CD4 and bile duct papillary neoplasm: Overall, more than half of the analysed IPN tissue samples exhibited intraepithelial CD3+ (64.6%, n = 42/65), CD4+ (63.1%, n = 41/65) and CD8+ (56.9%, n = 37/65) T-cell infiltration and the number of cases with intraepithelial CD3+, CD4+ and CD8+ cells gradually decreased throughout IPN-driven carcinogenesis (Fig. 3a).