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

Marisa Zallocchi,Dominic Cosgrove,Duane Delimont,Kyriacos A Mitrophanous,James Miskin,Katie Binley,Sharifah Iqball,Wei-Min Wang,Michelle Kelleher,Yatish Lad,Julie Loader,Vicky Scripps,You-Wei Peng,Peter Widdowson,Linda Cheung,Scott Ellis

doi:10.1371/journal.pone.0094272

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.

Highlights

Usher syndrome (USH) is a genetically heterogeneous disorder characterized by congenital deafness associated with delayed onset and progressive retinitis pigmentosa (RP)
We evaluate the potential of an EIAV-based lentiviral gene therapy vector, EIAV-CMV-MYO7A (UshStat), which expresses the functional human myosin VIIa protein to rescue these phenotypes in the shaker1 mouse model of USH1B
Immunoprecipitation of UshStat transduced cells lysates with a commercially available myosin VIIa antibody follow by immunoblot with the myosin VIIa antibody developed by our laboratory (IP/MYO7A) show a prominent band of similar molecular weight as the ones detected in mouse tissue

Summary

Introduction

Usher syndrome (USH) is a genetically heterogeneous disorder characterized by congenital deafness associated with delayed onset and progressive retinitis pigmentosa (RP). Usher syndrome type I, the most severe clinical sub-type, is characterized by total congenital deafness associated with early onset and rapidly progressing RP. Of the six genes linked to clinical sub-type I, the gene associated with USH1B is the most commonly mutated This gene encodes a non-conventional myosin motor protein, myosin VIIa. Several mouse models containing spontaneous or induced mutations in the USH1B gene have been described [13]. Several mouse models containing spontaneous or induced mutations in the USH1B gene have been described [13] All of these mice are congenitally deaf, but none show signs of retinal degeneration, raising questions as to how appropriate these mice are for studying retinal dysfunction in USH1B [14,15]. A small (approximately 20%) decrease in electroretinography (ERG) amplitudes has been demonstrated b-wave thresholds do not vary significantly from strain/age-matched wild type mice [16]

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