Gene therapy and genome editing in the retina and liver gene therapy and genome editing for mucopolysaccharidosis VI

Gene therapy and genome editing in the retina
Inherited retinal diseases (IRD) are a major cause of blindness worldwide mostly due to mutations in genes expressed in retinal photoreceptor cells (PR). Recently, our lab has contributed the development of safe and effective gene therapy using adeno-associated viral vectors (AAV). This has led to the approval of the first gene therapy product for an ocular disease (Luxturna) which treats patients with a rare form of inherited childhood blindness. However, several genes expressed in PR and involved in IRD are larger in size than the carrying capacities of AAV vectors. Our goal is to overcome the challenge of transferring large genes to PR in order to develop therapies for common IRDs. Retinal gene therapy has limited applicability in the treatment of dominant IRDs. This is because these diseases are due to gain-of-function mutations for which traditional gene replacement is ineffective. We are evaluating several AAV- and CRISPR-Cas9- based approaches that allow simultaneous blocking of the mutant allele and replacement with a wild type copy. The results from these projects may provide novel treatment options for common severe blinding conditions.

Liver gene therapy and genome editing for mucopolysaccharidosis VI
Mucopolysaccharidosis VI (MPS VI) is caused by deficient arylsulfatase B (ARSB) activity, resulting in lysosomal storage of glycosaminoglycans (GAGs). MPS VI is characterized by dysostosis multiplex, organomegaly, corneal clouding, and heart valve thickening without central nervous system involvement. Enzyme replacement therapy for MPS VI has limited efficacy and requires multiple administrations of costly enzymes. Gene transfer to a factory organ like the liver may provide a life-time source of secreted ARSB. We have shown that single intravascular administration of adeno-associated viral vectors (AAV) 2/8-TBG-ARSB in MPS VI is both safe and effective in animal models and, more recently in humans, with therapeutic levels of ARSB produced by liver that are stable for several years. The long-term outcomes of gene therapy in patients as well as AAV vector dose-refining are in progress. Patients under 4 years of age are currently excluded from trials because potential hepatocyte proliferation may result in AAV episomal DNA dilution and loss of transgene expression. We are evaluating an AAV- and CRISPR Cas9-based approach that integrates the ARSB coding sequence at the highly transcribed albumin locus to obtain stable therapeutic levels of ARSB following newborn administration in animal models. This could be applied to other models of lysosomal storage diseases targetable by liver gene therapy.

The "Total Award" amount indicated for this project represents the share of the funding of the Telethon Foundation for research by the Tigem institute from January 2022 until last budget year, calculated based on the size of the research group.