Investigation into immunological responses against a native recombinant CTB whole-cell Vibrio cholerae vaccine in a rabbit model

Aim The aim of this study was to express and purify the recombinant CTB (rCTB) protein from Vibrio cholerae and investigate the biological and immunological characteristics of purified protein in rabbit animal model and in combination with Iranian inactivated V. cholerae whole cells as a domestic recombinant WC-CTB vaccine. Methods and Results Expressed 6XHis-tagged rCTB was properly purified, and its identity was confirmed by Western blotting using cholera toxin-specific antibody. Concentration of purified protein was assessed to be 700 mg l-1. GM1-ELISA assay showed that purified rCTB pentamer was functionally active and able to bind GM1 in a dose-dependent manner. Recombinant CTB was inoculated into rabbits through intestinal rout alone and in combination with inactivated whole-cell V. cholerae strains (WC). The anti-CTB IgG titre showed that serum IgG responses were significantly increased in groups immunized with rCTB mixed with inactivated WC in comparison with control group. Furthermore, rCTB without V. cholerae WC also stimulated the IgG responses when inoculated into rabbit intestine. Challenge experiments of immunized rabbits showed an adequate protection against V. cholerae strains. Conclusions Recombinant CTB alone and in combination with inactivated Iranian strains was protective against live toxigenic V. cholerae strains, made it a potential candidate for an indigenous vaccine. Significance and Impact of the Study It was proved that rCTB produced in this system can be used as a potent immunogenic protein to stimulate the immunity against V. cholerae strains and can be used for developing a native vaccine composed of our local strains with their own surface structures and antigenic determinants against cholera.