Synergistic inhibition of tumor growth in a murine mammary adenocarcinoma model by combinational gene therapy using IL-12, pro-IL-18, and IL-1 beta converting enzyme cDNA

We report here that a cancer gene therapy protocol using a combination of I L-12, pro-IL-18, and IL-1 beta converting enzyme (ICE) cDNA expression vect ors simultaneously delivered via gene gun can significantly augment antitum or effects, evidently by generating increased levels of bioactive IL-18 and consequently IFN-gamma. First, we compared the levels of IFN-gamma secrete d by mouse splenocytes stimulated with tumor cells transfected with various test genes, including IL-12 alone; pro-IL-18 alone; pro-IL-18 and ICE; IL- 12 and pro-IL-18; and IL-12, pro-IL-18, and ICE. Among these treatments, th e combination of IL-12, pro-IL-ll, and ICE cDNA resulted in the highest lev el of IFN-gamma production from splenocytes in vitro, and similar results w ere obtained when these same treatments were delivered to the skin of a mou se by gene gun and IFN-gamma levels were measured at the skin transfection site in vivo. Furthermore, the triple gene combinatorial gene therapy proto col was the most effective among all tested groups at suppressing the growt h of TS/A (murine mammary adenocarcinoma) tumors previously implanted intra dermally at the skin site receiving DNA transfer by gene gun on days 6, 8. 10, and 12 after tumor implantation. Fifty percent of mice treated with the combined three-gene protocol underwent complete tumor regression. In vivo depletion experiments showed that this antitumor effect was CD8(+) T cell-m ediated and partially IFN-gamma-dependent. These results suggest that a com binatorial gene therapy protocol using a mixture of IL-12, pro-IL-18, and I CE cDNAs can confer potent antitumor activities against established TS/A tu mors via cytotoxic CD8+ T cells and IFN-gamma-dependent pathways.