Background/Purpose: Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by recurrent inflammation in the same joints, a feature termed joint-specific memory. We previously demonstrated that joint-specific memory in arthritis is mediated by resident memory T (T_RM) cells in the synovium. T_RM cells are present in the synovium of previously inflamed joints and antigen-specific activation of T_RM cells can drive recurrent arthritis flare. In evaluating the mediators of T_RM cell development in the joint, we have previously shown that TNF can induce T_RM cell formation in synovial organoids. Here, we investigated the roles of both fibroblasts and T cells in TNF stimulation promoting T_RM cell formation.

Methods: CD8 memory T cells were isolated from peripheral blood mononuclear cells of healthy donors and fibroblast-like synoviocytes (FLS) were isolated from the synovium of rheumatoid arthritis patients (RA-FLS). To determine if T_RM cell formation is mediated by RA-FLS, we generated 3D synovial organoids with T cells and RA-FLS encapsulated in Matrigel, with or without human umbilical vein endothelial cells (HUVEC) and assessed for T_RM cell formation 3 weeks later. To assess the respective roles of T cells and RA-FLS in TNF-driven T_RM cell formation, T cells and RA-FLS were stimulated with TNF independently for 3 days before TNF was removed, and then the two cell types were cultured together for 14 days. As controls, cells were either left unstimulated or stimulated together in the same well. Transwells with 5.0µm pore size were utilized to spatially separate T cells and RA-FLS to assess for the necessity of cell contact. Flow cytometric analysis was performed after 14 days in culture to evaluate for the presence of T_RM cells and markers of T cell activation.

Results: T_RM cells can form in a 3D synovial organoid with T cells and RA-FLS alone. Simultaneous stimulation of T cells and RA-FLS together in co-culture was necessary for the formation of CD45RO+CD62L-CCR7-HLADR-CD25-CD69+CD49a+CD103+/- T_RM cells. TNF stimulation of T cells or RA-FLS independently did not result in T_RM cell formation. Transwell studies spatially separating the T cells from RA-FLS also abrogated T_RM cell formation, demonstrating that cell contact is required during TNF stimulation to drive the differentiation process.

Conclusion: We show that TNF-driven T_RM cell formation is mediated by FLS. Specifically, cell contact between T cells and RA-FLS is required at the time of TNF stimulation to drive the T_RM cell differentiation process. Our data offer further insight into why T_RM cells only form in arthritic joints and how inflammation plays an important role in the development of long-term joint-specific memory.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/synovial-resident-memory-t-cell-formation-during-inflammation-requires-cell-contact-with-fibroblast-like-synoviocytes/