Trichinella spiralis: intranasal immunization with attenuated Salmonella enterica carrying a gp43 antigen-derived 30mer epitope elicits protection in BALB/c mice.

Trichinellosis is a public health problem and is considered an emergent/re-emergent disease in various countries. The etiological agent of trichinellosis is the nematode Trichinella, which infects domestic animals such as pigs and horses, as well as wild animals and humans. A veterinary vaccine could be an option to control the disease in domestic animals. Although several vaccine candidates have shown promising results, a vaccine against trichinellosis remains unavailable to date. Attenuated Salmonella strains are especially attractive live vectors because they elicit mucosal immunity, which is known to be important for the control of Trichinella spiralis infection at the intestinal level and can be administered by oral or intranasal routes. In this study, the autotransporter ShdA was used to display, on the surface of the Salmonella enterica serovar Typhimurium SL3261, the 210-239 amino acid epitope, (designated as Ag30) derived from the 43 kDa glycoprotein of T. spiralis muscle larvae. The fusion protein elicited antibodies in BALB/c mice that were able to recognize the native epitope on the surface of T. spiralis muscle larvae. Mice immunized by intranasal route with the recombinant Salmonella induced a protective immune response against the T. spiralis challenge, reducing by 61.83% the adult burden at day eight postinfection. This immune response was characterized by the induction of antigen-specific IgG1 and of IL-5 production. This study demonstrates the usefulness of Salmonella as a carrier of nematode epitopes providing a surface display system for intestinal parasite vaccine applications.

A fusogenic peptide expressed on the surface of Salmonella enterica elicits CTL responses to a dengue virus epitope.

Attenuated Salmonella strains are used widely as live carriers of antigens because they elicit both mucosal and systemic immunity against passenger antigens. However, they generally evoke poor cytotoxic T cell (CTL) responses because Salmonella resides within vacuolar compartments and the passenger antigens must travel to the cytosol and be processed through the MHC class I-dependent pathway to simulate CTLs. To address this problem, we designed a fusion protein to destabilize the phagosome membrane and allow a dengue epitope to reach the cytosol. The fusion protein was displayed on the bacterial surface of Salmonella enterica serovar Typhimurium SL3261 through the beta domain of the autotransporter MisL. The passenger alpha domain contained, from the N-terminus, a fusogenic sequence, the NS3 protein 298-306-amino acid CTL epitope from the dengue virus type 2, a molecular tag, and a recognition site for the protease OmpT to release it to the milieu. Display of the fusion protein on the bacterial surface was demonstrated by IFA and flow cytometry using antibodies against the molecular tag. Cleavage of the fusogenic protein-dengue peptide was demonstrated by flow cytometry using OmpT+ Escherichia coli strains. The recombinant Salmonella strains displaying the fusogenic-dengue peptide were able to lyse erythrocytes, induced specific proliferative responses, and elicited CTL responses. These results suggest that the recombinant fusion proteins containing fusogenic sequences provide a promising system to induce CTLs by live vector vaccines.