Background/Purpose: Rheumatoid arthritis (RA), psoriatic arthritis (PsA), peripheral spondyloarthritis (pSpA), and undifferentiated arthritis (UA) are chronic immune-mediated conditions characterized by joint inflammation. The specific role and differences of synovial T cells in these diseases remain unknown.

Methods: Ultrasound guided synovial biopsies were performed in 10 RA, 4 PsA, 4 pSpA, and 3 UA patients fulfilling the respective classification criteria. Three osteoarthritis (OA) samples were obtained from joint replacement surgery. Synovial pathotype (pauci-immune, diffuse-myeloid and lympho-myeloid), Krenn score, and presence of neutrophils were assessed by histology. We dissociated fresh synovial tissues and targeted the encapsulation of up to 6000 cells. ScRNA-seq libraries were generated according to 10X Genomics workflow (v3.1) and subsequently sequenced on NovaSeq 6000. Cell Ranger and Seurat R packages were used for data analysis. P-values were calculated using Welch t-test with Bonferroni correction. T cells were identified by high CD3D gene expression. Cells with mitochondrial content greater than 10% were excluded. The repertoire of T cell receptors (TCR) was analyzed through V-gene usage.

Results: Unsupervised graph-based clustering identified one CD8 positive cluster and four CD4 positive clusters with respective marker gene in box brackets: effector memory cells re-expressing CD45RA (EMRA) [GZMK],T follicular helper cells (Tfh) [CXCL13], regulatory T cells (Treg) [FOXP3], and resting naive/central memory T cells (naive/CM) [CCR7]. The subset proportions were similar between diseases, with EMRA and Tfh populations being the most frequent, representing together more than 50% of T cells. However, the proportion was strikingly different in OA, with EMRA occupying more than 75% of all T cells. Total numbers of T cells in OA were low, reflecting the degenerative, non-immune mediated nature of the disease.

T cell subset proportions were similar between histological pathotypes across all diseases suggesting a comparable relative increase in all subpopulations in the lympho-myeloid pathotype.

Further clustering of CD4 EMRA cells revealed two subpopulations differing in expression of genes associated with activation (GZMK, GZMA, DUSP2, DUSP4, CCL5). HLA-B*27-positive patients had significantly reduced (mean 31% vs 60%, p-value=0.0001) and patients with histologically present neutrophils significantly higher proportions of activated CD4 EMRA (mean 65% vs 42%, p-value=0.0038). In addition, activated EMRA subpopulation correlated positive with Krenn score (R=0.4, p-value=0.003).

TCR repertoire was polyclonal with high Simpson diversity in all conditions. No bias in V-gene usage between the conditions was observed.

Conclusion: This analysis of T cells in different chronic inflammatory diseases shows an association of activated EMRA T cells with histological presence of neutrophils, HLA-B*27 negativity and Krenn Score. Deeper analyses are required to find disease specific T cell characteristics and to understand whether this T cell activation influences clinical outcomes such as treatment efficacy and overall prognosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterization-of-t-cell-subsets-in-the-synovium-of-chronic-inflammatory-joint-diseases/