Hepatocellular carcinoma (HCC) can have viral or non-viral causes1–5. Non-alcoholic steatohepatitis (NASH) is an important driver of HCC. Immunotherapy has been approved for treating HCC, but biomarker-based stratification of patients for optimal response to therapy is an unmet need6,7. Here we report the progressive accumulation of exhausted, unconventionally activated CD8+PD1+ T cells in NASH-affected livers. In preclinical models of NASH-induced HCC, therapeutic immunotherapy targeted at programmed death-1 (PD1) expanded activated CD8+PD1+ T cells within tumours but did not lead to tumour regression, which indicates that tumour immune surveillance was impaired. When given prophylactically, anti-PD1 treatment led to an increase in the incidence of NASH–HCC and in the number and size of tumour nodules, which correlated with increased hepatic CD8+PD1+CXCR6+, TOX+, and TNF+ T cells. The increase in HCC triggered by anti-PD1 treatment was prevented by depletion of CD8+ T cells or TNF neutralization, suggesting that CD8+ T cells help to induce NASH–HCC, rather than invigorating or executing immune surveillance. We found similar phenotypic and functional profiles in hepatic CD8+PD1+ T cells from humans with NAFLD or NASH. A meta-analysis of three randomized phase III clinical trials that tested inhibitors of PDL1 (programmed death-ligand 1) or PD1 in more than 1,600 patients with advanced HCC revealed that immune therapy did not improve survival in patients with non-viral HCC. In two additional cohorts, patients with NASH-driven HCC who received anti-PD1 or anti-PDL1 treatment showed reduced overall survival compared to patients with other aetiologies. Collectively, these data show that non-viral HCC, and particularly NASH–HCC, might be less responsive to immunotherapy, probably owing to NASH-related aberrant T cell activation causing tissue damage that leads to impaired immune surveillance. Our data provide a rationale for stratification of patients with HCC according to underlying aetiology in studies of immunotherapy as a primary or adjuvant treatment.

Hepatocellular carcinoma (HCC), the fastest rising cancer in the United States and increasing in Europe, often occurs with nonalcoholic steatohepatitis (NASH). Mechanisms underlying NASH and NASH-induced HCC are largely unknown. We developed a mouse model recapitulating key features of human metabolic syndrome, NASH, and HCC by long-term feeding of a choline-deficient high-fat diet. This induced activated intrahepatic CD8(+) T cells, NKT cells, and inflammatory cytokines, similar to NASH patients. CD8(+) T cells and NKT cells but not myeloid cells promote NASH and HCC through interactions with hepatocytes. NKT cells primarily cause steatosis via secreted LIGHT, while CD8(+) and NKT cells cooperatively induce liver damage. Hepatocellular LTβR and canonical NF-κB signaling facilitate NASH-to-HCC transition, demonstrating that distinct molecular mechanisms determine NASH and HCC development.

Summary Hepatocellular carcinoma (HCC) is the second most common cause of cancer related death. Non-alcoholic fatty liver disease (NAFLD) affects a large proportion of the US population and is considered a metabolic predisposition to liver cancer 1-5. However, the role of adaptive immune responses in NAFLD-promoted HCC is largely unknown. Here, we show that dysregulation of lipid metabolism in NAFLD causes a selective loss of intrahepatic CD4+ but not CD8+ T lymphocytes leading to accelerated hepatocarcinogenesis. We also found that CD4+ T lymphocytes have greater mitochondrial mass than CD8+ T lymphocytes and generate higher levels of mitochondrially-derived reactive oxygen species (ROS). Disruption of mitochondrial function by linoleic acid, a fatty acid accumulated in NAFLD, causes more oxidative damage than other free fatty acids such as palmitic acid, and mediates selective loss of intrahepatic CD4+ T lymphocytes. In vivo blockade of ROS reversed NAFLD-induced hepatic CD4+ T lymphocyte decrease and delayed NAFLD-promoted HCC. Our results provide an unexpected link between lipid dysregulation and impaired anti-tumor surveillance.

Humoral autoimmunity paralleled by the accumulation of follicular helper T cells (T(FH) cells) is linked to mutation of the gene encoding the RNA-binding protein roquin-1. Here we found that T cells lacking roquin caused pathology in the lung and accumulated as cells of the T(H)17 subset of helper T cells in the lungs. Roquin inhibited T(H)17 cell differentiation and acted together with the endoribonuclease regnase-1 to repress target mRNA encoding the T(H)17 cell-promoting factors IL-6, ICOS, c-Rel, IRF4, IκBNS and IκBζ. This cooperation required binding of RNA by roquin and the nuclease activity of regnase-1. Upon recognition of antigen by the T cell antigen receptor (TCR), roquin and regnase-1 proteins were cleaved by the paracaspase MALT1. Thus, this pathway acts as a 'rheostat' by translating TCR signal strength via graded inactivation of post-transcriptional repressors and differential derepression of targets to enhance T(H)17 differentiation.