Tumor-associated macrophages promoting PD-L1 expression in infiltrating B cells through the CXCL12/CXCR4 axis in human hepatocellular carcinoma.

The inflammation-related tumor microenvironment (TME) is one of the major driving forces of hepatocarcinogenesis. We aimed to investigate cell-to-cell communication among Hepatocellular Carcinoma (HCC) through re-analyzing HCC single-cell RNA-seq data, and to confirm such cellular interaction through and study. We found a subset of Regulatory B cells with PD-L1 expression (PD-L1 Bregs), mainly located in adjacent HCC tissues. In co-localization with PD-L1 Bregs, a subset of Tumor Associated Macrophages with high expression of CXCL12 (CXCL12 TAMs) was also mainly located in adjacent HCC tissues. Moreover, CXCL12 TAMs can be stimulated using an HCC conditional medium. Using CellChat analysis and Multiplex Immunohistochemistry staining (mIHC), CXCL12 TAMs were found to be first recruited by Cancer-Associated Fibroblasts (CAFs) through a CD74/macrophage migration inhibitory factor (MIF) pattern, and further differentiated into TGF-β-enriched tissues. Furthermore, CXCL12 TAMs recruited PD-L1 Bregs via the CXCL12/CXCR4 axis, and CXCR4 expression was significantly positively correlated to PD-L1 expression in PD-L1 Bregs. At last, we confirmed the communications among CAFs, Macrophages and B cells and their tumor-promoting effects by using an orthotopic mouse model of HCC. Immunosuppressive HCC TME involving cell-to-cell communications comprised MIF-secreting CAFs, CXCL12-secreting TAMs, and PD-L1-producing Bregs, and their regulation could be promising therapeutic targets in future immunotherapy for human HCC.