Abstract

BackgroundType A influenza viruses are contagious and even life-threatening if left untreated. So far, no broadly protective vaccine is available due to rapid antigenic changes and emergence of new subtypes of influenza virus. In this study, we exploited bioinformatics tools in order to design a subunit chimeric vaccine from the antigenic and highly conserved regions of HA and M2 proteins of H7N9 subtype of influenza virus. We used mucosal adjuvant candidates, including CTxB, STxB, ASP-1, and LTB to stimulate mucosal immunity and analyzed the combination of HA2, M2e, and the adjuvant. Furthermore, to improve the antigen function and to maintain their three-dimensional structure, 12 different linkers including six rigid linkers and six flexible linkers were used. The 3D structure model was generated using a combination of homology and ab initio modeling methods and the molecular dynamics of the model were analyzed, either.ResultsAnalysis of different adjuvants showed that using CtxB as an adjuvant, results in higher overall vaccine stability and higher half-life among four adjuvant candidates. Fusion of antigens and the CTxB in the form of M2e-linker-CTxB-linker-HA2 has the most stability and half life compared to other combination forms. Furthermore, the KPKPKP rigid linker showed the best result for this candidate vaccine among 12 analyzed linkers. The changes in the vaccine 3D structure made by linker insertion found to be negligible, however, although small, the linker insertion between the antigens causes the structure to change slightly. Eventually, using predictive tools such as Ellipro, NetMHCpan I and II, CD4episcore, CTLpred, BepiPred and other epitope analyzing tools, we analyzed the conformational and linear epitopes of the vaccine. The solubility, proteasome cleavage sites, peptidase and potential chemical cutters, codon optimization, post translational modification were also carried out on the final vaccine.ConclusionsIt is concluded that M2e-Linker-CTxB-Linker-HA2 combination of chimeric vaccine retains its 3D structure and antigenicity when KPKPKP used as linker and CTxB used as adjuvant.

Highlights

  • Type A influenza viruses are contagious and even life-threatening if left untreated

  • Influenza viruses belong to a family of RNA viruses, Orthomyxoviridae, that are categorized as types A, B, C, and Thogotovirus, which among them, only type A and B are clinically relevant for humans disease [1]

  • ProtParam server was used to find which combination of these antigens and which adjuvant could result in the most stable structure and longest half-life

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Summary

Introduction

Type A influenza viruses are contagious and even life-threatening if left untreated. So far, no broadly protective vaccine is available due to rapid antigenic changes and emergence of new subtypes of influenza virus. Based on HA and NA surface antigens, 18 HA subtypes and 11 NA subtypes have been observed for type A influenza viruses that are theoretically expected to generate 198 potential new viral subtypes [3]. The M2 antigen of the influenza A virus is a surface protein that acts as a tetrameric ion channel pump on the surface of the virus. This activity is carried out after the virus entry into the cell and attaching to endosomes to regulate the pH of the virus capsid and pump the protons via a pH-inducible proton transport mechanism [4]. Various modifications have been utilized to enhance their immunogenicity and production of neutralizing antibodies against these two proteins [7, 8]

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