Macrophage-derived IL-15 imprints peritoneal TRM-like CD8 T cells in cirrhosis and spontaneous bacterial peritonitis

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.