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Modeling and treating retinal degenerative disease

Periodic Reporting for period 3 - REGENETHER (Modeling and treating retinal degenerative disease)

Reporting period: 2018-12-01 to 2020-05-31

Gene therapy using adeno-associated viral (AAV) vectors has shown early promise in clinical trials. The therapeutic transgene cassette can be packaged in different AAV capsid pseudotypes, each having a unique transduction profile. At present, AAV capsid serotype selection for a specific clinical trial is based on effectiveness in small animal models. We (and others) have shown substantial progress in improving gene therapy for eye diseases in rodents. However, small animal studies are not often predictive of human outcome when it comes to the efficacy of viral delivery. Moreover, non-human primates used as pre-clinical animal models do not display any pathology making them unsuitable for testing efficacy. Here, I propose to overcome these bottlenecks in translational gene therapy by generating non-human primate models of retinal degeneration where effects of therapies and prosthesis on sight restoration can be tested. Generating transgenic primates using germline transgenesis would be very costly and ethically problematic. I thus propose to induce retinal disease locally, following delivery of pathogenic genes within specific subsets of cells in the non-human primate retina (Aim A). In Aim B, I propose to develop novel AAVs for use in human gene therapy using directed evolution. This bioengineering approach has yielded AAVs with enhanced delivery properties in the murine retina and applying it to post-mortem human retinas will generate AAVs responding to a clinical need in gene therapy. All together, the creation of models of disease in primates combined with novel AAVs tested in human post-mortem retinas will enable us to validate therapies aiming at vision restoration and neuroprotection in retinas with a macula and high central visual acuity, removing a major roadblock in the development of ocular therapeutics for humans.
The objectives set for the first reporting period of the grant were the establishment of the viral dosage to achieve photoreceptor ablation via the expression of killer red in mouse for aim A and the creation of diverse AAV libraries for the directed evolution screen in post-mortem human retinal explants for aimB. Both of these objectives have been met with success and have progressed towards the subsequent sub-aims. Furthermore, in continuation of aim A, tests have been started to implement the same strategy in macaques by the optimization of the vectors for efficient rod targeting in order to obtain Killer Red expression comparable to what was obtained in mouse rods on a per cell basis. Following up on aim B1, we have also started screening the AAV libraries on human post-mortem retinal explants and have completed several cycles. We will now increase the selection pressure in order to continue as detailed in the Annex1 SubAim B2.1. Further details can be found in the technical report (Part B.).
REGENETHER aims to go beyond the current methods in building a pre-clinical testing platform for gene and cell therapies in the retina. Creation of a nonhuman primate model with retinal degenerative phenotype will push the boundaries of our understanding of disease and how vectors act in such a system both in terms of delivery and function. Such animal models will accurately predict potential efficacy of treatments aiming to fight blindness in humans and yield biological insight into disease mechanisms in rod-cone dystrophy.

Moreover, the progress brought upon by this project will extend beyond the field of retinal gene therapy as the much larger field of neurodegenerative diseases including diseases like Parkinsons and Alzheimers disease which constitute a huge burden on society face the same translational problems. The principals that will allow us to create a NHP model of retinal degeneration can potentially be applied to other neurodegenerative diseases of the brain. Moreover the bioengineering strategy using human samples can also be applied to other organs and can be a brilliant alternative to the state of the art xenograft models.

At this reporting period, we have not yet completed the progress towards the generation of the animal model and the discovery of the AAV capsid adapted to human retina. Therefore we need to await further, in order to fully measure the impact the project will have at the higher levels. However on a smaller scale, the progress has been up to our expectations and we have met the technical milestones that pave the way to achieve the broader objectives.