Immune-Mediated Hepatitis During Immune Checkpoint Inhibitor cancer Immunotherapy: Lessons From Autoimmune Hepatitis and Liver Immunology

Immune checkpoint inhibitors (ICI) are being increasingly used to successfully treat several types of cancer. However, due to their mode of action, these treatments are associated with several immune-related adverse events (irAEs), including immune-mediated autoimmune-like hepatitis in 5 to 10% of cases. The specific immune mechanism responsible for the development of immune-mediated liver injury caused by immune checkpoint inhibitors (ILICI) is currently unknown. This review summarizes the current knowledge on hepatic irAEs during cancer immunotherapy. It also addresses the clinical management of ILICI and how it is becoming an increasingly important clinical issue. Clinical, histological, and laboratory features of autoimmune hepatitis (AIH) and ILICI are compared, and their shared and distinctive traits are discussed in an effort to better understand the development of hepatic irAEs. Finally, based on the current knowledge of liver immunology and AIH pathogenesis, we propose a series of events that could trigger the observed liver injury in ICI-treated patients. This model could be useful in the design of future studies aiming to identify the specific immune mechanism(s) at play in ILICI and improve immune checkpoint inhibitor cancer immunotherapy.

B lymphocytes repress hepatic tumorigenesis but not development in Hras12V transgenic mice

Increasing reports show noninflammation underlying HCC, challenging our understanding of the roles of the immune system in hepatocarcinogenesis. By exploring a mouse model of hepatic tumor induced by hepatocyte-specific expression of the Hras12V oncogene without obvious inflammation, we found that the proportion of B cells, but not T cells, progressively and significantly decreased in 3, 5-month-old transgenic mice (Tg) compared with non-transgenic mice. Notably, the proportions of total and activated B and T cells all significantly decreased in 9-month-old Tg with multiple massive hepatic tumors. Together with the decreased B cell proportion, serum IgG1/2 also significantly decreased in 5, 9-month-old Tg. Interestingly, homozygous Tg showed significantly higher B cell proportion and IgG2 levels, accompanied by significantly lower incidences of liver nodules but not adenomas and carcinomas compared with heterozygous Tg. Treatment of Tg with PCI-32765, a potent Bruton's tyrosine kinase (BTK) inhibitor for suppressing B cell proliferation and activation, significantly decreased the B cell proportion and IgG2 levels, accompanied by a significantly higher incidence of liver nodules, but had no effects on adenoma and carcinoma. Treatment of Tg with insulin-like growth factor 1 (IGF-1) significantly increased the B cell proportion and IgG2 levels, accompanied by a significantly lower incidence of liver nodules and carcinoma, but had no effects on adenoma. Conclusively, B cells and IgG2 may play important roles in suppressing hepatic tumorigenesis, but not development. In addition, hepatocyte-specific expression of the ras oncogene may play roles in suppressing B cells, while developed hepatic tumors suppress both B and T cells.