T cells and monocyte-derived myeloid cells mediate immunotherapy-related hepatitis in a mouse model.

BACKGROUND & AIMS: Immune checkpoint inhibitors (ICIs) are associated with immune-related adverse events (irAEs) which are more severe when ICIs are used in combination. We aimed to use a mouse model to elucidate the molecular mechanisms of immune-related hepatitis, one of the common irAEs associated with ICIs. METHODS: Immune phenotyping and molecular profiling were performed on Pdcd1-/- mice treated with anti-CTLA4 and/or the IDO1 inhibitor epacadostat or a 4-1BB agonistic antibody. RESULTS: ICI combination-induced hepatitis and 4-1BB agonist-mediated hepatitis share similar features yet maintain distinct immune signatures. Both were characterized by an expansion of periportal infiltrates and pan-zonal inflammation albeit with different morphologic characteristics. In both cases, infiltrates were predominantly CD4+ and CD8+ T cells with upregulated T-cell activation markers, ICOS and CD44. Depletion of CD8+ T cells abolished ICI-mediated hepatitis. Single-cell transcriptomics revealed that the hepatitis induced by combination ICIs is associated with a robust immune activation signature in all subtypes of T cells and T helper 1 skewing. Expression profiling revealed a central role for IFNγ and liver monocyte-derived macrophages in promoting a pro-inflammatory T-cell response to ICI combination and 4-1BB agonism. CONCLUSION: We developed a novel mouse model which offers significant value in yielding deeper mechanistic insight into immune-mediated liver toxicity associated with various immunotherapies. LAY SUMMARY: Hepatitis is one of the common immune-related adverse events in cancer patients receiving immune checkpoint inhibitor (ICI) therapy. The mechanisms of ICI-induced hepatitis are not well understood. In this paper, we identify key molecular mechanisms mediating immune intracellular crosstalk between liver T cells and macrophages in response to ICI in a mouse model.

Evaluating the Sensitivity and Specificity of Promising Circulating Biomarkers to Diagnose Liver Injury in Humans.

Early diagnosis of drug-induced liver injury (DILI) continues to be a major hurdle during drug development and postmarketing. The objective of this study was to evaluate the diagnostic performance of promising biomarkers of liver injury-glutamate dehydrogenase (GLDH), cytokeratin-18 (K18), caspase-cleaved K18 (ccK18), osteopontin (OPN), macrophage colony-stimulating factor (MCSF), MCSF receptor (MCSFR), and microRNA-122 (miR-122) in comparison to the traditional biomarker alanine aminotransferase (ALT). Biomarkers were evaluated individually and as a multivariate model in a cohort of acetaminophen overdose (n = 175) subjects and were further tested in cohorts of healthy adults (n = 135), patients with liver damage from various causes (n = 104), and patients with damage to the muscle (n = 74), kidney (n = 40), gastrointestinal tract (n = 37), and pancreas (n = 34). In the acetaminophen cohort, a multivariate model with GLDH, K18, and miR-122 was able to detect DILI more accurately than individual biomarkers alone. Furthermore, the three-biomarker model could accurately predict patients with liver injury compared with healthy volunteers or patients with damage to muscle, pancreas, gastrointestinal tract, and kidney. Expression of K18, GLDH, and miR-122 was evaluated using a database of transcriptomic profiles across multiple tissues/organs in humans and rats. K18 mRNA (Krt18) and MiR-122 were highly expressed in liver whereas GLDH mRNA (Glud1) was widely expressed. We performed a comprehensive, comparative performance assessment of 7 promising biomarkers and demonstrated that a 3-biomarker multivariate model can accurately detect liver injury.

Inhibition of immune checkpoints PD-1, CTLA-4, and IDO1 coordinately induces immune-mediated liver injury in mice.

Cancer cells harness immune checkpoints such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and indoleamine 2,3-dioxygenase 1 (IDO1) to evade immune control. Checkpoint inhibitors have demonstrated durable anti-tumor efficacy in human and preclinical models. Liver toxicity is one of the common immune-related adverse events associated with checkpoint inhibitors (CPIs) and its frequency and severity often increase significantly during CPI combination therapies. We aim to develop a mouse model to elucidate the immune mechanisms of CPI-associated liver toxicity. Co-administration of CTLA-4 blocking antibody, 9D9, and/or an IDO1 inhibitor, epacadostat in wild-type and PD-1-/- mice (to simulate the effect of PD1 blockade) synergistically induced liver injury and immune cell infiltration. Infiltrated cells were primarily composed of CD8+ T cells and positively associated with hepatocyte necrosis. Strikingly, sites of hepatocyte necrosis were frequently surrounded by clusters of mononuclear immune cells. CPI treatments resulted in increased expression of genes associated with hepatocyte cell death, leukocyte migration and T cell activation in the liver. In conclusion, blockade of immune checkpoints PD-1, CTLA-4, and IDO1 act synergistically to enhance T cell infiltration and activity in the liver, leading to hepatocyte death.