CHARacterizing Monocyte-Macrophage and B-cell reprogrammING by therapeutic mesenchymal stromal cells in Systemic Sclerosis to improve treatment response – CHARMING-SSc

Systemic sclerosis (SSc) is a rare life-threatening autoimmune disease characterized by lung and skin fibrosis and lacking validated disease-modifying treatments. The use of mesenchymal stromal cells (MSC) is a novel immune reprogramming strategy that could reduce skin and lung fibrosis in severe SSc patients and in SSc murine models. However, the mechanisms of action of clinical-grade MSC in vivo remain elusive and biomarkers predicting treatment response are lacking. B cells and monocytes/macrophages (MoMac) have emerged as major mediators of SSc pathogenesis. By combining state-of-the-art approaches in two SSc mouse models (bleomycin- and HOCl-induced) and analyses of patient samples from 2 clinical trials evaluating MSC infusion in SSc patients, this CHARMING SSc project plans to decipher the effects of MSC on MoMac and B-cells in SSc, to identify potential biomarkers predicting treatment response in future trials assessing MSC efficacy. WP1 will fully characterize immune and stromal cell reprogramming by MSC, pre-treated or not by inflammatory stimuli, in SSc mice at early and late stages of the disease, using unsupervised single cell technologies and bulk RNASeq of skin, spleen, and lung. WP2 will characterize the mechanisms of action of MSC on the immunosuppressive and pathogenic properties of B cell and MoMac subsets in SSc mice, through i) the analysis of B-cell fate and reprogramming, notably using B10 reporter mice ii) the analysis of MSC efferocytosis by MoMac using apoptosis-resistant MSC. WP3 will translate WP1&2 major results to humans to better understand and predict MSC effects, and to identify potential biomarkers predicting treatment response. Based on two SSc clinical trials (1 completed phase I/II and 1 funded phase II), WP3 will interrogate B cell/MoMac/stromal cell reprogramming within patient skin and peripheral blood through in situ imaging, flow cytometry, scRNAseq, and functional assays, linking them to clinical response.