Immunogenicity characterization of the multi-epitope vaccine CTB-UE with chitosan-CpG as combination adjuvants against Helicobacter pylori

• The solubility rate of the CTB-UE from EnBase flo medium group could reach ∼90%.
• The chitosan-CpG plus CTB-UE could elicit higher level specific IgG and IgG2a.
• The chitosan-CpG adjuvants could changed the ratio of IgG2a/IgG1.
• The splenocytes amounts from CTB-UE plus chitosan or CpG increase obviously.
• The chitosan-CpG group showed a high level of the IFN-γ and IL-17, but not IL-4.

Urease is considered as an excellent vaccine candidate antigen against Helicobacter pylori (H. pylori) infection. Our previous study reported a novel multi-epitope vaccine CTB-UE which was composed of the mucosal adjuvant cholera toxin B subunit (CTB) and five cell epitopes from urease subunits. Murine experiments indicated that it could induce cellular and humoral immune responses intensively and attenuate H. pylori infection effectively in mice model. However, the body expression and lack of suitable adjuvant of this epitope vaccine restricted its application. In this study, new recombinant Escherichia coli strains was established to increase the solubility by fusing thioredoxin (Trx) and the combination adjuvants which composed of the chitosan and CpG were adopted to enhance the immunogenicity of CTB-UE for oral immunization. The experimental results indicated that the levels of IgG2a, IgG1 and IgA in the serum and the levels of sIgA in stomach, intestine and feces were significantly higher in the vaccinated group compared with the model control group. Additionally, chitosan-CpG combination adjuvants changed the ratio of IgG2a/IgG1 and conferred Th1/Th17-mediated protective immune responses. These results demonstrate that the oral vaccine with chitosan-CpG as combination adjuvants may be a promising vaccine candidate against H. pylori infection.