Dysfunctional KLRB1+CD8+ T-cell responses are generated in chronically inflamed systemic sclerosis skin

To analyse the immune mechanisms of diffuse cutaneous systemic sclerosis (dcSSc) skin disease focusing on CD8+ T-cell responses in the affected skin of patients because chronic inflammation, vasculopathy, and extensive cutaneous fibrosis are prominent features of dcSSc skin disease, causing pain and disability in patients, with no effective therapy. Single-cell transcriptomics and epigenomics were applied to well-characterised patient skin samples to identify transcriptomes and key regulators of skin-resident CD8+ T-cell subsets. Multicolor immunofluorescence miscoscopy was used to validate molecular findings. Ex vivo skin explant assays were used to functionally characterise dysfunctional CD8+ T-cell subsets on nonlesional autologous skin. We identified 2 major developmentally connected CD8+ T-cell subpopulations that were expanded in SSc skin lesions compared with healthy control skin. The first was a heterogeneous subset of effector-memory CD8+KLRB1+IL7R+ cells characterised by increased cytolytic and Tc2/Tc17 effector functions that appear to induce tissue damage and fibrosis in early-stage dcSSc skin lesions. The second, found primarily in patients with late-stage disease, was an exhausted CD8+KLRG1+IL7R- subset that exhibited transcriptional features of long-lived effector cells, likely contributing to chronic inflammation. Significantly, both subsets were also expanded in other benign dermatoses, implicating these cell populations in the pathogenesis of chronic human skin inflammation. This study provides new insight into core regulatory programmes modulating skin-resident CD8+ T-cell plasticity and identifies distinct CD8+ T-cell subpopulations that contribute to initiation and chronicity of inflammatory responses in systemic sclerosis skin lesions. These findings reveal prospective molecular targets for new therapeutic strategies against this incurable disease.