Interestingly, the proportion of intraepithelial CD3+, CD4+ and CD8+ T-cell infiltration decreased progressively from non-tumorous biliary tissue, through IPN, to invasive BTC, most significantly in early carcinogenesis (P < 0.001, P = 0.024 and P < 0.001, respectively; Fig. 3b–d). The gene discussed is CD4; the disease is bile duct papillary neoplasm.