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Annahita Keravala, Kathryn W Woodburn, Sharmila Vijay, Carmelo Romano, Stanley J Wiegand, Andrew Murphy, Thomas Walter Chalberg, Mehdi Gasmi; In vivo assessment of the impact of neutralizing antibodies on intravitreal AAV2.7m8 administration. Invest. Ophthalmol. Vis. Sci. 2016;57(12):782.
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© ARVO (1962-2015); The Authors (2016-present)
AAV-mediated gene therapy has been effective for some ocular diseases when administered sub-retinally (SR). Available data suggests that neutralizing antibodies (nAbs) do not block transduction of AAV vectors delivered SR because of ocular immune privilege, but how pre-existing nAbs impact transduction following intravitreal (IVT) delivery is poorly understood. We are developing AAV2.7m8, a novel variant of AAV2 that can effectively transduce several layers of the non-human primate (NHP) retina following IVT injection. However, the role of pre-existing as well as generation of new nAbs following IVT administration that could possibly limit effectiveness of AAV2.7m8 is currently unknown and merits further study.
We performed an exploratory study in NHPs to evaluate the transduction as well as immune response to the AAV2.7m8 vector in a staged manner. African green monkeys were pre-screened for nAbs to AAV2 prior to study enrollment. Varying amounts of pooled human intravenous immunoglobulin (IVIG), which contains nAbs to AAV2, or a monoclonal antibody to AAV2 (A20 clone) were IVT injected to model potentially relevant clinical conditions. 24 hours later, different doses of AAV2.7m8-GFP vector were IVT delivered. Fluorescence fundus imaging was performed at 2, 4, 8, and 12 weeks to assess GFP expression. Also, serum, aqueous, and vitreous samples were collected at baseline and termination to measure nAb levels and to demonstrate whether there was a correlation between nAbs in serum versus aqueous or vitreous humor.
Our findings showed no direct correlation between nAb levels in the different compartments, suggesting that serum nAb levels may not readily be used to predict the outcome of IVT vector delivery for therapeutic usefulness. In terms of effect on IVT transduction, we observed 100% inhibition in the presence of high titer IVIG (1:40), but no significant inhibition when the IVIG concentration was lowered 4-fold. In addition, higher doses of AAV2.7m8-GFP showed transduction even in the presence of comparatively high IVIG levels in vitro, suggesting that a higher AAV2.7m8 vector dose may overcome inhibition by high levels of nAbs in vivo.
Our results suggest that an optimal dose of IVT AAV2.7m8 can possibly be effective in overcoming antibody neutralization in this model designed to mimic potentially relevant clinical conditions of pre-existing nAbs to AAV.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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