704. Long-Term Correction of Crigler-Najjar Syndrome and Scale-Up Production of an Optimized AAV8 Vector Expressing the UGT1A1 Transgene

Abstract

Crigler-Najjar syndrome (CN) is an autosomal recessive rare disorder caused by mutations in the UDP-glucuronosyltransferase 1 isotype A1 (UGT1A1) gene. In severe CN, lack or reduced activity of UGT1A1 results in high levels of serum unconjugated bilirubin (UCB), which can lead to brain damage and death. Treatment of CN consists of phototherapy for 10-12 hours per day to convert UCB into soluble photoisomers without the need of conjugation, which presents several limitations and has a major impact on life quality of the patients. Liver transplantation is the only curative option for CN. The limited therapeutic options available prompted us to develop a new therapy for CN based on the transfer of a corrected copy of the UGT1A1 gene to hepatocytes.We developed an AAV8 vector optimized for the liver expression of the hUGT1A1 transgene (AAV8-hUGT1A1). Safety and efficacy of correction of total serum bilirubin (TB) levels with AAV-hUGT1A1 were demonstrated in mouse and rat models of CN at vector doses as low as 5×10 11 vector genomes (vg)/kg, a result confirmed also by the detection of conjugated bilirubin in bile of treated rats. In juvenile CN rats, long-term correction of total bilirubin levels were observed for more than 8 months following AAV8-hUGT1A1 gene transfer. In neonate Ugt1a1–/– mice, intraperitoneal delivery of the vector at doses as low as 1×10 9 vg/mouse resulted in correction of TB at 4 weeks. However, vector delivery in P2 and P4 animals resulted in lower efficiency of correction when compared with P11-transduced mice, a finding likely due to the more advanced development of the liver at later time points.Based on these data, dose finding studies were performed in CN rats, which showed a profile of liver transduction with AAV8 vectors similar to humans, i.e. lower efficiency of transduction than mice. No differences in efficacy of correction of TB were observed in male vs. female rats.A scalable process for the production of AAV8-hUGT1A1 production was established based on a protocol of triple transfection of suspension HEK293 cells, leading to high yield vector preparations with excellent purity profile. In vitro transduction assays in human hepatocytes based on Western blot for hUGT1A1 protein and in vivo studies in CN rats demonstrated that vectors produced with the suspension process have potency characteristics undistinguishable from research grade vectors produced by triple transfection of adherent cells and purified by cesium chloride gradient centrifugation.In conclusion, our data demonstrate the safety and efficacy of gene transfer for Crigler-Najjar syndrome in two relevant animal models of the disease and provide tools and a strong rationale for the translation of these results in human subjects.