Efficient adeno-associated virus–mediated (AAV-mediated) gene delivery remains a significant obstacle to effective retinal gene therapies. Here, we apply directed evolution — guided by deep sequencing and followed by direct in vivo secondary selection of high-performing vectors with a GFP-barcoded library — to create AAV viral capsids with the capability to deliver genes to the outer retina in primates. A replication-incompetent library, produced via providing rep in trans, was created to mitigate risk of AAV propagation. Six rounds of in vivo selection with this library in primates — involving intravitreal library administration, recovery of genomes from outer retina, and extensive next-generation sequencing of each round — resulted in vectors with redirected tropism to the outer retina and increased gene delivery efficiency to retinal cells. These viral vectors expand the toolbox of vectors available for primate retina, and they may enable less invasive delivery of therapeutic genes to patients, potentially offering retina-wide infection at a similar dosage to vectors currently in clinical use.
Leah C. Byrne, Timothy P. Day, Meike Visel, Jennifer A. Strazzeri, Cécile Fortuny, Deniz Dalkara, William H. Merigan, David V. Schaffer, John G. Flannery
Workflow of directed evolution of AAV in the primate retina.