A new gene therapy technology, termed StitchR, has shown promise in overcoming the size limitations that have previously hindered the treatment of muscular dystrophies and other diseases caused by large genes. Developed by researchers at the University of Rochester School of Medicine and Dentistry, StitchR delivers two halves of a gene separately, which then combine within the cell to restore the expression of a missing or inactive protein. This breakthrough, published in Science, could significantly expand the scope of treatable genetic diseases.
Overcoming Size Constraints in Gene Therapy
Traditional gene therapy approaches often struggle to deliver large genes due to the limited capacity of viral vectors. StitchR addresses this challenge by employing a dual vector system. "Instead of delivering the full gene in a single vector, which isn’t possible, we’ve developed an efficient dual vector system where two halves of a gene are delivered separately but come together to reconstitute the large mRNA in the affected tissues," explained Douglas M. Anderson, PhD, lead study author and assistant professor of Medicine at the Aab Cardiovascular Research Institute.
The technology hinges on the use of ribozymes, which cleave messenger RNAs (mRNAs), creating ends that are then joined by the cell's natural repair pathways. This process results in a full-length mRNA capable of producing the desired protein.
Restoring Protein Expression in Muscular Dystrophy Models
The researchers demonstrated the efficacy of StitchR in animal models of two distinct muscular dystrophies. In models of limb girdle muscular dystrophy type 2B/R2, StitchR restored the expression of Dysferlin. Similarly, in models of Duchenne muscular dystrophy, the technology facilitated the production of Dystrophin. Duchenne muscular dystrophy, the most common early-onset form, leads to significant disability and reduced lifespan, highlighting the urgent need for effective therapies.
Mechanism and Advantages of StitchR
StitchR leverages adeno-associated virus (AAV) vectors to deliver the two gene halves. Once inside the cell, ribozymes cut the ends of the mRNAs, which then seamlessly join to form a functional mRNA. According to the researchers, the resulting stitched mRNAs behave similarly to their natural counterparts, effectively translating genetic information into functional proteins.
"The concept sounds simple, but this required considerable bench work to optimize the molecules involved, ensure they are stable in cells, and make the process as efficient as possible," said Lynne E. Maquat, PhD, director of the UR Center for RNA Biology.
A key advantage of StitchR is that it produces only the full-length protein, avoiding the potential complications associated with truncated protein fragments. "Because StitchR occurs at the level of RNA, we can control and ensure that only the full-length protein product gets made. This differentiates StitchR from other dual vector technologies," added Anderson.
Future Directions
The research team is now focused on forming collaborations to develop StitchR vectors for a wide range of diseases caused by large genes. The technology's modular nature and compatibility with various vector types make it a promising platform for addressing previously untreatable genetic conditions. "With StitchR and other tools we are working towards treatments for some of the most debilitating genetic diseases on the planet, many of which have no current treatments or cures," said Anderson.
