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Paul D Gamlin, Christianne E Strang, Kevin Chang, Li-Fang Hung, Baskar Arumugam, Laura J Frishman, Earl L Smith, Lisa A Ostrin; Immunotoxin-Induced Ablation of the Intrinsically Photosensitive Retinal Ganglion Cells in Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4125.
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© ARVO (1962-2015); The Authors (2016-present)
The intrinsically photosensitive retinal ganglion cells (ipRGCs) are photosensitive cells in the inner retina that control pupil size and entrain circadian rhythm. Evidence suggests they are involved in a range of other non-image forming functions, such as ocular development and refractive error. The goal of this study was to develop and validate a targeted ipRGC immunotoxin to ultimately examine the role of these cells in Rhesus monkeys.
An OPN4 immunotoxin, consisting of a saporin-conjugated antibody directed at the N-terminus of macaque OPN4, was prepared in solutions of 50, 10, 3.16, 1 and 0.316 µg in sterile BSS, and delivered intravitreally to the right eye of six Rhesus monkeys, respectively. Left eyes were injected with BSS only. The ipRGC-driven pupil responses were recorded and OCT imaging was performed before and after injection. One and five second (s) pulses of light were presented to the dilated right eye while the left pupil was recorded. Stimulation included 651 nm (133 cd/m2), and 4 intensities of 456 nm light (16 to 500 cd/m2). The 6s post illumination pupil response (PIPR), normalized to baseline, was calculated as a measure of ipRGC activity. OCT imaging was performed, and eyes underwent OPN4 immunohistochemistry (IHC) to evaluate specificity of the toxin.
Before injection, animals showed robust ipRGC-driven pupil responses to 1s 456nm light, with an average 6s PIPR of 0.7±0.1 to the highest intensity. Pupil constriction was sustained during 5s light pulses. After injection, delayed redilation was eliminated in all but the lowest dose, which had a 6s PIPR to 456nm of 0.88. During 5s stimulation, pupil constriction was no longer sustained. Baseline pupil size increased 12±17% and maximum transient pupil constriction to 456 nm light decreased 16±5%. For the highest concentrations of immunotoxin, some inflammation and structural changes were observed; however, eyes injected with lower concentrations appeared normal. IHC showed significantly decreased numbers of ipRGCs in experimental eyes.
Findings show that the newly developed OPN4 macaque immunotoxin induced a graded reduction in the ipRGC-driven pupil response with concentration and was specific for ipRGCs. Further refinement and validation of the immunotoxin will allow for better elucidation of the functions of ipRGCs in primates.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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