Subretinal Human Umbilical Tissue-Derived Cell Transplantation Preserves Retinal Synaptic Connectivity and Attenuates Müller Glial Reactivity.

Human umbilical tissue-derived cells (hUTC or palucorcel) are currently under clinical investigation for the treatment of geographic atrophy, a late stage of macular degeneration, but how hUTC transplantation mediates vision recovery is not fully elucidated. Subretinal administration of hUTC preserves visual function in the Royal College of Surgeons (RCS) rat, a genetic model of retinal degeneration caused by Mertk loss of function. hUTC secrete synaptogenic and neurotrophic factors that improve the health and connectivity of the neural retina. Therefore, we investigated the progression of synapse and photoreceptor loss and whether hUTC treatment preserves photoreceptors and synaptic connectivity in the RCS rats of both sexes. We found that RCS retinas display significant deficits in synaptic development already by postnatal day 21 (P21), before the onset of photoreceptor degeneration. Subretinal transplantation of hUTC at P21 is necessary to rescue visual function in RCS rats, and the therapeutic effect is enhanced with repeated injections. Synaptic development defects occurred concurrently with morphological changes in Müller glia, the major perisynaptic glia in the retina. hUTC transplantation strongly diminished Müller glia reactivity and specifically protected the α2δ-1-containing retinal synapses, which are responsive to thrombospondin family synaptogenic proteins secreted by Müller glia. Müller glial reactivity and reduced synaptogenesis observed in RCS retinas could be recapitulated by CRISPR/Cas9-mediated loss-of-Mertk in Müller glia in wild-type rats. Together, our results show that hUTC transplantation supports the health of retina at least in part by preserving the functions of Müller glial cells, revealing a previously unknown aspect of hUTC transplantation-based therapy.SIGNIFICANCE STATEMENT Despite the promising effects observed in clinical trials and preclinical studies, how subretinal human umbilical tissue-derived cell (hUTC) transplantation mediates vision improvements is not fully known. Using a rat model of retinal degeneration, the RCS rat (lacking Mertk), here we provide evidence that hUTC transplantation protects visual function and health by protecting photoreceptors and preserving retinal synaptic connectivity. Furthermore, we find that loss of Mertk function only in Müller glia is sufficient to impair synaptic development and cause activation of Müller glia. hUTC transplantation strongly attenuates the reactivity of Müller glia in RCS rats. These findings highlight novel cellular and molecular mechanisms within the neural retina, which underlie disease mechanisms and pinpoint Müller glia as a novel cellular target for hUTC transplantation.

Human Umbilical Tissue-Derived Cells Promote Synapse Formation and Neurite Outgrowth via Thrombospondin Family Proteins.

Cell therapy demonstrates great potential for the treatment of neurological disorders. Human umbilical tissue-derived cells (hUTCs) were previously shown to have protective and regenerative effects in animal models of stroke and retinal degeneration, but the underlying therapeutic mechanisms are unknown. Because synaptic dysfunction, synapse loss, degeneration of neuronal processes, and neuronal death are hallmarks of neurological diseases and retinal degenerations, we tested whether hUTCs contribute to tissue repair and regeneration by stimulating synapse formation, neurite outgrowth, and neuronal survival. To do so, we used a purified rat retinal ganglion cell culture system and found that hUTCs secrete factors that strongly promote excitatory synaptic connectivity and enhance neuronal survival. Additionally, we demonstrated that hUTCs support neurite outgrowth under normal culture conditions and in the presence of the growth-inhibitory proteins chondroitin sulfate proteoglycan, myelin basic protein, or Nogo-A (reticulon 4). Furthermore, through biochemical fractionation and pharmacology, we identified the major hUTC-secreted synaptogenic factors as the thrombospondin family proteins (TSPs), TSP1, TSP2, and TSP4. Silencing TSP expression in hUTCs, using small RNA interference, eliminated both the synaptogenic function of these cells and their ability to promote neurite outgrowth. However, the majority of the prosurvival functions of hUTC-conditioned media was spared after TSP knockdown, indicating that hUTCs secrete additional neurotrophic factors. Together, our findings demonstrate that hUTCs affect multiple aspects of neuronal health and connectivity through secreted factors, and each of these paracrine effects may individually contribute to the therapeutic function of these cells. SIGNIFICANCE STATEMENT: Human umbilical tissue-derived cells (hUTC) are currently under clinical investigation for the treatment of geographic atrophy secondary to age-related macular degeneration. These cells show great promise for the treatment of neurological disorders; however, the therapeutic effects of these cells on CNS neurons are not fully understood. Here we provide compelling evidence that hUTCs secrete multiple factors that work synergistically to enhance synapse formation and function, and support neuronal growth and survival. Moreover, we identified thrombospondins (TSPs) as the hUTC-secreted factors that mediate the synaptogenic and growth-promoting functions of these cells. Our findings highlight novel paracrine effects of hUTC on CNS neuron health and connectivity and begin to unravel potential therapeutic mechanisms by which these cells elicit their effects.

Ocular biodistribution of bevasiranib following a single intravitreal injection to rabbit eyes.

PURPOSE: The primary objective of these investigations was to determine the ocular biodistribution of bevasiranib, a small interfering RNA (siRNA) targeting vascular endothelial growth factor A (VEGF-A), following a single intravitreal injection to rabbit eyes. METHODS: A tissue distribution and pharmacokinetic study was conducted with (3)H-bevasiranib prepared in balanced-salt solution (BSS). Single doses of either 0.5 mg/eye or 2.0 mg/eye of (3)H-bevasiranib were given by intravitreal injection to Dutch-Belted rabbits (both eyes were treated). Subgroups of rabbits were serially-sacrificed at various times up to 7 days following dosing for collection of tissue samples. The right eye of each rabbit was collected whole, and the left eye was dissected to isolate five ocular tissues. All samples were analyzed by liquid scintillation counting to determine the concentrations of bevasiranib equivalents. An ocular disposition study was also performed with non-radiolabeled bevasiranib, which was administered to Dutch-Belted rabbit eyes via intravitreal injection at a dose of 2.0 mg/eye. Twenty-four hours post-dose, the eyes were enucleated and dissected into eight individual ocular structures that were analyzed for intact bevasiranib using a locked nuleic acid (LNA) noncompetitive hybridization-ligation enzyme-linked immunosorbent assay. RESULTS: Following intravitreal injection of 0.5 mg or 2.0 mg radiolabeled bevasiranib to Dutch-Belted rabbits, bevasiranib was detected in the vitreous, iris, retina, retinal pigment epithelium (RPE), and sclera (+choroid). As expected, the highest concentrations were found in the vitreous, and vitreous levels steadily decreased over time, while concentrations of radioactivity in the other ocular tissues increased to maximum values between 24 h and 72 h after dosing. Of these tissues, the highest concentration of radioactivity was detected in the retina. The LNA assay further confirmed the presence of intact bevasiranib in these tissues 24 h following intravitreal injection of non-radiolabeled bevasiranib (2 mg/eye). CONCLUSIONS: These studies demonstrate distribution of bevasiranib throughout the eye following intravitreal injection, including extensive uptake into the retina.

A Subretinal Cell Delivery Method via Suprachoroidal Access in Minipigs: Safety and Surgical Outcomes.

Purpose: This study evaluated a new subretinal method for delivery of human or pig umbilical tissue-derived cells (hUTC or pUTC, respectively) using a novel subretinal injection cannula and suprachoroidal approach in Göttingen minipig eyes. hUTC (palucorcel) are currently under development for treating geographic atrophy in humans. Methods: Twenty-four Göttingen minipigs (divided into eight groups) were subretinally administered palucorcel, pUTC, or vehicle. In some cases, fluorescently labeled cells and vehicle were administered. Conjunctival cutdown and sclerotomy were performed, then a flexible cannula containing a microneedle was inserted and advanced into the suprachoroidal space. The microneedle was deployed and visualized; 50 µL cells (target concentration, 11.2 × 106 cells/mL [560,000 cells/eye]) or vehicle was injected subretinally. Safety outcomes were evaluated. Results: For all animals, cells and vehicle were successfully administered. Labeled cells or fluorescent vehicle were contained in the subretinal bleb, without leakage into the vitreous. No retinal detachment or vitreous traction band was identified by ophthalmologic examination. At all time points, observed microscopic changes were attributable to experimental procedures. On histopathology immediately after injection, localized retinal detachments were seen, along with focal retinal, choroidal, and/or scleral discontinuities. A moderate inflammatory response was seen in a limited number of animals. In the allogeneic setting, no antibody responses were detectable. Anti-human UTC antibodies were detected in the xenogeneic setting. Conclusions: Palucorcel, pUTC, and vehicle were successfully administered to Göttingen minipigs using a novel subretinal injection cannula via a suprachoroidal surgical approach, with no significant adverse events; therefore, this technique appears to be feasible for further clinical development.

Systemic rapamycin inhibits retinal and choroidal neovascularization in mice.

PURPOSE: Rapamycin exhibits significant antitumor/antiangiogenic activity that is coupled with a decrease in vascular endothelial growth factor (VEGF) production and a reduction in the response of vascular endothelial cells to stimulation by VEGF. VEGF plays a significant role in neovascular pathologies of the eye, thus we tested the possibility of using rapamycin to inhibit retinal and choroidal neovascularization (CNV). METHODS: CNV was induced in adult mice with laser photocoagulation. Retinal neovascularization was induced using the retinopathy of prematurity (ROP) hyperoxia/hypoxia model. Experimental animals received intraperitoneal (ip) injections of rapamycin (2 mg/kg/day or 4 mg/kg/day) for 1-2 weeks. Controls were not treated or received ip injections of phosphate buffered saline (PBS). Eyes were analyzed histologically for evidence of CNV or retinal neovascularization. ROP eyes were further analyzed for changes in VEGF and VEGF receptor (Flt-1 and Flk-1) protein content following rapamycin treatment. RESULTS: Rapamycin significantly reduced the extent of neovascularization in both the CNV and the ROP model. Immunohistochemical staining of treated and untreated ROP retina did not reveal a significant reduction in levels of VEGF protein or its receptors. Immunostaining for Flt-1 increased, while no obvious changes in Flk-1 were observed. Quantitative analysis of total protein via enzyme linked immunosorbent assay (ELISA) confirmed an increase in Flt-1 and VEGF, following drug treatment, with no effect on Flk-1. CONCLUSIONS: These results suggest rapamycin may provide an effective new treatment for ocular neovascularization.

Gene therapy and animal models for retinal disease.

Those plagued by retinal diseases are often robbed of their vision, as often, effective treatments do not exist. Knowledge of the pathophysiology of retinal diseases stems from research on available animal models. Gene therapy may be useful for both genetic and acquired retinal diseases. This review will focus on retinal diseases for which gene therapy has demonstrated promise. The diseases are presented in order of the age at which they are generally first symptomatic and include retinopathy of prematurity, Leber congenital amaurosis, mucopolysaccharidoses, retinoblastoma, retinitis pigmentosa, diabetic retinopathy, glaucoma and age-related macular degeneration. We will describe the animal models used to study these disorders and emphasize the progress that has been made in using gene therapy for the treatment of retinal disease.

Adeno-associated viruses containing bFGF or BDNF are neuroprotective against excitotoxicity.

PURPOSE: Brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) hold much promise for the protection of retinal ganglion cells against excitotoxic cell death. We tested the possibility of delivering these growth factors to retinal ganglion cells via an adeno-associated viral (AAV) vector and tested their efficacy in two models of excitotoxicity. METHODS: Rat retinas were infected with AAV vectors encoding bFGF or BDNF. A control vector containing green fluorescent protein (GFP) was injected in the contralateral eye. Eyes were subjected to either an intravitreal injection of N-methyl-D-aspartate (NMDA) or optic nerve crush, and ganglion cell survival was evaluated. RESULTS: AAV.CMV.bFGF and AAV.CBA.BDNF were neuroprotective against NMDA injection 1 month post-treatment. Additionally, AAV.CMV.bFGF was protective against optic nerve crush. CONCLUSION: AAV-mediated delivery of bFGF and BDNF can promote retinal cell survival following excitotoxic insult.

Long-term restoration of rod and cone vision by single dose rAAV-mediated gene transfer to the retina in a canine model of childhood blindness.

The short- and long-term effects of gene therapy using AAV-mediated RPE65 transfer to canine retinal pigment epithelium were investigated in dogs affected with disease caused by RPE65 deficiency. Results with AAV 2/2, 2/1, and 2/5 vector pseudotypes, human or canine RPE65 cDNA, and constitutive or tissue-specific promoters were similar. Subretinally administered vectors restored retinal function in 23 of 26 eyes, but intravitreal injections consistently did not. Photoreceptoral and postreceptoral function in both rod and cone systems improved with therapy. In dogs followed electroretinographically for 3 years, responses remained stable. Biochemical analysis of retinal retinoids indicates that mutant dogs have no detectable 11-cis-retinal, but markedly elevated retinyl esters. Subretinal AAV-RPE65 treatment resulted in detectable 11-cis-retinal expression, limited to treated areas. RPE65 protein expression was limited to retinal pigment epithelium of treated areas. Subretinal AAV-RPE65 vector is well tolerated and does not elicit high antibody levels to the vector or the protein in ocular fluids or serum. In long-term studies, wild-type cDNA is expressed only in target cells. Successful, stable restoration of rod and cone photoreceptor function in these dogs has important implications for treatment of human patients affected with Leber congenital amaurosis caused by RPE65 mutations.

A deviant immune response to viral proteins and transgene product is generated on subretinal administration of adenovirus and adeno-associated virus.

The immune response after ocular exposure to foreign antigens varies substantially from that of a typical systemic response. Anterior chamber associated immune deviation (ACAID) has been well documented. The immune response of the subretinal space has not been studied in as much detail. Here, we characterized the immune response of the subretinal space when it encounters the antigens AdV-GFP and AAV-GFP (recombinant adenovirus or adeno-associated virus, respectively), each delivering the reporter gene encoding green fluorescent protein (GFP). Results indicate that the subretinal space possesses an immune-deviant property similar to ACAID. AdV-elicited immune responses following subretinal injections are significantly reduced compared with systemic responses elicited by intradermal injections of the same virus. Furthermore, subretinal AdV administration results in transduction of retinal pigment epithelial cells (RPE), which are the potential antigen presenting cells of the retina. This subsequently generates a population of immunosuppressive Th2-type, cytokine-secreting, splenic T cells. This response may be advantageous to the development of ocular gene therapy.

In utero gene therapy rescues vision in a murine model of congenital blindness.

The congenital retinal blindness known as Leber congenital amaurosis (LCA) can be caused by mutations in the RPE65 gene. RPE65 plays a critical role in the visual cycle that produces the photosensitive pigment rhodopsin. Recent evidence from human studies of LCA indicates that earlier rather than later intervention may be more likely to restore vision. We determined the impact of in utero delivery of the human RPE65 cDNA to retinal pigment epithelium cells in a murine model of LCA, the Rpe65(-/-) mouse, using a serotype 2 adeno-associated virus packaged within an AAV1 capsid (AAV2/1). Delivery of AAV2/1-CMV-hRPE65 to fetuses (embryonic day 14) resulted in efficient transduction of retinal pigment epithelium, restoration of visual function, and measurable rhodopsin. The results demonstrate AAV-mediated correction of the deficit and suggest that in utero retinal gene delivery may be a useful approach for treating a variety of blinding congenital retinal diseases.