POS0004 T-CELL REPERTOIRE OF SYNOVIAL FLUID IN SPONDYLOARTHROPATHIES EXHIBITS HALLMARKS OF HLA-DEPENDENT CLONAL EXPANSIONS AND REMAINS STABLE OVER 1.5 YEARS

Background: Different studies show involvement of T-cells in pathogenesis of spondyloarthropathies (SpAs) - a group of rheumatic diseases strongly associated with presence of several MHC-I alleles (HLA-B*27, -B*38, -B*39, etc). Recently we and others identified a specific T-cell receptor motif in blood and synovial fluid of HLA-B*27+ AS patients that reinforces the “arthritogenic peptide” hypothesis of AS pathogenesis [1-2]. However, common characteristics of clonal T-cell repertoire of synovial fluid in SpAs remain poorly investigated. Objectives: We aimed to investigate synovial fluid T-cell repertoires of SpA patients with different HLA-genotypes and stability of the clonal composition in recurring flares of the disease. Methods: Mononuclear cells were isolated from paired peripheral blood (PB) and synovial fluid (SF) samples of SpA patients (ankylosing spondylitis and psoriatic arthritis, n=27). For 3 patients additional SF samples were collected during relapse of the synovitis (after 9-15 months). CD4 and CD8 T-cells were isolated by immunomagnetic separation. Deep sequencing of UMI-tagged TCR beta cDNA libraries was used to accurately reconstruct clonal T-cell repertoires. HLA class I and II were typed for each donor using an in-house NGS-based system. Results: We observed restricted T-cell clonal composition in synovial fluid: on average only 6% of PB T-cell clonotypes were detected in SF of the same donor. T-cell repertoires of both CD4 and CD8 SF subsets compared to PB were highly oligoclonal (index Gini PB vs SF: CD4 0.36±0.10 vs 0.68±0.08, CD8 0.57±0.17 vs 0.81±0.12) in all patients. Number of identical amino acid CDR3 sequences between two repertoires correlated with the number of identical HLA-alleles for the donors. This trend was exhibited more strikingly in SF compared to PB, suggesting that common antigens may play a role in accumulation of identical T-cell clonotypes in the inflamed joint. Using several bioinformatic approaches we identified groups of highly similar SF clonotypes linked to HLA-B*27 and/or HLA-B*38 genotype. Total SF repertoires of relapsing synovitis of the same donor showed huge clonal overlap, and the most frequent clonotypes remained almost unchanged (Morisita’s overlap index for total SF repertoires 0.69±0.26; for top 1000 clonotypes 0.79±0.19, n=3). Conclusion: We report HLA-dependent sharing of identical and similar T-cell clonotypes in SF of patients with ankylosing spondylitis and psoriatic arthritis and high stability of SF repertoire during several flares that support antigen-driven accumulation of T-cells in the site of inflammation. References: [1]Komech EA et al. Rheumatology (Oxford). 2018;57(6):1097-1104. [2]Faham M et al. Arthritis Rheumatol. 2016;11(10):300-308. Acknowledgements: The work is supported by Russian Science Foundation grant №20-75-00041. Disclosure of Interests: None declared.