Background: Combination therapy with systemically administered interleukin-2 (IL-2) and interferon alpha (IFN-alpha) has resulted in long-term objective remissions in 30% of patients with metastatic renal cell carcinoma (RCC), but toxic effects are clinically significant.
Purpose: We have thus investigated an alternative therapeutic approach--continuous intratumoral production of IL-2 and/or IFN-alpha by a cytokine-transfected human RCC tumor cell line.
Methods: Plasmid vectors were used to transfect the R11 RCC line with the genes for human IL-2 and/or IFN-alpha by the calcium phosphate precipitation method. Biologic characteristics of the cytokine-transfected tumor cells were determined by assays of thymidine incorporation and cytotoxicity, fluorescence-activated cell-sorter analysis, Northern blotting, and in vivo studies in C3Hf/Sed/Kam mice rendered T-cell deficient.
Results: The transfected cell lines produced the following amounts of cytokine per 10(6) cells per day: R11-IL-2 (220 U), R11-IFN-alpha (10,240 U), and R11-IL-2 + IFN-alpha (95 U + 1270 U, respectively). Gamma irradiation did not eliminate cytokine secretion. Morphology and growth rates were identical to those for the parental R11 cell line, except for IFN-alpha-producing clones, which showed significant growth inhibition. All cytokine-producing cells demonstrated increased susceptibility to cell killing by peripheral blood leukocytes (PBL). IFN-alpha producers exhibited enhanced HLA antigen expression and suppressed c-myc messenger RNA expression; when cocultured in vitro, they induced similar changes in parental R11 cells. IL-2 producers could stimulate growth and cytotoxicity of naive (i.e., freshly isolated, uncultured) and activated PBL. All cytokine-producing cells lost their tumorigenicity, as evidenced by failure to grow in the T-cell-depleted mice. When co-injected at a local site but not at a distant site, these cells prevented growth of parental R11 cells. Histologic examination of the injection sites revealed a substantial influx of macrophages. Intraperitoneal administration of IL-2 and/or IFN-alpha could not, however, prevent growth of the parental R11 tumors.
Conclusion: Local production of high concentrations of IL-2 and IFN-alpha at the tumor site is more effective in preventing tumor growth than systemic administration.
Implication: Continuous local delivery of cytokines via transfer of cytokine genes into tumor cells for use as live cancer vaccines is a novel strategy for manipulation of host-mediated antitumor immune response in patients with advanced RCC.