Hepatocyte spheroids as an alternative to single cells for transplantation after ex vivo gene therapy in mice and pig models

Background: Autologous hepatocyte transplantation after ex vivo gene therapy is an alternative to liver transplantation for metabolic liver disease. Here we evaluate ex vivo gene therapy followed by transplantation of single-cell or spheroid hepatocytes. Methods: Pig and mouse hepatocytes were isolated, labeled with zirconium-89 and returned to the liver as single cells or spheroids. Biodistribution was evaluated through positron emission tomography–computed tomography. Fumarylacetoacetate hydrolase–deficient pig hepatocytes were isolated and transduced with a lentiviral vector containing the Fah gene. Animals received portal vein infusion of single-cell or spheroid autologous hepatocytes after ex vivo gene delivery. Portal pressures were measured and ultrasound was used to evaluate for thrombus. Differences in engraftment and expansion of ex vivo corrected single-cell or spheroid hepatocytes were followed through histologic analysis and animals’ ability to thrive off 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione. Results: Positron emission tomography–computed tomography imaging showed spheroid hepatocytes with increased heterogeneity in biodistribution as compared with single cells, which spread more uniformly throughout the liver. Animals receiving spheroids experienced higher mean changes in portal pressure than animals receiving single cells (P <.01). Additionally, two animals from the spheroid group developed portal vein thrombi that required systemic anticoagulation. Immunohistochemical analysis of spheroid- and single-cell–transplanted animals showed similar engraftment and expansion rates of fumarylacetoacetate hydrolase–positive hepatocytes in the liver, correlating with similar weight stabilization curves. Conclusion: Ex vivo gene correction of autologous hepatocytes in fumarylacetoacetate hydrolase–deficient pigs can be performed using hepatocyte spheroids or single-cell hepatocytes, with spheroids showing a more heterogeneous distribution within the liver and higher risks for portal vein thrombosis and increased portal pressures.