Protective efficacy against tuberculosis of ESAT-6 secreted by a live Salmonella typhimurium vaccine carrier strain and expressed by naked DNA.

We have constructed a recombinant (r) attenuated Salmonella typhimurium strain which secretes ESAT-6 of Mycobacterium tuberculosis via the hemolysin secretion system of E. coli. Additionally, we have ligated ESAT-6 to different commercially available mammalian expression systems for use as naked DNA vaccines. We studied protection against M. tuberculosis induced by vaccination with each of these constructs alone or in combination in mice. Vaccination with a single dose of r S. typhimurium secreting ESAT-6 reduced numbers of tubercle bacilli in the lungs throughout the course of infection. The combined prime-boost vaccination did not considerably enhance protection.