Background: The progression of Systemic Sclerosis (SSc) is driven by pathogenic Th cell polarization, a process primarily orchestrated by type 2 conventional dendritic cells (cDC2s). However, the upstream drivers of cDC2s dysregulation remain elusive. Mesenchymal stromal cells (MSCs) exhibit immunoregulatory function in SSc, yet their potential to correct metabolic dysregulation, a critical determinant of immune phenotype, has been largely overlooked.

Objectives: This study aims to elucidate the upstream drivers for the pathogenic phenotype of cDC2s in SSc. Furthermore, beyond the traditional immunoregulation-centric perspective, we elucidate the potential of MSCs to restore immune homeostasis through metabolic reprogramming.

Methods: To systematically dissect the peripheral immune landscape of SSc, we performed single-cell RNA-seq analysis on peripheral blood mononuclear cells (PBMCs) from SSc patients and healthy controls. To determine whether these pathogenic phenotypes persist across varying disease stages, we further analyzed bulk RNA-seq profiles of the cDC2s from early SSc, established SSc and healthy controls. Subsequently, to investigate whether MSCs could rectify these specific pathogenic phenotypes, we conducted a clinical trial (NCT00962923) enrolling 8 SSc patients who received intravenous umbilical cord-derived MSCs (1×10^6 cells/kg) with 6-month follow-up. We performed multi-omics analysis on paired samples (Baseline vs. 1 month): deep 4D-DIA proteomics and untargeted metabolomics on plasma, and bulk transcriptomic sequencing on PBMCs. We employed Rank-Rank Overlap and enrichment analysis to quantify the reversal of pathogenic signatures.

Results: We identified a significantly expanded pathogenic cDC2s subset in SSc patients. They are characterized by diminished oxidative phosphorylation (OXPHOS) levels and elevated pro-inflammatory activity. In contrast, the homeostatic cDC2 subset was depleted compared to healthy controls. These perturbations are particularly pronounced in early SSc. Notably, MSCs effectively rectified these specific pathological dysregulations and alleviated skin fibrosis and improved pulmonary function. Mechanistically, these therapeutic effects were mediated by systemic metabolic reprogramming. Plasma profiling analysis revealed the restoration of OXPHOS activation and the consequent suppression of hedgehog-mediated fibrosis and lymphocyte activation. In PBMC, MSCs restore conventional dendritic cells abundance by recovering OXPHOS activity and effectively dampens the pathogenic inflammatory signatures associated with SSc-cDC2s. Importantly, stratification based on clinical efficacy reveals that patients with better clinical response are characterized by pronounced OXPHOS activation.

Conclusions: We reveal that intrinsic metabolic dysfunction drives the pathogenic phenotype of cDC2s in SSc. Furthermore, we demonstrate that MSCs restore immune homeostasis by reversing metabolic defects, underscoring the potential of targeted metabolic reprogramming as a vital therapeutic strategy for SSc.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: None declared.