Single cell analysis reveals multiple subsets of CD8+ TRM and non-TRM cells with a type 17 signature in the inflamed psoriatic arthritis joint

CD69+CD103+ tissue-resident memory T-cells (TRM) are increasingly recognised as important drivers of inflammation. To decipher their potential role in inflammatory arthritis, we applied single cell, high-dimensional profiling (CyTOF and scRNAseq) to T-cells isolated from the joint of patients with psoriatic arthritis (PsA) or rheumatoid arthritis (RA). We identified three broad groups of synovial CD8+ TRM cells: cytotoxic and Treg-like TRM cells were present in the inflamed joints of patients with both PsA and RA, while CD161+CXCR6+ type 17-like TRM cells with a pro-inflammatory cytokine profile (IL-17A+TNFa+IFNg+) and a distinct transcriptomic signature and a polyclonal, but distinct TCR repertoire, were specifically enriched in the inflamed joints of patients with PsA. Type 17-like cells were also enriched in non-TRM CD8+ T-cells in PsA compared to RA. These findings add substantively to the accumulating evidence that the immunopathology of PsA and RA is different, with a particular role for type 17 cells in PsA. Single cell RNAseq analysis of synovial fluid memory CD8+ T cells from patients with psoriatic arthritis