Single-cell landscape of immunocytes in patients with extrahepatic cholangiocarcinoma

Background: The intricate landscape of immunocytes in the tumor microenvironment (TME) is fundamental to immunotherapy but notably under-researched in extrahepatic cholangiocarcinoma (ECCA). Methods: Single-cell RNA sequencing technology was conducted to make an in-depth analysis of immunocytes from matched tumor tissues, paratumor tissues and peripheral blood from ECCA patients. The potential cellular interactions between two cell populations were analyzed with software CellPhoneDB (v2.1.7). Results: We obtained 13526 cells and characterized the transcriptomes and heterogeneity of different clusters and subclusters of immunocytes from ECCA, including CD4+ T cells, CD8+ T cells, B cells and myeloid immunocytes. We observed the rarely described immunocyte subclusters "intermediate" exhausted CD8+ T (CD8+ Tex) cells and “nonclassic” plasmacytes (CD27+ CD138+ CD38−). In addition, we identified potential immunotherapy targets, for example, ACP5, MAGEH1, TNFRSF9 and CCR8 for Tregs and MT1 for CD8+ Tex cells. We also found strong cellular interactions among Treg cells, M2 macrophages and CD8+ Tex cells through ligand–receptor analysis, implying that potential cellular cross-linkage promoted the immunosuppressive nature of the TME. Conclusions: In a word, our study illuminated the components of the TME and revealed potential cellular interactions at the individual cellular level in ECCA, we aimed to provide a new perspective for further immunological studies and immunotherapy of ECCA.