Globoid cell leukodystrophy (GLD) is a neurodegenerative inherited genetic disease, due to defects in an enzyme that normally degrades sphingolipids, a class of biological molecules present in the myelin sheath, necessary for nervous tissue function. The name of this enzyme is beta-galactosylceramidase (GALC). Impairment of GALC activity in GLD results in progressive demyelination and nerve tissue degeneration. Most individuals with infantile forms die before the age of two. Currently, there is no cure for GLD.

Several gene replacement therapy strategies have been attempted in pre-clinical models with varying degree of success, however, still facing the challenge of providing widespread enzymatic reconstitution and full correction of pathology in affected tissues, particularly the central and peripheral nervous systems (CNS and PNS). Previous evidence suggests effective transport across the blood brain barrier of several therapeutic proteins when fused with parts of other proteins, known to be able to reach CNS and PNS. Thus, GALC will be endowed with these additional portions, which may be sufficient to ensure its transport across the blood brain barrier.

In addition, we will equip GALC with small portions of highly secreted proteins to improve GALC secretion by cells. The long-term objective of the proposed research is thus to develop a safe and effective liver gene therapy for GLD. In vivo gene therapy to the liver indeed offers the attractive prospects of a minimally invasive, one-time potentially curative treatment for GLD, by providing sustained pervasive high amounts of a functional GALC enzyme to the CNS and PNS through the bloodstream.

Here we propose a project to obtain an early proof-of-principle in a mouse model of the disease. The CNS and PNS are naturally protected by a blood brain barrier that ensures selective passage of necessary substances, while blocking potentially dangerous molecules. Lentiviral vectors (LV) are attractive gene delivery vehicles for liver gene therapy thanks to their ability to insert their DNA into the host cell DNA. For this reason, LV are maintained following liver cell proliferation in liver growth and turnover, including potentially in newborns, that would be the target population in GLD. We have developed LV that allow stable expression of therapeutic proteins in the liver of mice and dogs, following systemic administration. More recently, we have generated engineered LV with increased resistance to capture by cells of the immune system, a process called phagocytosis. Thanks to this feature, these LV are more efficient at reaching the target cells in the liver.

Here we propose to generate LV expressing the above-described optimized GALC from the liver, administer them intravenously to newborn mice affected by GLD and assess survival and correction of the hallmarks of the GLD disease. We also propose to engineer LV to further escape phagocytosis by exposing on their surface additional inhibitors of phagocytosis. If successful, the work proposed here will allow the generation of novel LV with increased protection from phagocytosis and efficiency of gene transfer into liver cells that will facilitate development and manufacturing to quality and scale required for use in humans and alleviate concerns of possible LV particle dose dependent acute toxicity. These LV, transporting the engineered GALC enzymes, may become a feasible, sustainable, safe and effective liver gene therapy for GLD and potentially for other leukodystrophies.

Project financed by ELA up to: 96 000 €