The pattern recognition receptors (PRRs) that sense nucleic acids and their derivatives and brief signalling pathways. The natural ligands and clinical candidates for each receptor are shown. The clinical status of PRR activators and the combination agents for immuno-oncology are shown in Table 1 cGAMP, cyclic guanosine monophosphate–adenosine monophosphate; cGAS, cyclic GMP-AMP synthase; IFN, interferon; IKKα/β, inhibitor of nuclear factor κ-B kinase subunit α or β; IRF3/7, interferon regulatory factor 3 or 7; ISGs, interferon stimulatory genes; MyD88, myeloid differentiation factor 88; MAVS, mitochondrial antiviral-signalling protein; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; RIG-I, retinoic acid inducible gene I; STING, stimulator of interferon genes; TLR3/7/8/9, Toll-like receptor 3, 7, 8 or 9; TBK1, TANK binding kinase 1.