CGAS and viral infectious disease: The activation of cGAS relies on its recognition of cytoplasmic chromatin DNA generated upon cell-to-cell fusion, a widespread phenomenon in SARS-CoV-2-infected cells,22 organoids,23 animals,24 and in COVID-19 patients.25 Our study revealed a mechanism, distinct from the classical PAMP-PRR paradigm, by which the host innate immune system responds to viral infection by producing “danger signals” using self-materials.