Tumor suppression after tumor cell-targeted tumor necrosis factor α gene transfer

Abstract

The tumor necrosis factor a (TNF-α) gene was introduced by retroviral gene transfer into the TNF-α-insensitive tumor cell line J558L. Production of 40 pg/ml TNF-α by clone J2T12 consistently did not change the growth rate in vitro, but drastically suppressed tumor growth when injected into syngeneic BALB/c mice. Within 2 wk, 90% of the mice inoculated with J558L cells developed a tumor, but none of the mice injected with J2T12 did so. Within the observation period (>3 mo), 60% of the mice inoculated with J2T12 did not develop a tumor. In the other 40% of the mice, tumor manifestation was significantly delayed. Mice injected simultaneously with J2T12 cells and an anti-TNF-α monoclonal antibody developed tumors similar to parental J558L cells. Similarly, the tumor-suppressive effects of TNF-α were abolished, e.g., by injection of an anti-type 3 complement receptor (CR3) monoclonal antibody that is known to prevent migration of inflammatory cells. These results and the observation of tumor-infiltrating macrophages suggest that lack of tumorigenicity of J2T12 cells is due to the TNF-α secretion by the tumor cells and that TNF-α acts indirectly by a mechanism that involves chemotactic recruitment and activation of cells, predominantly of macrophages. In contrast, the tumor growth was not affected when, instead of TNF-α, interleukin 6 was expressed by J558L cells. Together, our results support the concept of tumor cell-targeted cytokine gene transfer as a tool for cancer treatment, and particularly demonstrate that extremely low doses of TNF-α produced by tumor cells are sufficient to inhibit tumor growth without detectable side effects.