Physician outlines latest emerging technologies to treat condition
Ophthalmology has benefited from many new devices, pharmaceuticals and biologics to treat diseases of the back of the eye. More recently, innovations addressing corneal diseases have proliferated. Fuchs endothelial corneal disease, keratoconus, bullous keratopathy and other corneal dystrophies have sparked many new technologies.
Corneal innovations started with surgical innovations (eg, anterior lamellar keratoplasty, Descemet stripping automated endothelial keratoplasty [DSAEK], Descemet membrane endothelial keratoplasty [DMEK]) and associated tissue processing improvements and devices, with the aim of making better use of precious donor cornea tissue and improving patient outcomes.
Today, that innovation has branched into several exciting new areas, including biosynthetic engineering, biomaterials engineering, small molecule growth factors and growth inhibitors and novel biopharmaceuticals including cell therapy.
Sound confusing? It is. The purpose of this article is to provide a practical introduction to some emerging technologies.
Although the underlying production methods are complex, the goal of engineering synthetic tissues is straightforward: to alleviate the scarce supply of human donor corneas.
Synthetic materials are being explored for a variety of uses in corneal tissue production. For example, one recent paper1 investigated the use of a biocompatible/biodegradable polyester polycaprolactone as a potential source material for corneal tissue engineering. One innovator (EyeYon Medical) uses an acrylic polymer to produce artificial corneal tissue of varying thicknesses for DSAEK/DMEK procedures. Another company (CorNeat Vision) has developed an artificial extracellular matrix for use in corneal keratoprosthesis for shunts in glaucoma procedures and for other eye indications.
Synthetic materials are regulated as medical devices, which may mean a more rapid regulatory pathway than with pharmaceuticals. As synthetic materials, their production does not rely on the scarce resource of human corneal tissue (or other biomaterials). Although some biosynthetic engineered technologies have demonstrated favourable outcomes in human studies, some corneal specialists are concerned that patients’ visual acuity—while improved—may not be as good as with DSAEK/DMEK. Concerns remain about potential biocompatibility problems resulting from non–biologic matter implanted in the eye, such as rejection reaction or immune response. Nevertheless, we will likely see more novel biosynthetic tissues targeting corneal dystrophies.
Also referred to as ‘bioprinting,’ bioengineering for the cornea involves use of biomaterials (eg, porcine collagen, recombinant human collagen) and sometimes even combinations of biomaterials and biosynthetics (eg, collagen plus chemical cross-linking) to fabricate corneal tissue in multiple thicknesses for multiple indications.
Researchers at the University of Ottawa in Canada and Linköping University in Sweden published results2 of a 10-participant clinical trial using bioengineered corneas in patients with advanced keratoconus or corneal scarring. Participants received implants of biosynthetic corneas made of synthetically cross-linked human collagen. More recently, other scientists at Linköping University published results of a study3 of 10 human participants who received implants of bioengineered corneas created from porcine collagen. Both these technologies have subsequently been out-licenced (to Eluminex Biosciences Limited and to LinkoCare Life Sciences AB, respectively) for additional clinical and commercial development.
A proprietary bioprinting platform leveraging laser-induced forward transfer technology has been developed (by Precise Bio) to address the fabrication of human corneal tissue with ultra-high precision and reproducibility. Using human corneal tissue as its source materials, this platform can build complex tissue structures with high cell resolution and precise spatial positioning of cells within the cellular matrix as well as the growth factors and cross-link materials to ensure tissue maturity and viability. Although still in preclinical studies, this platform holds promise for corneal tissue bioengineering.
Bioengineering approaches have the advantages (and potential disadvantages) afforded by their source biomaterials: cells/tissue with inherent immune privilege, nutritional capabilities and biologic function but also finite supply of source biomaterials with finite lifecycles.
Biosynthetic and/or combination approaches may possibly yield the best of all worlds: the use of fabricated source materials in combination with biologics to produce high-functioning, longer-lasting corneal tissues. Although both bioengineering and biosynthetic engineering innovations may ultimately address corneal tissue supply challenges, these approaches
do not fundamentally improve the patient experience nor do they alleviate the surgical complexity of current standards of care for endothelial keratoplasties. That said, there will likely be more innovations in this area.
Cells used in cell therapies may be derived from human embryonic stem cells, induced pluripotent stem cells (iPSCs), human umbilical tissue–derived cells, or fully differentiated human cells from various organs, connective tissues and so on. The merits of stem cells include their capacity to morph and differentiate into specialised cell types, which can then be applied to cell regeneration to address a wide variety of therapeutic categories. The challenges of stem cells are effectively regulating their differentiation and turning off cell reproduction. By contrast, fully differentiated cells already ‘know who they are.’ They perform all the essential biologic functions inherent in their specific cell types.
First-generation cell therapy innovations using fully differentiated cells target cancer indications with chimeric antigen receptor (CAR) T-cell therapies (tisagenlecleucel [Kymriah], axicabtagene ciloleucel [Yescarta], brexucabtagene autoleucel [Tecartus], lisocabtagene maraleucel [Breyanzi], idecabtagene vicleucel [Abecma], and ciltacabtagene autoleucel [Carvykti]). With CAR T-cell therapy, a patient’s T cells are extracted from the patient’s blood and modified in the lab to attack cancer cells. Then the gene for a special CAR that binds to a certain protein on the patient’s cancer cells is added to the T cells in vitro, grown, and returned to the patient by infusion. Due to immune rejection obstacles, the catch is having to retrieve a patient’s own cells, culture and reproduce them in vitro, modify them genetically, and then insert them back into that same patient—which is not scalable. Nevertheless, the outcomes of CAR T-cell therapy are undeniably exciting.4
Back to ophthalmology. In contrast to other organs, the eye is immune privileged, which makes cell therapy both potentially favourable and scalable for the treatment of eye diseases because cells from one donor can multiply (or reproduce) to treat many recipients. Cell therapy in ophthalmology initially focused on modeling diseases affecting the retinal pigment epithelium, retinal ganglion cells, and photoreceptor cells.5 Next, researchers began exploring cell therapies to target key retinal indications such as age-related macular degeneration and Stargardt macular dystrophy.6 Many of these research efforts are ongoing and hold promise.
Cell therapy targeting corneal endothelial dystrophies is another focus of innovation.
Human corneal endothelial cells (HCECs) do not reproduce in vivo; a person is born with a finite number of HCECs, which over time will degrade or deteriorate due to age, disease, or surgical trauma. Once HCECs are gone, they are gone for good. Until very recently, getting fully differentiated HCECs to reproduce in vitro proved extremely challenging. Shigeru Kinoshita, MD, PhD, professor and chairman of ophthalmology at Kyoto Prefectural University of Medicine in Japan, is believed to be the first to overcome this hurdle with a combination cell therapy (fully differentiated HCECs and rho kinase inhibitor). Dr Kinoshita and colleagues conducted a first-in-human trial of participants with bullous keratopathy. They published 2-year outcomes of the first 11 participants in 20187 and the 5-year outcomes in 2021.8 Dr Kinoshita/Kyoto Prefectural University of Medicine have out-licenced this intellectual property (Aurion Biotech) for additional clinical and commercial development targeting corneal endothelial dystrophies with additional ex-US studies performed in 2020 to 2022. In total, more than 130 participants with corneal endothelial disease have now been treated with this cell therapy.
Another cell therapy approach involves the in vitro proliferation of differentiated HCECs with biocompatible magnetic nanoparticles (Emmetrope Ophthalmics LLC. A phase 1 study is underway to treat corneal edema secondary to corneal endothelial dysfunction in eyes that qualify for surgery involving full-thickness corneal transplantation or EK.9 Safety data from 9 participants treated in this study were presented at the 2022 Association for Research in Vision and Ophthalmology meeting.10
Still others are using iPSCs to produce HCECs (Cellusion Inc). Last year, an exploratory clinical study was initiated at Keio University in Tokyo, Japan, to examine safety and efficacy of iPS cell–derived corneal endothelial cell substitutes for bullous keratopathy in 3 participants.11 As of this publication date, no data are yet available.
Numerous research projects (and publication of their results) are underway at Singapore Eye Research Institute, including corneal endothelial cell therapy, corneal gene therapy, and corneal stromal cell therapy.12 The progress of this institution’s efforts is well worth following.
Although not cell therapy, another approach involves the removal of the endothelium’s central area through multiple injections of a combination rho kinase inhibitor and FGF growth factor to stimulate healthy endothelial cell movement and replacement across the endothelium’s central area (Trefoil Therapeutics). Because endothelial cells inherently do not reproduce in vivo, this method depends on cell movement (and potentially individual cell enlargement), which might compromise cell function if cells morph or expand over large gaps. Preliminary data from a phase 1/2 study13 were reported at the 2022 American Academy of Ophthalmology meeting,14 but it is too early to comment on this approach until additional data are presented or published.
Cell therapy involving fully differentiated HCECs holds the most immediate promise for patients suffering from corneal dystrophies and may address multiple drawbacks of current standards of care. In addition to addressing the chronic worldwide shortage of donor corneas, cell therapy procedures may prove to be less invasive and more tolerable than endothelial keratoplasties due to lower risk of rejection vs EKs or penetrating keratoplasty, which, in turn, could mean less onerous recovery for patients. It is an exciting time for innovations targeting corneal dystrophies and a space for us all to follow with interest.