Abstract
Purpose :
Subretinal gene therapy improves retinal phenotypes in retinoschisin gene knockout mice (Rs1-KO). Some studies suggested improvements in disease phenotype even after sham injections. This study aims to investigate efficacy of subretinal buffer injection in Rs1-KO mice compared to subretinal gene therapy and natural history.
Methods :
Subretinal injections of 2μL were performed on Rs1-KO mice with either AAV2/4-Ef1α -RS1 vector, 2E9 vg/mL (n=4), hypertonic (HT) buffer solution 0.001% F68/PBS pH 7.4 (n=10), or isotonic (IT) buffer 0.014% (v/v) Tween/Alcon BSS (n=3). Injections occurred at postnatal day 24-31. Endpoints include electroretinogram (ERG) and optical coherence tomography (OCT). OCT images were scored for severity of schisis using an adapted standardized cyst severity score (1: absent cysts, 2: < 30μm, 3: 30-49μm, 4: 50-69μm, 5: 70-99μm, 6: > 99μm, averaged at 4 points 500μm from optic nerve), and outer nuclear layer (ONL) thickness. Untreated mice as well as fellow eyes were used for comparison (n=10).
Results :
Gene therapy vector and HT buffer treated groups tended toward reduced cyst severity scores at 3 weeks post injection (PI) (untreated: 3.150±1.664, HT buffer: 1.25±0.306, vector: 1.438±0.515) and greater ERG amplitudes. The b- to a-wave ratio was improved in the HT buffer treated group (p=0.0054), vector treated group (p=0.0026), and IT buffer treated group (p=0.024) at 1 month PI compared to untreated. Improvements in ERG amplitudes were less notable in those treated with isotonic buffer than hypertonic. 5 month follow up data for the vector and HT buffer groups showed persistent improvement. The degeneration of the ONL was comparable over five months in vector, HT buffer, and untreated groups.
Conclusions :
A reduction in schisis severity score was observed in mice receiving either gene therapy or buffer injections along with improvements in ERG amplitudes. We speculate that the resolution of cysts caused the observed partial correction of ERG phenotypes, although these decreases in cyst severity did not prevent photoreceptor cell death. The unexpected improvements observed in buffer-injected mice may be dependent on either the osmolarity of the buffer or the mechanical effect of injection. The resolution of cysts after subretinal delivery of buffer alone emphasizes the need for including sham controls when evaluating gene therapy efficacy for retinoschisis.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.