Biodistribution and Immunological Responses to the Lentiviral-Vector Based Gene Therapy Product RetinoStat® Following Subretinal Injection in Rabbits and Rhesus Macaques

Abstract

Purpose: : RetinoStat^® is a lentiviral vector-based gene therapy for the treatment of wet AMD designed to express the angiostatic proteins endostatin and angiostatin. GLP regulatory studies in rabbits and rhesus macaques were performed to examine the biodistribution of vector following subretinal delivery and the subsequent immune responses to the vector.

Methods: : Subretinally-delivered RetinoStat was examined in the Dutch-belted pigmented rabbit and the rhesus macaque. RetinoStat was injected in the right eye only and compared to animals injected with formulation buffer. Ocular structures, tears, plasma, urine, cerebrospinal fluid and organ samples were collected at 3 days, 1 week, 1 month, 3 month and 6 months in the rabbits. Tears and plasma samples were taken at regular intervals in the macaques along with terminal 6 month organ samples. All samples were measured for the presence of vector by qPCR. Serum samples were harvested from both species to assess immunological responses to RetinoStat at regular intervals. The endostatin and angiostatin protein levels were measured by ELISA in the vitreous samples taken from the rabbits at different timepoints through the study.

Results: : Quantitation of RetinoStat genome copies in fluids and organs following subretinal dosing demonstrated that the vector remained within the ocular compartment. Vector was detected in the vitreous and the target retina/choroid, with a low signal in the sclera. Non-target ocular tissues that tested positive were below the levels of quantification and may represent minor contamination during collection. No antibody responses to RetinoStat components were detected in serum of either rabbits or macaques up to 6 months post dosing. Both endostatin and angiostatin proteins were detected in the rabbit vitreous samples rising to a maximum between 1 month and 3 months after dosing and remaining high at 6 months. Levels of these proteins were determined to be within the expected therapeutic range.

Conclusions: : RetinoStat largely remains within the ocular compartment following subretinal dosing in rabbits and macaques and there was no immunological response to components of the vector. Production of the two therapeutic angiostatic proteins at therapeutic levels was detected in the rabbit eyes up to 6 months demonstrating that a single subretinal dose of RetinoStat may provide long-term therapeutic benefit in patients with age-related macular degeneration.

Keywords: gene transfer/gene therapy • drug toxicity/drug effects • macula/fovea