Irradiation‐induced localization of IL‐12‐expressing mesenchymal stem cells to enhance the curative effect in murine metastatic hepatoma

Irradiation in conjunction with gene therapy is considered for efficient cancer treatment. Mesenchymal stem cells (MSCs), due to their irradiation‐promotable tumor tropism, are ideal delivery vehicles for gene therapy. In this study, we investigated whether treatment with radiation and interleukin (IL)‐12‐expressing MSCs (MSCs/IL‐12) exerts improved antitumor effects on murine metastatic hepatoma. HCa‐I and Hepa 1‐6 cells were utilized to generate heterotopic murine hepatoma models. Tumor‐bearing mice were treated with irradiation or MSCs/IL‐12 alone, or a combination. Monocyte chemoattractant protein‐1 (MCP‐1/CCL2) expression was assessed in irradiated hepatoma tissues to confirm a chemotactic effect. Combination treatment strategies were established and their therapeutic efficacies were evaluated by monitoring tumor growth, metastasis and survival rate. IL‐12 expression was assessed and the apoptotic activity and immunological alterations in the tumor microenvironment were examined. MCP‐1/CCL2 expression and localization of MSCs/IL‐12 increased in the irradiated murine hepatoma cells. The antitumor effects, including suppression of pulmonary metastasis and survival rate improvements, were increased by the combination treatment with irradiation and MSCs/IL‐12. IL‐12 expression was increased in tumor cells, causing proliferation of cluster of differentiation 8+ T‐lymphocytes and natural killer cells. The apoptotic activity increased, indicating that the cytotoxicity of immune cells was involved in the antitumor effect of the combined treatment. Treatment with irradiation and MSCs/IL‐12 showed effectiveness in treating murine metastatic hepatoma. IL‐12‐induced proliferation of immune cells played an important role in apoptosis of tumor cells. Our results suggest that treatment with irradiation and MSCs/IL‐12 may be a useful strategy for enhancing antitumor activity in metastatic hepatoma. What's new? Mesenchymal stem cells (MSCs) are promising gene‐delivery vehicles, with the potential to improve antitumor effects when used in combination with existing therapies. In the present study, the combined use of interleukin (IL)‐12‐expressing MSCs (MSCs/IL‐12) and radiation therapy increased antitumor activity in murine metastatic hepatoma, a model that is representative of human metastatic hepatocellular carcinoma (HCC), which affects nearly half of HCC patients. Treatment with MSCs/IL‐12 resulted in increased IL‐12 expression in tumor cells and immune cell prolif