Enhanced Gene Therapy for DMD Using Larger Dystrophins and Lower Vector Doses
Abstract
Duchenne muscular dystrophy (DMD) is caused by mutations in the enormous DMD, or dystrophin, gene. Progress over the past 35 years in understanding the structure and function of dystrophin, together with advances in gene delivery technology, have enabled the development of gene therapy approaches to treat this disorder. Adeno-associated viral vector (AAV) gene replacement therapies that aim to delivery miniaturized, or micro- dystrophins are in clinical trials. While the early results are encouraging, showing a significant slowing of disease progression while leading to modest increases in strength in some boys, the micro-dystrophin results have been less effective than seen in animal models. Furthermore, there have been a number of adverse events associated with the high doses of AAV needed for body-wide gene delivery and, in a few cases, due to immune reaction against the dystrophin protein itself. Our proposal is to further advance exciting developments we have made that have the potential to greatly increase both the safety and effectiveness of gene therapy for DMD in the near future. Two issues appear critical to the under-performance of AAV/micro-dystrophin therapies. One is a limitation of the AAV vectors, as current doses used in the clinic are lower than what are typically used in animal studies. Increasing the dose is not an option as many of the observed adverse events result from the already very high dose of these vectors. However, a new generation of AAV vectors has been developed over the past 2 years that enable gene delivery at doses up to 40 times lower than with current AAVs, and they also show reduced uptake by the liver. A second issue is due to reduced function of micro-dystrophin proteins, which are only one-third the size of the normal full-length dystrophin. Thus, the ability to deliver larger and more potent dystrophin proteins with lower doses of AAV could be a game changer in terms of gene therapy for DMD. Studies in another ongoing project by our groups are focused on a third issue, namely an immune response against dystrophin itself, which has been seen in 5 patients to date. Those studies will also be adapted here. The rationale for our new gene therapy system is our discovery that much larger and more functional dystrophins can be efficiently delivered to muscles using a dual AAV vector system. Despite the need for two vectors, we find that no increase in dose is needed for co-delivery. Furthermore, the new classes of myotropic AAVs enable these larger dystrophins to be delivered at one-tenth the dose being used now in the clinic. The basis for this new dual vector system derives from the use of split inteins, which can join, in muscle cells, two co-delivered proteins into one larger and functional protein in a remarkably efficient manner. Our preliminary studies already show a dramatic and rapid increase in function compared with micro-dystrophin when these split intein vectors are delivered systemically to mouse and rat DMD models. Furthermore, by using three vectors, we have been able to deliver FULL-LENGTH dystrophin to muscle using myotropic AAVs. Our proposal is to refine and optimize this system such that it can be advanced into clinical trials. While we have already demonstrated the proof-of-principle of this system, our proposed studies will select for optimal myotropic AAVs, engineer the most functional split inteins, identify the best ways to split dystrophin into two or three AAVs, and adapt our previous efforts to reduce potential immune issues associated with delivery. Translation of these studies into the clinic will be accelerated by several partnerships. First, the University of Washington has filed patent applications on the key technologies needed to advance the split intein dystrophin system, making it feasible for Biotech company adoption. Second, we have established partnerships with two biotech companies that have licensed the technology
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 04, 2024
- Source ID
- HT94252310971
Entities
People
- Julie Crudele
Organizations
- United States Army
- University of Washington