Evaluation of Dose and Safety of AAV7m8 and AAV8BP2 in the Non-Human Primate Retina

Abstract

Within the next decade, we will see many gene therapy clinical trials for eye diseases, which may lead to treatments for thousands of visually impaired people around the world. To target retinal diseases that affect specific cell types, several recombinant adeno-associated virus (AAV) serotypes have been generated and used successfully in preclinical mouse studies. Because there are numerous anatomic and physiologic differences between the eyes of mice and "men" and because surgical delivery approaches and immunologic responses also differ between these species, this study evaluated the transduction characteristics of two promising new serotypes, AAV7m8 and AAV8BP2, in the retinas of animals that are most similar to those of humans: non-human primates (NHPs). We report that while AAV7m8 efficiently targets a variety of cell types by subretinal injection in NHPs, transduction after intravitreal delivery was mostly restricted to the inner retina at lower doses that did not induce an immune response. AAV8BP2 targets the cone photoreceptors efficiently but bipolar cells inefficiently by subretinal injection. Additionally, transduction by both serotypes in the anterior chamber of the eye and the optic pathway of the brain was observed post-intravitreal delivery. Finally, we assessed immunogenicity, keeping in mind that these AAV capsids may be used in future clinical trials. We found that AAV8BP2 had a better safety profile compared with AAV7m8, even at the highest doses administered. These studies underscore the differences in AAV transduction between mice and primates, highlighting the importance of careful evaluation of therapeutic vectors in NHPs prior to moving to clinical trials.

Noninvasive gene delivery to foveal cones for vision restoration

“…We and others have shown transduction of macaque cones using AAV variants with ubiquitous promoters (16,(29)(30)(31)(32), but achieving cone transduction by vitreally administered AAV has only been possible at high doses, leading to inflammation (16,29). We reasoned that foveal cone targeting could be achieved if we use a strong cone-specific promoter at lower intravitreally injected AAV doses compatible with safety (29,33). To test if such "dose sparing" is possible, we injected 2 macaque eyes with AAV2-7m8-PR1.7-GFP and 2 other macaque eyes were injected with AAV2-7m8-GFP under the control of the cytomegalovirus (CMV) promoter at a dose of 1 × 10 11 viral genomes (vg) per eye (Table 1).…”

“…Altogether, our data in NHPs show for the first time to our knowledge noninvasive, specific, and high-level primate foveal cone transduction compatible with optogenetic applications for vision restoration. However, as promoter activity shows important variations across species (16,29,36), we deemed it necessary to validate PR1.7 in human cells and tissues. Due to the lack of a good human photoreceptor cell line or other model that could be used to test efficiency of cone promoter activity, we used 3-D retinal organoids derived from human induced pluripotent stem cells (iPSCs) (37).…”

A New Promoter Allows Optogenetic Vision Restoration with Enhanced Sensitivity in Macaque Retina

“…Several AAVs have been tested for retinal gene delivery via the intravitreal route, and some have evoked safety concerns that have not been fully addressed at this stage. 25,43 For example, a recent study suggested that the engineered AAV variant AAV2-7m8 might be more immunogenic when used at high doses via intravitreal injections. 25 Therefore, we chose AAV2 for its known safety and efficacy in targeting RGCs in NHP studies [27][28][29] and the large body of work using this vector in human clinical trials.…”

“…25,43 For example, a recent study suggested that the engineered AAV variant AAV2-7m8 might be more immunogenic when used at high doses via intravitreal injections. 25 Therefore, we chose AAV2 for its known safety and efficacy in targeting RGCs in NHP studies [27][28][29] and the large body of work using this vector in human clinical trials. [20][21][22][23]44 High-level expression with a limited viral dose being a major parameter in obtaining functional expression, we designed a new RGC-specific promoter, driving strong transgene expression in RGCs.…”

“…First, optogenetically equipped cells require very high-level opsin expression, as there is no amplification cascade behind microbial opsins. 19 Although adeno-associated viruses (AAVs) have a favorable safety profile in clinical gene therapy, [20][21][22][23] their safety is dose dependent, 24,25 limiting the injected dose. This makes our ability to obtain functional-level microbial opsin expression with a safe viral dose uncertain.…”