Fig. 4

Visual representation of two uses of radiation and how low-dose radiation and high-dose radiation affect the immune cell cycle. High-dose radiation is beneficial in directly killing primary tumor cells (1), which allows antigen release (2) and leads to T-cell priming (3). Immunotherapy decreases T-cell exhaustion and enhances lymphocyte trafficking to secondary tumors (4). Low-dose radiation, by contrast, modulated the tumor stroma and enhances infiltration of natural killer (NK) cells and T cells into secondary tumor sites (5), leading to enhanced immune-cell recognition of tumor cells (6) and resulting in ongoing tumor cell killing (1) and antigen release (2). Abbreviations: DAMPs, danger-associated molecular patterns; MHC1, major histocompatibility complex 1; ICOS, the immune checkpoint ‘inducible co-stimulator’; MDSCs, myeloid-derived suppressor cells; Tregs, T regulatory cells; TGF-β, tumor growth factor-beta; TAMs, tumor-associated macrophages