Fig. 1

Proposed mechanisms of synergy between RT and PD-1/PD-L1 inhibitors. Emerging evidence demonstrates that immune modulation from PD-1/PD-L1 inhibitors and RT through nonredundant pathways contributes to synergistic antitumor activity, thereby forming the basis for the rationale combination of the two modalities. RT, radiation therapy; PD-1, programmed cell death 1 receptor; PD-L1, programmed death ligand 1; IFN-γ, interferon-γ; cGAS, cyclic GMP-AMP (cGAMP) synthase; STING, stimulator of interferon genes; MHC, major histocompatibility complex; TCR, T-cell receptor; TILs, tumor-infiltrating lymphocytes, Tregs; regulatory T cells; MDSCs, myeloid-derived suppressor cells