AAV Gene Therapy Successfully Restores Hearing in Hereditary Deafness Models Using Targeted GRE Expression

December 16, 2025 — A groundbreaking study published in Nature Communications reveals a highly effective gene therapy strategy to treat DFNB1, the most common form of hereditary hearing loss. The research, which utilized advanced AAV (adeno-associated virus) vectors, demonstrates that cell-specific delivery of the GJB2 gene can rescue hearing sensitivity and prevent cochlear degeneration.

DFNB1 deafness is caused by mutations in the GJB2 gene, which encodes the gap junction protein connexin26. While many children are born with profound hearing loss, a significant number possess residual hearing at birth that rapidly declines, creating a critical developmental window for therapeutic intervention using AAV technology.

Overcoming Off-Target Expression with GREs

Previous attempts at AAV gene therapy for GJB2-related deafness failed because universal promoters often caused inappropriate expression in sensory hair cells and neurons, leading to toxicity or lethal electrical coupling.

To solve this, researchers used ATAC-seq to identify specific Gene Regulatory Elements (GREs). These GREs act as a genetic “GPS,” ensuring the AAV vector only activates the gene in the appropriate cochlear epithelial cells and fibrocytes, while remaining silent in hair cells.

• Precision Targeting: By flanking the GJB2 coding sequence with these human-derived GREs, the team created a more clinically relevant AAV vector.

• Safety Profile: Unlike ubiquitous promoters that caused lethality in mice, the AAV-GRE approach was well-tolerated and restricted expression to native GJB2-expressing tissues.

Full Hearing Restoration in Partial Knockdown Models

The study tested the AAV treatment across different models of deafness with varying results:

1. Conditional Knockout (Severe): In mice completely lacking GJB2, the AAV-GRE-hsGJB2 vector prevented the typically observed flat sensory epithelium and restored cochlear structure, though hearing rescue was partial (~50 dB SPL improvement).

2. Partial Knockdown (Mild): In a milder model of DFNB1 that better mimics patients with residual hearing, a single AAV injection at birth led to a complete restoration of hearing. Treated mice showed ABR (Auditory Brainstem Response) and DPOAE (otoacoustic emissions) thresholds identical to normal-hearing controls.

Translational Success in Non-Human Primates

To assess the safety and potential for human application, the researchers delivered the AAV-GRE vector into the cochleas of cynomolgus monkeys.

• Accurate Localization: The human GJB2 gene delivered by the AAV was found precisely in the target cell types.

• Minimal Toxicity: The AAV treatment caused little to no compromise of hearing sensitivity in the monkeys, suggesting that the GRE-mediated expression is both safe and effective for translation to clinical trials.

The research represents a significant step forward in treating hereditary deafness. By proving that AAV vectors can be “programmed” to avoid sensitive hair cells while restoring the supporting cellular network, scientists have opened a new door for curing the most prevalent cause of genetic hearing loss worldwide.