TL1A Inhibition in Systemic Sclerosis-Related Skin Fibrosis and Immunological Alterations: A Proof-of-Concept In Vitro Study (FIBROSTOP)

Systemic Sclerosis (SSc) is a rare autoimmune connective tissue disease characterized by microvascular injury, immune activation, and progressive fibrosis of the skin and internal organs. Diffuse cutaneous SSc (dcSSc), particularly in its early phase, is associated with aggressive fibrotic evolution and high morbidity. Despite advances in immunomodulatory therapy, no treatment has proven capable of consistently halting or reversing fibrosis, highlighting the need for new mechanistic targets. TL1A (TNF-like ligand 1A) is a cytokine of the TNF superfamily expressed by endothelial and immune cells, which interacts with death receptor 3 (DR3) to regulate immune activation, endothelial dysfunction, and tissue remodeling. Elevated TL1A levels have been observed in SSc patients and correlate with disease activity. TL1A has also been shown to promote lung fibrosis in preclinical models. The FIBROSTOP study is a proof-of-concept, in vitro, interventional study on biological samples aimed at elucidating the immunological and fibrotic mechanisms regulated by TL1A, and at assessing whether TL1A inhibition can reverse pathogenic processes in SSc. Ten (n=10) patients with early diffuse cutaneous SSc and ten (n=10) age- and sex-matched healthy controls will be enrolled at a single center (Fondazione Policlinico Universitario Campus Bio-Medico, Rome). Each participant will undergo a single visit (T0) involving peripheral blood sampling and skin biopsy. No follow-up visits are planned. The study pursues three co-primary objectives: (1) evaluating the role of TL1A and its inhibition in modulating T lymphocyte activity; (2) assessing the effects of TL1A and its inhibition on endothelial cell activation and function; (3) investigating the impact of TL1A and its inhibition on fibrotic remodeling in ex vivo SSc skin cultures using single-cell RNA sequencing. The findings may inform future targeted antifibrotic interventions in SSc and other fibrotic diseases.

Inclusion Criteria: For both SSc and healthy control populations: * Signed written informed consent * Age ≥18 years at the time of consent For SSc population only: * Diagnosis of SSc according to ACR/EULAR 2013 classification criteria * Diffuse cutaneous SSc subtype (LeRoy et al., 1988) * Disease onset (defined as the first non-Raynaud symptom) within 5 years prior to recruitment * No new initiation of immunosuppressive therapy (including methotrexate, mycophenolate mofetil, cyclophosphamide, rituximab, tocilizumab, or prednisone \>20 mg/day) within the 2 months preceding recruitment * Ongoing immunosuppressive therapy must be at a stable dose for at least 1 month prior to enrollment Exclusion Criteria: * Coexisting active or treated skin diseases (e.g., atopic dermatitis), except for SSc * Diagnosis of other systemic autoimmune rheumatic diseases, including overlap syndromes (e.g., SSc + dermatomyositis) * History or current signs/symptoms of severe or uncontrolled non-rheumatic diseases * Active malignancy or history of malignancy within the previous 5 years (except adequately treated non-melanoma skin cancer or in situ cervical carcinoma) * Chronic or recurrent infections, including viral hepatitis B/C, HIV, or untreated tuberculosis * Severe active infection or major surgery within 8 weeks before enrollment * Non-serious skin infections within 8 weeks before enrollment * Limited cutaneous SSc or SSc sine scleroderma * SSc patients unable to undergo therapeutic stabilization due to severe organ complications * Pregnancy or lactation * Inability to provide informed consent