Therapeutic effect of local Interleukin-15 with radiotherapy in breast cancer.

158Background: Interleukin (IL)-15 is a key regulator of T cell homeostasis with activity in cancer and a favorable toxicity profile compared to IL-2. IL-15 stimulates the proliferation and effector differentiation of CD8+T cells, and the proliferation and activation of natural killer (NK) cells. We observed IL-15 upregulation by gene arrays in radiotherapy (RT)-treated TSA mouse breast cancer, suggesting that it may play a role in RT-induced anti-tumor immunity. However, the upregulation was modest prompting us to test the hypothesis that administration of IL-15 may enhance in situ vaccination by RT. Methods: BALB/c mice with established poorly immunogenic TSA tumors were sham-treated, treated with tumor-targeted RT (8GyX3 days), IL-15 given peri-tumorally (2 ug/mouse/day for 10 days) starting on the first day of RT, and RT+IL-15, and monitored for tumor growth and survival. Tumor infiltrating lymphocytes (TIL) were analyzed by flow cytometry and immunostaining. In some experiments, Batf3-/-mice were use...