Agonists for cytosolic bacterial receptor ALPK1 induce antitumour immunity

Targeting innate immunity holds promise in cancer immunotherapy, particularly in improving checkpoint inhibitors. However, the use of agonists of the promising innate receptors TLRs and STING^1-4 is facing challenges. Here we examined the antitumour function of the α-kinase 1 (ALPK1) receptor for bacterial ADP-heptose (ADP-Hep)^5-7. Treatment of mice with ADP-Hep induced multiple proinflammatory factors including CXCL10 and CCL2, and stimulated Alpk1-dependent antitumour immunity. Mice bearing a gain-of-function ALPK1(T237M) disease variant⁸ also rejected grafted tumours. Using medicinal chemistry, we identified a more potent analogue, UDSP-Hep. In contrast to ADP-Hep, UDSP-Hep distinguished Alpk1 polymorphism, which correlates with mouse susceptibility to bacteria-associated colitis^9-12. UDSP-Hep exhibited a stronger Alpk1-mediated antitumour effect and synergized with checkpoint inhibitors. The effect required CD8⁺ T cells, dendritic cells (DCs) and macrophages, and was sensitive to antibodies that block CXCL10 or CCL2 function. ALPK1 agonists activated DCs for cross-presentation, promoting tumour-specific T cell expansion in the tumour-draining lymph nodes. ALPK1 has wider expression than STING in non-immune cells with a distinct inflammatory signature. UDSP-Hep is differentiated from STING agonists in stimulating tumour-cell antigen presentation, macrophage-DC cross-priming and protective memory T cell differentiation, and it does not induce T cell apoptosis. Our study elucidates the antitumour effect of ALPK1 agonism and suggests the potential of ALPK1 agonists in cancer immunotherapy.