Potentiation of E7 antisense RNA-induced antitumor immunity by co-delivery of IL-12 gene in HPV16 DNA-positive mouse tumor

Down-regulation of oncogene expression by antisense-based gene therapy has been extensively studied, and in some cases, therapeutic effects have been demonstrated. We have previously shown that down-regulation of HPV16 E6 and E7 gene expression inhibited HPV DNA-positive C3 mouse tumor growth. Although not all of the tumor cells were transfected by pU6E7AS plasmid , complete tumor regression was achieved if the tumor size was small at the start of therapy in a syngeneic host. This suggests that some other antitumor mechanisms may be involved in addition to the direct down-regulation of HPV16 E7 oncogene expression by the antisense effect of E7AS induces tumor cell apoptosis. More importantly, a strong antitumor immune response was elicited in the pU6E7AS-treated and tumor-regressed mice. There was no tumor growth after rechallenging the tumor-regressed mice with 1 million C3 cells. This E7AS-induced antitumor immune response was augmented by co-delivery of mIL-12 cytokine gene. The combination therapy strategy resulted in complete regression of 26 of 28 (93%) tumors. Only 12 of 31 (38%) tumors from the group treated with pU6E7AS alone and 14 of 28 (50%) tumors from the group treated with pCMVmIL-12 alone had completely regressed. Complete regression was also demonstrated in tumors located 1 cm from the treated tumors, which indicates that a systemic antitumor effect was induced by E7AS and mIL-12 . Immunohistochemistry demonstrated that a significant amount of CD4(+) and CD8(+) cells infiltrated into tumors treated with pU6E7AS, pCMVmIL-12 and pU6E7AS + pCMVmIL-12. These data indicate that host immunity is an important factor for antisense-based gene therapy approach which can be further enhanced by combination with cytokine gene therapy.