Mutation-independent rhodopsin gene therapy by knockdown and replacement with a single AAV vector

Area of Science:

• Ophthalmology
• Genetics
• Molecular Biology

Background:

• Inherited retinal degenerations (IRDs) cause vision loss due to mutations affecting photoreceptor cells or retinal pigment epithelium.
• Gene therapy has advanced for recessive and X-linked IRDs, but treatment for autosomal dominant retinitis pigmentosa (adRP), particularly RHO-adRP, remains challenging.
• Over 150 mutations in the rhodopsin (RHO) gene cause the most common form of adRP, with clinical translation of therapies stalled.

Purpose of the Study:

• To develop and test a mutation-independent gene therapy for RHO-adRP.
• To evaluate the efficacy of a combined shRNA and replacement cDNA approach in a large-animal model.

Main Methods:

• Developed a single adeno-associated viral (AAV) vector containing an shRNA targeting human and canine RHO, and a mutation-resistant human RHO replacement cDNA.
• Administered subretinal vector injections into a naturally occurring canine model of RHO-adRP.
• Assessed therapeutic efficacy using noninvasive retinal imaging, histopathology, and electroretinography.

Main Results:

• Achieved near-complete suppression of endogenous canine RHO RNA and restoration of RHO protein to 30% of normal levels.
• Demonstrated complete protection of photoreceptors from degeneration in treated areas.
• Confirmed stable structural and functional preservation of retinal integrity long-term (>8 months).

Conclusions:

• This gene therapy strategy effectively suppresses pathogenic RHO and restores RHO protein levels, preserving vision in a clinically relevant large-animal model.
• The mutation-independent approach and demonstrated efficacy in canines provide a strong foundation for clinical trials in patients with RHO-adRP.