Long-lasting anti-metastatic efficiency of interleukin 12-encoding plasmidDNA

Intramuscular injection of plasmid DNA encoding both subunits of the cytoki ne interleukin 12 (IL-12) exhibits strong antimetastatic activity against l ung metastases induced by the malignant melanoma cell line B16-F10. The pro tective effect of IL-12 DNA is long-lasting, since administration of tumor cells 9 days after IL-12 DNA treatment prevented metastasis formation. No e ffects were observed with empty plasmid controls, DNA encoding the melanoma -associated antigen pmel17/gp100, the granulocyte-macrophage colony-stimula ting factor GM-CSF, B7.1, or CpG-containing oligodeoxynucleotides. IL-12 DN A is required during early phases of metastasis formation and is ineffectiv e when administered later. Its efficiency is dose dependent. The cytotoxic T cell response contributes to the antimetastatic effect as evidenced by ge netically modified CD8(-) or perforin knockout mice. Depletion of natural k iller (NK) cells by antibodies completely abrogated the effect. In contrast , the IL-12-induced antimetastatic effect was not mediated by interferon ga mma (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha) as shown with IF N-gamma receptor and TNF-alpha knockout mice, respectively. Toxic side effe cts by IL-12 were low. Our results suggest that plasmid DNA encoding IL-12 might have potential value as gene medicine against the initiation of metas tasis formation.