Optimization of HITI-Mediated Gene Insertion for Rhodopsin and Peripherin-2 in Mouse Rod Photoreceptors: Targeting Dominant Retinitis Pigmentosa.

Purpose: Among the genome-editing methods for repairing disease-causing mutations resulting in autosomal dominant retinitis pigmentosa, homology-independent targeted integration (HITI)-mediated gene insertion of the normal form of the causative gene is useful because it allows the development of mutation-agnostic therapeutic products. In this study, we aimed for the rapid optimization and validation of HITI-treatment gene constructs of this approach in developing HITI-treatment constructs for various causative target genes in mouse models of retinal degeneration.

Methods: We constructed the Cas9-driven HITI gene cassettes in plasmid vectors to treat the mouse Rho gene. A workflow utilizing in vivo electroporation was established to validate the efficacy of these constructs. Single-cell genotyping was conducted to evaluate allelic donor gene insertion. The therapeutic potency of HITI-treatment plasmid and adeno-associated virus (AAV) vectors was examined by section immunohistochemistry and optomotor response (OMR) in Rho+/P23H mutant mice. We also targeted mouse Prph2 to examine the workflow.

Results: The optimized HITI-treatment constructs for mouse Rho genes achieved gene insertion in 80% to 90% of transduced mouse rod photoreceptor cells. This construct effectively suppressed degeneration and induced visual restoration in mutant mice. HITI-treatment constructs for the Rhodopsin gene demonstrated efficacy in AAV vectors and are adaptable for the mouse Prph2 gene locus.

Conclusions: The study showcases a workflow for the rapid optimization and validation of highly effective HITI-treatment gene constructs against dominant-negative inheritance in inherited retinal dystrophy. These findings suggest the potential utility of this approach in developing HITI-treatment constructs for various target genes, advancing gene therapy products for diverse genetic disorders.