Single-cell sequencing reveals clonal expansions of pro-inflammatory synovial CD8 T cells expressing tissue-homing receptors in psoriatic arthritis

Abstract

Psoriatic arthritis (PsA) is a debilitating immune-mediated inflammatory arthritis of unknown pathogenesis commonly affecting patients with skin psoriasis. Here we use complementary single-cell approaches to study leukocytes from PsA joints. Mass cytometry demonstrates a 3-fold expansion of memory CD8 T cells in the joints of PsA patients compared to peripheral blood. Meanwhile, droplet-based and plate-based single-cell RNA sequencing of paired T cell receptor alpha and beta chain sequences show pronounced CD8 T cell clonal expansions within the joints. Transcriptome analyses find these expanded synovial CD8 T cells to express cycling, activation, tissue-homing and tissue residency markers. T cell receptor sequence comparison between patients identifies clonal convergence. Finally, chemokine receptor CXCR3 is upregulated in the expanded synovial CD8 T cells, while two CXCR3 ligands, CXCL9 and CXCL10, are elevated in PsA synovial fluid. Our data thus provide a quantitative molecular insight into the cellular immune landscape of psoriatic arthritis.

Ex vivomass cytometry analysis reveals a profound myeloid proinflammatory signature in psoriatic arthritis synovial fluid

“…Both CXCL10 and CCL2 have been reported as upregulated in PsA serum 31 with CXCL10 increased in PsA SF 32 and CCL2 upregulated in RA SF. 33 We have previously suggested a potential role for the CXCL10 receptor CXCR3 on CD8 T cells in PsA pathogenesis, 11 and here we show that PsA SF monocytes are a key cellular source of CXCL10, likely contributing to the recruitment of these cells. A clinical trial of RA patients that combined a monoclonal antibody targeting CXCL10 with methotrexate had a modest clinical effect.…”

“…We here confirm previous findings where technical considerations frequently only allowed focus on a particular cell type. 8 11 40-42 We observed SF expansion of PD1hi memory CD4 T cells, representing T follicular helper cells/peripheral T helper cells, similar to that seen in rheumatoid arthritis (RA), 43 44 and of tissue-resident CD49a+ memory CD8 T cells 6 that we previously showed to be clonally expanded in PsA. 11 Interestingly these cells are phenotypically similar to the integrin-expressing (InEx) cells recently described in the joints in related SpA ankylosing spondylitis.…”

“…8 11 40-42 We observed SF expansion of PD1hi memory CD4 T cells, representing T follicular helper cells/peripheral T helper cells, similar to that seen in rheumatoid arthritis (RA), 43 44 and of tissue-resident CD49a+ memory CD8 T cells 6 that we previously showed to be clonally expanded in PsA. 11 Interestingly these cells are phenotypically similar to the integrin-expressing (InEx) cells recently described in the joints in related SpA ankylosing spondylitis. 45 46 Although PsA SF T cells have the capability to produce cytokines such as IFNγ, IL-17 and GM-CSF upon in vitro stimulation, 47 we did not see any significant T cell cytokine production in our ex vivo unstimulated CyTOF assay.…”

“…To confirm these findings we next interrogated single-cell RNA sequencing (scRNAseq) data from a recently described study of ex vivo PsA blood and SF. 11 Unsupervised clustering of combined PBMC and SFMC data identified two clusters of monocytes/macrophages as defined by lineage markers CD14, FCGR3A (gene for CD16), LYZ, MS4A7, CD163 and MRC1 (gene for CD206); the smaller cluster was defined by increased expression of APOE (figure 5A). We observed strongest expression of SPP1 and CCL2 in the myeloid clusters (figure 5A).…”

“…We performed further analysis of the single cell data from a previously published data-set. 11 All pre-processing, quality control, alignment and basic clustering of combined PBMC and SFMC samples was carried out as previously published. In this analysis, we used Seurat (Satija lab, version 3.0) to split the clusters according to their tissue of origin (PBMC vs SFMC) based on the metadata and performed differential gene expression analysis for the two main myeloid clusters.…”