A CCL5(+)CD20(+)CD8(+) T cell subset drives pathogenic transformation of synoviocytes in rheumatoid arthritis via JAK-STAT signaling.

BACKGROUND: In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) acquire an aggressive phenotype promoting inflammation and joint damage. While FLS interactions with recruited T cells are established, drivers of FLS aggressiveness and the role of CD20(+)CD8(+) T cells remain undefined. This study explores CD20(+)CD8(+) T cells in RA, focusing on inducing pathogenic FLS transformation. METHODS: Single-cell RNA sequencing (scRNA-seq) was employed to delineate the transcriptomic profile of CD20(+)CD8(+) T cells. Flow cytometric analysis was used to quantify the frequency of CCL5(+)CD20(+)CD8(+) T cells. To investigate cellular crosstalk, FLS were cultured with conditioned medium from CD20(+)CD8(+) T cells (CD20(+)CD8(+) T-CM). Phenotypic transformation of FLS was assessed through flow cytometry and transwell migration assays, and bulk RNA sequencing characterized the molecular signatures associated with the aggressive FLS phenotype. Signaling pathways associated with FLS activation induced by CD20(+)CD8(+) T-CM were examined using western blotting. In vivo functional validation using the collagen-induced arthritis (CIA) model included assessments of clinical scores, histopathology, radiographic bone integrity, and synovial immunofluorescence after adoptive transfer of CD20(+)CD8(+) T cells. RESULTS: scRNA-seq identified a CCL5-high subset within CD20(+)CD8(+) T cells, and flow cytometry revealed elevated CCL5(+)CD20(+)CD8(+) T cells in RA patients. This subset positively correlated with disease activity and exhibited heightened chemotactic and migratory capacity. Culturing FLS with CD20(+)CD8(+) T-CM induced transformation of FLS toward an invasive FAPα(+) phenotype, accompanied by enhanced migratory capacity and elevated CCL5 production in culture supernatants. Notably, CCR1 or CCR5 antagonists reduced the frequency of FAPα(+) FLS. Mechanistically, bioinformatics analysis identified JAK-STAT activation in FLS transcriptomes cultured with CD20(+)CD8(+) T-CM. In vitro experiments confirmed that pathway blockade inhibited the induction of invasive FAPα(+) FLS phenotype. Adoptive transfer of CD20(+)CD8(+) T cells exacerbated joint damage and accelerated disease progression in CIA models by promoting synovial infiltration and inducing pathogenic FAPα(+) FLS. CONCLUSIONS: Our findings suggest CCL5(+)CD20(+)CD8(+) T cells as key pathogenic drivers in RA, promoting aggressive FAPα(+) FLS transformation via CCL5-mediated JAK-STAT signaling, revealing a novel immunopathogenesis of RA and identifying CCL5(+)CD20(+)CD8(+) T cells as potential therapeutic targets. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13578-025-01516-5.