A humanized anti-M2 scFv shows protective in vitro activity against influenza

Influenza A Virus Infections Sense Host Membrane Tension to Dynamically Tune Assembly

Enveloped viruses often exhibit a pleomorphic morphology, ranging in size from 100nm spheres to tens-of-micron long filaments. For influenza A virus (IAV), spheres enable rapid replication and minimize metabolic cost, while filaments resist effects of antibodies or other cell-entry pressures. The current paradigm is that virion shape changes require genetic adaptation; however, a virus evolved to alter its shape phenotypically would outperform one that relies on genetic selection. Using a novel quantitative flow virometry assay to characterize virion shape dynamics we find that IAV rapidly tunes its shape distribution to favor spheres under optimal, and filaments under attenuating conditions including the presence of antibodies. We identify membrane tension as a key cue sensed by IAV determining shape distributions. This phenotypic shift outpaces genetic change and serves to enable additional life cycles under pressure. Our work expands knowledge of the complex host-virus interplay to include viral responses to the local environment by optimizing its structure to maximize replication and ultimately host-host transmission.

Direct selection of functional fluorescent-protein antibody fusions by yeast display

Antibodies are important reagents for research, diagnostics, and therapeutics. Many examples of chimeric proteins combining the specific target recognition of antibodies with complementing functionalities such as fluorescence, toxicity or enzymatic activity have been described. However, antibodies selected solely on the basis of their binding specificities are not necessarily ideal candidates for the construction of chimeras. Here, we describe a high throughput method based on yeast display to directly select antibodies most suitable for conversion to fluorescent chimera. A library of scFv binders was converted to a fluorescent chimeric form, by cloning thermal green protein into the linker between VH and VL, and directly selecting for both binding and fluorescent functionality. This allowed us to directly identify antibodies functional in the single chain TGP format, that manifest higher protein expression, easier protein purification, and one-step binding assays.

Enhancing neutralizing activity against influenza H1N1/PR8 by engineering a single-domain VL-M2 specific into a bivalent form

Flu disease, with high mortality and morbidity, is caused by the influenza virus. Influenza infections are most effectively prevented through vaccination, but it requires annual reformulation due to the antigenic shift or drift of hemagglutinin and neuraminidase proteins. Increasing resistance to available anti-influenza drugs was also recently reported. The M2 surface protein of the influenza virus is an attractive target for universal vaccine development as it is highly conserved and multifunctional throughout the viral life cycle. This study aimed to discover a single-chain variable fragment (scFv) targeting the M2 protein of influenza A H1N1/PR8, showing neutralizing activity through plaque inhibition in virus replication. Several candidates were isolated using bio-panning, including scFv and single-domain V_L target M2 protein, which was displayed on the yeast surface. The scFv/V_L proteins were obtained with high yield and high purity through soluble expression in E. coli BL21 (DE3) pLysE strains. A single-domain V_L-M2-specific antibody, NVLM10, exhibited the highest binding affinity to influenza virions and was engineered into a bivalent format (NVL2M10) to improve antigen binding. Both antibodies inhibited virus replication in a dose-dependent manner, determined using plaque reduction- and immunocytochemistry assays. Furthermore, bivalent anti-M2 single-domain V_L antibodies significantly reduced the plaque number and viral HA protein intensity as well as viral genome (HA and NP) compared to the monovalent single-domain V_L antibodies. This suggests that mono- or bivalent single-domain V_L antibodies can exhibit neutralizing activity against influenza virus A, as determined through binding to virus particle activity.

Non-classical autophagy activation pathways are essential for production of infectious Influenza A virus in vitro

Autophagy is a critical mechanism deployed by eukaryotic cells in response to stress, including viral infection, to boost the innate antimicrobial responses. However, an increasing number of pathogens hijack the autophagic machinery to facilitate their own replication. Influenza A virus (IAV), responsible for several global pandemics, has an intricate dependence on autophagy for successful replication in mammalian cells. To elucidate key chokepoints in the host stress responses facilitating IAV replication, we constructed a meta‐transcriptome of IAV and host gene expression dynamics during early (1–3 hpi), mid (4–6 hpi), and late (8–12 hpi) stages of the viral replication cycle at two multiplicities of infection (MOI): 1 and 5. We supplemented the global transcriptome study with phosphoproteomic analysis of stress‐activated protein kinase (SAPK/JNK) signaling in lung carcinoma (predominantly used as an in vitro model of IAV replication) and normal human bronchial epithelial cells. We report significant differences in the activation profiles of autophagy regulating genes upon IAV infection at the two MOI as well as divergent dependence on ULK1 signaling within the normal and cancer cells. Regardless of the cell model, JNK‐Thr187 signaling was crucial for the production of infectious viral particles.

Selection and verification of antibodies against the cytoplasmic domain of M2 of influenza, a transmembrane protein

Interactions between the cytoplasmic domains of viral transmembrane proteins and host machinery often determine the outcome of viral infection. The M2 protein of influenza A has been identified as a key player in autophagy-mediated viral replication. Here, we describe the engineering and validation of an antibody specific for the cytoplasmic domain of the M2 protein. Through phage and yeast display selection techniques, we obtained an antibody that recognizes: 1) the M2 cytoplasmic domain purified from bacterial inclusion bodies and refolded, 2) full-length M2 recombinant protein expressed in mammalian cells, and 3) native M2 protein in influenza A infected cells. This antibody can serve as a molecular tool to enhance our knowledge of protein–protein interactions between influenza A virus and the host cell machinery. We anticipate the methods described herein will further the development of antibodies specific to the cytoplasmic domains of transmembrane proteins.

Natural influenza infection produces a greater diversity of humoral responses than vaccination in immunosuppressed transplant recipients

The humoral immune response to influenza virus infection is complex and may be different compared to the antibody response elicited by vaccination. We analyzed the breadth of IgG and IgA responses in solid organ transplant (SOT) recipients to a diverse collection of 86 influenza antigens elicited by natural influenza A virus (IAV) infection or by vaccination. Antibody levels were quantified using a custom antigen microarray. A total of 120 patients were included: 80 IAV infected (40 A/H1N1 and 40 A/H3N2) and 40 vaccinated. Based on hierarchical clustering analysis, infection with either H1N1 or H3N2 virus showed a more diverse antibody response compared to vaccination. Similarly, H1N1-infected individuals showed a significant IgG response to 27.9% of array antigens and H3N2-infected patients to 43.0% of antigens, whereas vaccination elicited a less broad immune response (7.0% of antigens). Immune responses were not exclusively targeting influenza hemagglutinin (HA) proteins but were also directed against conserved influenza antigens. Serum IgA responses followed a similar profile. This study provides novel data on the breadth of antibody responses to influenza. We also found that the diversity of response is greater in influenza-infected rather than vaccinated patients, providing a potential mechanistic rationale for suboptimal vaccine efficacy in this population.

Matrix Protein 2 Extracellular Domain-Specific Monoclonal Antibodies Are an Effective and Potentially Universal Treatment for Influenza A

Influenza virus infection causes significant morbidity and mortality worldwide. Humans fail to make a universally protective memory immune response to influenza A. Hemagglutinin and Neuraminidase undergo antigenic drift and shift, resulting in new influenza A strains to which humans are naive. Seasonal vaccines are often ineffective and escape mutants have been reported to all treatments for influenza A. In the absence of a universal influenza A vaccine or treatment, influenza A will remain a significant threat to human health. The extracellular domain of the M2-ion channel (M2e) is an ideal antigenic target for a universal therapeutic agent, as it is highly conserved across influenza A serotypes, has a low mutation rate, and is essential for viral entry and replication. Previous M2e-specific monoclonal antibodies (M2e-MAbs) show protective potential against influenza A, however, they are either strain specific or have limited efficacy. We generated seven murine M2e-MAbs and utilized in vitro and in vivo assays to validate the specificity of our novel M2e-MAbs and to explore the universality of their protective potential. Our data shows our M2e-MAbs bind to M2e peptide, HEK cells expressing the M2 channel, as well as, influenza virions and MDCK-ATL cells infected with influenza viruses of multiple serotypes. Our antibodies significantly protect highly influenza A virus susceptible BALB/c mice from lethal challenge with H1N1 A/PR/8/34, pH1N1 A/CA/07/2009, H5N1 A/Vietnam/1203/2004, and H7N9 A/Anhui/1/2013 by improving survival rates and weight loss. Based on these results, at least four of our seven M2e-MAbs show strong potential as universal influenza A treatments.IMPORTANCE Despite a seasonal vaccine and multiple therapeutic treatments, Influenza A remains a significant threat to human health. The biggest obstacle is producing a vaccine or treatment for influenza A is their universality or efficacy against not only seasonal variances in the influenza virus, but also against all human, avian, and swine serotypes and, therefore, potential pandemic strains. M2e has huge potential as a target for a vaccine or treatment against influenza A. It is the most conserved external protein on the virus. Antibodies against M2e have made it to clinical trials, but not succeeded. Here, we describe novel M2e antibodies produced in mice that are not only protective at low doses, but that we extensively test to determine their universality and found to be cross protective against all strains tested. Additionally, our work begins to elucidate the critical role of isotype for an influenza A monoclonal antibody therapeutic.

Tetramerizing tGCN4 domain facilitates production of Influenza A H1N1 M2e higher order soluble oligomers that show enhanced immunogenicity in vivo

One strategy for the development of a next generation influenza vaccine centers upon using conserved domains of the virus to induce broader and long-lasting immune responses. The production of artificial proteins by mimicking native-like structures has shown to be a promising approach for vaccine design against diverse enveloped viruses. The amino terminus of influenza A virus matrix 2 ectodomain (M2e) is highly conserved among influenza subtypes, and previous studies have shown M2e-based vaccines are strongly immunogenic, making it an attractive target for further exploration. We hypothesized that stabilizing M2e protein in the mammalian system might influence the immunogenicity of M2e with the added advantage to robustly produce the large scale of proteins with native-like fold and hence can act as an efficient vaccine candidate. In this study, we created an engineered construct in which the amino terminus of M2e is linked to the tetramerizing domain tGCN4, expressed the construct in a mammalian system, and tested for immunogenicity in BALB/c mice. We have also constructed a stand-alone M2e construct (without tGCN4) and compared the protein expressed in mammalian cells and in Escherichia coli using in vitro and in vivo methods. The mammalian-expressed protein was found to be more stable, more antigenic than the E. coli protein, and form higher-order oligomers. In an intramuscular protein priming and boosting regimen in mice, these proteins induced high titers of antibodies and elicited a mixed Th1/Th2 response. These results highlight the mammalian-expressed M2e soluble proteins as a promising vaccine development platform.

Humanization of Antibodies using a Statistical Inference Approach

Antibody humanization is a key step in the preclinical phase of the development of therapeutic antibodies, originally developed and tested in non-human models (most typically, in mouse). The standard technique of Complementarity-Determining Regions (CDR) grafting into human Framework Regions of germline sequences has some important drawbacks, in that the resulting sequences often need further back-mutations to ensure functionality and/or stability. Here we propose a new method to characterize the statistical distribution of the sequences of the variable regions of human antibodies, that takes into account phenotypical correlations between pairs of residues, both within and between chains. We define a "humanness score" of a sequence, comparing its performance in distinguishing human from murine sequences, with that of some alternative scores in the literature. We also compare the score with the experimental immunogenicity of clinically used antibodies. Finally, we use the humanness score as an optimization function and perform a search in the sequence space, starting from different murine sequences and keeping the CDR regions unchanged. Our results show that our humanness score outperforms other methods in sequence classification, and the optimization protocol is able to generate humanized sequences that are recognized as human by standard homology modelling tools.

Selection of phage-displayed accessible recombinant targeted antibodies (SPARTA): methodology and applications

We developed a potentially novel and robust antibody discovery methodology, termed selection of phage-displayed accessible recombinant targeted antibodies (SPARTA). This combines an in vitro screening step of a naive human antibody library against known tumor targets, with in vivo selections based on tumor-homing capabilities of a preenriched antibody pool. This unique approach overcomes several rate-limiting challenges to generate human antibodies amenable to rapid translation into medical applications. As a proof of concept, we evaluated SPARTA on 2 well-established tumor cell surface targets, EphA5 and GRP78. We evaluated antibodies that showed tumor-targeting selectivity as a representative panel of antibody-drug conjugates (ADCs) and were highly efficacious. Our results validate a discovery platform to identify and validate monoclonal antibodies with favorable tumor-targeting attributes. This approach may also extend to other diseases with known cell surface targets and affected tissues easily isolated for in vivo selection.

Advances in the T7 phage display system (Review)

The present review describes the advantages and updated applications of the T7 phage display system in bioscience and medical science. Current phage display systems are based on various bacteriophage vectors, including M13, T7, T4 and f1. Of these, the M13 phage display is the most frequently used, however, the present review highlights the advantages of the T7 system. As a phage display platform, M13 contains single‑stranded DNA, while the T7 phage consists of double‑stranded DNA, which exhibits increased stability and is less prone to mutation during replication. Additional characteristics of the T7 phage include the following: The T7 phage does not depend on a protein secretion pathway in the lytic cycle; expressed peptides and proteins are usually located on the C‑terminal region of capsid protein gp10B, which avoids problems associated with steric hindrance; and T7 phage particles exhibit high stability under various extreme conditions, including high temperature and low pH, which facilitates effective high‑throughput affinity elutriation. Recent applications of the T7 phage display system have been instrumental in uncovering mechanisms of molecular interaction, particularly in the fields of antigen discovery, vaccine development, protein interaction, and cancer diagnosis and treatment.

Supplementation of inactivated influenza vaccine with norovirus P particle-M2e chimeric vaccine enhances protection against heterologous virus challenge in chickens

The current inactivated influenza vaccines provide satisfactory protection against homologous viruses but limited cross-protection against antigenically divergent strains. Consequently, there is a need to develop more broadly protective vaccines. The highly conserved extracellular domain of the matrix protein 2 (M2e) has shown promising results as one of the components of a universal influenza vaccine in different animal models. As an approach to overcome the limited, strain specific, protective efficacy of inactivated influenza vaccine (IIV), a combination of recombinant M2e expressed on the surface of norovirus P particle (M2eP) and IIV was tested in chickens. Co-immunization of birds with both vaccines did not affect the production of M2e-specific IgG antibodies compared to the group vaccinated with M2eP alone. However, the co-immunized birds developed significantly higher pre-challenge hemagglutination inhibition antibody titers against the homologous IIV antigen and heterologous challenge virus. These combined vaccine groups also had cross reactive antibody responses against different viruses (H5, H6, and H7 subtypes) compared to the IIV alone vaccinated group. Upon intranasal challenge with homologous and heterologous viruses, the combined vaccine groups showed greater reduction in viral shedding in tracheal swabs compared to those groups receiving IIV alone. Moreover, M2eP antisera from vaccinated birds were able to bind to the native M2 expressed on the surface of whole virus particles and infected cells, and inhibit virus replication in vitro. Our results support the potential benefit of supplementing IIV with M2eP, to expand the vaccine cross protective efficacy.

Indoleamine 2,3-dioxygenase (IDO) activity during the primary immune response to influenza infection modifies the memory T cell response to influenza challenge

The generation of a heterosubtypic memory T cell response is important for cross-protective immunity against unrelated strains of influenza virus. One way to facilitate the generation of the memory T cell population is to control the activity of immune modulatory agents. The enzyme, indoleamine 2,3-dioxygenase (IDO), is upregulated during influenza infection by the interferon response where IDO activity depletes tryptophan required in T cell response. In this study, IDO activity was pharmacologically inhibited with 1-methyl-tryptophan (1MT) during the primary response to influenza virus infection and the effect on the memory T cell response was evaluated. 1MT treatment improved the memory T cell response to influenza virus challenge by increasing interferon gamma expression by CD4 and CD8 T cells, and numbers of lung virus-specific CD8+ T cells, and increased the Th1 response as well as modifying the immunodominance hierarchy to increase the number of subdominant epitope specific CD8+ T cells, a feature which may be linked to decreased regulatory T cell function. These changes also accompanied evidence of accelerated lung tissue repair upon virus challenge. These findings suggest that modulation of IDO activity could be exploited in influenza vaccine development to enhance memory T cell responses and reduce disease burden.

A novel subnucleocapsid nanoplatform for mucosal vaccination against influenza virus that targets the ectodomain of matrix protein 2

In this study, subnucleocapsid nanorings formed by the recombinant nucleoprotein (N) of the respiratory syncytial virus were evaluated as a platform to anchor heterologous antigens. The ectodomain of the influenza virus A matrix protein 2 (M2e) is highly conserved and elicits protective antibodies when it is linked to an immunogenic carrier, making it a promising target to develop universal influenza vaccines. In this context, one or three M2e copies were genetically linked to the C terminus of N to produce N-M2e and N-3M2e chimeric recombinant nanorings. Mice were immunized intranasally with N-M2e or N-3M2e or with M2e or 3M2e control peptides. N-3M2e-vaccinated mice showed the strongest mucosal and systemic antibody responses. These mice presented a reduced viral load and minor weight loss, and all survived upon challenge with influenza virus A/PR8/34 (H1N1) (PR8). We compared the intranasal route to the subcutaneous route of N-3M2e immunization. Only the intranasal route induced a strong local IgA response and led to the protection of mice upon challenge. Finally, we demonstrated that the induction of anti-M2e antibodies by N-3M2e is not impaired by preexisting anti-N immunity. Overall, these results show that the N nanoring is a potent carrier for mucosal delivery of vaccinal antigens.

Passive immunization with a recombinant adenovirus expressing an HA (H5)-specific single-domain antibody protects mice from lethal influenza infection

One effective method for the prevention and treatment of influenza infection is passive immunization. In our study, we examined the feasibility of creating an antibody-based preparation with a prolonged protective effect against influenza virus. Single-domain antibodies (sdAbs) specific for influenza virus hemagglutinin were generated. Experiments in mouse models showed 100% survivability for both intranasal sdAbs administration 24h prior to influenza challenge and 24h after infection. sdAb-gene delivery by an adenoviral vector led to gene expression for up to 14days. Protection by a recombinant adenovirus containing the sdAb gene was observed in cases of administration prior to influenza infection (14d-24h). We also demonstrated that the single administration of a combined preparation containing sdAb DNA and protein expanded the protection time window from 14d prior to 48h after influenza infection. This approach and the application of a broad-spectrum sdAbs will allow the development of efficient drugs for the prevention and treatment of viral infections produced by pandemic virus variants and other infections.

Influenza B-cells protective epitope characterization: a passkey for the rational design of new broad-range anti-influenza vaccines

The emergence of new influenza strains causing pandemics represents a serious threat to human health. From 1918, four influenza pandemics occurred, caused by H1N1, H2N2 and H3N2 subtypes. Moreover, in 1997 a novel influenza avian strain belonging to the H5N1 subtype infected humans. Nowadays, even if its transmission is still circumscribed to avian species, the capability of the virus to infect humans directly from avian reservoirs can result in fatalities. Moreover, the risk that this or novel avian strains could adapt to inter-human transmission, the development of resistance to anti-viral drugs and the lack of an effective prevention are all incumbent problems for the world population. In this scenario, the identification of broadly neutralizing monoclonal antibodies (mAbs) directed against conserved regions shared among influenza isolates has raised hopes for the development of monoclonal antibody-based immunotherapy and "universal" anti-influenza vaccines.

Recombinant parainfluenza virus 5 vaccine encoding the influenza virus hemagglutinin protects against H5N1 highly pathogenic avian influenza virus infection following intranasal or intramuscular vaccination of BALB/c mice

New approaches for vaccination to prevent influenza virus infection are needed. Emerging viruses, such as the H5N1 highly pathogenic avian influenza (HPAI) virus, pose not only pandemic threats but also challenges in vaccine development and production. Parainfluenza virus 5 (PIV5) is an appealing vector for vaccine development, and we have previously shown that intranasal immunization with PIV5 expressing the hemagglutinin from influenza virus was protective against influenza virus challenge (S. M. Tompkins, Y. Lin, G. P. Leser, K. A. Kramer, D. L. Haas, E. W. Howerth, J. Xu, M. J. Kennett, J. E. Durbin, R. A. Tripp, R. A. Lamb, and B. He, Virology 362:139-150, 2007). While intranasal immunization is an appealing approach, PIV5 may have the potential to be utilized in other formats, prompting us to test the efficacy of rPIV5-H5, which encodes the HA from H5N1 HPAI virus, in different vaccination schemes. In the BALB/c mouse model, a single intramuscular or intranasal immunization with a live rPIV5-H5 (ZL46) rapidly induced robust neutralizing serum antibody responses and protected against HPAI challenge, although mucosal IgA responses primed by intranasal immunization more effectively controlled virus replication in the lung. The rPIV5-H5 vaccine incorporated the H5 HA into the virion, so we tested the efficacy of an inactivated form of the vaccine. Inactivated rPIV5-H5 primed neutralizing serum antibody responses and controlled H5N1 virus replication; however, similar to other H5 antigen vaccines, it required a booster immunization to prime protective immune responses. Taken together, these results suggest that rPIV5-HA vaccines and H5-specific vaccines in particular can be utilized in multiple formats and by multiple routes of administration. This could avoid potential contraindications based on intranasal administration alone and provide opportunities for broader applications with the use of a single vaccine vector.

Antibodies against conserved antigens provide opportunities for reform in influenza vaccine design

High-performance neutralizing antibody against influenza virus typically recognizes the globular head region of its hemagglutinin (HA) envelope glycoprotein. To-date, approved human vaccination strategies have been designed to induce such antibodies as a sole means of preventing the consequences of this infection. However, frequent amino-acid changes in the HA globular head allow for efficient immune evasion. Consequently, vaccines inducing such neutralizing antibodies need to be annually re-designed and re-administered at a great expense. These vaccines furthermore provide little-to-no immunity against antigenic-shift strains, which arise from complete replacement of HA or of neuraminidase genes, and pose pandemic risks. To address these issues, laboratory research has focused on inducing immunity effective against all strains, regardless of changes in the HA globular head. Despite prior dogma that such cross-protection needs to be induced by cellular immunity alone, several advances in recent years demonstrate that antibodies of other specificities are capable of cross-strain protection in mice. This review discusses the reactivity, induction, efficacy, and mechanisms of antibodies that react with poorly accessible epitopes in the HA stalk, with the matrix 2 membrane ion channel, and even with the internal nucleoprotein. These advances warrant further investigation of the inducibility and efficacy of such revolutionary antibody strategies in humans.

Characterization of a fully human monoclonal antibody against extracellular domain of matrix protein 2 of influenza A virus

The extra-cellular domain of the influenza virus matrix protein 2 (M2e) is highly conserved between influenza A virus strains compared to hemagglutinin and neuraminidase, and has long been viewed as a potential and universal vaccine target. M2e induces no or only weak and transient immune responses following infection, making it difficult to detect M2e-specific antibodies producing B-cells in human peripheral blood lymphocytes. Recently, using a single-cell manipulation method, immunospot array assay on a chip (ISAAC), we obtained an M2e-specific human antibody (Ab1-10) from the peripheral blood of a healthy volunteer. In this report, we have demonstrate that Ab1-10 reacted not only to seasonal influenza A viruses, but also to pandemic (H1N1) 2009 virus (2009 H1N1) and highly pathogenic avian influenza A virus, and that the antibody-bound M2e of 2009 H1N1 inactivated the virus with high affinity (∼10(-10)M). More importantly, it inhibited 2009 H1N1 viral propagation in vitro. These results suggest that Ab1-10 might be a potential candidate for antibody therapeutics for a wide range of influenza A viruses.

Characterization of the murine Th2 response to immunization with liposomal M2e influenza vaccine

While the current influenza vaccine strategy is dependent on eliciting neutralizing antibodies to the hemagglutinin (H or HA) surface glycoprotein, antigenic drifts and occasional antigenic shifts necessitate constant surveillance and annual updates to the vaccine components. The ectodomain of the matrix 2 (M2e) channel protein has been proposed as a universal vaccine candidate, although it has not yet been shown to elicit neutralizing antibodies. Utilizing a liposome-based vaccine technology, an M2e vaccine (L-M2e-HD/MPL) was tested and shown to stimulate the production of anti-M2e antibodies which precipitated with whole virus and inhibited viral cell lysis by multiple type A strains of influenza virus using a novel in vitro assay. The anti-M2e antibodies also conferred complete protection following passive transfer from L-M2e-HD/MPL vaccinated mice to naïve mice challenged with H1N1 virus. Significantly higher levels of IL-4 compared to IFN-γ were secreted by the splenocytes of L-M2e-HD/MPL vaccinated mice incubated with M2e. In addition, depletion of CD4 cells or CD4 cells plus CD8 cells from L-M2e-HD/MPL vaccinated mice using monoclonal antibodies markedly decreased the level of protection of the vaccine when compared to just CD8 depletion of L-M2e-HD/MPL vaccinated mice. These results suggest that the protective immune response elicited by this vaccine is mediated primarily by a Th2 mechanism.

Development and evaluation of an M2-293FT cell-based flow cytometric assay for quantification of antibody response to native form of matrix protein 2 of influenza A viruses

Matrix protein 2 (M2) of influenza A viruses is an attractive target for the development of broadly cross-protective influenza vaccines and therapeutic antibodies. The available evidence suggests that antibodies reactive to the natural tetrameric form of M2 proteins, rather than those to synthetic peptides of M2 ectodomain (M2e), best correlate with M2-mediated immune protection. However, the current ability to quantify strain-specific and/or subtype-cross-reactive M2 antibodies against the natural form of M2 antigens from influenza A viruses of different host origin is limited. In the present study, we generated a panel of 293FT transfected cell lines stably expressing full-length tetrameric forms of M2 molecules from human, avian and the swine-origin 2009 pandemic H1N1 influenza A virus, respectively, and developed an M2-293FT cell line-based flow cytometric assay (M2-FCA). Side-by-side comparison of M2-FCA with a synthetic M2e peptide-based indirect ELISA (M2e-ELISA) reveals that M2-FCA is highly efficient in quantifying both M2e sequence-specific and cross-reactive antibodies to the native form of M2 antigens. In contrast, promiscuity was evident when specificity and cross-reactivity of anti-M2 antibodies were assessed by M2e-ELISA. These results demonstrate that M2-FCA represents a rapid, simple and sensitive method to quantitatively assess specificity and cross-reactivity of anti-M2 antibodies after infection or vaccination.

Influenza vaccines: from surveillance through production to protection

Influenza is an important contributor to population and individual morbidity and mortality. The current influenza pandemic with novel H1N1 has highlighted the need for health care professionals to better understand the processes involved in creating influenza vaccines, both for pandemic as well as for seasonal influenza. This review presents an overview of influenza-related topics to help meet this need and includes a discussion of the burden of disease, virology, epidemiology, viral surveillance, and vaccine strain selection. We then present an overview of influenza vaccine-related topics, including vaccine production, vaccine efficacy and effectiveness, influenza vaccine misperceptions, and populations that are recommended to receive vaccination. English-language articles in PubMed published between January 1, 1970, and October 7, 2009, were searched using key words human influenza, influenza vaccines, influenza A, and influenza B.