Mesenchymal stromal cells attenuate primary sjogren's syndrome by modulating PD-1⁺CXCR5^- T peripheral helper cells...

To investigate the role of PD-1⁺CXCR5^-CD4⁺ 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.

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. Fluorescence-activated cell sorting (FACS) was used to detect the changes of Tph, Tfh, and Treg cell subsets 24 h pre- and post-mesenchymal stromal cells transplantation (MSCT). 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.

PD-1⁺CXCR5^- CD4⁺ Tph cells and the Tph/Treg ratio were significantly higher in the 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) scores, and the ESSDAI scores. 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. Galectin-1 (Gal-1) was identified through proteomic profiling as a highly upregulated factor after MSCT. Given its known immunomodulatory role in T cell homeostasis, it was selected for further investigation. 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 Gal-1, thereby inhibiting Tph cell-associated inflammatory responses.

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.