenges in mouse and hamster models. This study supports Syrian hamsters as a useful complementary animal model to mice for pre-clinical evaluation of influenza virus vaccines.

A human monoclonal antibody targeting the monomeric N6 neuraminidase confers protection against avian H5N6 influenza virus infection

The influenza neuraminidase (NA) is a potential target for the development of a next-generation influenza vaccine, but its antigenicity is not well understood. Here, we isolate an anti-N6 human monoclonal antibody, named 18_14D, from an H5N6 avian influenza virus (AIV) infected patient. The antibody weakly inhibits enzymatic activity but confers protection in female mice, mainly via ADCC function. The cryo-EM structure shows that 18_14D binds to a unique epitope on the lateral surface of the N6 tetramer, preventing the formation of tightly closed NA tetramers. These findings contribute to the molecular understanding of protective immune responses to NA of AIVs in humans and open an avenue for the rational design of NA-based vaccines.

Dual neutralization of influenza virus hemagglutinin and neuraminidase by a bispecific antibody leads to improved antiviral activity

Targeting multiple viral proteins is pivotal for sustained suppression of highly mutable viruses. In recent years, broadly neutralizing antibodies that target the influenza virus hemagglutinin and neuraminidase glycoproteins have been developed, and antibody monotherapy has been tested in preclinical and clinical studies to treat or prevent influenza virus infection. However, the impact of dual neutralization of the hemagglutinin and neuraminidase on the course of infection, as well as its therapeutic potential, has not been thoroughly tested. For this purpose, we generated a bispecific antibody that neutralizes both the hemagglutinin and the neuraminidase of influenza viruses. We demonstrated that this bispecific antibody has a dual-antiviral activity as it blocks infection and prevents the release of progeny viruses from the infected cells. We show that dual neutralization of the hemagglutinin and the neuraminidase by a bispecific antibody is advantageous over monoclonal antibody combination as it resulted an improved neutralization capacity and augmented the antibody effector functions. Notably, the bispecific antibody showed enhanced antiviral activity in influenza virus-infected mice, reduced mice mortality, and limited the virus mutation profile upon antibody administration. Thus, dual neutralization of the hemagglutinin and neuraminidase could be effective in controlling influenza virus infection.

Mosaic neuraminidase-based vaccine induces antigen-specific T cell responses against homologous and heterologous influenza viruses

Seasonal influenza is an annually severe crisis for global public health, and an ideal influenza vaccine is expected to provide broad protection against constantly drifted strains. Compared to highly flexible hemagglutinin (HA), increasing data have demonstrated that neuraminidase (NA) might be a potential target against influenza variants. In the present study, a series of genetic algorithm-based mosaic NA were designed, and then cloned into recombinant DNA and replication-defective Vesicular Stomatitis Virus (VSV) vector as a novel influenza vaccine candidate. Our Results showed that DNA prime/VSV boost strategy elicited a robust NA-specific Th1-dominated immune response, but the traditional inactivated influenza vaccine elicited a Th2-dominated immune response. More importantly, the superior NA-specific immunity induced by our strategy could confer both a full protection against lethal homologous influenza challenge and a partial protection against heterologous influenza infection. These findings will provide insights on designing NA-based universal vaccine strategy against influenza variants.

Isolation of human antibodies against influenza B neuraminidase and mechanisms of protection at the airway interface

Influenza B viruses (IBVs) comprise a substantial portion of the circulating seasonal human influenza viruses. Here, we describe the isolation of human monoclonal antibodies (mAbs) that recognized the IBV neuraminidase (NA) glycoprotein from an individual following seasonal vaccination. Competition-binding experiments suggested the antibodies recognized two major antigenic sites. One group, which included mAb FluB-393, broadly inhibited IBV NA sialidase activity, protected prophylactically in vivo, and bound to the lateral corner of NA. The second group contained an active site mAb, FluB-400, that broadly inhibited IBV NA sialidase activity and virus replication in vitro in primary human respiratory epithelial cell cultures and protected against IBV in vivo when administered systemically or intranasally. Overall, the findings described here shape our mechanistic understanding of the human immune response to the IBV NA glycoprotein through the demonstration of two mAb delivery routes for protection against IBV and the identification of potential IBV therapeutic candidates.

Development and characterization of an antibody that recognizes influenza virus N1 neuraminidases

Influenza A viruses (IAVs) continue to pose a huge threat to public health, and their prevention and treatment remain major international issues. Neuraminidase (NA) is the second most abundant surface glycoprotein on influenza viruses, and antibodies to NA have been shown to be effective against influenza infection. In this study, we generated a monoclonal antibody (mAb), named FNA1, directed toward N1 NAs. FNA1 reacted with H1N1 and H5N1 NA, but failed to react with the NA proteins of H3N2 and H7N9. In vitro, FNA1 displayed potent antiviral activity that mediated both NA inhibition (NI) and blocking of pseudovirus release. Moreover, residues 219, 254, 358, and 388 in the NA protein were critical for FNA1 binding to H1N1 NA. However, further validation is necessary to confirm whether FNA1 mAb is indeed a good inhibitor against NA for application against H1N1 and H5N1 viruses.

Preclinical animal models to evaluate therapeutic antiviral antibodies

Despite the availability of effective preventative vaccines and potent small-molecule antiviral drugs, effective non-toxic prophylactic and therapeutic measures are still lacking for many viruses. The use of monoclonal and polyclonal antibodies in an antiviral context could fill this gap and provide effective virus-specific medical interventions. In order to develop these therapeutic antibodies, preclinical animal models are of utmost importance. Due to the variability in viral pathogenesis, immunity and overall characteristics, the most representative animal model for human viral infection differs between virus species. Therefore, throughout the years researchers sought to find the ideal preclinical animal model for each virus. The most used animal models in preclinical research include rodents (mice, ferrets, …) and non-human primates (macaques, chimpanzee, ….). Currently, antibodies are tested for antiviral efficacy against a variety of viruses including different hepatitis viruses, human immunodeficiency virus (HIV), influenza viruses, respiratory syncytial virus (RSV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and rabies virus. This review provides an overview of the current knowledge about the preclinical animal models that are used for the evaluation of therapeutic antibodies for the abovementioned viruses.

Protective human monoclonal antibodies target conserved sites of vulnerability on the underside of influenza virus neuraminidase

Continuously evolving influenza viruses cause seasonal epidemics and pose global pandemic threats. Although viral neuraminidase (NA) is an effective drug and vaccine target, our understanding of the NA antigenic landscape still remains incomplete. Here, we describe NA-specific human antibodies that target the underside of the NA globular head domain, inhibit viral propagation of a wide range of human H3N2, swine-origin variant H3N2, and H2N2 viruses, and confer both pre- and post-exposure protection against lethal H3N2 infection in mice. Cryo-EM structures of two such antibodies in complex with NA reveal non-overlapping epitopes covering the underside of the NA head. These sites are highly conserved among N2 NAs yet inaccessible unless the NA head tilts or dissociates. Our findings help guide the development of effective countermeasures against ever-changing influenza viruses by identifying hidden conserved sites of vulnerability on the NA underside.

Anti-neuraminidase immunity in the combat against influenza

INTRODUCTION

Anti-neuraminidase (NA) immunity correlates with the protection against influenza virus infection in both human and animal models. The aim of this review is to better understand the mechanism of anti-NA immunity, and also to evaluate the approaches on developing NA-based influenza vaccines or enhancing immune responses against NA for current influenza vaccines.

AREAS COVERED

In this review, the structure of influenza neuraminidase, the contribution of anti-NA immunity to protection, as well as the efforts and challenges of targeting the immune responses to NA were discussed. We also listed some of the newly discovered anti-NA monoclonal antibodies and discussed their contribution in therapeutic as well as the antigen design of a broadly protective NA vaccine.

EXPERT OPINION

Targeting the immune response to both HA and NA may be critical for achieving the optimal protection since there are different mechanisms of HA and NA elicited protective immunity. Monoclonal antibodies (mAbs) that target the conserved protective lateral face or catalytic sites are effective therapeutics. The epitope discovery using monoclonal antibodies may benefit NA-based vaccine elicited broadly reactive antibody responses. Therefore, the potential for a vaccine that elicits cross-reactive antibodies against neuraminidase is a high priority for next-generation influenza vaccines.

Influenza B virus neuraminidase: a potential target for next-generation vaccines?

INTRODUCTION

Influenza B viruses (IBV) cause a significant health and economic burden annually. Due to lower antigenic drift rate, less extensive antigenic diversity, and lack of animal reservoirs, the development of highly effective universal vaccines against IBV might be in reach. Current seasonal influenza vaccines are formulated to induce antibodies against the Hemagglutinin (HA) protein, but their effectiveness is reduced by mismatch between vaccine and circulating strains.

AREAS COVERED

Given antibodies against the Neuraminidase (NA) have been associated with protection during influenza infection, there is considerable interest in the development of NA-based influenza vaccines. This review summarizes insights into the role of NA-based immunity against IBV and highlights knowledge gaps that should be addressed to inform the design of next-generation influenza B vaccines. We discuss how antibodies recognize broadly cross-reactive epitopes on the NA and the lack of understanding of IBV NA antigenic evolution which would benefit vaccine development in the future.

EXPERT OPINION

Demonstrating NA antibodies as correlates of protection for IBV in humans would be paramount. Determining the extent of IBV NA antigenic evolution will be informative. Finally, it will be critical to determine optimal strategies for incorporating the appropriate NA antigens in existing clinically approved vaccine formulations.

Chicken dendritic cell-targeting nanobodies mediated improved protective effects against H9N2 influenza virus challenge in a homologous sequential immunization study

Global poultry production is still severely affected by H9N2 avian influenza virus (AIV), and the development of a novel universal AIV vaccine is still urgently needed. Neuraminidase (NA) has recently been shown to be an efficient conserved protective antigen. In this study, we fused the extracellular region of the NA gene with a ferritin cassette (pYL281), which resulted in self-assembled 24-mer nanoparticles with the NA protein displayed outside the nanoparticles. In addition, a chicken dendritic cell-targeting nanobody-phage74 was also inserted ahead of the NA protein to yield pYL294. Incubation with chicken bone marrow-derived dendritic cells (chBMDCs) showed that the DC-targeting nanoparticles purified from the pYL294 strain significantly increased the maturation of chBMDCs, as shown by increased levels of CCL5, CCR7, CD83 and CD86 compared with nontargeting proteins. Then, a chicken study was performed using Salmonella oral administration together with intranasal boost with purified proteins. Compared with the other groups, oral immunization with Salmonella harboring pYL294 followed by intranasal boost with purified DC-targeting nanoparticles dramatically increased the humoral IgY and mucosal IgA antibody response, as well as increased the cellular immune response, as shown by elevated splenic lymphocyte proliferation and intracellular mRNA levels of IL-4 and IFN-γ. Finally, sequential immunization with DC-targeting nanoparticles showed increased protection against G57 subtype H9N2 virus challenge compared with other groups, as shown by significantly decreased virus RNA copy numbers in oropharyngeal washes (Days 3, 5 and 7 post challenge) and cloacal washes (Day 7), significantly decreased lung virus titers on Day 5 post challenge and increased body weight gains during the challenge.

New insights into the neuraminidase-mediated hemagglutination activity of influenza A(H3N2) viruses

Influenza virus neuraminidase (NA) can act as a receptor-binding protein, a role commonly attributed to hemagglutinin (HA). In influenza A(H3N2) viruses, three NA amino acid residues have previously been associated with NA-mediated hemagglutination: T148, D151, and more recently, H150. These residues are part of the 150-loop of the NA monomer. Substitutions at 148 and 151 arise from virus propagation in laboratory cell cultures, whereas changes at 150 occurred during virus evolution in the human host. In this study, we examined the effect of natural amino acid polymorphism at position 150 on NA-mediated hemagglutination. Using the A/Puerto Rico/8/34 backbone, we generated a comprehensive panel of recombinant A(H3N2) viruses that have different NAs but shared an HA that displays poor binding to red blood cells (RBCs). None of the tested substitutions at 150 (C, H, L, R, and S) promoted NA-binding. However, we identified two new determinants of NA-binding, Q136K and T439R, that emerged during virus culturing. Similar to T148I, both Q136K and T439R reduced NA enzyme activity by 48-86% and inhibition (14- to 173-fold) by the NA inhibitor zanamivir. NA-binding was observed when a virus preparation contained approximately 10% of NA variants with either T148I or T439R, highlighting the benefit of using deep sequencing in virus characterization. Taken together, our findings provide new insights into the molecular mechanisms underlying the ability of NA to function as a binding protein. Information gained may aid in the design of new and improved NA-targeting antivirals.

Antiviral susceptibility of clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) viruses isolated from birds and mammals in the United States, 2022

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) A(H5N1) viruses that are responsible for devastating outbreaks in birds and mammals pose a potential threat to public health. Here, we evaluated their susceptibility to influenza antivirals. Of 1,015 sequences of HPAI A(H5N1) viruses collected in the United States during 2022, eight viruses (∼0.8%) had a molecular marker of drug resistance to an FDA-approved antiviral: three adamantane-resistant (M2-V27A), four oseltamivir-resistant (NA-H275Y), and one baloxavir-resistant (PA-I38T). Additionally, 31 viruses contained mutations that may reduce susceptibility to inhibitors of neuraminidase (NA) (n = 20) or cap-dependent endonuclease (CEN) (n = 11). A panel of 22 representative viruses was tested phenotypically. Overall, clade 2.3.4.4b A(H5N1) viruses lacking recognized resistance mutations were susceptible to FDA-approved antivirals. Oseltamivir was least potent at inhibiting NA activity, while the investigational NA inhibitor AV5080 was most potent, including against NA mutants. A novel NA substitution T438N conferred 12-fold reduced inhibition by zanamivir, and in combination with the known marker N295S, synergistically affected susceptibility to all five NA inhibitors. In cell culture-based assays HINT and IRINA, the PA-I38T virus displayed 75- to 108-fold and 37- to 78-fold reduced susceptibility to CEN inhibitors, baloxavir and the investigational AV5116, respectively. Viruses with PA-I38M or PA-A37T showed 5- to 10-fold reduced susceptibilities. As HPAI A(H5N1) viruses continue to circulate and evolve, close monitoring of drug susceptibility is needed for risk assessment and to inform decisions regarding antiviral stockpiling.

A pan-influenza antibody inhibiting neuraminidase via receptor mimicry

Rapidly evolving influenza A viruses (IAVs) and influenza B viruses (IBVs) are major causes of recurrent lower respiratory tract infections. Current influenza vaccines elicit antibodies predominantly to the highly variable head region of haemagglutinin and their effectiveness is limited by viral drift¹ and suboptimal immune responses². Here we describe a neuraminidase-targeting monoclonal antibody, FNI9, that potently inhibits the enzymatic activity of all group 1 and group 2 IAVs, as well as Victoria/2/87-like, Yamagata/16/88-like and ancestral IBVs. FNI9 broadly neutralizes seasonal IAVs and IBVs, including the immune-evading H3N2 strains bearing an N-glycan at position 245, and shows synergistic activity when combined with anti-haemagglutinin stem-directed antibodies. Structural analysis reveals that D107 in the FNI9 heavy chain complementarity-determinant region 3 mimics the interaction of the sialic acid carboxyl group with the three highly conserved arginine residues (R118, R292 and R371) of the neuraminidase catalytic site. FNI9 demonstrates potent prophylactic activity against lethal IAV and IBV infections in mice. The unprecedented breadth and potency of the FNI9 monoclonal antibody supports its development for the prevention of influenza illness by seasonal and pandemic viruses.