Feasibility and safety of porcine Descemet’s membrane as a carrier for generating tissue-engineered corneal endothelium

Approaches for corneal endothelium regenerative medicine

The state of the art therapy for treating corneal endothelial disease is transplantation. Advances in the reproducibility and accessibility of surgical techniques are increasing the number of corneal transplants, thereby causing a global deficit of donor corneas and leaving 12.7 million patients with addressable visual impairment. Approaches to regenerate the corneal endothelium offer a solution to the current tissue scarcity and a treatment to those in need. Methods for generating corneal endothelial cells into numbers that could address the current tissue shortage and the possible strategies used to deliver them have now become a therapeutic reality with clinical trials taking place in Japan, Singapore and Mexico. Nevertheless, there is still a long way before such therapies are approved by regulatory bodies and become clinical practice. Moreover, acellular corneal endothelial graft equivalents and certain drugs could provide a treatment option for specific disease conditions without the need of donor tissue or cells. Finally, with the emergence of gene modulation therapies to treat corneal endothelial disease, it would be possible to treat presymptomatic patients or those presenting early symptoms, drastically reducing the need for donor tissue. It is necessary to understand the most recent developments in this rapidly evolving field to know which conditions could be treated with which approach. This article provides an overview of the current and developing regenerative medicine therapies to treat corneal endothelial disease and provides the necessary guidance and understanding towards the treatment of corneal endothelial disease.

Treatment of corneal endothelial damage in a rabbit model with a bioengineered graft using human decellularized corneal lamina and cultured human corneal endothelium

Objective

We aimed to investigate the functionality of human decellularized stromal laminas seeded with cultured human corneal endothelial cells as a tissue engineered endothelial graft (TEEK) construct to perform endothelial keratoplasty in an animal model of corneal endothelial damage.

Methods

Engineered corneal endothelial grafts were constructed by seeding cultured human corneal endothelial cell (hCEC) suspensions onto decellularized human corneal stromal laminas with various coatings. The functionality and survival of these grafts with cultured hCECs was examined in a rabbit model of corneal endothelial damage after central descemetorhexis. Rabbits received laminas with and without hCECs (TEEK and control group, respectively).

Results

hCEC seeding over fibronectin-coated laminas provided an optimal and consistent endothelial cell count density and polygonal shape on the decellularized laminas, showing active pump fuction. Surgery was performed uneventfully as standard Descemet stripping automated endothelial keratoplasty (DSAEK). Corneal transparency gradually recovered in the TEEK group, whereas haze and edema persisted for up to 4 weeks in the controls. Histologic examination showed endothelial cells of human origin covering the posterior surface of the graft in the TEEK group.

Conclusions

Grafting of decellularized stroma carriers re-surfaced with human corneal endothelial cells ex vivo can be a readily translatable method to improve visual quality in corneal endothelial diseases.

Ex vivo construction of rabbit corneal endothelial cell sheets on a porcine descemet membrane graft

The aim of the present study was to investigate the feasibility of a new graft construction method using rabbit corneal endothelial cells (RCECs) and a porcine descemet membrane (DM) carrier. RCECs were isolated and the experimental group was treated with Y-27632, whereas the control group were cultured in medium without Y-27632. RCEC morphology was observed using an inverted microscope, and cell proliferation and apoptosis were detected by flow cytometry. To confirm the presence of RCECs, reverse transcription-quantitative PCR was used to detect gene expression levels of Na+-K+-ATPase, aquaporin 1, collagen α₂ (IV), collagen α₁ (VIII) and keratin-12. Histocompatibility testing was used to detect porcine DM antigenicity. A DM-RCEC graft was constructed, and morphology was observed using alizarin red-trypan blue and haematoxylin and eosin staining. Cell membrane potential was measured to evaluate the physical function of the DM-RCEC graft. Complex graft tension was measured using a modified tension detector and compared with fresh porcine DM-endothelium complex. In vitro-cultured RCECs formed a monolayer with a polygon morphology and cobblestone-like arrangement. In vitro-cultured RCECs exhibited typical RCEC characteristics before and after transplantation. The proliferation rates of the experimental and control groups were 62.68 and 34.50%, respectively (P<0.05); the apoptosis rates of the experimental and control groups were 8.99 and 35.68%, respectively (P<0.05). There was no antigenicity observed with the porcine DM. The action potential amplitude of the experimental and control groups was over −80 mV, reflecting normal RCEC physiological function. The tension measurements of the experimental and control groups were 20.0248±1.048 and 20.5013±0.657 g, respectively (P>0.05). Taken together, the results of the present study demonstrated that Y-27632 enhanced RCEC proliferation. In addition, the findings revealed the successful ex vivo construction of a RCEC sheet on a porcine DM graft.

Reducing porcine corneal graft rejection, with an emphasis on porcine endogenous retrovirus transmission safety: a review

Donor cornea shortage is a primary hurdle in the development of corneal transplantation. Of all species, porcine corneas are the ideal transplantation material for humans. However, the xenoimmune rejection induced by porcine corneal xenotransplantation compromises surgical efficacy. Although the binding of IgM/IgG in human serum to a genetically modified porcine cornea is significantly weaker than that of the wild type (WT), genetically modified porcine corneas do not display a prolonged graft survival time in vivo. Conversely, costimulatory blockade drugs, such as anti-CD40 antibodies, can reduce the xenoimmune response and prolong graft survival time in animal experiments. Moreover, porcine endothelial grafts can survive for more than 6mo with only the subconjunctival injection of a steroid-based immunosuppressants regime; therefore, they show great value for treating corneal endothelial disease. In addition, zoonotic transmission is a primary concern of xenotransplantation. Porcine endogenous retrovirus (PERV) is the most significant virus assessed by ophthalmologists. PERV integrates into the porcine genome and infects human cells in vitro. Fortunately, no evidence from in vivo studies has yet shown that PERV can be transmitted to hosts.

Evaluation of Patent Blue as the Vital Dye in an Animal Model of Descemet Membrane Endothelial Keratoplasty

PURPOSE

To evaluate the safety and feasibility of patent blue (PB) as the vital dye in Descemet membrane endothelial keratoplasty (DMEK).

METHODS

Bovine corneal endothelial cells were incubated with different concentrations (0.02%-2.5%) of PB. The cell viability, which was assessed by Cell Counting Kit-8 assay, was compared with that of untreated control and 0.06% to 0.4% trypan blue. The dyes were also used for graft preparation and implantation in the porcine eye model to evaluate stain quality, dye retention, and the feasibility of using PB in DMEK surgery.

RESULTS

No obvious increase in cytotoxicity was detected for 0.06% to 0.4% trypan blue and PB at concentrations up to 1.0%, but the cell viability after incubating with 1.5% to 2.5% PB was significantly reduced. PB at 0.5% to 1.0% generated good staining quality that can be used to facilitate graft implantation. Although the staining quality of 0.5% to 1.0% PB faded to an intermediate level after a 30-minute wash in phosphate-buffered saline, dye retention persisted for up to 24 hours.

CONCLUSIONS

PB at 0.5% to 1.0% is biocompatible and can stain the graft sufficiently, making it an alternative for DMEK surgery.