Robert Brenig

Background & Aims: Infectious complications determine the prognosis of cirrhosis patients. Their infection susceptibility relates to the development of immuneparesis, a complex interplay of different immunosuppressive cells and soluble factors. Mechanisms underlying the dynamics of immuneparesis of innate immunity remain inconclusive. We aimed to dissect the heterogeneity of circulating monocyte states in different cirrhosis stages, and pursued the function of selected differentially expressed (DE) genes. Methods: We systematically investigated circulating monocytes in health, compensated and not-acutely decompensated (NAD) cirrhosis using single cell RNA sequencing. Selective genes were confirmed by flow cytometry and diverse functional assays on monocytes ex vivo . Results: We identified seven monocyte clusters. Their abundances varied between cirrhosis stages, confirming previously reported changes i.e. reduction in CD14 ^low CD16 ⁺⁺ and emergence of M-MDSC in advanced stages. DE genes between health and disease and among stages were detected, including for the first time CD52. CD52-expression on monocytes significantly enhanced throughout compensated and NAD cirrhosis. Heretofore the biological significance of CD52-expression on monocytes remained unknown. CD52 ^high CD14 ⁺ CD16 ^high HLA-DR ^high monocytes in patients with cirrhosis revealed a functional phenotype of active phagocytes with enhanced migratory potential, increased cytokine production, but poor T cell activation. Following acute decompensation (AD), CD52 was cleaved by elevated phospholipase C (PLC), and soluble CD52 (sCD52) was detected in the circulation. Inhibition and cleavage of CD52 significantly suppressed monocyte functions ex vivo and in vitro , and the predominance of immunosuppressive CD52 ^low circulating monocytes in patients with AD was associated with infection and low transplant-free survival. Conclusion: CD52 may represent a biologically relevant target for future immunotherapy. Stabilising CD52 may enhance monocyte functions and infection control in the context of cirrhosis, guided by sCD52/PLC as biomarkers indicating immuneparesis. Lay summary: Recurrent infections are a major cause of death in patients with liver cirrhosis. A fundamental understanding of the mechanisms that suppress immune responses in patients with cirrhosis is lacking, but required for the development of strategies to restore innate immunity in cirrhosis patients and prevent infection. The current study identified a novel marker for deficient immune responses and a potential target for such a future immune-based therapy. Abstract Figure: Graphical Abstract scRNA-seq identified seven circulating monocyte states, changing in cirrhosis patients at different stages of disease. Circulating monocytes overexpress CD52 in cirrhosis, but are absent in AD/ACLF due to PLC. CD52-expressing monocytes show high capability for phagocytosis, cytokine production, adhesion and migration potential and T cell suppression. Created with BioRender.com

Infectious complications in patients with cirrhosis frequently initiate episodes of decompensation and substantially contribute to the high mortality. Mechanisms of the underlying immuneparesis remain underexplored. TAM receptors (TYRO3/AXL/MERTK) are important inhibitors of innate immune responses. To understand the pathophysiology of immuneparesis in cirrhosis, we detailed TAM receptor expression in relation to monocyte function and disease severity prior to the onset of acute decompensation. TNF-α/IL-6 responses to lipopolysaccharide were attenuated in monocytes from patients with cirrhosis (n = 96) compared with controls (n = 27) and decreased in parallel with disease severity. Concurrently, an AXL-expressing (AXL⁺) monocyte population expanded. AXL⁺ cells (CD14⁺CD16^highHLA-DR^high) were characterised by attenuated TNF-α/IL-6 responses and T cell activation but enhanced efferocytosis and preserved phagocytosis of Escherichia coli. Their expansion correlated with disease severity, complications, infection, and 1-yr mortality. AXL⁺ monocytes were generated in response to microbial products and efferocytosis in vitro. AXL kinase inhibition and down-regulation reversed attenuated monocyte inflammatory responses in cirrhosis ex vivo. AXL may thus serve as prognostic marker and deserves evaluation as immunotherapeutic target in cirrhosis.