Quantifiable In Vivo Imaging Biomarkers of Retinal Regeneration by Photoreceptor Cell Transplantation

Abstract

Short-term improvements in retinal anatomy are known to occur in preclinical models of photoreceptor transplantation. However, correlative changes over the long term are poorly understood. We aimed to develop a quantifiable imaging biomarker grading scheme, using noninvasive multimodal confocal scanning laser ophthalmoscopy (cSLO) imaging, to enable serial evaluation of photoreceptor transplantation over the long term. Methods: Photoreceptor cell suspensions or sheets from rhodopsin-green fluorescent protein mice were transplanted subretinally, into either NOD.CB17-Prkdc scid /J or C3H/HeJ-Pde6b rd1 mice. Multimodal cSLO imaging was performed serially for up to three months after transplantation. Imaging biomarkers were scored, and a grade was defined for each eye by integrating the scores. Image grades were correlated with immunohistochemistry (IHC) data. Results: Multimodal imaging enabled the extraction of quantitative imaging biomarkers including graft size, GFP intensity, graft length, on-target graft placement, intra-graft lamination, hemorrhage, retinal atrophy, and periretinal proliferation. Migration of transplanted material was observed. Changes in biomarker scores and grades were detected in 14/16 and 7/16 eyes, respectively. A high correlation was found between image grades and IHC parameters. Conclusions: Serial evaluation of multiple imaging biomarkers, when integrated into a per-eye grading scheme, enabled comprehensive tracking of longitudinal changes in photoreceptor cell grafts over time. The application of systematic multimodal in vivo imaging could be useful in increasing the efficiency of preclinical retinal cell transplantation studies in rodents and other animal models. Translational Relevance: By allowing longitudinal evaluation of the same animal over time, and providing quantifiable biomarkers, non-invasive multimodal imaging improves the efficiency of retinal transplantation studies in animal models. Such assays will facilitate the development of cell therapy for retinal diseases.

A Surgical Kit for Stem Cell-Derived Retinal Pigment Epithelium Transplants: Collection, Transportation, and Subretinal Delivery

“…Spectral Domain Optical coherence tomography (SD-OCT) is an imaging technique that can provide in vivo morphological evaluation of the transplants after surgery (Li et al, 2017;Liu et al, 2020). Thus, using OCT we assessed the outcome of the hiPSC-RPE graft transplantation 1 week post-surgery and found that all the transplants were located stably at the target position, with no retinal detachment, hemorrhage or any other visible damage to the host tissues (Figures 4G,H).…”

The Prospects for Retinal Organoids in Treatment of Retinal Diseases

“…95 Similarly, Liu and colleagues applied confocal scanning laser ophthalmoscopy to evaluate in vivo biomarkers of transplanted PR cells qualitatively and quantitatively. They were able to observe migration of the transplanted tissue as well 38. While these 2 techniques demonstrated high resolution and dynamic imaging, it relied on genetically engineered reporter cell lines ( CRX +/tdTomato and Rho +/GFP ) to emit fluorescent light, which is not applicable for future clinical use in human subjects.…”

“…They were able to observe migration of the transplanted tissue as well. 38 While these 2 techniques demonstrated high resolution and dynamic imaging, it relied on genetically engineered reporter cell lines (CRX +/tdTomato and Rho +/GFP ) to emit fluorescent light, which is not applicable for future clinical use in human subjects.…”

Outer Retinal Cell Replacement: Putting the Pieces Together

“… 20 , 21 , 217 Several recent studies have demonstrated the utility of noninvasive imaging for comprehensively studying integration and therapeutic efficacy in hPSC-PRP cell therapies. 160 , 218 The Singh laboratory at Johns Hopkins identified quantifiable biomarkers for tracking fluorescent mouse cells after transplantation, developing a scoring system for multimodal confocal scanning laser ophthalmoscopy (cSLO) imaging. 218 Several properties, including fluorescence size and intensity, graft placement, lamination, and peri-retinal proliferation, were scored longitudinally, facilitating long-term tracking of individual grafts over time.…”

“… 160 , 218 The Singh laboratory at Johns Hopkins identified quantifiable biomarkers for tracking fluorescent mouse cells after transplantation, developing a scoring system for multimodal confocal scanning laser ophthalmoscopy (cSLO) imaging. 218 Several properties, including fluorescence size and intensity, graft placement, lamination, and peri-retinal proliferation, were scored longitudinally, facilitating long-term tracking of individual grafts over time. Similarly, Aboualizadeh et al recently used fluorescence adaptive optics scanning light ophthalmoscopy (FAOSLO) to follow individual PRs in vivo in a laser-damage NHP model of PR loss.…”