Fotis Sampaziotis, Ludovic Vallier
Wellcome Trust-Medical Research Council Stem Cell Institute, Cambridge Stem Cell Institute, Anne McLaren Laboratory, Department of Surgery, University of Cambridge, Cambridge, UK.

Q. CAN YOU EXPLAIN TO US WHY IS BILE DUCT ENGINEERING SUCH AN IMPORTANT UNMET CLINICAL NEED?

Bile duct disease accounts for a third of adult and 70% of pediatric liver transplantations. Several of these disorders are widespread and affect the small branches of the intrahepatic bile ducts which are not amenable to surgical replacement or reconstruction. However, some of the most impactful cholangiopathies associated with liver transplantation can be limited to the large ducts of the extrahepatic biliary tree. These include Biliary Atresia, which constitutes the leading cause for pediatric liver transplantation and ischemic dominant strictures which represent one of the most common causes for graft failure following rejection. Surgical replacement of the affected bile ducts could address such challenges, but it is restricted by the lack of suitable healthy tissue. Portoenterostomy can be used as an alternative intervention; however, it is associated with complications such as reflux cholangitis. Furthermore, it is not therapeutic for the majority of the patients with biliary atresia who will proceed to have a liver transplantation later in life. The generation of bioengineered bile ducts could provide a viable alternative for the management of these disorders with a potential for reducing the need for transplantation.

Q. HOW FAR IS YOUR MOUSE MODEL FROM BEING UTILISED IN HUMANS?

Our mouse model demonstrated the capacity of our cells to survive and repair the biliary epithelium in vivo, while maintaining their functional properties. Furthermore, we illustrated their potential for generating bioengineered bile ducts in vitro, which then remodel and fully integrate to the mouse biliary tree following transplantation. However, several challenges remain prior to translation in humans. From an engineering perspective, we need to adapt our method to address challenges associated with the generation of human sized constructs and these new constructs would require additional in vivo testing in animals of appropriate size. Furthermore, there is a requirement to assess the immunogenicity of the constructs and the need for immunosuppression in the context of non-autologous and autologous transplantation studies. Finally, in terms of the cells, we would have to adapt our culture system to comply with Good Manufacturing Practice (GMP) guidelines which is a pre-requisite for any transplantation in patients. Only when these goals are met, we would be able to proceed to the first pilot safety studies in humans.

Q. WHAT ARE THE NEXT STEPS IN REGENERATIVE MEDICINE IN THE LAB?

Clinical translation of the bioengineered bile ducts technology requires up-scaling these constructs to near-human dimensions. Larger constructs with thicker wall will require incorporation of a vascular network to achieve adequate tissue oxygenation, long-term cholangiocyte survival and function. Once we address this challenge our goal is to integrate these constructs in a large animal model resembling human anatomy and assess the capacity of our constructs to integrate to the host vascular network, maintain their functional properties and sustain bile transport through a patent lumen. In parallel we are taking advantage of recent advances in organoid culture such as chemically defined hydrogels, to transfer our culture system to GMP-compliant conditions.

Importantly, cholangiopathies extend beyond disorders of the common bile duct. A significant proportion of biliary disease represents widespread disorders of the small or intermediate size intrahepatic bile ducts, which are not amenable to surgical replacement with bioengineered constructs. We have already illustrated the potential of our cholangiocyte organoids to remodel and spontaneously organize into ductular structures when transplanted in vivo. Therefore, is possible that these cells could also repopulate or regenerate damaged intrahepatic bile ducts when delivered to the biliary tree and we have already started exploring this approach in the context of diffuse cholangiopathies.

Q. TO WHAT EXTENT IS YOUR MODEL APPLICABLE TO A BIOARTIFICIAL LIVER?

In addition to the importance of bioengineered bile ducts for the management of cholangiopathies, our method represents the first step towards the generation of a bioartifical biliary tree which is a crucial component for the development of a bioartificial liver. Indeed, bile is constantly produced by hepatocytes and its toxicity is well established. The bile ducts play an essential role for the transfer of bile, the modification of its composition and act as a necessary barrier for the protection of the other parenchymal cells. Defective bile transport in cholangiopathies results in biliary cirrhosis and liver failure. Therefore, the incorporation of a bioengineered biliary system is pivotal for the success of a bioengineered liver and through this application bioengineered bile ducts could contribute to the management of any end-stage liver disease.