Integrated Single Cell Analysis Reveals An Atlas of Tumor Associated Macrophages in Hepatocellular Carcinoma

Effective anti-tumor immune responses are orchestrated by immune cell partnership network that functions through tissue homeostatic pathways, not direct cytotoxicity

The liver hosts a diverse array of immune cells that play pivotal roles in both maintaining tissue homeostasis and responding to disease. However, the precise contributions of these immune cells in the progression of nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC) remain unclear. Utilizing a systems immunology approach, we reveal that liver immune responses are governed by a dominant-subdominant hierarchy of ligand-receptor-mediated homeostatic pathways. In healthy individuals, inflammatory immune responses operate within these pathways, challenging the notion of the liver as a purely tolerogenic organ. Chronic consumption of a Western diet (WD) disrupts hepatocyte function and reconfigures immune interactions, resulting in hepatic stellate cells (HSCs), cancer cells, and NKT cells driving 80% of the immune activity during NAFLD. In HCC, 80% of immune response involves NKT cells and monocytes collaborating with hepatocytes and myofibroblasts to restore disrupted homeostasis. Interestingly, dietary correction during NAFLD yields nonlinear outcomes: tumor progression coincides with the failure of mounting homeostatic immune responses, whereas tumor prevention is associated with sustained immune responses, predominantly orchestrated by monocytes. These monocytes actively target fibroblasts and myofibroblasts, creating a tumor-suppressive microenvironment. Notably, only 5% of T cells displayed apoptosis-inducing activity, selectively contributing to the turnover of hepatic stromal cells, particularly myofibroblasts and fibroblasts. Our findings suggest that effective anti-tumor immune responses in the liver are primarily mediated by immune cells sustaining tissue homeostasis, rather than relying on direct cytotoxic mechanisms.