Ex vivo liver gene therapy provides an attractive alternative to orthotopic liver transplantation for the treatment of liver diseases. We previously reported a protocol in which human primary hepatocytes are highly transduced in Suspension with Lentiviral vectors and Immediately Transplanted (SLIT). Here, we evaluated the SLIT approach in Gunn rats, the animal model for Crigler-Najjar syndrome type 1, a defect in bilirubin UDP-glucuronosyltransferase (BUGT).