Viral Vector Delivery Techniques for CRISPR-based Homology-Directed Repair Gene Therapy with a Focus on Cystic Fibrosis

CRISPR-Cas9 is a revolutionary technology used to edit or alter an organism’s DNA sequence and gene functions. CRISPR-Cas9 technology is implemented using gene therapy vectors to effectively deliver gene editing reagents while protecting the genetic material and bypassing extracellular and cellular barriers [1]. Among current gene therapy vector technologies, viral vectors have demonstrated highly specific targeted delivery and high transduction efficiency. Viral vectors are modeled after pathogenic virus systems and integrate therapeutic genes into an organism’s genome [2]. Due to their diverse types and unique advantages and disadvantages, thorough deliberation must be applied to select an optimal classification to maintain efficacy and safety of CRISPR-Cas9 gene therapy techniques. Viral vectors can be used to effectively deliver gene therapies to repair mutations employing 2 techniques: Homology-Directed Repair (HDR) and prime editing [3, 4]. Single mutations can cause certain genetic diseases, such as cystic fibrosis, which is most commonly caused by a deletion of the 508th amino acid residue (phenylalanine) of the cystic fibrosis transmembrane conductance regulator (CFTR) protein [5, 6]. HDR repairs double-stranded breaks following the gene editing process, while prime editing, a newer technology, edits and repairs DNA without creating double-stranded breaks. These techniques are both effective options for employing CRISPR-Cas9 to repair the CFTR mutation [7, 8]. This review explores the range of available viral vector technologies used for gene delivery and compares prime editing with HDR with an emphasis on the application of repairing the CFTR deletion mutation that causes cystic fibrosis.