Breakdown of adaptive immunotolerance induces hepatocellular carcinoma in HBsAg-tg mice

Hepatitis B virus (HBV) can induce chronic inflammation, cirrhosis, and eventually hepatocellular carcinoma (HCC). Despite evidence suggesting a link between adaptive immunity and HBV-related diseases in humans, the immunopathogenic mechanisms involved are seldom described. Here we show that expression of TIGIT, a promising immune checkpoint in tumor immunotherapy, increases with age on hepatic CD8⁺ T cells in HBsAg-transgenic (HBs-tg) mice whose adaptive immune system is tolerant to HBsAg. TIGIT blockade or deficiency leads to chronic hepatitis and fibrosis, along with the emergence of functional HBsAg-specific cytotoxic T lymphocytes (CTLs), suggesting adaptive immune tolerance could be broken by TIGIT blockade or deficiency. Importantly, HBsAg vaccination further induces nonresolving inflammation and HCC in a CD8⁺ T cell-dependent manner in TIGIT-blocked or -deficient HBs-tg mice. Therefore, CD8⁺ T cells play an important role in adaptive immunity-mediated tumor progression and TIGIT is critical in maintenance of liver tolerance by keeping CTLs in homeostatic balance.