Transplantation of human pluripotent stem cell-derived retinal sheet in a primate model of macular hole.

Macular hole (MH) is a retinal break involving the fovea that causes impaired vision. Although advances in vitreoretinal surgical techniques achieve >90% MH closure rate, refractory cases still exist. For such cases, autologous retinal transplantation is an optional therapy showing good anatomic success, but visual improvement is limited and peripheral visual field defects are inevitable after graft harvesting. Here, using a non-human primate model, we evaluated whether human embryonic stem cell-derived retinal organoid (RO) sheet transplantation can be an effective option for treating MH. After transplantation, MH was successfully closed by continuous filling of the MH space with the RO sheet, resulting in improved visual function, although no host-graft synaptic connections were confirmed. Mild xeno-transplantation rejection was controlled by additional focal steroid injections and rod/cone photoreceptors developed in the graft. Overall, our findings suggest pluripotent stem cell-derived RO sheet transplantation as a practical option for refractory MH treatment.

Cellular and circuit remodeling of the primate foveal midget pathway after acute photoreceptor loss.

The retinal fovea in human and nonhuman primates is essential for high acuity and color vision. Within the fovea lies specialized circuitry in which signals from a single cone photoreceptor are largely conveyed to one ON and one OFF type midget bipolar cell (MBC), which in turn connect to a single ON or OFF midget ganglion cell (MGC), respectively. Restoring foveal vision requires not only photoreceptor replacement but also appropriate reconnection with surviving ON and OFF MBCs and MGCs. However, our current understanding of the effects of cone loss on the remaining foveal midget pathway is limited. We thus used serial block-face electron microscopy to determine the degree of plasticity and potential remodeling of this pathway in adult Macaca fascicularis several months after acute photoreceptor loss upon photocoagulation. We reconstructed MBC structure and connectivity within and adjacent to the region of cone loss. We found that MBC dendrites within the scotoma retracted and failed to reach surviving cones to form new connections. However, both surviving cones and ON and OFF MBC dendrites at the scotoma border exhibited remodeling, suggesting that these neurons can demonstrate plasticity and rewiring at maturity. At six months postlesion, disconnected OFF MBCs clearly lost output ribbon synapses with their postsynaptic partners, whereas the majority of ON MBCs maintained their axonal ribbon numbers, suggesting differential timing or extent in ON and OFF midget circuit remodeling after cone loss. Our findings raise rewiring considerations for cell replacement approaches in the restoration of foveal vision.

Safety and stable survival of stem-cell-derived retinal organoid for 2 years in patients with retinitis pigmentosa.

Transplantation of induced pluripotent stem cell (iPSC)-derived retinal organoids into retinal disease animal models has yielded promising results, and several clinical trials on iPSC-derived retinal pigment epithelial cell transplantation have confirmed its safety. In this study, we performed allogeneic iPSC-derived retinal organoid sheet transplantation in two subjects with advanced retinitis pigmentosa (jRCTa050200027). The primary endpoint was the survival and safety of the transplanted retinal organoid sheets in the first year post-transplantation. The secondary endpoints were the safety of the transplantation procedure and visual function evaluation. The grafts survived in a stable condition for 2 years, and the retinal thickness increased at the transplant site without serious adverse events in both subjects. Changes in visual function were less progressive than those of the untreated eye during the follow-up. Allogeneic iPSC-derived retinal organoid sheet transplantation is a potential therapeutic approach, and the treatment's safety and efficacy for visual function should be investigated further.

Competency of iPSC-derived retinas in MHC-mismatched transplantation in non-human primates.

Transplantation of embryonic/induced pluripotent stem cell-derived retina (ESC/iPSC-retina) restores host retinal ganglion cell light responses in end-stage retinal degeneration models with host-graft synapse formation. We studied the immunological features of iPSC-retina transplantation using major histocompatibility complex (MHC)-homozygote monkey iPSC-retinas in monkeys with laser-induced retinal degeneration in MHC-matched and -mismatched transplantation. MHC-mismatched transplantation without immune suppression showed no evident clinical signs of rejection and histologically showed graft maturation without lymphocytic infiltration, although immunological tests using peripheral blood monocytes suggested subclinical rejection in three of four MHC-mismatched monkeys. Although extensive photoreceptor rosette formation was observed on histology, evaluation of functional integration using mouse models such as mouse ESC-retina (C57BL/6) transplanted into rd1(C3H/HeJ, MHC-mismatched model) elicited light responses in the host retinal ganglion cells after transplantation but with less responsiveness than that in rd1-2J mice (C57BL/6, MHC-matched model). These results suggest the reasonable use of ESC/iPSC-retina in MHC-mismatched transplantation, albeit with caution.

Human iPS cell derived RPE strips for secure delivery of graft cells at a target place with minimal surgical invasion.

Several clinical studies have been conducted into the practicality and safety of regenerative therapy using hESC/iPSC-retinal pigment epithelium (RPE) as a treatment for the diseases including age-related macular degeneration. These studies used either suspensions of RPE cells or an RPE cell sheet. The cells can be injected using a minimally invasive procedure but the delivery of an intended number of cells at an exact target location is difficult; cell sheets take a longer time to prepare, and the surgical procedure is invasive but can be placed at the target area. In the research reported here, we combined the advantages of the two approaches by producing a quickly formed hiPSC-RPE strip in as short as 2 days. The strip readily expanded into a monolayer sheet on the plate, and after transplantation in nude rats, it showed a potency to partly expand with the correct apical/basal polarity in vivo, although limited in expansion area in the presence of healthy host RPE. The strip could be injected into a target area in animal eyes using a 24G canula tip.

Stem-cell-based therapies for retinal degenerative diseases: Current challenges in the establishment of new treatment strategies.

Various advances have been made in the treatment of retinal diseases, including new treatment strategies and innovations in surgical devices. However, the treatment of degenerative retinal diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), continues to pose a significant challenge. In this review, we focus on the use of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to treat retinal diseases by harnessing the ability of stem cells to differentiate into different body tissues. The retina is a tissue specialized for light sensing, and its degradation leads to vision loss. As part of the central nervous system, the retina has very low regenerative capability, and therefore, treatment options are limited once it degenerates. Nevertheless, innovations in methods to induce the generation of retinal cells and tissues from ESCs/iPSCs enable the development of novel approaches for these irreversible diseases. Here we review some historical background and current clinical trials involving the use of stem-cell-derived retinal pigment epithelial cells for AMD treatment and stem cell-derived retinal cells/tissues for RP therapy. Finally, we discuss our future vision of regenerative treatment for retinal diseases with a partial focus on our studies and introduce other interesting approaches for restoring vision.

Optical coherence tomography angiography changes in radial peripapillary capillaries in Leber hereditary optic neuropathy.

PURPOSE: To present a report of longitudinal changes in radial peripapillary capillaries (RPC) and changes in retinal full thickness (RFT) and peripapillary retinal nerve fiber layer (RNFL) in a patient with Leber hereditary optic neuropathy (LHON). OBSERVATIONS: A 42-year-old man presented with acute- and presymptomatic-stage LHON in the left (OS) and right (OD) eyes, respectively, at the initial visit. Onset of LHON in the OD was observed 2 months after the initial visit. Once the temporal RNFL started to decrease in thickness, the areas of temporal RPC defects and RFT thinning gradually increased, indicating that these factors might be correlated. CONCLUSIONS AND IMPORTANCE: Optical coherence tomography angiography showed LHON from the presymptomatic stage. The results indicate that temporal RPC defects and RFT thinning start to spread once the pseudoedema begins to resolve.

Incidence of outer retinal tubulation in eyes with choroidal neovascularization under intravitreal anti-vascular endothelial growth factor therapy in a Japanese population.

PURPOSE: The purpose of this study was to investigate the occurrence of outer retinal tubulation (ORT) among patients with different types of choroidal neovascularization (CNV) over time. MATERIALS AND METHODS: In this retrospective chart review, disease type was classified as typical age-related macular degeneration (t-AMD), polypoidal choroidal vasculopathy (PCV), retinal angiomatous proliferation (RAP), or myopic CNV (mCNV). Spectral domain-optical coherence tomography (SD-OCT) images were evaluated for the appearance of ORT and subretinal fibrosis and fluid. Furthermore, the association of the presence of ORT with clinical data and OCT findings was investigated. RESULTS: Among the 136 eyes studied, the overall rates of occurrence of ORT were 7.8%, 18.8%, and 31.6% after 12, 24, and 36 months from baseline, respectively. Among patients with t-AMD, RAP, and mCNV, the occurrence of ORT increased soon after the initial visit. In contrast, among patients with PCV, the occurrence of ORT increased slowly over time. Patients with and without ORT - ORT(+) and ORT(-) groups, respectively - differed significantly in terms of sex ratio and presence of intraretinal fluid at the initial visit and presence of subretinal fibrosis at 3 years from baseline. The ORT(+) group exhibited lower visual acuity (VA; 0.67±0.43) than that of the ORT(-) group (0.41±0.36; P<0.001). CONCLUSION: The occurrence of ORT tended to increase more slowly among eyes diagnosed with PCV than among eyes with other types of CNV.

Vessel Visibility Assessment of Low Tube Voltage Coronary Computed Tomography Angiography Determined with Contrast-to-Noise Ratio.

PURPOSE: The purpose of this study was to investigate the association of vessel visibility and radiation dose using contrast-to-noise ratio (CNR) method with low tube voltage in coronary computed tomography angiography (c-CTA). METHODS: We performed electrocardiogram-gated scan of 2.0-mm diameter simulated vessel in the center of the cardiac phantom by the use of a 64-detector CT scanner. Reference CNR was calculated from the target coronary CT number (CTnumberA; 350 Hounsfield units [HU]), epicardial fat CT number (CTnumberB; -100 HU), and target epicardial fat standard deviation (SD) number (SDB; 25 HU) at the 120 kV. We obtained the tube current at low tube voltage (100 and 80 kV) to perform the similar reference CNR at 120 kV. The full widths at half maximum from axial images were evaluated with quantitative evaluation and three types of visualizations of the vessel phantom were evaluated with the qualitative evaluations. RESULTS: CTnumberA of 100 and 80 kV were increased by 26% and 50%, respectively, compared with 120 kV (P<0.01). SDB was also increased by a similar ratio (P<0.01). CTDIvol of 100 and 80 kV were decreased by 39% and 51%, respectively, compared with 120 kV (P<0.05). There were no significant voltage differences among three tubes in quantitative and qualitative evaluations at the same CNR (P> 0.05). CONCLUSION: In this phantom study, these results show that the CNR method with low tube voltage achieves radiation dose reduction without decreasing the image quality.