A method of treating cancer comprising administering a therapeutically effective amount of a therapeutic composition, the composition comprising an anti-immunosuppressant vector that disrupts tumor-derived immune suppression and suppresses tumor growth, wherein the anti-immunosuppressant vactor comprises an attenuated Salmonella typhimurium strain selected from the group consisting of YS1646 (ATCC #202165), RE88, SL7207, x8429, x8431, and x8468 comprising a plasmid that expresses an shRNA molecule that suppresses the expression of an immunosuppressive target IDO1 and suppresses tumor growth.