Challenges and opportunities when transitioning from in vivo gene replacement to in vivo CRISPR/Cas9 therapies - a spotlight on hemophilia

Gene therapy shines light on congenital stationary night blindness for future cures

Congenital Stationary Night Blindness (CSNB) is a non-progressive hereditary eye disease that primarily affects the retinal signal processing, resulting in significantly reduced vision under low-light conditions. CSNB encompasses various subtypes, each with distinct genetic patterns and pathogenic genes. Over the past few decades, gene therapy for retinal genetic disorders has made substantial progress; however, effective clinical therapies for CSNB are yet to be discovered. With the continuous advancement of gene-therapy tools, there is potential for these methods to become effective treatments for CSNB. Nonetheless, challenges remain in the treatment of CSNB, including issues related to delivery vectors, therapeutic efficacy, and possible side effects. This article reviews the clinical diagnosis, pathogenesis, and associated mutated genes of CSNB, discusses existing animal models, and explores the application of gene therapy technologies in retinal genetic disorders, as well as the current state of research on gene therapy for CSNB.

Gene Therapy in Hemophilia A: Achievements, Challenges, and Perspectives

Strides in advancements of care of persons with hemophilia include development of long-acting factor replacement therapies, novel substitution and hemostatic rebalancing agents, and most recently approved gene therapy. Several decades of preclinical and clinical trials have led to development of adeno-associated viral (AAV) vector-mediated gene transfer for endogenous production of factor VIII (FVIII) in hemophilia A (HA). Only one gene therapy product for HA (valoctocogene roxaparvovec) has been approved by regulatory authorities. Results of valoctocogene roxaparvovec trial show significant improvement in bleeding rates and use of factor replacement therapy; however, sustainability and duration of response show variability with overall decline in FVIII expression over time. Further challenges include untoward adverse effects involving liver toxicity requiring immunosuppression and development of neutralizing antibodies to AAV vector rendering future doses ineffective. Real-life applicability of gene therapy for HA will require appropriate patient screening, infrastructure setup, long-term monitoring including data collection of patient-reported outcomes and innovative payment schemes. This review article highlights the success and development of HA gene therapy trials, challenges including adverse outcomes and variability of response, and perspectives on approach to gene therapy including shared decision-making and need for future strategies to overcome the several unmet needs.

Genome editing, a superior therapy for inherited retinal diseases

Gene augmentation and genome editing are promising strategies for the treatment of monogenic inherited retinal diseases. Although gene augmentation treatments are commercially available for inherited retinal diseases, there are many shortcomings that need to be addressed, like progressive retinal degeneration and diminishing efficacy over time. Innovative CRISPR-Cas9-based genome editing technologies have broadened the proportion of treatable genetic disorders and can greatly improve or complement treatment outcomes from gene augmentation. Progress in this relatively new field involves the development of therapeutics including gene disruption, ablate-and-replace strategies, and precision gene correction techniques, such as base editing and prime editing. By making direct edits to endogenous DNA, genome editing theoretically guarantees permanent gene correction and long-lasting treatment effects. Improvements to delivery modalities aimed at limiting persistent gene editor activity have displayed an improved safety profile and minimal off-target editing. Continued progress to advance precise gene correction and associated delivery strategies will establish genome editing as the preferred treatment for genetic retinal disorders. This commentary describes the applications, strengths, and drawbacks of conventional gene augmentation approaches, recent advances in precise genome editing in the retina, and promising preclinical strategies to facilitate the use of robust genome editing therapies in human patients.