CGAS and cancer: When the drug effect of a DNMT1 inhibitor induces the activation of CD8+ T cells, which kill cancer cells, the dying tumor cells release double-stranded DNA (dsDNA) into the tumor microenvironment, where cGAS (cyclic GMP-AMP synthase) detects and binds dsDNA, catalyzing the production of cyclic 2′3′-GMP-AMP (cGAMP) from ATP and GTP.