Tumour‐activated liver stromal cells regulate myeloid‐derived suppressor cells accumulation in the liver

Regulating mechanisms underlying hepatic myeloid‐derived suppressor cell (MDSC) accumulation remain to be described. Here, we provide evidence for the involvement of tumour‐activated liver stromal cells in the process of hepatic MDSCs migration and accumulation. Our data showed an elevated frequency of MDSCs in the liver of tumour‐bearing mice. Moreover, tumour‐activated liver stromal cells promote MDSC migration into the liver site. Further investigation indicated higher levels of cytokine and chemokine expression in liver stromal cells after exposure to the tumour‐conditioned supernatant. Notably, the expression levels of proinflammatory factors, mainly including macrophage colony stimulating factor (M‐CSF), transforming growth factor‐β (TGF‐β), monocyte chemotactic protein‐1 (MCP‐1) and stromal‐derived factor‐1 (SDF‐1), increased after treatment with tumour‐conditioned supernatant, and blockade of MCP‐1 or SDF‐1 decreased the proportion of tumour infiltrated MDSCs in mice co‐transplanted with liver stromal cells and tumour cells, but not in mice with only tumour cells injection. These findings demonstrate that tumour‐activated liver stromal cells produce higher levels of chemokines and cytokines, which may contribute to MDSC accumulation into the liver site in patients with liver cancer.