Ab1158 Mesenchymal Stem Cells Attenuate Systemic Sclerosis Related Lung Fibrosis by Inhibiting T Follicular Helper Cells in Tertiary Lymphoid Structure Through Pd-1/Pd-L1 Pathway

Background: Systemic sclerosis (SSc) is an autoimmune disease that is mediated by the dysregulation of the innate and adaptive immune systems. Among all complications of systemic sclerosis, interstitial lung disease (ILD) remains a leading cause of morbidity and mortality. Mesenchymal stem cells (MSC) can reverse or slow down the fibrotic process of liver, lung and other important organs, but there is little research of MSC in the field of SSc-ILD. Objectives: This study aims to investigate the therapeutic effects and immunomodulatory mechanisms of mesenchymal stem cells (MSCs) in systemic sclerosis related interstitial lung disease (SSc-ILD). Methods: The existence of CXCR5+PD-1+CD4+T cells in SSc-ILD patients was verified by flow cytometry, immunohistochemistry and immunofluorescence. In vitro differentiated Tfh cells were cocultured with huamn lung fibroblasts. PBMCs were cocultured with UC-MSCs by cell-to-cell contactor. Naive CD4+ T cells isolated from PBMCs were cocultured with UC-MSCs under Tfh cell-polarizing conditions. The percentage of CXCR5+PD-1+CD4+T cells, carboxyfluorescein succinimidyl ester (CFSE) fluorescence intensity and annexin V were determined by flow cytometric analysis. Bleomycin-induced SSc-ILD mice model received Bcl-6 inhibitor or MSC transplantation treatment respectively. Then, the histopathology of lungs and pulmonary Tfh cells were examined in these mice. Results: Increased frequency of cTfh cells and IL-21+Tfh cells were found in SSc-ILD patients and positively correlated with mRSS scale. And CXCR5+PD-1+ Tfh cells could drive the differentiation of myofibroblasts in vitro. Tertiary lymphoid structures (TLS), where Tfh cells localized, was found in lung biopsies from pulmonary fibrosis patients and BLM mice. The upregulated frequency of Tfh cells and GC B cells were also found in the lung and spleen of BLM mice model. After depletion of Tfh cells, the proportion of GC B cells in BLM lungs was reduced and the manifestation of the mice model was attenuated. In addition, MSC treatment contributed to remissive pulmonary fibrosis and reduced number of pulmonary TLS, followed by decreased frequency of Tfh cells both in lung of mice model and in peripheral circulation of SSc patients. While after knocking down the expression of PD-L1 on MSC, its theraputic effect on the remission of fibrosis and the reduction of Tfh cells frequency were diminished. In vitro, MSCs could downregulated the proportion of Tfh cells in SSc patients through suppressing their differentiation and proliferation. Conclusion: Our results together suggested that Tfh cells in lung TLS contribute to SSc-ILD by IL-21. Targeting the Bcl-6-signaling pathway network could reduce Tfh cell infifiltration and alleviate pulmonary fibrosis. And the inhibitory effect of UC-MSCs on the differentiation and proliferation of Tfh cells is a PD-1/PD-L1-dependent manner. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.