M2e Peptide Research Articles

Modulation of Antigen Display on PapMV Nanoparticles Influences Its Immunogenicity.

Background: The papaya mosaic virus (PapMV) vaccine platform is a rod-shaped nanoparticle made of the recombinant PapMV coat protein (CP) self-assembled around a noncoding single-stranded RNA (ssRNA) template. The PapMV nanoparticle induces innate immunity through stimulation of the Toll-like receptors (TLR) 7 and 8. The display of the vaccine antigen at the surface of the nanoparticle, associated with the co-stimulation signal via TLR7/8, ensures a strong stimulation of the immune response, which is ideal for the development of candidate vaccines. In this study, we assess the impact of where the peptide antigen is fused, whether at the surface or at the extremities of the nanoparticles, on the immune response directed to that antigen. Methods: Two different peptides from influenza A virus were used as model antigens. The conserved M2e peptide, derived from the matrix protein 2 was chosen as the B-cell epitope, and a peptide derived from the nucleocapsid was chosen as the cytotoxic T lymphocytes (CTL) epitope. These peptides were coupled at two different positions on the PapMV CP, the N- (PapMV-N) or the C-terminus (PapMV-C), using the transpeptidase activity of Sortase A (SrtA). The immune responses, both humoral and CD8+ T-cell-mediated, directed to the peptide antigens in the two different fusion contexts were analyzed and compared. The impact of coupling density at the surface of the nanoparticle was also investigated. Conclusions: The results demonstrate that coupling of the peptide antigens at the N-terminus (PapMV-N) of the PapMV CP led to an enhanced immune response to the coupled peptide antigens as compared to coupling to the C-terminus. The difference between the two vaccine platforms is linked to the enhanced capacity of the PapMV-N vaccine platform to stimulate TLR7/8. We also demonstrated that the strength of the immune response increases with the density of coupling at the surface of the nanoparticles.

Virus-like Particle Vaccines: A Prospective Panacea Against an Avian Influenza Panzootic.

Epizootics of highly pathogenic avian influenza (HPAI) have resulted in the deaths of millions of birds leading to huge financial losses to the poultry industry worldwide. The roles of migratory wild birds in the harbouring, mutation, and transmission of avian influenza viruses (AIVs), and the lack of broad-spectrum prophylactic vaccines present imminent threats of a global panzootic. To prevent this, control measures that include effective AIV surveillance programmes, treatment regimens, and universal vaccines are being developed and analysed for their effectiveness. We reviewed the epidemiology of AIVs with regards to past avian influenza (AI) outbreaks in birds. The AIV surveillance programmes in wild and domestic birds, as well as their roles in AI control were also evaluated. We discussed the limitations of the currently used AI vaccines, which necessitated the development of a universal vaccine. We evaluated the current development of AI vaccines based upon virus-like particles (VLPs), particularly those displaying the matrix-2 ectodomain (M2e) peptide. Finally, we highlighted the prospects of these VLP vaccines as universal vaccines with the potential of preventing an AI panzootic.

Highly Immunogenic Nanoparticles Based on a Fusion Protein Comprising the M2e of Influenza A Virus and a Lipopeptide.

The highly conserved extracellular domain of the transmembrane protein M2 (M2e) of the influenza A virus is a promising target for the development of broad-spectrum vaccines. However, M2e is a poor immunogen by itself and must be linked to an appropriate carrier to induce an efficient immune response. In this study, we obtained recombinant mosaic proteins containing tandem copies of M2e fused to a lipopeptide from Neisseria meningitidis surface lipoprotein Ag473 and alpha-helical linkers and analyzed their immunogenicity. Six fusion proteins, comprising four or eight tandem copies of M2e flanked by alpha-helical linkers, lipopeptides, or a combination of both of these elements, were produced in Escherichia coli. The proteins, containing both alpha-helical linkers and lipopeptides at each side of M2e repeats, formed nanosized particles, but no particulate structures were observed in the absence of lipopeptides. Animal study results showed that proteins with lipopeptides induced strong M2e-specific antibody responses in the absence of external adjuvants compared to similar proteins without lipopeptides. Thus, the recombinant M2e-based proteins containing alpha-helical linkers and N. meningitidis lipopeptide sequences at the N- and C-termini of four or eight tandem copies of M2e peptide are promising vaccine candidates.

Preparation and characterization of HBc virus like particles with site-directed coupling function

Hepatitis B virus core protein can self-assemble into icosahedral symmetrical viral-like particles (VLPs) in vitro, and display exogenous sequences repeatedly and densely on the surface. VLPs also have strong immunogenicity and biological activity. When the nanoparticles enter the body, they quickly induce specific humoral and cellular immune responses to exogenous antigens. In this study, we designed an HBc-VLPs that can be coupled with antigens at specific sites, and developed a set of efficient methods to prepare HBc-VLPs. Through site-specific mutation technology, the 80th amino acid of peptide was changed from Ala to Cys, a specific cross-linking site was inserted into the main immunodominant region of HBc-VLPs, and the prokaryotic expression vector pET28a(+)-hbc was constructed. After expression and purification, high purity HBc(A80C) monomer protein was assembled into HBc-VLPs nanoparticles in Phosphate Buffer. The results of particle size analysis show that the average particle size of nanoparticles was 29.8 nm. Transmission electron microscopy (TEM) showed that HBc-VLPs formed spherical particles with a particle size of about 30 nm, and its morphology was similar to that of natural HBV particles. The influenza virus antigen M2e peptide as model antigen was connected to Cys residue of HBc-VLPs by Sulfo-SMCC, an amino sulfhydryl bifunctional cross-linking agent, and M2e-HBc-VLPs model vaccine was prepared. The integrity of HBc-VLPs structure and the correct cross-linking of M2e were verified by cell fluorescence tracing. Animal immune experiments showed that the vaccine can effectively stimulate the production of antigen-specific IgG antibody in mice, which verified the effectiveness of the vaccine carrier HBc-VLPs. This study lays a foundation for the research of HBc-VLPs as vaccine vector, and help to promote the development of HBc-VLPs vaccine and the application of HBc-VLPs in other fields.

Intranasal immunization with a recombinant protein based on the M2e peptide and second subunit of influenza A viral hemagglutinin fragment induces a cross-protective humoral and Tcell response in mice

Development of vaccines with a broad-spectrum of protection is one of the priorities in the programs of influenza prevention. Recently, the conserved fragments of influenza virus proteins (M1, M2, NP, the second subunit of the hemagglutinin HA2) provoke interest of investigators as the object of the development a broad-spectrum vaccines. Low immunogenicity present a problem when developing vaccines based on such conserved fragments. However, fusion of low immunogenic antigens into the high immunogenic carrier protein may significantly enhance their immunogenicity. The candidate vaccine protein Flg-HA2-2-4M2e was developed which containins two highly conserved viral antigens (the ectodomain of the M2 protein (M2e), 76130 region of the second subunit of HA2), fused with flagellin as a carrier protein. Flagellin (bacterial flagella protein) is a natural ligand of TLR-5, and has a strong adjuvant activity at different ways of its administration. The purpose of this study was to assess development of humoral and T cell immune response, along with broad-spectrum protection after mice immunization with the candidate Flg-HA2-2-4M2e vaccine protein. Mice were immunized intranasally three times with two-week intervals. Two weeks after the final immunization, the mice were challenged at the 5 LD50dose with influenza viruses A/California/07/09 (H1N1) pdm09 (phylogenetic group I), or A/Shanghai/2/2013 (H7N9) (phylogenetic group II). The results obtained in this study showed induction of strong M2e-specific humoral response (serum IgG and A) in the immunized mice. Immunization with recombinant protein stimulated formation of M2e-specific and virus-specific CD4+and CD8+T cells in lung which produced TNFα or IFNγ. Production of antigen-specific effector and central memory T cells was also detected in lungs of immunized mice. The formation of cross-protective immunity in immunized mice was demonstrated in a model of lethal influenza infection. The experimental animals were almost completely protected from the high dose of the pandemic virus A/H1N1pdm09, and highly pathogenic avian influenza A/H7N9 (90-100% survival). We also evaluated the changes of antigen-specific immune response in immunized mice after sublethal infection with A/H3N2 influenza virus. Mice of control and experimental groups were infected with MID100of influenza virus A/Aichi/2/68 (H3N2). It was shown that the M2e-specific response (IgG, IgA) was significantly increased in immunized mice after sublethal infection with influenza virus A/H3N2, and we detected the changes in profile of M2e-specific IgG subclasses. Following sublethal infection in immunized mice, the proportion of M2e-specific IgG2a was increased 10-fold. The results showed that the recombinant protein Flg-HA2-2-4M2e is a promising candidate for development of universal vaccines, which induces a protective humoral and T-cell response to conserved viral epitopes and protects against influenza A viruses of both phylogenetic groups.

Plant-Produced Recombinant Influenza A Virus Candidate Vaccine Based on Flagellin Linked to Conservative Fragments of M2 Protein and Hemagglutintin.

The development of recombinant influenza vaccines with broad spectrum protection is an important task. The combination of conservative viral antigens, such as M2e, the extracellular domain of the transmembrane protein M2, and conserved regions of the second subunit of hemagglutinin (HA), provides an opportunity for the development of universal influenza vaccines. Immunogenicity of the antigens could be enhanced by fusion to bacterial flagellin, the ligand for Toll-like receptor 5, acting as a powerful mucosal adjuvant. In this study, we report the transient expression in plants of a recombinant protein comprising flagellin of Salmonella typhimurium fused to the conserved region of the second subunit of HA (76–130 a.a.) of the first phylogenetic group of influenza A viruses and four tandem copies of the M2e peptide. The hybrid protein was expressed in Nicotiana benthamiana plants using the self-replicating potato virus X-based vector pEff up to 300 µg/g of fresh leaf tissue. The intranasal immunization of mice with purified fusion protein induced high levels of M2e-specific serum antibodies and provided protection against lethal challenge with influenza A virus strain A/Aichi/2/68(H3N2). Our results show that M2e and hemagglutinin-derived peptide can be used as important targets for the development of a plant-produced vaccine against influenza.

Rapid High-Yield Transient Expression of Swine Hepatitis E ORF2 Capsid Proteins in Nicotiana benthamiana Plants and Production of Chimeric Hepatitis E Virus-Like Particles Bearing the M2e Influenza Epitope.

The Hepatitis E virus (HEV) is a causative agent of acute hepatitis, mainly transmitted by the fecal-oral route or zoonotic. Open reading frame (ORF) 2 encodes the viral capsid protein, which is essential for virion assembly, host interaction, and inducing neutralizing antibodies. In this study, we investigated whether full-length and N- and C-terminally modified versions of the capsid protein transiently expressed in N. benthamiana plants could assemble into highly-immunogenic, virus-like particles (VLPs). We also assessed whether such VLPs can act as a carrier of foreign immunogenic epitopes, such as the highly-conserved M2e peptide from the Influenza virus. Plant codon-optimized HEV ORF2 capsid genes were constructed in which the nucleotides coding the N-terminal, the C-terminal, or both parts of the protein were deleted. The M2e peptide was inserted into the P2 loop after the residue Gly556 of HEV ORF2 protein by gene fusion, and three different chimeric constructs were designed. Plants expressed all versions of the HEV capsid protein up to 10% of total soluble protein (TSP), including the chimeras, but only the capsid protein consisting of aa residues 110 to 610 (HEV 110–610) and chimeric M2 HEV 110–610 spontaneously assembled in higher order structures. The chimeric VLPs assembled into particles with 22–36 nm in diameter and specifically reacted with the anti-M2e antibody.

Characterisation of M2e Antigenicity using anti-M2 Monoclonal Antibody and anti-M2e Polyclonal Antibodies

Matrix 2 ectodomain (M2e) protein is a potential antigen for detection of influenza A virus infection in vaccinated poultry (DIVA test). However the M2e antigenicity and immune response it induces in either humans or animals are poorly understood. Seventeen M2e peptides and sixteen recombinant M2e (rM2e) proteins with amino acid (aa) changes introduced at position 10, 11, 12, 13 14, 16, 18 and 20 were compared by western blot (WB) and enzyme-linked immunosorbent assay (ELISA) using mouse anti-M2 monoclonal antibody (mAb) 14C2, and anti-M2e peptide chicken and rabbit polyclonal antibody (pAb). The mAb 14C had the best discriminating power and indicated that all six positions contributed to the M2e antigenicity. Position 11 was the important immunodominant and affected Mab14C binding to a greatest degree. Changes in the adjacent position 14, 16 and 18 also influenced the binding, and it detected regardless of the method (WB or ELISA), or the antigen used (M2e peptide or rM2e). For chicken pAb and rabbit pAb, the immunodominant aa was position 10 and the antibody reaction was not affected by aa change at 11. The binding of rabbit pAb was also affected by changes at 14 and 16, which confirm the contribution of these positions to the M2e antigenicity. Position 10 was the only important position for the binding of chicken pAb to M2e. Overall, the study showed that the M2e antigenic sites are located between residues 10 – 18 and that aa changes at position 10, 11, 12, 14, 16 and 18 may all affect the antibody binding within the M2e protein.

An amphiphilic invertible polymer as a delivery vehicle for a M2e-HA2-HA1 peptide vaccine against an Influenza A virus in pigs

Influenza A viruses (IAVs) are a group of genetically diverse and economically important zoonotic pathogens. Despite decades of research, effective and broadly protective vaccines are yet to be developed. Recent breakthroughs in epitope-based immunization for influenza viruses identify certain conserved regions of the HA2 and M2e proteins as capable of inducing broad protection against multiple influenza strains. The M2e and HA2 peptides have been evaluated in mice but not as a combination in pigs, which play an important role in the transmission and evolution of IAV. Peptides are inherently weak immunogens; and effective delivery of peptide antigens is challenging. To enhance the delivery and immunogenicity of peptide-based vaccines, the conserved M2e and HA2 and a strain-specific HA1 epitope of Influenza A (H1N1) pdm09 were expressed as a chain in a bacterial expression system and entrapped in a novel amphiphilic invertible polymer made from polyethyelene glycol (PEG, molecular weight 600 g/mol) and polytetrahydrofuran (PTHF, molecular weight 650 g/mol), PEG600PTHF650. Piglets vaccinated with polymeric peptide vaccine mounted significantly stronger antibody responses against the peptide construct when compared to piglets immunized with the multi-epitope peptide alone. When vaccinated pigs were challenged with Influenza A (H1N1) pdm09, viral shedding in nasal secretions and lung lesion scores were significantly reduced when compared to the unvaccinated controls and pigs vaccinated with the peptide alone at six days post-challenge. Thus, the combination of the PEG600PTHF650 polymer and trimeric peptide construct enhanced delivery of the peptide antigen, acted as an adjuvant in stimulating strong antibody responses, reduced the effects of viral infection in vaccinated pigs.

Targeting M2e to DEC-205 induces an enhanced serum antibody-dependent heterosubtypic protection against influenza A virus infection

The ectodomain of the influenza A virus (IAV) M2 protein (M2e) is highly conserved, and it represents a promising candidate for the development of an “universal vaccine”. However, the low immunogenicity associated to M2e in a natural infection or in response to seasonal vaccines has led to explore new approaches to enhance it. In recent years, it has become clear that targeting antigens to dendritic cells (DC) is an efficient way to enhance immune responses against pathogens. In this work, the M2e peptide was chemically cross-linked to a monoclonal antibody (mAb) specific for DEC-205 (α-DEC-205:M2e), present on DC. BALB/c mice were inoculated subcutaneously (s.c.) three times with the conjugate equivalent to 1 µg of M2e, in the presence of polyinosinic-polycytidylic acid (poly I:C) as adjuvant. As controls, other groups of mice were inoculated under the same conditions with M2e cross-linked to an isotype control mAb (isotype:M2e), 5 µg of free M2e peptide, ovalbumin (OVA) cross-linked to the α-DEC-205 mAb (α-DEC-205:OVA) or poly I:C alone. Immunization with α-DEC-205-M2e induced high levels of serum antibodies (Abs) compared to isotype:M2e or to free M2e peptide, and in all cases IgG1 was predominant over IgG2a Abs. Furthermore, immunization with the α-DEC-205:M2e conjugate did not prevent morbidity, but it induced up to 76% protection against a heterosubtypic IAV lethal challenge. Contrasting with the 20 to 40% protection induced by isotype:M2e or by free M2e peptide. The protection induced by α-DEC-205:M2e conjugate was dependent on non-neutralizing serum Abs and independent of effector CD4+ T cells. These results show that targeting M2e to DEC-205 is a very effective alternative to induce strong heterosubtypic protection against an IAV infection.

Application of an immunoglobulin Y-alkaline phosphatase bioconjugate as a diagnostic tool for influenza A virus

ABSTRACT The diagnosis of influenza A virus is essential since it can be confused with influenza A like illness and lead to inaccurate drug prescription. In this study, the M2e peptide, a strategic antigen that is conserved in all virus subtypes, was used as a diagnostic marker of influenza A. For the first time, M2e-specific IgY antibody was covalently conjugated to alkaline phosphatase (ALP) enzyme in the presence of glutaraldehyde. The antibody-enzyme bioconjugate was characterized by fluorescence and Fourier-transform infrared spectroscopy. Subsequently, the diagnostic value of this bioconjugate was evaluated by direct sandwich ELISA using nasopharyngeal swab samples positive/negative for H1N1 and H3N2, which were previously analyzed by rRT-PCR for influenza. In conclusion, the M2e-specific IgY-ALP bioconjugate demonstrated positive results for Influenza A in samples that were diagnosed as Influenza A via the RT-PCR method.

Production and characterization of a conserved M2e peptide-based specific IgY antibody: evaluation of the diagnostic potential via conjugation with latex nanoparticles

Antibodies play an important role in combating and controlling viral diseases such as influenza. Immunoglobulin Y (IgY) antibodies have several advantages such as a less invasive manufacturing process, ease of isolation, higher affinity compared with IgG antibodies, and cost-effectiveness. To date, although specific IgY production has been performed for different strains of influenza A, to the best of our knowledge, an IgY against the M2e peptide has not been produced. In the current study, IgY antibodies are produced, purified, and characterized using the M2e peptide sequence for the first time with the intent to apply them for the diagnosis of influenza A virus. Anti-M2e IgY antibodies are obtained from eggs using a two-step purification method. The activity and characterization of the antibodies are determined using an enzyme-linked immunosorbent assay, a nano-spectrophotometer, an SDS-Page assay, and a Western Blot analysis. Finally, anti-M2e IgY antibodies are conjugated to the latex nanoparticles, and the reaction between the influenza A virus and the nanoparticles is demonstrated using light microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. In conclusion, this study shows that anti-M2e IgY antibodies can contribute to the diagnosis, treatment, and prevention of the influenza A virus.

Chimeric protein consisting of 3M2e and HSP as a universal influenza vaccine candidate: from in silico analysis to preliminary evaluation.

The 23-amino acid ectodomain of influenza virus M2 protein (M2e) is highly conserved among human influenza virus variants and represents an attractive target for developing a universal vaccine. Although this peptide has limited potency and low immunogenicity, the degree of M2e density has been shown to be a critical factor influencing the magnitude of epitope-specific responses. The aim of this study was to design a chimer protein consisting of three tandem repeats of M2e peptide sequence fused to the Leishmania major HSP70 gene and evaluate its characteristics and immunogenicity. The structure of the deduced protein and its stability, aliphatic index, biocomputed half-life and the anticipated immunogenicity were analyzed by bioinformatics software. The oligonucleotides encoding 3M2e and chimer 3M2e-HSP70 were expressed in Escherichia coli and affinity purified. The immunogenicity of the purified recombinant proteins was preliminary examined in mouse model. It was predicted that fusion of HSP70 to the C-terminal of 3M2e peptide led to increased stability, hydropathicity, continuous B cell epitopes and antigenic propensity score of chimer protein. Also, the predominant 3M2e epitopes were not hidden in the chimer protein. The initial in vivo experiment showed that 3M2e-HSP chimer protein stimulates specific immune responses. In conclusion, the results of the current study suggest that 3M2e-HSP chimer protein would be an effective universal subunit vaccine candidate against influenza infection.

Combination of M2e peptide with stalk HA epitopes of influenza A virus enhances protective properties of recombinant vaccine.

BackgroundInfluenza infection could be more effectively controlled if a multi-purpose vaccine with the ability to induce responses against most, or all, influenza A subtypes could be generated. Conserved viral proteins are a promising basis for the creation of a broadly protective vaccine. In the present study, the immunogenicity and protective properties of three recombinant proteins (vaccine candidates), comprising conserved viral proteins fused with bacterial flagellin, were compared.MethodsBalb/c mice were immunized intranasally with recombinant proteins comprising either one viral protein (the ectodomain of the M2 protein, ‘M2e’) or two viral proteins (M2e and the hemagglutinin second subunit ‘HA2’ epitope) genetically fused with flagellin. Further, two different consensus variants of HA2 were used. Therefore, three experimental positives were used in addition to the negative control (Flg-his). The mucosal, humoral, and T-cell immune responses to these constructs were evaluated.ResultWe have demonstrated that insertion of the HA2 consensus polypeptide (aa 76–130), derived from either the first (HA2-1) or second (HA2-2) virus phylogenetic group, into the recombinant Flg4M2e protein significantly enhanced its immunogenicity and protective properties. Intranasal administration of the vaccine candidates (Flg-HA2-2-4M2e or Flg-HA2-1-4M2e) induced considerable mucosal and systemic responses directed at both the M2e-protein and, in general, the influenza A virus. However, the immune response elicited by the Flg-HA2-1-4M2e protein was weaker than the one generated by Flg-HA2-2-4M2e. These recombinant proteins containing both viral peptides provide complete protection from lethal challenge with various influenza viruses: A/H3N2; A/H2N2; and A/H5N1.ConclusionThis study demonstrates that the intranasal administration of Flg-HA2-2-4M2e recombinant protein induces a strong immune response which provides broad protection against various influenza viruses. This construct is therefore a strong candidate for development as a universal vaccine.

Effect of M2e peptide–gold nanoparticle conjugates on development of anti-influenza antibodies

Gold nanoparticles (AuNPs) are successfully used as an adjuvant in the design of effective vaccines and in the preparation of high-affinity antibodies to haptens and complete antigens. Here, we assessed the adjuvant properties of AuNPs conjugated to a synthetic M2e peptide of the influenza A virus capsid. The resulting conjugate, a commercial influenza vaccine, and M2e in combination with different adjuvants were used to immunize laboratory mice. The highest titer was detected in the sera of mice immunized with two adjuvants: AuNPs and AuNP-conjugated CpG oligodeoxynucleotide 1826. With this combination, we also recorded increases in the respiratory activity of splenic lymphocytes, in the respiratory activity of peritoneal macrophages, and in the production of proinflammatory cytokines (IL-6 and IFN-γ). The results indicate that simultaneous immunization of the animals with two conjugates—M2e + AuNPs and CpG + AuNPs—activates antibody development. Therefore, the use of AuNPs as an antigen carrier leads to a complete and coordinated immune response from both cellular and humoral immunity.

CONSTRUCTION OF MOSAIC HBC PARTICLES PRESENTING CONSERVATIVE FRAGMENTS OF M2 PROTEIN AND HEMAGGLUTININ OF INFLUENZA A VIRUS.

Virus-like HBc particles formed as a result of the self-assembly of the nuclear antigen of the hepatitis B virus can be used as a highly immunogenic carrier for the presentation of foreign epitopes when creating recombinant vaccines. We use this vehicle to create influenza vaccines based on the conservative antigens of the influenza virus, the extracellular domain of the transmembrane protein M2 (M2e) and the fragment of the second subunit of hemagglutinin (HA2). Presentation on the surface of HBc particles should improve the immunogenicity of these peptides. Using genetic engineering techniques, we obtained a fusion protein in which the HA2 sequence is attached to the N-terminus of the HBc antigen, and the M2e peptide is included in the immunodominant loop region exposed on the surface of HBc particle. The hybrid protein expressed in Escherichia coli and purified under denaturing conditions formed virus-like HBc particles after refolding in vitro. Refolding of this protein in the presence of a previously denatured HBc antigen carrying no inserts resulted in formation of mosaic virus-like particles. The developed method will allow construction of mosaic HBc particles carrying different target epitopes of the influenza virus by combining the corresponding modified HBc proteins, which opens the possibility of creating vaccines with a wider spectrum of protection.

Expression and Immunogenicity of M2e Peptide of Avian Influenza Virus H5N1 Fused to Ricin Toxin B Chain Produced in Duckweed Plants.

The amino acid sequence of the extracellular domain of the virus-encoded M2 matrix protein (peptide M2e) is conserved among all subtypes of influenza A strains, enabling the development of a broad-range vaccine against them. We expressed M2e from avian influenza virus A/chicken/Kurgan/5/2005 (H5N1) in nuclear-transformed duckweed plants for further development of an avian influenza vaccine. The 30-amino acid N-terminal fragment of M2, including M2e (denoted M130), was selected for expression. The M2e DNA sequence fused in-frame to the 3′ end of ricin toxin B chain (RTB) was cloned under control of the CaMV 35S promoter into pBI121. The resulting plasmid was used for duckweed transformation, and 23 independent transgenic duckweed lines were obtained. Asialofetuin-binding ELISA of protein samples from the transgenic plants using polyclonal anti-RTB antibodies confirmed the expression of the RTB–M130 fusion protein in 20 lines. Quantitative ELISA of crude protein extracts from these lines showed RTB–M130 accumulation ranging from 0.25–2.5 μg/g fresh weight (0.0006–0.01% of total soluble protein). Affinity chromatography with immobilized asialofetuin and western blot analysis of protein samples from the transgenic plants showed expression of fusion protein RTB–M130 in the aggregate form with a molecular mass of about 70 kDa. Mice were immunized orally with a preparation of total soluble protein from transgenic plants, receiving four doses of 7 μg duckweed-derived RTB–M130 each, with no additional adjuvant. Specific IgG against M2e was detected in immunized mice, and the endpoint titer of nti-M2e IgG was 1,024. It was confirmed that oral immunization with RTB-M130 induces production of specific antibodies against peptide M2e, one of the most conserved antigens of the influenza virus. These results may provide further information for the development of a duckweed-based expression system to produce a broad-range edible vaccine against avian influenza.

An influenza A virus vaccine based on an M2e-modified alphavirus.

The 23-residue external domain of the influenza A virus M2 protein (M2e) has significant potential as a vaccine antigen. Here, we describe the construction and characterization of an M2e-modified Sindbis virus designated E2S1-M2e. E2S1-M2e virions contain M2e as an N-terminal extension of the E2 glycoprotein and therefore express 240 copies of the M2e peptide on their surface. The E2S1-M2e virus expressed M2e in an accessible and immunogenic form and induced M2e-specific antibodies when administered to mice. Mice that received an intranasal vaccination with E2S1-M2e were protected against a lethal challenge with a virulent, mouse-adapted strain of influenza A virus.

Self-assembly polymerization enhances the immunogenicity of influenza M2e peptide

The extracellular domain of Influenza M2 protein (M2e) was considered as a promising target for universal influenza vaccine development. Several M2e-based influenza vaccines have been developed and many of them used a mutant M2e peptide, in which the two conserved cysteine residues were substituted by serine residues. In this paper, we compared the antigenicity and immunogenicity of wild type and cysteine-mutant M2e peptides. We found that the cysteine substitution slightly affected the antigenicity of M2e epitope, but greatly reduced the immunogenicity of M2e peptide. The cysteine substitution also disabled the M2e peptide from inducing protection against influenza virus challenge in mice. Further analysis revealed that the immunogenicity of M2e peptide was enhanced by the self-assembly of the peptide through inter-peptide disulfide bonds. These results provide new information to improve the design of M2e-based vaccines against potential influenza pandemics.

A single dose and long lasting vaccine against pandemic influenza through the controlled release of a heterospecies tandem M2 sequence embedded within detoxified bacterial outer membrane vesicles.

The influenza A virus undergoes genetic drift and shift, leaving the general population susceptible to emerging pandemic strains, despite seasonal flu vaccination. Here we describe a single dose influenza vaccine derived from recombinant outer membrane vesicles (rOMVs) that display an antigen-mapped heterospecies tandem sequence of the M2 protein from the influenza A virus, released over 30days from poly(lactic-co-glycolide) (PLGA) microparticles. Four weeks post vaccination, BALB/c mice developed high anti-M2e IgG titers that were equivalent to those generated at 8weeks in a typical prime/boost vaccine regimen. Challenge of mice with a lethal dose of mouse adapted influenza virus PR8 (H1N1) 10weeks post vaccination resulted in 100% survival for both rOMV single-dose microparticle and prime/boost vaccinated mice. Anti-M2e IgG1 and IgG2a antibody titers were weighted toward IgG1, but splenocytes isolated from rOMV single-dose microparticle vaccinated mice produced high levels of IFNγ relative to IL-4 in response to stimulation with M2e peptides, supporting a more Th1 biased immune response. The protective immune response was long lasting, eliciting sustained antibody titers and 100% survival of mice challenged with a lethal dose of PR8 six months post initial vaccination. Together, these data support the potential of controlled release rOMVs as an effective single dose, long lasting and rapidly effective vaccine to protect against influenza.