Gene Therapy for Cystic Fibrosis: Progress and Challenges of Genome Editing

Abstract

Since the early days of its conceptualization and application, human gene transfer held the promise of a permanent solution to genetic diseases including cystic fibrosis (CF). This field went through alternated periods of enthusiasm and distrust. The development of refined technologies allowing site specific modification with programmable nucleases highly revived the gene therapy field. CRISPR nucleases and derived technologies tremendously facilitate genome manipulation offering diversified strategies to reverse mutations. Here we discuss the advancement of gene therapy, from therapeutic nucleic acids to genome editing techniques, designed to reverse genetic defects in CF. We provide a roadmap through technologies and strategies tailored to correct different types of mutations in the cystic fibrosis transmembrane regulator (CFTR) gene, and their applications for the development of experimental models valuable for the advancement of CF therapies.

Keywords: CRISPR-Cas; genome editing; programmable nucleases.

Figure 1

Gene therapy strategies to restore CFTR function in CF. CFTR genes containing any mutation causing cystic fibrosis are colored in orange, genes bearing the correct sequence in blue. Elongated bars indicate the 27 exons distributed over the entire length (188702 bp) of CFTR gene. Striped right arrows indicate the transcription process. In the center panel a typical CF patient condition is depicted; a genetic defect is present on each allele preventing transcription of suitable amount of mRNA molecules with correct sequence. In the gene complementation panel, green arrow indicates the exogenous promoter randomly integrated into the cell genome (grey lines) and able to produce mRNA with correct sequence (blue) in amount sufficient to restore CFTR function. Genome editing strategies able to correct at least a copy of the CFTR gene at the endogenous locus. Graphical representation for the HITI and super-exon strategies: targeted gene correction restores specifically the production of correct mRNA molecules (always in blue). Directed NHEJ is also able to reestablish production of correct mRNA molecules for certain splicing defects thanks to small changes introduced in specific intron regions. RNA treatments intervene (green arrow) during the transcription process to rectify correct mRNA molecules production.