To facilitate the study of cGAS modulators, Cayman Chemical has developed a novel cGAS Inhibitor Screening Assay that directly measures the product of the cGAS reaction, 2’3’-cGAMP, formed in the presence of DNA, ATP, and GTP. The cyclic dinucleotide product is quantified via enzyme-linked immunoassay (ELISA) with a 2’3’-cGAMP specific polyclonal antiserum. This poster presentation will focus on the production of an active recombinant human cGAS protein and the optimization and validation of an inhibitor screening assay using the protein.