An orally available, genetically engineered Salmonella typhimurium strain expressing a truncated form of the human cytokine interleukin-2 (IL-2) gene, with antitumor activity. Upon administration of recombinant attenuated S. typhimurium expressing IL-2 (SalpIL2), this Salmonella strain may selectively accumulate and divide in a variety of tumor types, and express IL-2. In turn, IL-2 may induce natural killer (NK) cell proliferation thereby enhancing their activity. This may inhibit the growth of tumor cells.