Towards a clinical trial to treat GUCY2D Leber congenital amaurosis (LCA1)

Abstract

Purpose : Mutations in GUCY2D are a leading cause of the most severe form of early-onset retinal dystrophy, Leber congenital amaurosis (LCA1). GUCY2D encodes retinal guanylate cyclase-1 (retGC1), a protein expressed in photoreceptor outer segments that plays a role in the recovery phase of phototransduction. Proof of concept for gene replacement has been established in mouse models of LCA1 using AAV vectors. Despite a high degree of visual disturbance stemming predominantly from severe cone dysfunction, LCA1 patients largely retain normal photoreceptor laminar architecture. Together, these results suggest LCA1 is a worthy target for gene replacement therapy and prompted initiation of additional IND-enabling preclinical studies. First we asked whether the AAV capsid of our choice, containing a human photoreceptor-specific promoter, was capable of driving murine Gucy2e or human GUCY2D in photoreceptors of GCDKO mice and restoring retinal function to this mouse model. Second, using this AAV vector/promoter combination, we evaluated transduction efficiency using GFP as the transgene in photoreceptors of the non-human primate (NHP).

Methods : All AAV vectors were titered and characterized by analytical ultracentrifugation prior to injection. GCDKO mice were subretinally injected between P21-P35 in one eye with either AAV-Gucy2e or AAV-GUCY2D at varying doses. Photopic and scoptopic electroretinogram was performed at 1, 2 or 3 months post-injection. Cynomolgous NHPs were subretinally injected with AAV-GFP at varying doses. Spectralis imaging and immunohistochemistry of retinal sections were used to document GFP expression in life and post mortem, respectively.

Results : Both AAV-Gucy2e and AAV-GUCY2D restored significant cone and rod function to retinas of GCDKO mice. In NHP, transduction of ~75% of photoreceptors was achieved following subretinal injection of AAV-GFP vector.

Conclusions : These results expand on our knowledge of GUCY2D gene replacement in mouse models of LCA1 and transduction efficiency for AAV delivered transgene under the control of a photoreceptor-specific promoter in NHP. These studies also confirm biological potency of the clinical candidate vector for human clinical trials.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.