Intercellular cGAMP transmission induces innate immune activation and tissue inflammation in Trex1 deficiency

Intercellular transmission of the second messenger 2′,3′‐cGAMP, synthesized by the viral DNA sensor cGAMP synthase (cGAS), is a potent mode of bystander activation during host defense. However, whether this mechanism also contributes to cGAS-dependent autoimmunity remains unknown. Here, using a murine bone marrow transplantation strategy, we demonstrate that, in Trex1-/--associated autoimmunity, cGAMP shuttling from radioresistant to immune cells induces NF-κB activation, interferon regulatory protein 3 (IRF3) phosphorylation and subsequent interferon signaling. cGAMP travel prevented myeloid cell and lymphocyte death, promoting their accumulation in secondary lymphoid tissue. Nonetheless, it did not stimulate B cell differentiation into autoantibody-producing plasmablasts or aberrant T cell priming in the steady state. Although cGAMP-mediated bystander activation did not induce spontaneous organ disease, it did trigger interface dermatitis after UV light exposure, similar to cutaneous lupus erythematosus. These findings reveal that, in Trex1-deficiency, intercellular cGAMP transfer propagates cGAS signaling and, under conducive conditions, causes tissue inflammation. Total RNA was isolated from single-cell suspensions of bone marrow from Cgas-/- mice and Trex1-/-;Sting1gt/gt mice (called dKO). In addition, total RNA was isolated from single-cell suspensions of spleens from dKO mice 12 weeks after they were lethally irradiated and transplanted with Cgas-/- or dKO bone marrow. 3'-mRNA Seq was performed on an Illumina HiSeq 2500.