Background/Purpose: cGAS-STING is a cytosolic dsDNA sensing pathway whose regulation is vital to immune homeostasis. Pediatric patients with constitutively active STING mutations develop an autoinflammatory syndrome known as STING Associated Vasculopathy with onset in Infancy (SAVI) and suffer from treatment resistant lung fibrosis. Interestingly, SAVI patients develop immune abnormalities including lymphopenia concomitant with hyperactivation, and lung biopsies from SAVI patients show lymphocyte predominant immune aggregates which strongly resemble bronchus associated lymphoid tissues (BALT), suggesting a role for lymphocytes in SAVI lung disease. We have genetically engineered a mouse model of SAVI (STING V154M or VM mice) that recapitulates the development of lymphocyte rich BALTs in the lung as early as 6 weeks of age and develops progressive fibrotic disease by 16 weeks. Here, we test our hypothesis that lymphocytes are required for inflammatory lung disease in SAVI mice and use radiation-chimera mice to investigate the mechanism of lymphocyte activation.

Methods: To test the requirement of lymphocytes in SAVI disease, we bred VM Rag1^-/- and VM TCRβ^-/- and treated VM mice with αCD20 antibodies. We also generated chimeric mice to test if immune abnormalities were due to hematopoietic or radioresistant cell intrinsic STING Gain-of-Function (GOF) by transferring donor VM bone marrow (BM) into irradiated WT mice or vice versa. We then assessed autoinflammatory disease by body weight, spleen weight, lung histopathology, and performed flow cytometric profiling of central, peripheral, and tissue resident immune cells.

Results: We found that although lymphocytes were required for SAVI inflammatory disease, ablation of only αβ T cells or B cells failed to rescue disease. These results support the notion that T and B cells could independently contribute to SAVI lung disease. Moreover, we found that VM splenic αβ T and B cells depended on each other for maximal hyperactivation, suggesting a potential synergistic interaction as well.

Using chimeric mice, we found that BM intrinsic STING GOF was insufficient for lymphocyte activation, and instead, lymphocyte hyperactivation was dependent on STING GOF in radioresistant recipient cells, as donor WT splenic T cells transferred into a VM host developed hyperactivation that phenocopied VM mice. Finally, we found that radio-resistant cell STING GOF was sufficient to perpetuate a progressive SAVI inflammatory lung fibrosis.

Conclusion: Together, these findings suggest that STING GOF in radioresistant cells organizes and activates a profibrotic inflammatory lymphocyte response in the lung. We are currently investigating candidate radioresistant cell populations as initiators of this process including lung epithelium, which is known to robustly express STING, as well as mechanisms by which lymphocytes drive SAVI lung pathology. These findings are clinically relevant for SAVI patients, as well as more broadly for patients suffering from interstitial lung disease associated with rheumatic disease and suggest that lymphocyte depleting therapies may mitigate further lung injury and worsening of fibrosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sting-gain-of-function-in-radio-resistant-cells-supports-a-lymphocyte-dependent-auto-inflammatory-lung-disease/