IL-2 immunotherapy rescues irradiation-induced T cell exhaustion in mouse colon cancer.

Radiotherapy (RT) can stimulate anti-cancer T cell responses, and cytokines, notably interleukin-2 (IL-2), are necessary for optimal T cell function and memory. However, timing and IL-2 receptor (IL-2R) bias of IL-2 signals are ill-defined. Using image-guided RT in a mouse colon cancer model, we observed single high-dose (20 Gy) RT transiently upregulated IL-2Rα (CD25) on effector CD8(+) T cells, facilitating the use of CD25-biased IL-2 immunotherapy. Timed administration of CD25-biased IL-2 treatment after RT favored intratumoral expansion of CD8(+) T cells over regulatory T cells, which resulted in comparable anti-tumor effects as with RT plus IL-2Rβ (CD122)-biased IL-2 immunotherapy. Moreover, intratumoral CD8(+) T cells of animals receiving combined IL-2R-biased IL-2 and RT showed reduced markers of exhaustion. These combination treatments affected both primary irradiated and distant non-irradiated tumors and achieved durable responses. We demonstrate that timed IL-2R subunit-biased IL-2 immunotherapy synergizes with single high-dose RT to achieve potent anti-cancer immunity.