Dynamic Duo: Synergy between Cancer Radiation Therapy and Immunotherapy

Immunotherapy is increasingly being applied in conjunction with any of the three commonly accepted treatment modalities of surgery, chemotherapy, and radiation therapy in the treatment of solid and hematological malignancies. Radiation therapy, which can be applied as a monotherapy, has immunostimulatory properties that are specifically augmented when used together with immunotherapy. High-dose irradiation has significant effects on both the targeted tumor and the immune system that are mutually enhancing when applied appropriately. Immunogenic cell death and changes in gene expression in irradiated tumor cells fuel the immune system, allowing for immunemediated killing that leads to improved overall survival. Herein, we discussed the recent advances in radiation therapy and immunotherapy, covering myeloid-derived suppressor cells (MDSCs), radioimmunotherapy, immunocheckpoint inhibition, cancer treatment vaccine, and chimeric antigen receptor (CAR) engineered T cells and NK cells. We put forth our current understanding of the mechanisms behind how immunotherapy and radiation therapy complement each other, and suggest some topics that are worthy of further exploration.