NAFLD causes selective CD4+ T lymphocyte loss and promotes hepatocarcinogenesis

Non-alcoholic fatty liver disease (NAFLD) is shown to promote hepatocellular carcinoma through the generation of linoleic acid, disruption of mitochondrial function and selective loss of CD4+ T cells, leading to impaired anti-tumour immunity. Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease and is recognized as a metabolic predisposition to liver cancer. Using mouse models and samples from patients with NAFLD and healthy controls, Tim Greten and colleagues show that NAFLD promotes hepatocellular carcinoma through the generation of linoleic acid, disruption of mitochondrial function and selective loss of CD4+ T cells, leading to impaired anti-tumour immunity. 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 to be a metabolic predisposition to liver cancer1,2,3,4,5. However, the role of adaptive immune responses in NAFLD-promoted HCC is largely unknown. Here we show, in mouse models and human samples, 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 demonstrate 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-tumour surveillance.