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Lisa Lining Wei, Yong Zeng, Suja Hiriyanna, Zhijian Wu, Paul Sieving, Ronald A Bush; Repeat Administration of AAV8 Vector in the Mouse Eye Results in Transgene Expression. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5656. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Adeno-associated viral (AAV) vectors are commonly used for gene transfer in preclinical and clinical studies because of their demonstrated safety profile and efficacy. Prior delivery of AAV2 vector into the vitreous space in mice blocked transgene expression of the same vector re-administered into the contralateral eye. This is attributed to neutralizing antibodies (NAb) to vector. We undertook a similar series of studies and hypothesized that repeat intravitreal injections of the less immunogenic AAV8 vector may be feasible and result in transgene expression.
Three groups of retinoschisin knockout (Rs1-KO) mice received two intravitreal injections of AAV8RS (n= 8-9 eyes/grp): one at 3-4 weeks of age and the second 3 weeks later in the fellow eye. Three groups received one intravitreal injection. At 14 weeks of age, retinal immunohistochemistry for RS1 (Zeng et al, 2016) and serum Nab assays were performed. RS1 staining per retinal section was scored, and the mean score for multiple sections from each retina was determined. For the Nab assay, serum samples were mixed with AAV8-luciferase vector and then incubated with 293 cells. NAb titers are the highest dilution that inhibits luciferase expression by ≥ 50%.
Group 1 mice at 3-4 weeks of age received 3e9 vector genomes (vg) in one eye and, at 6-7 weeks of age, 3e9 vg in the 2nd eye. Group 2 mice received 3e9 vg in one eye and 1e10 vg in the 2nd eye. Group 3 received 1e10 vg in one eye and 1e10 vg in the 2nd eye. There were no statistical differences comparing the RS1 (mean ± SEM) staining scores in the first and second injected eyes in any of the groups (p>0.05). Transgene expression was lower in repeat dosed animals compared to a single injection (p<0.05) at the 1e10vg dose but not at the low dose. Two vector injections boosted NAb titers in comparison to a single intravitreal injection.
An intravitreal injection of AAV8RS in Rs1-KO mice does not block RS1 protein expression by a second injection in the fellow eye several weeks later. Multiple intravitreal injections results in higher NAb titers than a single vector injection. Thus, these studies indicate that sequential intravitreal injection with AAV8 vectors is possible though neutralizing antibody titers rise with each subsequent injection.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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