H epatocellular carcinoma (HCC), the fifth most common cancer worldwide with 564,000 new cases each year, is also the third most common cause of cancer-related death. 1 HCC arises most frequently in males with cirrhosis, which is most often a consequence of chronic hepatitis infection or alcohol abuse. 2 Recent reports from different countries suggest that the incidence of HCC is increasing, probably as a consequence of the increased prevalence of hepatitis C virus (HCV) infection, although increased alcohol consumption may be significant. 3 The only effective approaches for patients with HCC are resection or liver transplantation. Following transplantation, there is an 83% 4-year recurrence-free survival in highly selected patients (single tumor Ͻ5 cm in diameter or fewer than three tumors Ͻ3 cm in diameter). 4 However, the majority of patients do not meet such strict criteria or have other contraindications. Local therapies such as percutaneous ethanol injection, thermal ablation, and intra-arterial chemoembolization are less successful, 5 and less than 10% of patients with moderate disease (Okuda stage 2) survive for 3 years. 6 Immunological mechanisms are important in the surveillance of malignancy and control of tumor progression. Cytotoxic CD8 ϩ lymphocytes (CTLs) and natural killer cells are potential effector cells in the control of tumor growth, although both require CD4 ϩ T helper 1 immune responses for optimal function. 7 Tumor-infiltrating lym-

Organoid technology holds great promise for regenerative medicine but has not yet been applied to humans. We address this challenge using cholangiocyte organoids in the context of cholangiopathies, which represent a key reason for liver transplantation. Using single-cell RNA sequencing, we show that primary human cholangiocytes display transcriptional diversity that is lost in organoid culture. However, cholangiocyte organoids remain plastic and resume their in vivo signatures when transplanted back in the biliary tree. We then utilize a model of cell engraftment in human livers undergoing ex vivo normothermic perfusion to demonstrate that this property allows extrahepatic organoids to repair human intrahepatic ducts after transplantation. Our results provide proof of principle that cholangiocyte organoids can be used to repair human biliary epithelium.

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