A 17-kilodalton (kDA) protein of the facultative intracellular bacterium Francisella tularensis is one of several membrane proteins that induce an in vitro response in T cells from F. tularensis-primed humans. A DNA fragment containing two genes, one of which encodes the 17-kDa protein, was cloned into an attenuated Salmonella typhimurium strain. Mice orally immunized with the recombinant S. typhimurium strain showed lower viable counts in livers and spleens after challenge with F. tularensis LVS (live vaccine strain) than did animals immunized with the non-recombinant strain. Cyclosporin A neutralized the protective effect of the recombinant S. typhimurium strain.