Therapeutic inhibition of monocyte recruitment prevents checkpoint inhibitor-induced hepatitis

Checkpoint inhibitor-induced hepatitis (CPI-hepatitis) is an emerging problem with the widening use of CPIs in cancer immunotherapy. Here, we developed a mouse model to characterise the mechanism of CPI-hepatitis and to therapeutically target key pathways driving this pathology. C57BL/6 wild-type (WT) mice were dosed with TLR9-agonist (TLR9-L) for hepatic priming combined with anti-CTLA-4 plus anti-PD-1 (CPI) or control (PBS) for up to 7 days. Co-administration of CPIs with TLR9-L induced liver pathology closely resembling human disease, with increased infiltration and clustering of granzyme B+perforin+CD8+ T cells and CCR2+ monocytes, 7 days post treatment. This was accompanied by apoptotic hepatocytes surrounding these clusters and elevated cytokeratin-18 and alanine transaminase plasma levels. Liver RNA sequencing identified key signalling pathways (JAK-STAT, NF-κB) and cytokine/chemokine networks ( Ifnγ, Cxcl9, Ccl2/Ccr2 ) as drivers of CPI-hepatitis. Using this model, we show that CD8+ T cells mediate hepatocyte damage in experimental CPI-hepatitis. However, their liver recruitment, clustering, and cytotoxic activity is dependent the presence of CCR2+ monocytes. Absence of hepatic monocyte recruitment in Ccr2rfp/rfp mice and CCR2 therapeutic inhibition by cenicriciroc (CVC) in WT mice prevented CPI-hepatitis. In conclusion, using this newly established mouse model, we demonstrate a central role of liver infiltrating CCR2+ monocyte interaction with cytotoxic CD8+ T cells in the pathogenesis of CPI-hepatitis and highlight novel therapeutic targets. ### Competing Interest Statement The authors have declared no competing interest. * ALT : alanine transaminase CK-18 : cytokeratin-18 CPI : checkpoint inhibitor CPI-hepatitis : checkpoint inhibitor-induced hepatitis CTLA-4 : cytotoxic T lymphocyte antigen-4 CVC : cenicriviroc DILI : drug-induced liver injury ELISA : enzyme-linked immunosorbent assay FFPE : formalin-fixed paraffin-embedded FMO : fluorescence minus one GZMB : granzyme B HBV : hepatitis B virus HCC : hepatocellular carcinoma IPA : ingenuity pathway analysis irAE : immune-related adverse event KC : Kupffer cells MoMF : Monocyte-derived macrophages NK cells : natural killer cells PCA : principal component analysis PD-1 : programmed cell death-1 PD-L1 : programmed cell death-ligand-1 RT-qPCR : quantitative reverse transcription polymerase chain reaction TF : transcription factor TLR-L : Toll-like receptor agonist Tregs : regulatory T cells.