The array of immune cells in the TME of BTCs is diverse, including tumor-infiltrating lymphocytes (B lymphocytes, cytotoxic CD8+ T lymphocytes, CD4+ regulatory T lymphocytes (Tregs), and CD4+ effector T lymphocytes), NK cells, macrophages (both tumor-associated macrophages and, for iCCA, Kupffer cells), and tumor-associated neutrophils (TANs) [7]. Here, CD4 is linked to neoplasm.