Long-term rescue of cone photoreceptor degeneration in retinitis pigmentosa 2 (RP2)-knockout mice by gene replacement therapy

• Published in: Human molecular genetics Vol. 24; no. 22; pp. 6446 - 6458
• Main Authors: Mookherjee, Suddhasil, Hiriyanna, Suja, Kaneshiro, Kayleigh, Li, Linjing, Li, Yichao, Li, Wei, Qian, Haohua, Li, Tiansen, Khanna, Hemant, Colosi, Peter, Swaroop, Anand, Wu, Zhijian
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 15.11.2015
• Subjects: Adeno-associated virus; Animals; Electroretinography; Eye Proteins - biosynthesis; Eye Proteins - genetics; Genetic Diseases, X-Linked - genetics; Genetic Therapy - methods; Genetic Vectors; HEK293 Cells; Humans; Intracellular Signaling Peptides and Proteins - biosynthesis; Intracellular Signaling Peptides and Proteins - genetics; Membrane Proteins - biosynthesis; Membrane Proteins - genetics; Mice; Mice, Knockout; Mutation; Pyrophosphatases - deficiency; Pyrophosphatases - genetics; Retinal Cone Photoreceptor Cells - metabolism; Retinal Cone Photoreceptor Cells - pathology; Retinal Cone Photoreceptor Cells - physiology; Retinal Degeneration - genetics; Retinitis Pigmentosa - genetics; Retinitis Pigmentosa - metabolism; Retinitis Pigmentosa - therapy
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddv354

Retinal neurodegenerative diseases are especially attractive targets for gene replacement therapy, which appears to be clinically effective for several monogenic diseases. X-linked forms of retinitis pigmentosa (XLRP) are relatively severe blinding disorders, resulting from progressive photoreceptor dysfunction primarily caused by mutations in RPGR or RP2 gene. With a goal to develop gene therapy for the XLRP-RP2 disease, we first performed detailed characterization of the Rp2-knockout (Rp2-KO) mice and observed early-onset cone dysfunction, which was followed by progressive cone degeneration, mimicking cone vision impairment in XLRP patients. The mice also exhibited distinct and significantly delayed falling phase of photopic b-wave of electroretinogram (ERG). Concurrently, we generated a self-complementary adeno-associated viral (AAV) vector carrying human RP2-coding sequence and demonstrated its ability to mediate stable RP2 protein expression in mouse photoreceptors. A long-term efficacy study was then conducted in Rp2-KO mice following AAV-RP2 vector administration. Preservation of cone function was achieved with a wide dose range over 18-month duration, as evidenced by photopic ERG and optomotor tests. The slower b-wave kinetics was also completely restored. Morphologically, the treatment preserved cone viability, corrected mis-trafficking of M-cone opsin and restored cone PDE6 expression. The therapeutic effect was achieved even in mice that received treatment at an advanced disease stage. The highest AAV-RP2 dose group demonstrated retinal toxicity, highlighting the importance of careful vector dosing in designing future human trials. The wide range of effective dose, a broad treatment window and long-lasting therapeutic effects should make the RP2 gene therapy attractive for clinical development.