New Fusion Promoters Show Promise for Retinal Gene Therapy
Researchers developed two synthetic fusion promoters, Pikali and Nocchu, that drive broader and more balanced gene expression across both rod and cone photoreceptors in human retinal organoids. The constructs were created by combining a cone-specific promoter (PR1.7) with a rod-active promoter (GRK1), achieving transduction in 30–45% of photoreceptors. This addresses a longstanding bottleneck in retinal gene therapy, where no single promoter has previously offered both sufficient cellular coverage and specificity across photoreceptor types.
A study posted to bioRxiv describes the development of two synthetic fusion promoters, Pikali and Nocchu, designed to overcome a key limitation in retinal gene therapy: the inability of existing promoters to efficiently target both rod and cone photoreceptors simultaneously. The constructs were engineered by combining PR1.7, a cone-specific promoter, with GRK1, a promoter predominantly active in rods. Testing in human iPSC-derived retinal organoids showed that both fusion promoters outperformed their parental counterparts, with Pikali and Nocchu achieving transduction rates of 30–45% of photoreceptors. Expression levels exceeded those of GRK1 alone, while cellular coverage was broader than that achieved by PR1.7 alone. The researchers argue these constructs represent a promising platform for next-generation gene therapy vectors targeting inherited retinal dystrophies, potentially advancing clinical translation of treatments for conditions affecting both photoreceptor types.
What's missing
As a preprint, this work has not yet undergone peer review. The study does not report in vivo data in animal models or human patients, leaving the translational efficacy and safety profile of these promoters unestablished. Long-term expression stability, immune responses to the viral vectors, and performance across different inherited retinal dystrophy genotypes are not addressed. The 30–45% transduction rate, while an improvement, still leaves the majority of photoreceptors untransduced, and the clinical threshold required for therapeutic benefit is not discussed.
What different sources said
- bioRxivCenter
Promfusion: a synthetic fusion promoter enabling enhanced and balanced photoreceptor transgene expression
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