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Proof of concept for MERTK gene replacement therapy has been demonstrated utilizing different viral vectors in the Royal College of Surgeon (RCS) rat, a well characterized model of recessive retinitis pigmentosa (RP) that contains a mutation in the Mertk gene. MERTK plays a key role in renewal of photoreceptor outer segments (OS) by phagocytosis of shed OS tips. Mutations in MERTK cause impaired phagocytic activity and accumulation of OS debris in the interphotoreceptor space that ultimately leads to photoreceptor cell death. In the present study, we conducted a series of preclinical potency and GLP compliant safety evaluations of an AAV2 vector expressing human MERTK cDNA driven by the RPE-specific, VMD2 promoter. We demonstrate the potency of the vector in RCS rats by improved electroretinogram responses in treated eyes compared to contralateral untreated controls. Toxicology and biodistribution studies were performed in Sprague Dawley (SD) rats injected with two different doses of AAV vectors and buffer control. Delivery of vector in SD rats did not result in a change in ERG amplitudes of rod and cone responses relative to Balanced Salt Solution (BSS) control injected eyes indicating that administration of AAV vector did not adversely affect normal retinal function. In vivo fundoscopic analysis and postmortem retinal morphology of the vector injected eyes were normal compared to controls. Evaluation of blood smears showed the lack of transformed cells in the. All injected eyes and day 1 blood samples were positive for vector genomes and all peripheral tissues were negative. Our results demonstrate the potency and safety of the AAV2-VMD2-hMERTK vector in animal models tested. A GMP vector has been manufactured and is presently in clinical trial.

BackgroundThe current method of delivering gene replacement to the posterior segment of the eye involves a three-port pars plana vitrectomy followed by injection of the agent through a 37-gauge cannula, which is potentially wrought with retinal complications. In this paper we investigate the safety and efficacy of delivering adeno-associated viral (AAV) vector to the suprachoroidal space using an ab externo approach that utilizes an illuminated microcatheter.Methods6 New Zealand White rabbits and 2 Dutch Belted rabbits were used to evaluate the ab externo delivery method. sc-AAV5-smCBA-hGFP vector was delivered into the suprachoroidal space using an illuminated iTrackTM 250A microcatheter. Six weeks after surgery, the rabbits were sacrificed and their eyes evaluated for AAV transfection using immunofluorescent antibody staining of GFP.ResultsImmunostaining of sectioned and whole-mounted eyes demonstrated robust transfection in all treated eyes, with no fluorescence in untreated control eyes. Transfection occurred diffusely and involved both the choroid and the retina. No apparent adverse effects caused by either the viral vector or the procedure itself could be seen either clinically or histologically.ConclusionsThe ab externo method of delivery using a microcatheter was successful in safely and effectively delivering a gene therapy agent to the suprachoroidal space. This method presents a less invasive alternative to the current method of virally vectored gene delivery.

Purpose To describe the clinical and pathologic characteristics of a case of retinal vasculitis and vitritis following brolucizumab administration and subsequent ranibizumab treatment. Observations A 76-year old Caucasian woman experienced pain, decreased vision and floaters one week after receiving her third monthly intravitreal brolucizumab injection in the right eye for exudative age-related macular degeneration. Examination was significant for 0.5+ anterior chamber cells, vitritis, mild peripheral vascular sheathing, and decreased vision from 20/70 to 20/200. She was started on topical 1% prednisolone acetate with improvement in her examination. She was switched to ranibizumab one month after her last brolucizumab injection of the right eye. Three weeks after her ranibizumab injection, she noticed photophobia, pain and decreased vision. Examination revealed worsening uveitis, vitritis, vascular sheathing, and decreased vision to count fingers. Despite starting on 0.05% difluprednate drops every 2 hours and oral high-dose methylprednisolone, the patient did not have any significant improvement in her symptoms or examination. She underwent pars plana vitrectomy and vitreous biopsy with intravitreal triamcinolone injection to the right eye. Vitreous biopsy and culture ruled out infectious endophthalmitis, and further cytopathologic analysis revealed chronic inflammatory infiltrate. Conclusion and importance Treatment with brolucizumab can result in intraocular inflammation and retinal vasculitis likely due to a delayed hypersensitivity reaction to the drug, supported by cytopathologic analysis of a vitreous sample. We demonstrate a case where retreatment with an alternative anti-VEGF agent resulted in worsening vision and vasculitis.