Development of a candidate influenza vaccine based on virus-like particles displaying influenza M2e peptide into the immunodominant loop region of hepatitis B core antigen: Insertion of multiple copies of M2e increases immunogenicity and protective efficiency

Nanoparticles Carrying Conserved Regions of Influenza A Hemagglutinin, Nucleoprotein, and M2 Protein Elicit a Strong Humoral and T Cell Immune Response and Protect Animals from Infection

Current influenza vaccines are mainly strain-specific and have limited efficacy in preventing new influenza A strains. Efficient control of infection can potentially be achieved through the development of broad-spectrum vaccines based on conserved antigens. A combination of several such antigens, including the conserved region of the second subunit of the hemagglutinin (HA2), the extracellular domain of the M2 protein (M2e), and epitopes of nucleoprotein (NP), which together can elicit an antibody- and cell-mediated immune response, would be preferred for vaccine development. In this study, we obtained recombinant virus-like particles formed by an artificial self-assembling peptide (SAP) carrying two epitopes from NP, tandem copies of M2e and HA2 peptides, along with a T helper Pan DR-binding epitope (PADRE). Fusion proteins expressed in Escherichia coli self-assembled in vitro into spherical particles with a size of 15-35 nm. Immunization of mice with these particles induced strong humoral immune response against M2e and the entire virus, and lead to the formation of cytokine-secreting antigen-specific CD4+ and CD8+ effector memory T cells. Immunization provided high protection of mice against the lethal challenge with the influenza A virus. Our results show that SAP-based nanoparticles carrying conserved peptides from M2, HA, and NP proteins of the influenza A virus, as well as T helper epitope PADRE, can be used for the development of universal flu vaccines.

Plant-Produced Nanoparticles Based on Artificial Self-Assembling Peptide Bearing the Influenza M2e Epitope

Despite advances in vaccine development, influenza remains a persistent global health threat and the search for a broad-spectrum recombinant vaccine against influenza continues. The extracellular domain of the transmembrane protein M2 (M2e) of the influenza A virus is highly conserved and can be used to develop a universal vaccine. M2e is a poor immunogen by itself, but it becomes highly immunogenic when linked to an appropriate carrier. Here, we report the transient expression of a recombinant protein comprising four tandem copies of M2e fused to an artificial self-assembling peptide (SAP) in plants. The hybrid protein was efficiently expressed in Nicotiana benthamiana using the self-replicating potato virus X-based vector pEff. The protein was purified using metal affinity chromatography under denaturing conditions. The hybrid protein was capable of self-assembly in vitro into spherical particles 15-30 nm in size. The subcutaneous immunization of mice with M2e-carrying nanoparticles induced high levels of M2e-specific IgG antibodies in serum and mucosal secretions. Immunization provided mice with protection against a lethal influenza A virus challenge. SAP-based nanoparticles displaying M2e peptides can be further used to develop a recombinant "universal" vaccine against influenza A produced in plants.

A Thermal-Stable Protein Nanoparticle That Stimulates Long Lasting Humoral Immune Response

A thermally stable vaccine platform is considered the missing piece of vaccine technology. In this article, we reported the creation of a novel protein nanoparticle and assessed its ability to withstand extended high temperature incubation while stimulating a long-lasting humoral immune response. This protein nanoparticle was assembled from a fusion protein composed of an amphipathic helical peptide derived from the M2 protein of the H5N1 influenza virus (AH3) and a superfolder green fluorescent protein (sfGFP). Its proposed structure was modeled according to transmission electronic microscope (TEM) images of protein nanoparticles. From this proposed protein model, we created a mutant with two gain-of-function mutations that work synergistically on particle stability. A protein nanoparticle assembled from this gain-of-function mutant is able to remove a hydrophobic patch from its surface. This gain-of-function mutant also contributes to the higher thermostability of protein nanoparticles and stimulates a long lasting humoral immune response after a single immunization. This assembled nanoparticle showed increasing particle stability at higher temperatures and salt concentrations. This novel protein nanoparticle may serve as a thermally-stable platform for vaccine development.

Rapid screening and scaled manufacture of immunogenic virus-like particles in a tobacco BY-2 cell-free protein synthesis system

Several vaccine platforms have been developed to fight pathogenic threats, with Virus-Like Particles (VLPs) representing a very promising alternative to traditional platforms. VLPs trigger strong and lasting humoral and cellular immune responses with fewer safety concerns and higher stability than other platforms. The use of extensively characterized carrier VLPs modified with heterologous antigens was proposed to circumvent the viral complexity of specific viruses that could lead to poor VLP assembly and yields. Although carrier VLPs have been successfully produced in a wide variety of cell-based systems, these are limited by low protein yields and protracted clone selection and optimization workflows that limit VLP screening approaches. In response, we have demonstrated the cell-free protein synthesis (CFPS) of several variants of the hepatitis B core (HBc) carrier VLP using a high-yielding tobacco BY-2 lysate (BYL). High VLP yields in the BYL system allowed in-depth characterization of HBc variants. Insertion of heterologous sequences at the spike region of the HBc monomer proved more structurally demanding than at the N-terminus but removal of the C-terminal domain allowed higher particle flexibility and insert acceptance, albeit at the expense of thermal and chemical stability. We also proved the possibility to scale the CFPS reaction up to 1L in batch mode to produce 0.45 grams of the native HBc VLP within a 48-hour reaction window. A maximum yield of 820 µg/ml of assembled VLP particles was observed at the 100µl scale and most remarkably the CFPS reaction was successfully scaled from 50µl to 1L without any reduction in protein yield across this 20,000-fold difference in reaction volumes. We subsequently proved the immunogenicity of BYL-derived VLPs, as flow cytometry and microscopy clearly showed prompt recognition and endocytosis of fluorescently labelled VLPs by human dendritic cells. Triggering of inflammatory cytokine production in human peripheral blood mononuclear cells was also quantitated using a multiplex assay. This research establishes BYL as a tool for rapid production and microscale screening of VLP variants with subsequent manufacturing possibilities across scales, thus accelerating discovery and implementation of new vaccine candidates using carrier VLPs.

Expression of Influenza M2e-NP Recombinant Fusion Protein in Escherichia coli BL21 (DE3) and Its Binding to Antibodies

The current influenza vaccines only confer protection against the circulating influenza subtypes, therefore universal vaccines are needed to prevent upcoming influenza outbreaks caused by emerging influenza subtypes. The extracellular domain of influenza A M2 protein (M2e) is highly conserved among different subtypes of influenza A viruses, and it is able to elicit protective immunity against the viruses. The influenza nucleoprotein (NP) was used to display the M2e in this study due to its promising T-cell response and adjuvanticity. The M2e gene was fused to the 5'-end of the NP gene and then cloned into pRSET B vector. The DNA sequencing analysis revealed six point mutations in the M2e-NP fusion gene, including one mutation in the M2e peptide and five mutations in the NP. The mutations were reverted using PCR site-directed mutagenesis. The recombinant plasmids (pRSET B-M2e-NP and pRSET B-mM2e-NP) were introduced into Escherichia coli (E. coli) BL21 (DE3) for protein expression. The mutated and non-mutated proteins were subsequently expressed and named mM2e-NP and M2e-NP, respectively. The expression of mM2e-NP and M2e-NP was not affected by the mutations. The binding of anti-M2e antibody to the purified native mM2e-NP and M2e-NP also remained active. However, when the anti-NP antibody was tested, the signal produced by mM2e-NP was very weak. The results implied that the amino acid changes in the NP had adversely impacted on the conformation of mM2e-NP and subsequently affected the antibody binding. In light of the remarkable antibody binding to the M2e-NP fusion protein, this study highly recommends the potential of M2e-NP as a universal influenza vaccine candidate.

Flagellin/Virus-like Particle Hybrid Platform with High Immunogenicity, Safety, and Versatility for Vaccine Development

Hepatitis B core (HBc) virus-like particles (VLPs) and flagellin are highly immunogenic and widely explored vaccine delivery platforms. Yet, HBc VLPs mainly allow the insertion of relatively short antigenic epitopes into the immunodominant c/e1 loop without affecting VLP assembly, and flagellin-based vaccines carry the risk of inducing systemic adverse reactions. This study explored a hybrid flagellin/HBc VLP (FH VLP) platform to present heterologous antigens by replacing the surface-exposed D3 domain of flagellin. FH VLPs were prepared by the insertion of flagellin gene into the c/e1 loop of HBc, followed by E. coli expression, purification, and self-assembly into VLPs. Using the ectodomain of influenza matrix protein 2 (M2e) and ovalbumin (OVA) as models, we found that the D3 domain of flagellin could be replaced with four tandem copies of M2e or the cytotoxic T lymphocyte (CTL) epitope of OVA without interfering with the FH VLP assembly, while the insertion of four tandem copies of M2e into the c/e1 loop of HBc disrupted the VLP assembly. FH VLP-based M2e vaccine elicited potent anti-M2e antibody responses and conferred significant protection against multiple influenza A viral strains, while FljB- or HBc-based M2e vaccine failed to elicit significant protection. FH VLP-based OVA peptide vaccine elicited more potent CTL responses and protection against OVA-expressing lymphoma or melanoma challenges than FljB- or HBc-based OVA peptide vaccine. FH VLP-based vaccines showed a good systemic safety, while flagellin-based vaccines significantly increased serum interleukin 6 and tumor necrosis factor α levels and also rectal temperature at increased doses. We further found that the incorporation of a clinical CpG 1018 adjuvant could enhance the efficacy of FH VLP-based vaccines. Our data support FH VLPs to be a highly immunogenic, safe, and versatile platform for vaccine development to elicit potent humoral and cellular immune responses.

Supplementation of H7N9 Virus-Like Particle Vaccine With Recombinant Epitope Antigen Confers Full Protection Against Antigenically Divergent H7N9 Virus in Chickens

The continuous evolution of the H7N9 avian influenza virus suggests a potential outbreak of an H7N9 pandemic. Therefore, to prevent a potential epidemic of the H7N9 influenza virus, it is necessary to develop an effective crossprotective influenza vaccine. In this study, we developed H7N9 virus-like particles (VLPs) containing HA, NA, and M1 proteins derived from H7N9/16876 virus and a helper antigen HMN based on influenza conserved epitopes using a baculovirus expression vector system (BEVS). The results showed that the influenza VLP vaccine induced a strong HI antibody response and provided effective protection comparable with the effects of commercial inactivated H7N9 vaccines against homologous H7N9 virus challenge in chickens. Meanwhile, the H7N9 VLP vaccine induced robust crossreactive HI and neutralizing antibody titers against antigenically divergent H7N9 viruses isolated in wave 5 and conferred on chickens complete clinical protection against heterologous H7N9 virus challenge, significantly inhibiting virus shedding in chickens. Importantly, supplemented vaccination with HMN antigen can enhance Th1 immune responses; virus shedding was completely abolished in the vaccinated chickens. Our study also demonstrated that viral receptor-binding avidity should be taken into consideration in evaluating an H7N9 candidate vaccine. These studies suggested that supplementing influenza VLP vaccine with recombinant epitope antigen will be a promising strategy for the development of broad-spectrum influenza vaccines.

Nanoparticles based on artificial self-assembling peptide and displaying M2e peptide and stalk HA epitopes of influenza A virus induce potent humoral and T-cell responses and protect against the viral infection

The extracellular domain of the M2 protein (M2e) and conserved region of the second subunit of the hemagglutinin (HA2) could be used for the development of broad-spectrum vaccines against influenza A. Here we obtained and characterized recombinant mosaic proteins containing tandem copies of M2e and HA2 fused to an artificial self-assembling peptide (SAP). The inclusion of SAP peptides in the fusion proteins enabled their self-assembly in vitro into spherical particles with a size of 30-50 nm. Intranasal immunization of mice with these particles without additional adjuvants induced strong humoral immune response against M2e and the whole virus. Particles carrying both M2e and HA2 induced antigen-specific multifunctional CD4+ effector memory T cells. Immunization provided high protection of mice against the lethal challenge with different subtypes of influenza A virus. The obtained self-assembling nanoparticles can be used to develop a universal influenza vaccine.

M2e-Based Influenza Vaccines with Nucleoprotein: A Review

Discovery of conserved antigens for universal influenza vaccines warrants solutions to a number of concerns pertinent to the currently licensed influenza vaccines, such as annual reformulation and mismatching with the circulating subtypes. The latter causes low vaccine efficacies, and hence leads to severe disease complications and high hospitalization rates among susceptible and immunocompromised individuals. A universal influenza vaccine ensures cross-protection against all influenza subtypes due to the presence of conserved epitopes that are found in the majority of, if not all, influenza types and subtypes, e.g., influenza matrix protein 2 ectodomain (M2e) and nucleoprotein (NP). Despite its relatively low immunogenicity, influenza M2e has been proven to induce humoral responses in human recipients. Influenza NP, on the other hand, promotes remarkable anti-influenza T-cell responses. Additionally, NP subunits are able to assemble into particles which can be further exploited as an adjuvant carrier for M2e peptide. Practically, the T-cell immunodominance of NP can be transferred to M2e when it is fused and expressed as a chimeric protein in heterologous hosts such as Escherichia coli without compromising the antigenicity. Given the ability of NP-M2e fusion protein in inducing cross-protective anti-influenza cell-mediated and humoral immunity, its potential as a universal influenza vaccine is therefore worth further exploration.

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.

Immunogenicity and Protective Efficacy of Influenza A DNA Vaccines Encoding Artificial Antigens Based on Conservative Hemagglutinin Stem Region and M2 Protein in Mice

Background: Development of a universal vaccine capable to induce antibody responses against a broad range of influenza virus strains attracts growing attention. Hemagglutinin stem and the exposed fragment of influenza virus M2 protein are promising targets for induction of cross-protective humoral and cell-mediated response, since they contain conservative epitopes capable to induce antibodies and cytotoxic T lymphocytes (CTLs) to a wide range of influenza virus subtypes. Methods: In this study, we generated DNA vaccine constructs encoding artificial antigens AgH1, AgH3, and AgM2 designed on the basis of conservative hemagglutinin stem fragments of two influenza A virus subtypes, H1N1 and H3N2, and conservative M2 protein, and evaluate their immunogenicity and protective efficacy. To obtain DNA vaccine constructs, genes encoding the designed antigens were cloned into a pcDNA3.1 vector. Expression of the target genes in 293T cells transfected with DNA vaccine constructs has been confirmed by synthesis of specific mRNA. Results: Immunization of BALB/c mice with DNA vaccines encoding these antigens was shown to evoke humoral and T-cell immune responses as well as a moderated statistically significant cross-protective effect against two heterologous viruses A/California/4/2009 (H1N1pdm09) and A/Aichi/2/68 (H3N2). Conclusions: The results demonstrate a potential approach to creating a universal influenza vaccine based on artificial antigens.

An approach to the influenza chimeric subunit vaccine (3M2e-HA2-NP) provides efficient protection against lethal virus challenge

OBJECTIVES

Vaccination is the most effective preventive strategy for influenza disease. As the virus undergoes high antigenic drift, it requires a constant reformulation to obtain high protection.

RESULTS

Immunogenicity of a purified chimeric protein containing conserved regions of influenza A/H1N1 viruses including the Hemagglutinin stalk domain, Nucleoprotein, and Matrix protein produced in a prokaryotic system was assessed in vitro and in vivo, alone or in combination with adjuvants by evaluating antibody responses, cytokine production, lymphocyte proliferative assay, and mortality rate after challenge. The animals that received the chimeric protein had specific antibody responses, elicited memory CD4 cells, cytokines of Th1 and Th2 cells and showed 75% protection against influenza virus lethal challenge. The animals injected with the chimeric protein supplemented with Alum showed improved immune responses, but they had 67% protection. In other words, although Alum adjuvant enriched the chimera specific immune responses potently, it could not enhance its protectivity.

CONCLUSION

Regarding the immunogenicity and protectivity of the chimeric protein construct against influenza, findings of the study suggested that the chimeric protein could be considered as a promising influenza vaccine candidate.

The Quest for a Truly Universal Influenza Vaccine

There is an unmet public health need for a universal influenza vaccine (UIV) to provide broad and durable protection from influenza virus infections. The identification of broadly protective antibodies and cross-reactive T cells directed to influenza viral targets present a promising prospect for the development of a UIV. Multiple targets for cross-protection have been identified in the stalk and head of hemagglutinin (HA) to develop a UIV. Recently, neuraminidase (NA) has received significant attention as a critical component for increasing the breadth of protection. The HA stalk-based approaches have shown promising results of broader protection in animal studies, and their feasibility in humans are being evaluated in clinical trials. Mucosal immune responses and cross-reactive T cell immunity across influenza A and B viruses intrinsic to live attenuated influenza vaccine (LAIV) have emerged as essential features to be incorporated into a UIV. Complementing the weakness of the stand-alone approaches, prime-boost vaccination combining HA stalk, and LAIV is under clinical evaluation, with the aim to increase the efficacy and broaden the spectrum of protection. Preexisting immunity in humans established by prior exposure to influenza viruses may affect the hierarchy and magnitude of immune responses elicited by an influenza vaccine, limiting the interpretation of preclinical data based on naive animals, necessitating human challenge studies. A consensus is yet to be achieved on the spectrum of protection, efficacy, target population, and duration of protection to define a “universal” vaccine. This review discusses the recent advancements in the development of UIVs, rationales behind cross-protection and vaccine designs, and challenges faced in obtaining balanced protection potency, a wide spectrum of protection, and safety relevant to UIVs.

Intragastric delivery of recombinant Lactococcus lactis displaying ectodomain of influenza matrix protein 2 (M2e) and neuraminidase (NA) induced focused mucosal and systemic immune responses in chickens

Compounding with the problem of frequent antigenic shift and occasional drift of the segmented genome of Avian Influenza Virus (AIV), vaccines based on major surface glycoproteins such as haemagglutinin (HA) to counter heterosubtypic AIV infection in chickens remain unsuccessful. In contrast, neuraminidase (NA), the second most abundant surface glycoprotein present in viral capsid is less mutable and, in some instances, successful in eliciting inter-species cross-reactive antibody responses. However, without selective activation of B-cells and T-cells, the ability of NA to induce strong cell mediated immune responses is limited, thus NA based vaccines cannot singularly address the risk of virus escape from host defence. To this end, the highly conserved ectodomain of influenza matrix protein-2 (M2e) has emerged as an attractive cross-protective vaccine target. The present study describes the potential of recombinant Lactococcus lactis (rL. lactis) in expressing functional influenza NA or M2e proteins and conferring effective mucosal and systemic immune responses in the intestine as well as in the upper respiratory airways (trachea) of chickens. In addition, lavages collected from trachea and intestine of birds administered with rL. lactis expressing influenza NA or M2e protein were found to protect MDCK cells against avian influenza type A/PR/8/34 (H1N1) virus challenge. Although minor, the differences in the expression of pro-inflammatory cytokines gene transcripts targeted in this study among the birds administered with either empty or rL. lactis could be attributed to the activation of innate response by L. lactis.

Immunogenicity of a Virus-Like-Particle Vaccine Containing Multiple Antigenic Epitopes of Toxoplasma gondii Against Acute and Chronic Toxoplasmosis in Mice

There is no effective protective vaccine against human toxoplasmosis, which is a potential threat to nearly a third of the world population. Vaccines based on virus-like particles (VLPs) have been highly successful in humans for many years, but have rarely been applied against Toxoplasma gondii infection. In this study, we inserted a B cell epitope (SAG1₈₂₋₁₀₂ or SAG1_301−320), a CD8⁺ cell epitope (HF10 or ROP7), and a CD4⁺ cell epitope (AS15) of T. gondii into a truncated HBc_Δ(amino acids1–149) particle to construct four chimeric VLP vaccine formulations, i.e., HBc_ΔH82, HBc_ΔH301, HBc_{Δ R82}, and HBc_{Δ R301}. When these chimeric HBc particles were expressed in Escherichia coli, they showed icosahedral morphology similar to that of the original VLPs and were evaluated as vaccine formulations against acute and chronic toxoplasmosis in a mouse model (BALB/c mice (H-2^d). All these chimeric HBc VLPs induced strong humoral and cellular immune responses with high IgG antibody titers and interferon(IFN)-γ production. Only the mice immunized with HBc_ΔH82 showed prolonged survival time (15.6 ± 3.8 vs. 5.6 ± 0.8 days) against acute infection with RH tachyzoites and decrease in brain parasite load (1,454 ± 239 vs. 2,091 ± 263) against chronic infection with Prugniuad cysts, as compared to the findings for the control group. These findings suggest that HBc VLPs would act as an effective carrier for delivering effective multiple antigenic epitopes and would be beneficial for developing a safe and long-acting vaccine against toxoplasmosis.

A two-step heat treatment of cell disruption supernatant enables efficient removal of host cell proteins before chromatographic purification of HBc particles

The thermal stability of HBc particles was systematically investigated for efficient removal of host cell proteins (HCP) by heat treatment before chromatographic step. The HBc particles were found stable up to 80°C for 30 min without any noticeable change in circular dichroism spectra, fluorescence spectra and transmission electron microscope observation. When heating was applied to precipitate the HCP in the cell disruption supernatant of HBc fermentation, the HCP removal effect was more obvious as the temperature went higher. However, a phenomenon was found beyond 70°C where the recovered HBc particles had larger than normal size and molecular weight as observed by dynamic light scattering and multi-angle laser light scattering. Analysis found that the HBc particles possess nanopores which expand with temperature. When the temperature was above 70℃, the pores were large enough for some HCP to penetrate in, but not being able to get out after cooling down. To fully utilize the thermal stability and avoid the interference of HCP entering, a two-step heat treatment strategy was designed. The supernatant was firstly heated up to 60°C for 30 min to precipitate most HCP, then another 30 min at 70°C was used to remove the rest impurities. The two-step heat treatment effectively avoided the HCP entering problem, achieving 85.8% particle recovery and 74.7% purity. With further one-step hydrophobic interaction chromatography, the purity was increased to 99.0% with overall process recovery of 77.7%, considerably higher than those reported in the literature. The same process design was applied to purify three HBc-related products, including OVA-HBc, M2e-HBc and NP-HBc. All recoveries were higher than 50% with purity greater than 97%.

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.

CROSS-PROTECTIVE PROPERTIES OF AN INFLUENZA VACCINE BASED ON HBC4M2E RECOMBINANT PROTEIN

One of the main problems in the area of influenza prophylaxis and pandemic prevention is the development of cross-reactive vaccines, i.e. vaccines directed against all subtypes of human influenza viruses. Such vaccines are being developed in many countries for more than 10 years. A number of vaccines are presently undergoing clinical trials. We created Uniflu candidate vaccine based on recombinant HBc4M2e protein consisting of 4 tandem-connected copies of the highly conserved ectodomain of M2 protein of the influenza A virus. These 4 copies were genetically fused to the carrier protein, namely hepatitis B core antigen. Commercially available Derinat was used as adjuvant in the candidate vaccine. Preclinical studies on laboratory animals (mice, ferrets) demonstrated that immunization with Uniflu leads to significantly higher level of specific immunoglobulins in the blood and bronchoalveolar lavages. Moreover, it produces immunoglobulins belonging to subtype IgG2a that is the most important mediator of antibody-dependent cytotoxicity. The vaccine under review stimulates the proliferation of T-lymphocytes, as well as the formation of CD4+ and CD8+ T-cells synthesizing ɣ-IFN. When infected with the lethal doses (5 LD50) of influenza A viruses of the subtypes H1N1, H2N2, H3N2, and H1N1pdm09, immunized animals typically developed mild form of illness. This kept them alive in 90-100% of cases, which demonstrated almost complete protection from death. Replication of the virus in the lungs of immunized mice was reduced by 1.8-4.8 log10. High immunogenicity of the vaccine, and reduced clinical symptoms following experimental infection, were demonstrated in ferrets as well. The developed recombinant vaccine Uniflu has high specific activity and cross-protection. Uniflu can be proposed as pre-pandemic vaccine, provided that it passes clinical trials.

Highly conserved M2e and hemagglutinin epitope-based recombinant proteins induce protection against influenza virus infection

Highly pathogenic influenza viruses continue to cause serious threat to public health due to their pandemic potential, calling for an urgent need to develop effective, safe, convenient, and universal vaccines against influenza virus infection. In this study, we constructed two recombinant protein vaccines, 2H5M2e-2H7M2e-H5FP-H7FP (hereinafter M2e-FP-1) and 2H5M2e-H5FP-2H7M2e-H7FP (hereinafter M2e-FP-2), by respectively linking highly conserved sequences of two molecules of ectodomain of M2 (M2e) and one molecule of fusion peptide (FP) epitope of hemagglutinin (HA) of H5N1 and H7N9 influenza viruses in different orders. The Escherichia coli-expressed M2e-FP-1 and M2e-FP-2 proteins induced similarly high-titer M2e-FP-specific antibodies in the immunized mice. Importantly, both proteins were able to prevent lethal challenge of heterologous H1N1 influenza virus, with significantly reduced viral titers and alleviated pathological changes in the lungs, as well as increased body weight and complete survivals, in the challenge mice. Taken together, our study demonstrates that highly conserved M2e and FP epitope of HA of H5N1 and H7N9 influenza viruses can be used as important targets for development of safe and economical universal influenza vaccines, and that the position of H7N9 M2e and H5N1 HA epitope sequences in the vaccine components has no significant effects on the immunogenicity and efficacy of M2e-FP-based subunit vaccines.

Recombinant M2e outer membrane vesicle vaccines protect against lethal influenza A challenge in BALB/c mice

Currently approved influenza vaccines predominantly protect through antibodies directed against the highly variable glycoprotein hemagglutinin (HA), necessitating annual redesign and formulation based on epidemiological prediction of predominant circulating strains. More conserved influenza protein sequences, such as the ectodomain of the influenza M2 protein, or M2e, show promise as a component of a universal influenza A vaccine, but require a Th1-biased immune response for activity. Recently, recombinant, bacterially derived outer membrane vesicles (OMVs) demonstrated potential as a platform to promote a Th1-biased immune response to subunit antigens. Here, we engineer three M2e-OMV vaccines and show that all elicit strong IgG titers, with high IgG2a:IgG1 ratios, in BALB/c mice. Additionally, the administration of one M2e-OMV construct containing tandem heterologous M2e peptides (M2e4xHet-OMV) resulted in 100% survival against lethal doses of the mouse-adapted H1N1 influenza strain PR8. Passive transfer of antibodies from M2e4xHet-OMV vaccinated mice to unvaccinated mice also resulted in 100% survival to challenge, indicating that protection is driven largely via antibody-mediated immunity. The potential mechanism through which M2e-OMVs initiated the immune response was explored and it was found that the constructs triggered TLR1/2, TLR4, and TLR5. Our data indicate that OMVs have potential as a platform for influenza A vaccine development due to their unique adjuvant profile and intrinsic pathogen-mimetic nature.

Use of computational and recombinant technologies for developing novel influenza vaccines

Influenza vaccine design has changed considerably with advancements in bioinformatics and computational biology. Improved surveillance efforts provide up-to-date information about influenza sequence diversity and assist with monitoring the spread of epidemics and vaccine efficacy rates. The advent of next-generation sequencing, epitope scanning and high-throughput analysis all help decipher influenza-associated protein interactions as well as predict immune responsiveness based on host genetic diversity. Computational approaches are utilized in nearly all aspects of vaccine design, from modeling, compatibility predictions, and optimization of antigens in various platforms. This overview discusses how computational techniques strengthen vaccine efforts against highly diverse influenza species.