Abstract
BACKGROUND & AIMS: Tissue-resident memory T cells (TRMs) are long-lived cells poised for rapid immune responses to pathogens. This study assesses whether peritoneal CD8 T cells from patients with cirrhosis exhibit TRM-like functionalities, focusing on how inflammatory events shape phenotype and function. METHODS: Peritoneal CD8 T cell subsets from patients with decompensated cirrhosis were analysed using mass cytometry, flow cytometry, RT-qPCR, single-cell RNA sequencing, in vitro culture, and cytokine profiling. Cells from 87 patients were used, of which 30 experienced spontaneous bacterial peritonitis (SBP). Soluble co-inhibitory (checkpoint) receptors were investigated in cell-free ascites from 80 patients, and TRM-activating cytokines were quantified in peritoneal macrophages. RESULTS: Unsupervised mass cytometry and subsequent flow cytometry validation confirmed the peritoneal abundance of CD103+ CD69+ CD8+ memory T cells in ascites compared with blood (2.2% vs. 0.4%; p <0.001). TRM-like cells, particularly the CD49a+ subset, were robust producers of interferon-γ (IFN-γ) post-T cell receptor ligation (35.1% vs. 15.3% in CD49- TRM-like cells; p <0.001), and were susceptible to bystander activation by IL-15. Single-cell RNA sequencing revealed tissue residency markers alongside transcriptional signatures of activation and exhaustion in IL-15-exposed peritoneal CD8 T cells. Peritoneal macrophages emerged as IL-15 sources during SBP (ascitic fluid concentration 18.6 pg/ml vs. 8.9 pg/ml; p <0.05), altering TRM-like cell phenotype even after inflammation had subsided. Despite the expression of co-inhibitory receptors, TRM-like cells maintained cytotoxic effector functions in a soluble checkpoint-rich environment, with PD-1/PDL-1 axis blockade not affecting their cytotoxic capacity. CONCLUSIONS: A subset of peritoneal CD8 T cells exhibits TRM-like traits and responds to macrophage-derived cytokines during peritoneal inflammation. TRM-like cells retain potent cytotoxic and proinflammatory responses after SBP resolution, underscoring their role in modulating peritoneal immunity and inflammation in cirrhosis. IMPACT AND IMPLICATIONS: Patients with decompensated cirrhosis exhibit impaired immune responses increasing the risk of spontaneous bacterial peritonitis. This study provides insight into a subset of human peritoneal CD8 T cells in patients with decompensated cirrhosis that have a long-lived and tissue-resident phenotype capable of effectively fighting recognised pathogens within a short period with the help of IL-15 produced by activated macrophages in a bystander fashion. This knowledge has the potential to improve immunomodulatory therapies aiming to enhance peritoneal immune surveillance, and by targeting TRM-like cells and/or IL-15 signalling pathways. In addition, high concentrations of soluble immune checkpoints in ascites should be considered when applying immune checkpoint inhibitors in decompensated cirrhosis.