Abstract
Vectors based on the adeno-associated virus (AAV) are currently the preferred tools for delivering genes to photoreceptors (PR) in small and large animals. AAVs have been applied successfully in various models of PR dystrophies. However, unknown barriers still limit AAV's efficient application in several forms of severe PR degenerations due to insufficient transgene expression and/or treated cells at the time of injection. Optimizations of PR gene therapy strategies will likely benefit from the identification of the cellular factors that influence PR transduction. Interestingly, recent studies have shown that the AAV transduction profile of PRs differs significantly between neonatal and adult mouse retinas after subretinal injection. This phenomenon may provide clues to identify host factors that influence the efficiency of AAV-mediated PR transduction. This study demonstrates that rod outer segments are critical modulators of efficient AAV-mediated rod transduction. During retinal development, rod transduction correlated temporally and spatially with the differentiation order of PRs when vectors were introduced subretinally but not when introduced intravitreally. All subretinally injected vectors had an initial preference to transduce cones in the absence of formed rod outer segments and then displayed a preference for rods as the cells matured, independently of the expression cassette or AAV serotype. Consistent with this observation, altered development of rod outer segments was associated with a strong reduction of rod transduction and an increase in the percentage of transduced cones by 2- to 2.8-fold. A similar increase of cone transduction was observed in the adult retinal degeneration 1 (rd1) retina compared to wild-type mice. These results suggest that the loss of rod outer segments in diseased retinas could markedly affect gene transfer efficiency of AAV vectors by limiting the ability of AAVs to infect dying rods efficiently. This information could be exploited for the development of more efficient AAV-based PR gene delivery procedures.
Highlights
RECOMBINANT associated virus (AAV) SEROTYPE 2 (AAV2) is currently being evaluated in Phase 1/2 and 3 gene therapy clinical trials for treating diverse inherited retinal diseases involving the retinal pigment epithelium (RPE), such as Leber congenital Amaurosis 2,1–9 retinitis pigmentosa,[10] and choroideremia.[11,12] These studies demonstrate that subretinal delivery of AAV is safe and can provide rescue of vision-guided behavior in patients with advanced disease at least for several years.[13]
Recent reports showed that subretinal injection of AAV8 into PND0 mice results primarily in cone transduction, whereas the vast majority of transduced cells after subretinal injection in adult mice are rods.[32,33,34]
To demonstrate further that PR postnatal development impacts the pattern of PR transgene expression, neonatal mice (PND1) were subretinally injected with 6 · 108–1.2 · 109 vg of single-stranded AAV2/5-CMV-dGFP (Table 1 and Supplementary Fig. S2a)
Summary
RECOMBINANT AAV SEROTYPE 2 (AAV2) is currently being evaluated in Phase 1/2 and 3 gene therapy clinical trials for treating diverse inherited retinal diseases involving the retinal pigment epithelium (RPE), such as Leber congenital Amaurosis 2,1–9 retinitis pigmentosa,[10] and choroideremia.[11,12] These studies demonstrate that subretinal delivery of AAV is safe and can provide rescue of vision-guided behavior in patients with advanced disease at least for several years.[13]. -2/5, -2/7, -2/8, -2/9, and -2/rh[10] were found to have the highest transduction efficiencies for PRs after a Lolita Petit et al 2017; Published by Mary Ann Liebert, Inc.
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