Ankylosing spondylitis patients present a distinct CD8 T-cell subset with osteogenic and cytotoxic potential

Ankylosing Spondylitis (AS) is a chronic inflammatory rheumatic disease affecting mainly the axial skeleton. Peripheral involvement (arthritis, enthesitis and dactylitis) and extra-musculoskeletal manifestations including uveitis, psoriasis and bowel inflammation occur in a relevant proportion of patients. AS is responsible for chronic and severe back pain caused by local inflammation that can lead to osteoproliferation and ultimately spinal fusion. The association of AS with the Human Leukocyte Antigen (HLA)‑B27 gene, together with elevated levels of chemokines CCL17 and CCL22 in the sera of patients with AS, lead us to study the role of CCR4+ T-cells in the disease pathogenesis. Here we show that, CD8+ CCR4+ T-cells display a distinct effector phenotype and upregulate the inflammatory chemokine receptors CCR1, CCR5, CX3CR1 and the L‑selectin CD62L, indicating an altered migration ability. Functionally, CD8+CCR4+T‑cells expressing CX3CR1 present an enhanced cytotoxic profile, expressing both perforin and granzymeB. Of note, these cells, isolated from patients in the active state of the disease, upregulate genes promoting the ossification process. Our results shed light to a new molecular mechanism by which T-cells may promote new bone formation and contribute to the pathological ossification process observed in AS. CD8+CCR4+ T-cells were sorted from 5 healthy donors and 6 AS patients and bulk RNA sequencing was perfomred on the isolated RNA using the NextSeq 500 or 600 (Illumina). RNA sequencing reads were aligned with the STAR-aligner. The Ensembl human genome build GRCh38 was used as reference. Gene expression values were computed with the function featureCounts from the R package Rsubread while gene expression analysis was performed using the BigOmics platform.