Mesenchymal Stromal Cells Attenuate Primary Sjogren's Syndrome by Modulating PD-1+CXCR5− T Peripheral Helper Cells via Galectin-1

Objective To investigate the role of PD-1 ⁺ CXCR5 ^- peripheral helper T (Tph) cells in patients with primary Sjogren's syndrome (pSS) and to assess the therapeutic efficacy of mesenchymal stromal cells (MSC) in pSS patients through modulating Tph cells. Methods We measured the frequencies and numbers of T cell subsets, including Tph cells, follicular helper T (Tfh) cells, and Treg cells, as well as the levels of IL-21 in patients with pSS and healthy controls (HC). Additionally, we analyzed their correlations with the levels of serological indicators (IgG, C3, C4) and the score of the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI). Immunofluorescence technique was employed to assess the infiltration of lymphocytes in labial gland tissues. Before and after mesenchymal stromal cell transplantation (MSCT). The alterations in Tph, Tfh, and Treg cell subsets were -evaluated using Fluorescence-activated cell sorting (FACS). Meanwhile, proteomic analysis of peripheral blood samples was conducted to identify the key proteins associated with Tph cells, and these proteins were subsequently validated in vitro. Results Compared with CXCR5 ^- PD-1 ⁺ CD4 ⁺ Tph cells and the Tph/Treg ratio were significantly higher in pSS patients than in the HC group. The proportion of circulating Tph cells and Tph/Treg ratio were significantly positively correlated with the ESSDAI score. MSC treatment effectively increased the levels of C3 and C4, while reducing the levels of IgG, the EULAR Sjogren's Syndrome Patient Reported Index (ESSPRI) score, and the ESSDAI score. MSC significantly reduced the proportion of Tph cells and the Tph/Treg ratio, while increased the proportion of Treg cells, which contributed to restoring immune homeostasis. Proteomic analysis and co-culture experiments of MSC and peripheral blood mononuclear cells (PBMC) indicated that MSC may ameliorate the immune imbalance in pSS patients by up-regulating galectin-1 (Gal-1), thereby inhibiting Tph cell-associated inflammatory responses. Conclusion Our study established a link between increased Tph cell counts and increased Tph/Treg ratios with enhanced disease activity in pSS patients. MSC therapy, which reduces the number of Tph cells by inducing the expression of galectin-1, emerges as a promising therapeutic approach for pSS.