Live Attenuated Salmonella Vaccines against Mycobacterium tuberculosis with Antigen Delivery via the Type III Secretion System

Abstract

ABSTRACTTuberculosis remains a global health threat, and there is dire need to develop a vaccine that is safe and efficacious and confers long-lasting protection. In this study, we constructed recombinant attenuatedSalmonellavaccine (RASV) strains with plasmids expressing fusion proteins consisting of the 80 amino-terminal amino acids of the type 3 secretion system effector SopE ofSalmonellaand theMycobacterium tuberculosisantigens early secreted antigenic target 6-kDa (ESAT-6) protein and culture filtrate protein 10 (CFP-10). We demonstrated that the SopE-mycobacterial antigen fusion proteins were translocated into the cytoplasm of INT-407 cells in cell culture assays. Oral immunization of mice with RASV strains synthesizing SopE–ESAT-6–CFP-10 fusion proteins resulted in significant protection of the mice against aerosol challenge withM. tuberculosisH37Rv that was similar to the protection afforded by immunization withMycobacterium bovisbacillus Calmette-Guérin (BCG) administered subcutaneously. In addition, oral immunization with the RASV strains specifying these mycobacterial antigens elicited production of significant antibody titers to ESAT-6 and production of ESAT-6- or CFP-10-specific gamma interferon (IFN-γ)-secreting and tumor necrosis factor alpha (TNF-α)-secreting splenocytes.