Optimizing tumor immune response through combination of radiation and immunotherapy

Radiation therapy and immunotherapy are two highly evolving modalities for the treatment of solid tumors. Immunotherapeutic drugs can either stimulate the immune system via immunogenic pathways or target co-inhibitory checkpoints. An augmented tumor cell recognition by host immune cells can be achieved post-irradiation, as irradiated tissues can release chemical signals which are sensed by the immune system resulting in its activation. Different strategies combining both treatment modalities were tested in order to achieve a better therapeutic response and longer tumor control. Both regimens act synergistically to one another with complimentary mechanisms. In this review, we explore the scientific basis behind such a combination, starting initially with a brief historical overview behind utilizing radiation and immunotherapies for solid tumors, followed by the different types of these two modalities, and the biological concept behind their synergistic effect. We also shed light on the common side effects and toxicities associated with radiation and immunotherapy. Finally, we discuss previous clinical trials tackling this multimodality combination and highlight future ongoing research.