WFH State‐of‐the‐art paper 2020: In vivo lentiviral vector gene therapy for haemophilia

Over the last decade, the development of new treatments for haemophilia has progressed at a very rapid pace. Despite all the promising advances in protein products, the prospect offered by gene therapy of a single potentially lifelong treatment remains attractive for people with haemophilia. Transfer to the liver of coagulation factor VIII (FVIII) or factor IX (FIX) transgenes has indeed the potential to stably restore the dysfunctional coagulation process. Recombinant adeno-associated virus (AAV)-derived vectors are widely employed for liver-directed gene therapy, given their very good efficacy and safety profile, shown in several preclinical and clinical studies. However, there are some limitations associated with AAV vectors, such as their predominantly episomal nature in the nucleus of target cells and the widespread pre-existing immunity against the parental virus in humans. By contrast, HIV-derived lentiviral vectors (LV) integrate into the target cell chromatin and are maintained as the cells duplicate their genome, a potential advantage for establishing long-term expression especially in paediatric patients, in which the liver undergoes substantial growth. Systemic administration of LV allowed stable multi-year transgene expression in the liver of mice and dogs. More recently, improved phagocytosis-shielded LV were generated, which, following intravenous administration to non-human primates, showed selective targeting of liver and spleen and enhanced hepatocyte gene transfer, achieving up to supra-normal activity of both human FVIII and FIX transgenes. These studies support further preclinical assessment and clinical evaluation of in vivo liver-directed LV gene therapy for haemophilia.