EIAV-Based Retinal Gene Therapy in the shaker1 Mouse Model for Usher Syndrome Type 1B: Development of UshStat

Abstract

Usher syndrome type 1B is a combined deaf-blindness condition caused by mutations in the MYO7A gene. Loss of functional myosin VIIa in the retinal pigment epithelia (RPE) and/or photoreceptors leads to blindness. We evaluated the impact of subretinally delivered UshStat, a recombinant EIAV-based lentiviral vector expressing human MYO7A, on photoreceptor function in the shaker1 mouse model for Usher type 1B that lacks a functional Myo7A gene. Subretinal injections of EIAV-CMV-GFP, EIAV-RK-GFP (photoreceptor specific), EIAV-CMV-MYO7A (UshStat) or EIAV-CMV-Null (control) vectors were performed in shaker1 mice. GFP and myosin VIIa expression was evaluated histologically. Photoreceptor function in EIAV-CMV-MYO7A treated eyes was determined by evaluating α-transducin translocation in photoreceptors in response to low light intensity levels, and protection from light induced photoreceptor degeneration was measured. The safety and tolerability of subretinally delivered UshStat was evaluated in macaques. Expression of GFP and myosin VIIa was confirmed in the RPE and photoreceptors in shaker1 mice following subretinal delivery of the EIAV-CMV-GFP/MYO7A vectors. The EIAV-CMV-MYO7A vector protected the shaker1 mouse photoreceptors from acute and chronic intensity light damage, indicated by a significant reduction in photoreceptor cell loss, and restoration of the α-transducin translocation threshold in the photoreceptors. Safety studies in the macaques demonstrated that subretinal delivery of UshStat is safe and well-tolerated. Subretinal delivery of EIAV-CMV-MYO7A (UshStat) rescues photoreceptor phenotypes in the shaker1 mouse. In addition, subretinally delivered UshStat is safe and well-tolerated in macaque safety studies These data support the clinical development of UshStat to treat Usher type 1B syndrome.

Contribution of non-coding mutations to RPGRIP1-mediated inherited retinal degeneration

“…The results of the first phase 3 human gene therapy randomized clinical trial, voretigene neparvovec for the treatment of LCA2, has been recently published (56). Furthermore, more than 10 clinical trials for retinal degeneration have either been completed or initiated (57)(58)(59)(60)(61)(62)(63). A multitude of additional candidates for gene therapy with already established animal models exist and RPGRIP1 is one such example (48,49).…”

Gene Therapy for the Retinal Degeneration of Usher Syndrome Caused by Mutations in MYO7A

“…Although this response is promising as read-out for MYO7A function in photoreceptors, it should be noted that, unlike the above mutant phenotypes, it has only been observed in one allele of shaker1 mice, . The specific mutation underlying this allele, and the effect that the mutation has on protein structure and levels are not known, except that mutant MYO7A protein is detectable (Zallocchi et al 2014). The same investigators have identified an increased susceptibility to light-induced photoreceptor degeneration in Myo7a sh1-11J mice (Peng et al 2011), which is the converse finding to that mentioned above for the null shaker1 allele, Myo7a sh1-4626SB (Lopes et al 2011).…”

Corticosteroids and Anti-Complement Therapy in Retinal Diseases

“…Toxicity and biodistribution were assessed in a 3-month study of the SAR421869 construct following a single subretinal injection in rhesus macaques (Macaca mulatta) (Zallocchi et al 2014) prior to entering into clinical trials. The ongoing phase I/II trials (NCT01505062, NCT02065011) are evaluating the safety of this integrating lentiviral vector.…”