Suppressive myeloid cells are expanded by biliary tract cancer-derived cytokines in vitro and associate with aggressive disease.

Background: BTC is an aggressive disease exacerbated by inflammation and immune suppression. Expansion of immunosuppressive cells occurs in biliary tract cancer (BTC), yet the role of BTC-derived cytokines in this process is unclear.
Methods: Activated signalling pathways and cytokine production were evaluated in a panel of human BTC cell lines. Human peripheral blood mononuclear cells (PBMCs) were cultured with BTC supernatants, with and without cytokine neutralising antibodies, and analysed by flow cytometry or immunoblot. A human BTC tissue microarray (TMA, n = 69) was stained for IL-6, GM-CSF, and CD33 ⁺ S100a9 ⁺ cells and correlated with clinical outcomes.
Results: Immunomodulatory factors (IL-6, GM-CSF, MCP-1) were present in BTC supernatants. BTC supernatants expanded CD33 ^dim CD11b ⁺ HLA-DR ^low/- myeloid-derived suppressor cells (MDSCs) from human PBMCs. Neutralisation of IL-6 and GM-CSF in BTC supernatants inhibited activation of STAT3/5, respectively, in PBMCs, with heterogeneous effects on MDSC expansion in vitro. Staining of a BTC TMA revealed a positive correlation between IL-6 and GM-CSF, with each cytokine and more CD33 ⁺ S100a9 ⁺ cells. Increased CD33 ⁺ S100a9 ⁺ staining positively correlated with higher tumour grade, differentiation and the presence of satellite lesions.
Conclusion: BTC-derived factors promote suppressive myeloid cell expansion, and higher numbers of CD33 ⁺ S100a9 ⁺ cells in resectable BTC tumours correlates with more aggressive disease.