IL-18 gene transfer results in regression of CT26 liver tumors. CT26 cells (1.0 × 105) were injected into a left lobe of the livers of 6-8-week-old BALB/c mice. pCEP4 or mIL-18 plasmid DNA was injected directly into the tumors on day 7. Tumor growth was measured on days 1, 4, 7, and 14 after plasmid implantation. Data are presented as the mean of tumor weights of 8 mice/group.