Mice Are Protected from Helicobacter pylori Infection by Nasal Immunization with Attenuated Salmonella typhimurium phoP(c) Expressing Urease A and B Subunits

Live Salmonella typhimurium phoP(c) bacteria were tested as mucosal vaccine vectors to deliver Helicobacter pylori antigens. The genes encoding the A and B subunits of H. pylori urease were introduced into S. typhimurium phoP(c) and expressed under the control of a constitutive tac promoter (tac-ureAB) or a two-phase T7 expression system (cT7-ureAB). Both recombinant Salmonella strains expressed the two urease subunits in vitro and were used to nasally immunize BALB/c mice. The plasmid carrying cT7-ureAB was stably inherited by bacteria growing or persisting in the spleen, lungs, mesenteric or cervical lymph nodes, and Peyer’s patches of immunized mice, while the plasmid carrying tac-ureAB was rapidly lost. Spleen and Peyer’s patch CD4(+) lymphocytes from mice immunized with S. typhimurium phoP(c) cT7-ureAB proliferated in vitro in response to urease, whereas cells from mice given S. typhimurium phoP(c) alone did not. Splenic CD4(+) cells from mice immunized with phoP(c) cT7-ureAB secreted gamma interferon and interleukin 10, while Peyer’s patch CD4(+) cells did not secrete either cytokine. Specific H. pylori anti-urease immunoglobulin G1 (IgG1) and IgG2A antibodies were detected following immunization, confirming that both Th1- and Th2-type immune responses were generated by the live vaccine. Sixty percent of the mice (9 of 15) immunized with S. typhimurium phoP(c) cT7-ureAB were found to be resistant to infection by H. pylori, while all mice immunized with phoP(c) tac-ureAB (15 of 15) or phoP(c) (15 of 15) were infected. Our data demonstrate that H. pylori urease delivered nasally by using a vaccine strain of S. typhimurium can trigger Th1- and Th2-type responses and induce protective immunity against Helicobacter infection.