Abstract

Metastasis to the liver remains an important problem in the treatment of patients with gastrointestinal cancer. We examined the mechanism and effect on liver metastasis of in vivo interleukin-2 (IL-2) gene transfer to the liver. RCN-9 cells derived from F344 rat colon adenocarcinoma were injected into syngeneic rats via the ileocecal vein to induce liver tumors. A total of 2.5x10(9) pfu of adenovirus vector harboring the human IL-2 gene (AdCMVhIL-2), or 2.5x10(9) pfu of control vector encoding beta-galactosidase was administered before RCN-9 cell challenge. On day 14, mean tumor weight was 4.0+/-2.4 g in the control group, whereas IL-2-transduced livers had no tumors. Survival of AdCMVhIL-2-treated rats was significantly longer than that of control rats (P<.01). Flow cytometry demonstrated that the proportion of natural killer (NK) cells had increased among sinusoidal cells collected from IL-2-transduced livers. These cells were highly cytotoxic to RCN-9 cells in vitro in the presence of a physiological high concentration of recombinant IL-2. Preventative effects of IL-2 transduction of the liver against liver metastasis were lost after depletion of NK cells by treatment with anti-asialo GM1 antibodies. Our results indicate that IL-2 gene transfer to the liver prevents liver metastasis by continuously providing physiological high concentrations of IL-2 in the liver, thereby activating sinusoidal NK cells.

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