Immunogenicity and protective efficacy of candidate universal influenza A nanovaccines produced in plants by Tobacco mosaic virus-based vectors

A new approach for super-expression of the influenza virus epitope M2e in plants has been developed on the basis of a recombinant Tobacco mosaic virus (TMV, strain U1) genome designed for Agrobacterium-mediated delivery into the plant cell nucleus. The TMV coat protein (CP) served as a carrier and three versions of the M2e sequence were inserted into the surface loop between amino acid residues 155 and 156. Cysteine residues in the heterologous peptide were thought likely to impede efficient assembly of chimeric particles. Therefore, viral vectors TMV-M2e-ala and TMV-M2e-ser were constructed in which cysteine codons 17 and 19 of the M2e epitope were substituted by codons for serine or alanine. Agroinfiltration experiments proved that the chimeric viruses were capable of systemically infecting Nicotiana benthamiana plants. Antisera raised against TMV-M2e-ala virions appear to contain far more antibodies specific to influenza virus M2e than those specific to TMV carrier particle (ratio 5:1). Immunogold electron microscopy showed that the 2-epitopes were uniformly distributed and tightly packed on the surface of the chimeric TMV virions. Apparently, the majority of the TMV CP-specific epitopes in the chimeric TMV-M2e particles are hidden from the immune system by the M2e epitopes exposed on the particle surface. The profile of IgG subclasses after immunization of mice with TMV-M2e-ser and TMV-M2e-ala was evaluated. Immunization with TMV-M2e-ala induced a significant difference between the levels of IgG1 and IgG2a (IgG1/IgG2a=3.2). Mice immunized with the chimeric viruses were resistant to five lethal doses (LD50) of the homologous influenza virus strain, A/PR/8/34 (H1N1) and TMV-M2e-ala also gave partial protection (5LD50, 70% of survival rate) against a heterologous strain influenza A/California/04/2009 (H1N1) (4 amino acid changes in M2e). These results indicate that a new generation candidate universal nanovaccine against influenza based on a recombinant TMV construct has been obtained.

Protection against multiple influenza A virus strains induced by candidate recombinant vaccine based on heterologous M2e peptides linked to flagellin

Matrix 2 protein ectodomain (M2e) is considered a promising candidate for a broadly protective influenza vaccine. M2e-based vaccines against human influenza A provide only partial protection against avian influenza viruses because of differences in the M2e sequences. In this work, we evaluated the possibility of obtaining equal protection and immune response by using recombinant protein on the basis of flagellin as a carrier of the M2e peptides of human and avian influenza A viruses. Recombinant protein was generated by the fusion of two tandem copies of consensus M2e sequence from human influenza A and two copies of M2e from avian A/H5N1 viruses to flagellin (Flg-2M2eh2M2ek). Intranasal immunisation of Balb/c mice with recombinant protein significantly elicited anti-M2e IgG in serum, IgG and sIgA in BAL. Antibodies induced by the fusion protein Flg-2M2eh2M2ek bound efficiently to synthetic peptides corresponding to the human consensus M2e sequence as well as to the M2e sequence of A/Chicken/Kurgan/05/05 RG (H5N1) and recognised native M2e epitopes exposed on the surface of the MDCK cells infected with A/PR/8/34 (H1N1) and A/Chicken/Kurgan/05/05 RG (H5N1) to an equal degree. Immunisation led to both anti-M2e IgG1 and IgG2a response with IgG1 prevalence. We observed a significant intracellular production of IL-4, but not IFN-γ, by CD4+ T-cells in spleen of mice following immunisation with Flg-2M2eh2M2ek. Immunisation with the Flg-2M2eh2M2ek fusion protein provided similar protection from lethal challenge with human influenza A viruses (H1N1, H3N2) and avian influenza virus (H5N1). Immunised mice experienced significantly less weight loss and decreased lung viral titres compared to control mice. The data obtained show the potential for the development of an M2e-flagellin candidate influenza vaccine with broad spectrum protection against influenza A viruses of various origins.

Flagellin-fused protein targeting M2e and HA2 induces potent humoral and T-cell responses and protects mice against various influenza viruses a subtypes

BACKGROUND

Current influenza vaccines are mainly strain-specific and have limited efficacy in preventing new, potentially pandemic, influenza strains. Efficient control of influenza A infection can potentially be achieved through the development of broad-spectrum vaccines based on conserved antigens. A current trend in the design of universal flu vaccines is the construction of recombinant proteins based on combinations of various conserved epitopes of viral proteins (M1, M2, HA2, NP). In this study, we compared the immunogenicity and protective action of two recombinant proteins which feature different designs and which target different antigens.

RESULTS

Balb/c mice were immunized subcutaneously with Flg-HA2-2-4M2ehs or FlgSh-HA2-2-4M2ehs; these constructs differ in the location of hemagglutinin's HA2-2(76-130) insertion into flagellin (FliC). The humoral and T-cell immune responses to these constructs were evaluated. The simultaneous expression of different M2e and HA2-2(76-130) in recombinant protein form induces a strong M2e-specific IgG response and CD4+/ CD8+ T-cell response. The insertion of HA2-2(76-130) into the hypervariable domain of flagellin greatly increases antigen-specific T-cell response, as evidenced by the formation of multi-cytokine-secreting CD4+, CD8+ T-cells, Tem, and Tcm. Both proteins provide full protection from lethal challenge with A/H3N2 and A/H7N9.

CONCLUSION

Our results show that highly conserved M2e and HA2-2(76-130) can be used as important targets for the development of universal flu vaccines. The location of the HA2-2(76-130) peptide's insertion into the hypervariable domain of flagellin had a significant effect on the T-cell response to influenza antigens, as seen by forming of multi-cytokine-secreting CD4+ and CD8+ T-cells.

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

Background

Influenza 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.

Methods

Balb/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.

Result

We 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.

Conclusion

This 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.

Study of immunogenicity of recombinant proteins based on hemagglutinin and neuraminidase conservative epitopes of influenza A virus

Background

Recombinant hemagglutinin (rHA) and neurominidase (rNA) developed in our investigation are amino acid sequence consensus variants of H1N1 2009 subtype influenza virus strain, also including immunogenic epitopes typical for other influenza virus subtypes (H3N1 and H5N1). Substitutions were made: typical for Russian virus isolates (in HA – S220T, NA – D248N) and in active centers of molecules – R118L, R293L, R368L; C92S, C417S to increase recombinant proteins stability in E. coli. The aim of the present work was to study immunogenicity of the obtained rHA and rNA.

Material/Methods

Fragments aa 83–469 of NA and aa 61–287 of HA were chosen because they include the main B-cell epitopes and are the minimal structures for correct folding of target proteins. The designed nucleotide sequences were synthesized and purified and the expression of rNA and rNA were analyzed. For immunization and virus challenge we used influenza viruses A/California/04/2009 (H1N1), A/PR/8/34 (H1N1), A/Perth/16/2009 (H3N2), A/Chicken/Kurgan/05/2005 R.G. (H5N1), and B/Florida/04/2006. Specific IgG levels were determined by ELISA in 96-well ELISA plates. Significant differences of survival in mouse groups were analyzed by Mantel-Cox (log-rank) and Gehan-Breslow-Wilcoxon tests.

Results

The obtained results demonstrate the high immunogenicity and ability of indicated proteins mixture to provide similar cross-protection against influenza viruses of the H1N1 subtype.

Conclusions

The data obtained suggest efficient pluripotent vaccine creation based on HA and NA conservative regions.

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 reproductive attenuated H2N2 and H7N9 reassortants on the basis of A/Hong Kong/1/68/162/35 donor virus

Reassortants with surface antigens from potentially pandemic A/H2N2 and A/H7N9 influenza viruses were created on the basis of attenuated and highly reproductive A/Hong Kong/1/68/162/35(H3N2) donor virus obtained in the Research institute of influenza. High reproductive activity of reassortant viruses and immunogenicity of live and inactivated influenza vaccines based on these viruses indicate the possibility to use obtained reassortants for production of live and inactivated vaccines against potentially pandemic influenza A viruses.

[Immunization with live attenuated A/H5N1 vaccine protects guinea pigs from reinfection]

Cold-adapted influenza virus A/HK/1/68/162/35(H3N2) was developed as unified donor of attenuation and high reproductive capacity forvaccine strains. The reassortant of this donor with surface antigens of highly pathogenic strain Alchicken/Astana/6/05 (H5N1) was tested in guinea pigs as a live or inactivated preparation. Immunization with both formulations induced equal levels of serum virus specific antibodies, while the level of mucosal antibodies was significantly higher in animals immunized with live virus. The challenge with the homologous virus demonstrated complete virus clearance only in this group, thereby indicating a direct correlation of the protection level with the level of mucosal antibodies.

[Immunogenicity of recombinant proteins including ectodomain of M2 influenza virus A]

Two recombinant proteins with three copies of the ectodomain of the conserved influenza protein M2 (M2e) of influenza viruses were developed: A (H1N1)pdm09, A/Kurgan/05/05 (H5N1), and M2e consensus sequence of the human influenza A virus (H1N1, H2N2, H3N2) based on flagellin and core antigen of hepatitis B (HBc). The first recombinant protein comprised flagellin fused to three tandem copies of M2e, the second preparation was based on non-covalent interaction between M2e peptides and HBc. The immunogenicity of two preparations was comparatively tested. A covalent linkage of flagellin with M2e significant increased the immunogenicity of the target antigen compared with non-covalent interaction M2e and HBc. Flagellin as a protein carrier of M2e induced mainly IgG1 subclass, whereas HBc stimulated more balanced Th1/Th2 response. Our study showed a decrease in the viral titers in lung tissues of immunized mice after lethal challenge of A/PR/8/34 (H1N1). The study revealed a possibility to obtain a vaccine preparation with equal immunogenicity both against human influenza viruses and highly pathogenic avian influenza viruses.

[Characterization of influenza virus reassortants based on new donor strain A/HK/1/68/162/35(H3N2)]

Influenza reassortant viruses A/SPb/HK/09(H1N1), A/Astana/HK/2009 (H5N1), A/Otar/HK/2010(H3N8), and A/Perth/ HK/2011(H3N2), carrying surface antigens of different subtypes, were constructed on the basis of new potential unified donor strain A/HK/1/68/162/35(H3N2). The virulence and reproduction activity of the obtained reassortants were tested. The safety of the candidate live and inactivated influenza vaccines produced from the reassortant viruses was demonstrated. The study demonstrates that A/HK/1/68/162/35 can be used as a unified donor for attenuated and high-yield vaccine reassortants.

[Impact of mutations in nucleoprotein on replication of influenza virus A/Hong Kong/1/68/162/35 reassortants at different temperatures]

The nucleoprotein (NP) of influenza virus is a multifunctional RNA binding protein. The role of NP in the adaptation of influenza viruses to a host has been experimentally proved. Ambiguous data are available on the role of nucleoprotein in the attenuation of influenza A viruses, which is characterized by ability to replicate at low temperature (26°C) and inability to replicate at high temperature (39°C). Influenza virus donor strain A/Hong Kong/1/68/162/35 (H3N2), adapted to growth at low temperature, differs from the wild type virus by 14 amino acid mutations in the internal and non-structural proteins. Two mutations occurred in the NP: Gly102Arg and Glu292Gly. We have obtained viruses with point reverse-mutations in these positions and compared their replication at different temperatures by measuring infectious activity in chicken embryos. It has been shown that reverse mutation Gly292Glu in the NP reduced virus ability to replicate at low temperature, the introduction of the second reverse mutation Arg102Gly completely abolished virus cold adaptation.

[Characterization of cold-adapted influenza strain A/HongKong/1/68/162/35 as a potential donor of attenuation and high reproduction]

Live and inactivated vaccines are currently produced using virus reassortants originating from various gene donors of internal proteins. Based on the pandemic virus A/Hong Kong/1/68 (H3N2), a cold-adapted thermo-sensitive strain A/Hong Kong/1/68/162/35 was generated. It is distinguished for its high reproductive capacity (9-9.5 lg EID50), and hemagglutinating activity (1:1024-1:2048). The strain has ts and ca phenotype: reproductive capacity at t = 39 degrees C is 1.0 lg EID50; at t = 26 degrees C, 8.5 lg EID50. A total of 16 mutations have emerged from comprehensive sequencing of the virus genome. Among them 10 mutations were located in the genes of polymerase complex and NP, with respective amino-acid substitutions. The stability of strain characteristics, such as attenuation to humans and high reproductive capacity, were confirmed by repeated sequencing of the genome after tenfold passing of the virus in chicken embryos. Reassortants of the strain A/Hong Kong/1/68/162/35 with the wild-type viruses have inherited useful features of donor virus.