Figure 3.

Radiation alters the response threshold to immunotherapy. (A) Growing tumors are by definition below the immune control response threshold since a lack of treatment will ultimately be lethal. (B) Checkpoint inhibition alone will result in cure for a portion of tumors that have an established T cell response and are responsive to immune control. (C) Radiation therapy boosts T cell responses by priming or boosting T cell responses and improves response to immune control within the treatment field due to increased antigen presentation or other inflammatory effects. (D) Immunotherapy changes the response threshold while radiation further changes the response threshold in radioimmunogenic tumors. A portion of remaining tumors fail to respond well to checkpoint inhibition with or without radiation therapy and will require additional therapeutic modalities that target additional resistance mechanisms.