Health Science Reviews

By Funeka Tyholo

Cystic fibrosis (CF) is a rare genetic disorder affecting multiple systems, primarily characterized by thick, sticky mucus that obstructs organs like the lungs, pancreas, and intestines, leading to severe respiratory and digestive issues. Inherited in an autosomal recessive manner, CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which affects the regulation of chloride and sodium ions in epithelial cells. Though CF is most common in individuals of European descent, with a carrier frequency of 1 in 25, its prevalence varies globally. The disorder is less frequent in African Americans, Hispanic Americans, and Asians, with notable cases in South Africa among people of European ancestry.

Currently, most therapies for CF focus on treating symptoms rather than addressing the root cause of the disease. In a study by researchers from Imperial College London, they review previous gene therapy approaches and their limitations. The study explores how these efforts have progressed and highlights what can be improved in future therapies to better target the genetic cause of CF, focusing on advancements in gene editing and delivery methods.

Gene addition therapy for CF initially employed viral vector-based delivery to introduce a functional CFTR gene into patient cells, aiming to produce the missing protein. However, this approach faced challenges such as vector-related issues and limited long-term effectiveness. Gene editing techniques, including Zinc Finger Nucleases (ZFNs) and Transcription Activator-Like Effector Nucleases (TALENs), were developed to create double- strand breaks at specific CFTR gene locations, facilitating the insertion of a correct CFTR copy and showing proof of concept in cell lines and iPS cells. The more recent and versatile CRISPR-Cas9 tool has been used to correct CFTR mutations in advanced cellular models and organoids, offering a precise approach compared to earlier methods. Homology-Directed Repair (HDR) enhances gene correction by using donor DNA sequences to replace mutated CFTR sequences, though HDR remains inefficient. An alternative, Homology-Independent Targeted Integration (HITI), involves CRISPR-Cas-mediated integration of DNA without relying on sequence homology, potentially improving efficiency over HDR. Additionally, Adeno-Associated Virus (AAV) vectors have been utilized to deliver donor templates and enhance HDR efficiency in primary cells, leading to functional CFTR recovery.

In conclusion, the investigation of innovative methods in gene therapy shows a significant shift from traditional approaches that predominantly concentrated on administering therapeutic nucleic acids to more specialized strategies meant to directly repair CFTR mutations. In addition to providing new therapeutic approaches, genome editing technologies like CRISPR-Cas9, ZFNs, and TALENs are setting the standard by developing experimental models that are important to implementing these advances in clinical applications. Even with the advancements, there are still obstacles to overcome, especially in creating efficient in vivo delivery methods for nucleic acids and genome editing tools. Nevertheless with clear obstacles and reasonable limitations, the way forward is becoming clearer. With more research to come, these developments could lead to more accurate and successful treatments for cystic fibrosis, improving patient outcomes and opening the door for new therapeutic developments.

Reference:

Alton EWFW, Gates AJ & Davies JC. 2021. Gene therapy for cystic fibrosis: An updated review of the field. Gene Therapy. 28(2):88-98.