Double-stranded RNA (dsRNA) has multiple antitumor mechanisms that may be used to control tumor growth. Previously we have shown that treatment of solid tumors with a plasmid that encodes Sindbis viral RNA replicase complex， pSIN-β， significantly inhibited the growth of tumors in mice. In the present study， we evaluated the feasibility of further improving the antitumor activity of the pSIN-β plasmid by incorporating interleukin-2 (IL2) gene into the plasmid. The resultant pSIN-IL2 plasmid was delivered to mouse melanoma cells that overexpress the sigma receptor. Here we report that the pSIN-IL2 plasmid was more effective at controlling the growth of B16 melanoma in mice when complexed with sigma receptor-targeted liposomes than with the untargeted liposomes. Importantly， the pSIN-IL2 plasmid was more effective than pSIN-β plasmid at controlling the growth of B16 melanoma in mice， and B16 tumor-bearing mice that were treated with pSIN-IL2 had an elevated number of activated CD4(+)， CD8(+)， and natural killer cells， as compared to those treated with pSIN-β. The RNA replicase-based， IL2-expressing plasmid may have applications in melanoma gene therapy.