Systemic sclerosis (SSc) is an autoimmune disease that culminates in excessive extra-cellular matrix deposition (fibrosis) in skin and internal organs. SSc is a severe disease in which fibrotic events lead to organ failure such as renal failure, deterioration of lung function and development of pulmonary arterial hypertension (PAH). Together, these disease hallmarks culminate in profound disability and premature death.Over the past three years several crucial observations by my group changed the landscape of our thinking about the ethiopathogenesis of this disease. First, plasmacytoid dendritic (pDCs) cells were found to be extremely frequent in the circulation of SSc patients (1000-fold) compared with healthy individuals. In addition, we observed that pDCs from SSc patients are largely dedicated to synthesize CXCL4 that was proven to be directly implicated in fibroblast biology and endothelial cell activation, two events recapitulating SSc. Finally, research aimed to decipher the underlying cause of this increased pDCs frequency led to the observation that Runx3, a transcription factor that controls the differentiation of DC subsets, was almost not expressed in pDC of SSc patients. Together, these observations led me to pose the “SSc immune postulate” in which the pathogenesis of SSc is explained by a multi-step process in which Runx3 and CXCL4 play a central role.The project CIRCUMVENT is designed to provide proof of concept for the role of CXCL4 and RUNX3 in SSc. For this aim we will exploit a unique set of patient material (cell subsets, protein and DNA bank), various recently developed in vitro techniques (siRNA for pDCs, viral over expression of CXCL4/RUNX3) and apply three recently optimised experimental models (CXCL4 subcutaneous pump model, DC specific RUNX3 KO and the SCID/NOD/rag2 KO mice).The project CIRCUMVENT aims to proof the direct role for Runx3 and CXCL4 that could provide the final step towards the development of novel therapeutic targets