TREM1+regulatory myeloid cells expand in steatohepatitis-HCC and associate with poor prognosis and therapeutic resistance to immune checkpoint blockade

Hepatocellular carcinoma (HCC) is an inflammation-associated cancer arising from viral and non-viral etiologies. Immune checkpoint blockade primarily benefits patients with viral HCC. Expansion of suppressive myeloid cells is a hallmark of chronic inflammation and cancer, but their heterogeneity in HCC is not fully resolved and might underlie immunotherapy resistance in the steatohepatitis setting. Here, we present a high resolution atlas of hepatic innate immune cells from patients with HCC that unravels a steatohepatitis contexture characterized by the emergence of high entropy myeloid cell states and myeloid-biased NK cell differentiation. We identify a discrete population of tumor-infiltrating myeloid cells, predominant in the steatohepatitis setting, that expresses a variety of myeloid lineage-affiliated genes, including granulocyte, macrophage and dendritic cell features, and can be identified in HCC tumors based on selective dual expression ofTREM1andCD163. Functional characterization reveals that TREM1+CD163+myeloid cells highly express TGFβ and IL-13RA, localize to HCC fibrotic lesions, and potently suppress T cell effector functionsex vivo, a function further potentiated by TREM1 engagement. We refer to this population as TREM1+CD163+regulatory myeloid cells (TREM1+CD163+Mreg). Deconvolution analyses in large cohorts of patients with HCC and other solid tumors reveals that the density of TREM1+CD163+Mregincreases in advanced stages, associates with poor prognosis, and therapeutic resistance to PD-1 blockade. Our data support myeloid subset-targeted immunotherapies to treat HCC and identify TREM1 as a therapeutic target.HIGHLIGHTSAtlas of hepatic innate immune cells (100,000 transcriptomes) from patients with HCCCore signatures to identify, discriminate and localize innate lymphoid and myeloid cellsA population of TREM1+CD163+myeloid cells, referred to as TREM1+CD163+Mreg, expands in steatohepatitis HCCTREM1+CD163+Mregexpress granulocyte- and macrophage/dendritic cell-lineage genesTREM1+CD163+Mregpotently suppress T cell effector functions, which is potentiated by TREM1 engagement by cognate ligandsTREM1+CD163+Mregproduce high levels of TGFβ and populate fibrotic lesionsThe density of TREM1+CD163+Mregincreases in advanced HCC and associate with poor patient survivalThe density of TREM1+CD163+Mregassociates with resistance to immune checkpoint blockade in other solid tumors