Single cell transcriptomes of hepatic immune cells from mice with and without colorectal cancer liver metastasis

Metastasis is the primary cause of cancer mortality. Cancer frequently metastasizes to the liver. We report that liver metastases diminish immunotherapy efficacy systemically in patients and preclinical models. Mechanistically, liver metastases siphon activated CD8+ T cells from systemic circulation. Within the liver, activated antigen-specific Fas+CD8+? T cells undergo apoptosis following their interaction with FasL+CD11b+F4/80+ monocyte-derived macrophages. Consequently, liver metastases create a systemic immune desert in both preclinical models and patients. Liver-directed radiotherapy eliminates immunosuppressive hepatic macrophages, increases hepatic T-cell survival, and reduces hepatic siphoning. Thus, liver metastases co-opt host peripheral tolerance mechanisms to cause acquired immunotherapy resistance through CD8+ T-cell deletion and the combination of liver-directed radiotherapy and immunotherapy is a novel therapeutic strategy to promote systemic anti-tumour immunity. Overall design: Single cell RNA sequencing of hepatic immune cells isolated from mouse livers with and without colorectal cancer metastasis