Treating retinal disease

With the advent of gene and stem cell-based cell therapy, vision research has accelerated towards an exciting age where treatment is becoming possible. However, this requires both knowledge of the patient population and disease process. To that effect, this thesis will focus on both complex (i.e. age related macular degeneration (AMD)) and monogenetic (RPGR-associated x-linked retinitis pigmentosa) causes of retinal degeneration. Age-related macular degeneration is a major cause of irreversible blindness worldwide. The data show that loss of choriocapillaris endothelial cells, a vascular bed, occurs as one of the earliest events in part due to variation in the gene, CFH, a negative regulator of the complement cascade. The data presented show that the choroid is the major source of CFH in the posterior eye and patients with a high risk CFH genotype have high levels of membrane attack complex (MAC) formation, which is associated with endothelial cell loss.

For mendelian disease of the retina, vision loss affects approximately 140,000 people in the US with about 1700 new cases diagnosed annually. While more than 100 different disease-causing genes have been identified, mutations in ABCA4, USH2A, RPGR and RHO account for more than 40 percent of all cases. Importantly, for early-stage disease gene therapy presents a viable treatment modality. Yet, both ABCA4 and USH2A both exceed the carrying capacity of clinically relevant AAV vectors, and RHO-associated retinitis pigmentosa is predominantly a dominant gain of function disorder. As a result, among these 4 genes, only RPGR is expected to be amenable to traditional AAV-based gene augmentation therapy. Unfortunately, the sequence for RPGR is unstable when cloned complicating the production of a viral vector product. To overcome this obstacle, we generated a stable version of RPGR, IA-RPGR, and showed it functions similar to the RPGR ORF15. Finally, for patients require cell replacement therapy, we developed genome-editing techniques to correct mutations in the genome to allow for autologous iPSC-derived photoreceptor cell delivery.

In summary, this work has contributed to our understanding and development of treatments for vision loss associated with retinal degenerative blindness. For AMD, this work provides support for local production of CFH by choroidal endothelial cells as a means to regulate MAC formation and preservation of cell function. For RPGR-associated retinal degeneration, we developed a rationally designed gene therapy construct and developed tools for genome-editing of patient cells for subsequent cell replacement therapy.