CD4+ tissue resident memory Th17 cells drive IL-17A-mediated joint pathology in Spondyloarthritis

Interleukin (IL)-17A plays a central role in driving joint pathology in Spondyloarthritis (SpA). In this study, synovial tissues from patients with Axial SpA and Psoriatic arthritis were analyzed using single-cell RNA sequencing and spatial RNA profiling to pinpoint the cellular source of IL-17A. The results revealed that IL-17A expression is exclusively localized to CD4⁺CXCR6⁺ tissue resident memory Th17 (TRM17) cells, which interact with activated CLEC10A⁺ dendritic cells within the joint. These interactions coincide with an enhanced IL-17A response signature in both sublining and lining fibroblasts. Furthermore, in vitro-generated TRM17-like cells from blood memory CD4⁺ T cells recapitulated the in situ characteristics by producing IL-17A in response to T cell receptor stimulation, while IL-23 selectively amplified TCR-mediated IL-17F and IFN-γ production. Importantly, perturbation of the epigenetic regulator BRD1 impaired the generation of TRM17-like cells. These findings underscore the predominant role of TRM17 cells as the source of IL-17A in SpA and suggest that targeting BRD1 or depleting TRM17 cells may offer promising therapeutic strategies for achieving long-term disease remission. Synovial tissues from patients with spondyloarthritis (SpA) were analyzed by single-cell RNA sequencing, including five axial SpA (AxSpA) and six psoriatic arthritis (PsA) samples. Due to national regulations governing genetic data, three of the five AxSpA datasets generated at Shanghai Sixth People’s Hospital are not deposited in the GEO repository; these datasets are available upon request through a formal data access application.