To determine whether 2′3′-cGAMP produced by cancer cells could activate STING/TBK1/IRF3 signaling in the neighboring tumor vasculature (Figure 5A), we first measured intracellular and extracellular 2′3′-cGAMP levels in H1355-LUC and H1355-LKB1 cells using the same concentration of double-stranded DNA used in co-culture experiments. Here, STING1 is linked to cancer.