Immunotherapy and radiotherapy

Radiotherapy, primarily known for its cytotoxic effect on the tumor cells, via the induction of DNA damages, has the ability to induce a systemic antitumoral response. By an immunologic cell death, tumor cells exposed to radiation release a large amount of neoantigenes and pro-inflammatory mediators, acting as an in situ vaccine, resulting in an tumor regression within the primary irradiated site, but also in the distant “out of field” secondary tumors. However, this phenomenon is extremly rare with radiotherapy alone, suggesting that the radiation-induced antitumor immunity is not sufficient for overcoming the tumor's and its microenvironnement immunosuppressing effect. Over the last years, many scientific data and preclinical studies have demonstrated that the combination of local irradiation with immune therapy has a synergistic action in inducing an antitumoral immunity, thus enhancing an abscopal effect. In this article, we summarize the main mechanisms cancer harnesses to evade the control of the immune system and how ionising radiations can induce an antitumor immunity. A focus reports then on recent preclinical and clinical research built on this background of combined radiation and immune therapy, which bear the great potential to further improve anticancer therapies.