sub-retinal delivery of the hesc-derived photoreceptor progenitor cells in rd10 mice

Revitalizing Sight: Stem Cell Therapy for Retinal Degeneration

Inherited retinal diseases and age-related macular degeneration lead to photoreceptor cell loss and eventual blindness. The retinal photoreceptor is the outer segment layer of the retina comprised of specialized cells responsible for phototransduction (i.e., conversion of light to neuronal signals). The rod and cone photoreceptor cells are adjacent to the retinal pigmented layer (RPE)1. Photoreceptor cell replacement therapy to compensate the cell loss has been an emerging and developing therapeutic approach. Embryonic stem cells (ESCs)2,3,4, induced pluripotent stem cells (iPSCs)-derived RPE cells, and retinal progenitor cells (RPCs)4,5,6,7,8 were used to restore the damaged photoreceptor cells. Sub-retinal space, a confined space between the retina and the RPE, is an attractive location to deposit these cells to replace damaged photoreceptor cells, RPE, and Mueller cells due to its vicinity9,10,11.
Gene and cell therapies have been utilizing the sub-retinal space for regenerative medicine for various retinal diseases in pre-clinical studies. This includes the delivery of functional copies of the gene or gene editing tools in the form of either anti-sense oligonucleotide therapy12,13 or CRISPR/Cas9 or base editing via adeno-associated virus (AAV) based strategy14,15,16, implantation of materials (e.g., RPE sheet, retinal prosthetics17,18,19) and differentiated stem cell-derived retinal organoids20,21,22 to treat retinal and RPE-related diseases. Clinical trials using hESC-RPE31 in the sub-retinal space to treat RPE65-associated Leber congenital amaurosis (LCA)23,24, CNGA3-linked achromatopsia25, MERTK-associated retinitis pigmentosa26, choroideremia27,28,29,30 have been proven to be an effective approach. Direct injection of cells to the vicinity of the damaged area greatly improves the chance of cell settlement at the appropriate region, synaptic integration, and eventual visual improvement.
Even though sub-retinal injection in human and large-eyed models (i.e., pig32,33,34,35, rabbit36,37,38,39,40, and non-human primate41,42,43) has been&#160;established, such injection in the murine model is still challenging due to the constrain of the eyeball size and enormous lens occupying the mouse eye44,45,46. However, genetically modified models are only readily available in small animals and not in large animals (i.e., rabbits and non-human primates), therefore sub-retinal injection in mice draws attention to investigate novel therapeutic approaches in retinal genetic disorders. Three major approaches are being used to deliver cells or AAVs into the sub-retinal space, namely the trans-corneal route, trans-scleral route, and the pars plana route (See Figure 2). Trans-corneal and trans-scleral routes are associated with cataract formation, synechiae, choroidal bleeding, and reflux from the injection site11,44,45,47,48,49. We adopted the pars plana approach as a direct visualization of the injection process, and the injection site can be achieved in real-time under the microscope.
We recently described a method that can differentiate human embryonic stem cells (hESCs) into photoreceptor progenitors under xenofree, chemically defined conditions using recombinant human retina-specific laminin isoform LN523. Since LN523 was found to be present in the retina, we hypothesized that the extracellular matrix niche of the human retina could be recapitulated in vitro and thereby support photoreceptor differentiation from the hESCs36. Single-cell transcriptomic analysis showed that photoreceptor progenitors co-expressing cone-rod homeobox and recoverin were generated after 32 days. A retinal degeneration 10 (rd10) mutant mouse model that mimics autosomal human retinitis pigmentosa was used to evaluate the efficacy of the day 32 hESC-derived photoreceptor progenitors in-vivo. The hESC-derived photoreceptor progenitor cells were injected into the sub-retinal space of rd10 mice at P20, where photoceptor dysfunction and degeneration are ongoing36. Here, we describe a detailed protocol for the preparation of the post-cryopreserved hESC-derived photoreceptor progenitors and delivery into the sub-retinal space of rd10 mice. This method can also be used to administer AAVs, cell suspensions, peptides, or chemicals into the sub-retinal space in mice.

Author Spotlight: Advancing Vision Restoration - Stem Cell-Based Therapy for Retinal Diseases 

Sub-Retinal Delivery of Human Embryonic Stem Cell Derived Photoreceptor Progenitors in rd10 Mice

My research focuses on the development of stem cell based therapy for advanced stages of retinal diseases that cause photoreceptor degeneration. The goal of our research is to replace the loss of photoreceptors in patients with clinically safe and functional photoreceptor progenitors with the aim of improving their visual acuity or even restoring their vision. The main preclinical model is mice, but their small sized eyeball make it challenging to inject materials, especially under the retina.Developing the skill to perform successful subretinal injections requires patience and perseverance. We have successfully developed a laminin base for the receptor differentiation method that is able to generate photoreceptor progenitors in 32 days. The subretinal transplantations of this photoreceptor progenitors cell suspensions in the rodents resulted in synaptic connectivity between the holes and graft in the eyes.This has led to partial visual restoration. Our approach is simple, the right visualization helps the surgeon handle the needle to the area of interest.

Watch this Scientific Journal Video about Sub-Retinal Delivery of the hESC-Derived Photoreceptor Progenitor Cells in  rd10  Mice at JoVE.com

Sub-Retinal Delivery of the hESC-Derived Photoreceptor Progenitor Cells in  rd10  Mice  

Sub-Retinal Delivery of the hESC-Derived Photoreceptor Progenitor Cells in rd10 Mice

To begin, take an anesthetized mouse and apply one drop of 1%tropicamide and 2.5%phenylephrine into the eye to dilate the pupil. Then apply an ophthalmic gel to the cornea to prevent dryness and anesthesia induced cataracts. Next, set up an upright operating microscope with a direct light path in a sterile environment to perform the subretinal injection.To prepare the 10 microliter glass syringe, detach the needle hub and attach the 33 gauge blunt needle. Take the metal hub cover and securely fasten the needle onto the syringe. Flush the needle with distilled water to test leakage and needle patency.Then empty the syringe and set it aside carefully. Next, position the anesthetized mouse on a cushion and orient the treatment eye toward the microscope's objective. Apply 0.5%proparacaine hydrochloride and wait for 30 seconds.Then apply 150 microliters of ophthalmic gel to the eye and affix a round cover slip. Perform a preliminary eye examination observing the cornea, iris, pupil, lens, and conjunctiva. Adjust the focal plane to visualize the fundus of the mouse eye through the pupil.Then align the head so that the optic head aligns with the center of the pupil. Afterwards, tap the base of the tube containing HESC derived photoreceptor progenitors to get a uniform cell suspension. Using a 10 microliter glass microliter syringe with a 33 gauge blunt needle, draw two microliters of cell mixture.Use a 30 gauge disposable needle to create a sclerectomy wound positioned two millimeters behind the limbus. Maintain the needle's angle at approximately 45 degrees to prevent contact with the lens. Once the needle tip becomes visible within the eye, carefully retract the needle.Discard the used needle into a sharp bin to prevent needle prick injuries. Now take the glass syringe and insert the blunt needle into the sclerectomy wound. Advance the blunt needle without touching the lens until it reaches the opposite retina of the entry wound.Gently penetrate the retina until a pressure branch on the sclera is seen. Then inject two microliters of the cell suspension or PRDM media into the subretinal space while maintaining gentle pressure on the syringe. The formation of a visible bleb indicates successful injection.Wait 10 seconds to allow the cells to settle down. Gently retract the needle from the eye. To visualize the bleb, move the mouse head to position the eye under the microscope and secure the position by gently holding the head.For intraoperative OCT, use the IOCT function on the operating microscope and select cube on the OCT screen. Position the scanning area on the bleb by pressing the arrow buttons. To adjust the OCT, slide centering and focus for the best OCT quality, press capture or scan to acquire the OCT scan of the bleb area and review the images to check the quality of the scans.Finally, remove the cover slip and gently clean the gel from the eye using gauze. Administer antibiotic ointment once after the injection to prevent infection. The OCT scan revealed distinct HESC entities suspended in the cell treated eye.In contrast, the media treated eye displayed unclouded fluid, void of cells within the subretinal space.

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Regeneration of photoreceptor cells using human pluripotent stem cells is a promising therapy for the treatment of both hereditary and aging retinal ...