756. Stable Amelioration of Hemophilia B in Dogs by Intravenous Administration of Lentiviral Vectors Expressing Hyper-Functional Factor IX

Abstract

Lentiviral vectors (LVs) are attractive vehicles for liver-directed gene therapy by virtue of their ability to stably integrate in the genome of target cells and the low prevalence of pre-existing immunity against HIV in humans. Over the past years, we have developed a LV platform that can achieve stable transgene expression in the liver, induce transgene-specific immune tolerance and establish correction of hemophilia in mouse models upon systemic administration. This LV is designed to stringently target transgene expression to hepatocytes through transcriptional and microRNA-mediated regulation. We then investigated the efficacy and safety profile of portal vein administration of LVs expressing canine factor IX (FIX) in a canine model of hemophilia B. We produced large-scale batches of LVs qualified for in vivo administration and treated adult hemophilia B dog by portal vein administration. We observed long-term stable reconstitution of canine FIX activity up to 1% of normal and significant amelioration of the clinical phenotype in 3 treated dogs with 6, 3.5 and 2.5 years of follow up. LV infusion was associated with transient signs of inflammatory response and mild hepatotoxicity, which could be abrogated by pretreatment with anti-inflammatory drugs. There was no detectable long-term toxicity or development of FIX inhibitors. In the perspective of clinical translation and to increase therapeutic efficacy, we next treated two 10-kg hemophilia B dogs by peripheral vein administration of LVs expressing a codon-optimized and hyperfunctional canine FIX at a 5-fold higher dose than those previously administered. Intravenous LV administration was well tolerated with mild and self-limiting elevation of aminotransferases in one dog. In the dog that reached more than 1 year of follow up FIX activity ranged between 4-8% of normal. Treatment of two more dogs at a higher dose is underway. Overall, our studies position LV-mediated liver gene therapy for further pre-clinical development and clinical translation. LVs may thus complement other available vectors to address some of the outstanding challenges posed by liver gene therapy of hemophilia and conceivably other diseases.