Surface expression of Helicobacter pylori HpaA adhesion antigen on Vibrio cholerae, enhanced by co-expressed enterotoxigenic Escherichia coli fimbrial antigens.

Abstract

Helicobacter pylori infection can cause peptic ulceration and is associated with gastric adenocarcinoma. This study aimed to construct and characterize a non-virulent Vibrio cholerae O1 strain, which grows more rapidly than H.pylori, as vector for H.pylori antigens for possible use as a vaccine strain against H.pylori. This was done by recombinant expression of the H.pylori adhesion antigen HpaA alone or, as a proof of principle, together with different colonization factor (CF) antigens of enterotoxigenic Escherichia coli (ETEC) which may enhance immune responses against HpaA. A recombinant V.cholerae strain co-expressing HpaA and a fimbrial CF antigens CFA/I or CS5, but not the non-fimbrial CF protein CS6, was shown to express larger amounts of HpaA on the surface when compared with the same V.cholerae strain expressing HpaA alone. Mutations in the CFA/I operon showed that the chaperon, possibly together with the usher, was involved in enhancing the surface expression of HpaA. Oral immunization of mice with formaldehyde-inactivated recombinant V.cholerae expressing HpaA alone or together with CFA/I induced significantly higher serum antibody responses against HpaA than mice similarly immunized with inactivated HpaA-expressing H.pylori bacteria. Our results demonstrate that a non-virulent V.cholerae strain can be engineered to allow strong surface expression of HpaA, and that the expression can be further increased by co-expressing it with ETEC fimbrial antigens. Such recombinant V.cholerae strains expressing HpaA, and possibly also other H.pylori antigens, may have the potential as oral inactivated vaccine candidates against H.pylori.