Exosomes reveal the dual nature of radiotherapy in tumor immunology.

Radioresistance is the potential cause of cancer metastasis and recurrence. Radiation-induced changes in exosomes can partially explain the undesirable prognosis of radiotherapy (RT). Exosomes, newly discovered ways of cell communication, carry the characteristics of their origin, resulting in their diversity. Various exosomes in the tumor microenvironment exert different function in immune response. In this review, the dual effect of RT on the immune system was described, and the effect of radiotherapy on tumors via exosomes was explored. The molecules in exosomes after RT were described to play immunosuppressive and immunocompetent roles: immune-related receptors and cell signaling molecules involved in both adaptive and innate immune system were present. CD69, TIGIT, TIM-3, LAG-3 and the tumor necrosis factor (TNF) family that signal to T cells were shown to be regulated by exosomes after irradiation. The change in innate immunity-derived like receptors, Leukocyte Immunoglobin-Like Receptors (LILR) was described, as well as B7-H3, V-domain containing Ig suppressor of T cell activation (VISTA), and CD155 on tumor cells. These changed molecules inhibit and activate the immune system through different mechanisms. By analyzing the relationship between exosome-derived molecules and immunity, this review shows that radiotherapy can induce immunosuppression and immune clearance through exosomes, thereby treating tumors and improving patient prognosis.