Background and Aims: Metabolic dysfunction-associated steatohepatitis (MASH) can progress to fibrosis. We previously found an increased number and activation of peripheral blood T cells in patients with MASH compared to steatosis and healthy controls. However, clonality and activation status of T cells in early stages of MASH fibrosis remain unclear and may give unique insights into pathogenesis. Here, we characterised the phenotype and T cell receptor repertoire of T cells in blood, liver, and adipose tissue sampled simultaneously from patients ranging from healthy to non-cirrhotic fibrosis.

Methods: We performed CITE-seq and TCR sequencing on CD45+ immune cells from liver, subcutaneous (SAT), visceral adipose tissue (VAT), and peripheral blood (PBMC) of 19 MASLD patients (F0-F3 fibrosis) and one healthy control. Histology was assessed using NASH CRN criteria. Results: TCR sequencing revealed progressive TCR diversity loss and increased clonal expansion from health to MASLD with fibrosis, with expanded clones enriched in different subsets of CD8 T cells (effector memory, cytotoxic, and NK-like). Clonotype tracking demonstrated shared expanded clones across tissues, often targeting non-infectious antigens. Cell-cell interaction analysis identified clonally expanded CD8 T cells as major signal recipients and TAGLN EndoMT-like endothelial cells as dominant senders in fibrosis. Gene set enrichment of expanded clones in fibrotic tissues showed metabolic rewiring, suppression of exhaustion programs, and tissue-specific signaling, consistent with immunometabolic adaptation.

Conclusions: Clonal expansion of CD8 T cells with cytotoxic and pro-inflammatory expression profiles occurs early in MASH-related fibrosis and may be a key pathogenic factor in progressive disease.