Exploring Different Serotypes And Promoters In rAAV-mediated Gene Replacement Therapy Of Achromatopsia Type 2 (ACHM2)

Abstract

Purpose: : Achromatopsia type 2 (ACHM2) is caused by loss-of-function mutations in CNGA3 and is characterized by congenital absence of cone photoreceptor function. Here, we evaluated rAAV-mediated gene replacement as a potential treatment for this disease.

Methods: : Therapeutic rAAVs expressing mouse CNGA3 were injected into the subretinal space of 2-week-old CNGA3-/- mice. We tested two different AAV serotypes (AAV5 and AAV8) and promoters (mouse S opsin and human M/L opsin). The treatment success was monitored using immunohistochemical, electrophysiological and behavioral methods.

Results: : In contrast to untreated mice, treated CNGA3-/- mice became able to generate cone photoreceptor responses and to transfer these signals to bipolar and ganglion cells and were able to solve a water-maze task designed to test for cone-mediated vision. In support, we found morphologically that treated cones, in contrast to untreated cones, expressed regular CNG channel complexes and opsins in outer segments. Moreover, the treatment normalized cGMP levels in cones, reduced Müller cell gliosis and delayed cone cell loss. In AAV5-treated animals functional restoration was observed at 9 weeks after administration. In contrast, in AAV8-treated mice the therapeutic effect was already observed 4 weeks post injection. Long-term experiments indicated a stable therapeutic effect for at least 8 months.

Conclusions: : We provide a proof-of-concept in mice for the treatment of ACHM2 by rAAV-mediated gene replacement. The therapeutic success did not depend on the AAV serotype used. However, in the AAV8-treated mice the onset of functional restoration was earlier than in the AAV5-group.

Keywords: gene transfer/gene therapy • color vision • retinal degenerations: hereditary