CX3CR1+ macrophages interact with hepatic stellate cells to promote hepatocellular carcinoma through CD8+ T cell suppression

Abstract

Background and Aims: Hepatic stellate cells (HSCs) contribute to hepatocellular carcinoma (HCC) progression by regulating multiple factors. However, the entire immunoregulatory functions of HSCs are still obscure. Here, we aim to investigate whether HSCs impose CX3CR1+ macrophages to pro-tumorigenic properties in the peritumoral area. Approach and Results: In single cell RNA-sequencing analysis of HCC patients, a subpopulation of macrophages specifically expressed Arg1 and Cx3cr1 in the peritumoral area, and were highly enriched with retinol metabolism-related genes. Flow cytometry analysis showed significantly increased frequencies of CD14+CD11b+HLA-DR‒ macrophages with CX3CR1 in the HCC adjacent region where α-SMA-expressing activated HSCs (aHSCs) showed co-localized expression of CX3CL1. Accordingly, in tumor-bearing mice, Cx3cl1 mRNA expression was notably increased in aHSCs within the adjacent HCC, where infiltration of CX3CR1+Ly6C+ macrophages was mostly observed with decreased CD8+ T cells. In adoptive transfer and in vitro co-culture of myeloid cells, we demonstrated that CX3CR1+Ly6C+ macrophages migrated and highly expressed arginase-1 by interacting with retinoid-enriched aHSCs in the adjacent HCC. Direct treatment of retinoids or co-culturing with retinol-storing mouse aHSCs or human LX-2 cells significantly increased arginase-1 expression in CX3CR1+Ly6C+ macrophages and human blood CD14+ cells, leading to the suppression of CD8+ T cell proliferation. Moreover, genetic deficiency of CX3CR1 in myeloid cells or pharmacological inhibition of retinol metabolism remarkably attenuated HCC development. Conclusion: We showed that CX3CR1+Ly6C+ macrophages migrate and interact with aHSCs in the peritumoral region where retinoids induce arginase-1 expression in CX3CR1+Ly6C+ macrophages, subsequently depriving CD8+ T cells of arginine and promoting HCC.