Abstract 5614: Interleukin-10 inhibits the induction of macrophage cytotoxicity against bladder cancer cells by Mycobacterium bovis bacillus Calmette-Guérin (BCG)

Abstract

Abstract Intravesical BCG therapy has been used for the treatment of superficial bladder cancer for three decades. However, the mechanisms underlying BCG therapy currently remain elusive. We have focused on BCG induction of macrophage cytotoxicity against bladder cancer cells. Previously, we observed that macrophages are cytotoxic to bladder cancer cells upon stimulation with BCG in vitro. However, we found that macrophages from C57BL/6 mice are less potent than those from C3H/HeN mice for the killing of both bladder cancer MBT-2 cells and MB49 cells. This study was to determine whether macrophage-derived interleukin (IL)-10 is responsible for this discrepancy between these two commonly used murine bladder cancer models. Thioglycollate-elicited peritoneal exudate cells were harvested from mice 3 days after intraperitoneal injection of 2 ml 3% thioglycollate. Cells were incubated for 3 hours and non-adherent cells were removed after incubation. The remaining cells were 96% F4/80-positive cells as determined by flow cytometry. The prepared macrophages were then used for the analysis of BCG induction of cytotoxicity, cytokines, and nitric oxide (NO) in vitro. Studies demonstrated that BCG-stimulated C57BL/6 macrophages produced a substantially high level of IL-10 compared to BCG-stimulated C3H/HeN macrophages. This high IL-10 production correlated with reduced production of tumor necrosis factor (TNF)-α, IL-6 and NO in BCG-stimulated C57BL/6 macrophages. Neutralizing endogenous IL-10 during BCG stimulation increased C57BL/6 macrophage cytotoxicity against MB49 cells by 3.2-fold, along with increased production of TNF-α by 6.4-fold and NO by 3.6-fold, respectively. Macrophages from genetically modified C57BL/6 mice lacking IL-10 (IL-10−/−) also exhibited increased killing of MB49 cells and production of TNF-α and NO upon BCG stimulation. In addition, supplementation of exogenous recombinant IL-10 reduced BCG-induced C3H/HeN macrophage cytotoxicity against both MBT-2 cells and MB49 cells in a dose-dependent manner. Taken together, our results reveal the inhibitory role of IL-10 in BCG-induced macrophage cytotoxicity, suggesting that blockage of IL-10 may potentially enhance the effect of BCG in the treatment of bladder cancer patients, particularly for BCG non-responders who are often associated with high IL-10 production in response to BCG treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5614.