Recombinant Mycobacterium smegmatis mc155 vaccine expressing outer membrane protein 26 kDa antigen affords therapeutic protection against Helicobacter pylori infection

Orally administered recombinant Mycobacterium smegmatis (rM. smegmatis) vaccines represent an attractive option for mass vaccination programmes against various infectious diseases. Therefore, in the present study, we evaluated the capacity of the outer membrane protein 26 kDa antigen (Omp26) of Helicobacter pylori (H. pylori) to induce therapeutic protection against H. pylori infection in mice. Omp26 was cloned and expressed in M. smegmatis mc²155 as a fusion with the Mycobacterium fortuitum β-lactamase protein under the control of the up-regulated M. fortuitum β-lactamase promoter, pBlaF*. The rM. smegmatis strain was shown to be relatively stable in vitro in terms of plasmid stability and bacterial persistence. We found that oral immunization of H. pylori-infected mice with rM. smegmatis-Omp26 induced protection, i.e., significant reduction in bacterial colonization in the stomach. The protection was strongly related to serum specific antibodies with a Th₁ and Th₂ profile as well as to local cytokines in the stomach and spleen. These findings suggest that Omp26 is a promising vaccine candidate antigen for use in a therapeutic vaccine against H. pylori. The rM. smegmatis expressing Omp26 antigen could constitute an effective, low-cost combined vaccine against H. pylori.