Xenotransplantation--the future of corneal transplantation?

Severe ulcerative keratopathy following implantation of an acellular porcine corneal stromal lenticule in a patient with keratoconus

PURPOSE

To report a case of ulcerative keratopathy following implantation of acellular porcine corneal stroma (APCS) in a patient with keratoconus (KC).

METHODS

A 58 year-old patient initially presented with an ulcerative keratopathy in the left eye. Previously, several corneal procedures (including radial keratotomy, laser-in-situ keratomileusis, crosslinking) were performed for KC. Eight months ago, an APCS lenticule (Xenia corneal implant, Gebauer Medizintechnik GmbH, Neuhausen, Germany) was implanted into a stromal pocket because of progressive keratectasia. Visual acuity was hand movement. Anterior segment optical coherence tomography showed a space between the APCS lenticule and the host stroma. Excimer laser-assisted penetrating keratoplasty (PKP, 8.0/8.1 mm) was performed in the left eye. The corneal explant was investigated by light and transmission electron microscopy.

RESULTS

Best-corrected visual acuity was 20/40 six weeks after PKP. Light microscopy demonstrated a stromal ulceration down to the APCS lenticule. No stromal cells could be found within the APCS lenticule eight months after implantation. The APCS lenticule did not show a green stain of the collagens with Masson-Goldner staining and exhibited a strong Periodic acid-Schiff positive reaction. Electron microscopy of the APCS lenticule revealed cross-linked collagen lamellae without cellular components. Close to the interface, corneal collagen lamellae of the host cornea were disorganized. Few vital keratocytes were present on the surface of the lenticule and appeared to cause mechanical disruption of the host stroma along the lenticule-stroma interface.

CONCLUSION

APCS implantation may lead to severe complications such as ulcerative keratopathy in otherwise uncomplicated KC corneas. In such cases, excimer laser-assisted PKP or Deep Anterior Lamellar Keratoplasty are the methods of choice to restore visual acuity.

Complement networks in gene-edited pig xenotransplantation: enhancing transplant success and addressing organ shortage

The shortage of organs for transplantation emphasizes the urgent need for alternative solutions. Xenotransplantation has emerged as a promising option due to the greater availability of donor organs. However, significant hurdles such as hyperacute rejection and organ ischemia-reperfusion injury pose major challenges, largely orchestrated by the complement system, and activated immune responses. The complement system, a pivotal component of innate immunity, acts as a natural barrier for xenotransplantation. To address the challenges of immune rejection, gene-edited pigs have become a focal point, aiming to shield donor organs from human immune responses and enhance the overall success of xenotransplantation. This comprehensive review aims to illuminate strategies for regulating complement networks to optimize the efficacy of gene-edited pig xenotransplantation. We begin by exploring the impact of the complement system on the effectiveness of xenotransplantation. Subsequently, we delve into the evaluation of key complement regulators specific to gene-edited pigs. To further understand the status of xenotransplantation, we discuss preclinical studies that utilize gene-edited pigs as a viable source of organs. These investigations provide valuable insights into the feasibility and potential success of xenotransplantation, offering a bridge between scientific advancements and clinical application.

Temperature Dependence of Membrane Permeability Parameters for Five Cell Types Using Nonideal Thermodynamic Assumptions to Mathematically Model Cryopreservation Protocols

Cryopreservation is the process of preserving biological matter at subzero temperatures for long-term storage. During cryopreservation, cells are susceptible to various injuries that can be mitigated by controlling the cooling and warming profiles and cryoprotective agent (CPA) addition and removal procedures. Mathematical modeling of the changing cell volume at different temperatures can greatly reduce the experiments needed to optimize cryopreservation protocols. Such mathematical modeling requires as inputs the cell membrane permeabilities to water and CPA and the osmotically inactive fraction of the cell. Since the intra- and extracellular solutions are generally thermodynamically nonideal, our group has been incorporating the osmotic virial equation to model the solution thermodynamics that underlie the cell volume change equations, adding the second and third osmotic virial coefficients of the grouped intracellular solute to the cell osmotic parameters that must be measured. In our previous work, we reported methods to obtain cell osmotic parameters at room temperature by fitting experimental cell volume kinetic data with equations that incorporated nonideal solution thermodynamics assumptions. Since the relevant cell volume excursions occur at different temperatures, the temperature dependence of the osmotic parameters plays an important role. In this work, we present a new two-part fitting method to obtain five cell-type-specific parameters (water permeability, dimethyl sulfoxide permeability, osmotically inactive fraction, and the second and third osmotic virial coefficients of the intracellular solution) from experimental measurements of equilibrium cell volume and cell volume as a function of time at room temperature and 0 °C for five cell types, namely, human umbilical vein endothelial cells (HUVECs), H9c2 rat myoblasts, porcine corneal endothelial cells (PCECs), the Jurkat T-lymphocyte cell line, and human cerebral microvascular endothelial cells (hCMECs/D3 cell line). The fitting method in this work is based on both equilibrium and kinetic cell volume data, enabling us to solve some technical challenges and expand our previously reported measurement technique to 0 °C. Finally, we use the measured parameters to model the cell volume changes for a HUVEC cryopreservation protocol to demonstrate the impact of the nonideal thermodynamic assumptions on predicting the changing cell volume during freezing and thawing.

A proposed model of xeno-keratoplasty using 3D printing and decellularization

Corneal opacity is a leading cause of vision impairment and suffering worldwide. Transplantation can effectively restore vision and reduce chronic discomfort. However, there is a considerable shortage of viable corneal graft tissues. Tissue engineering may address this issue by advancing xeno-keratoplasty as a viable alternative to conventional keratoplasty. In particular, livestock decellularization strategies offer the potential to generate bioartificial ocular prosthetics in sufficient supply to match existing and projected needs. To this end, we have examined the best practices and characterizations that have supported the current state-of-the-art driving preclinical and clinical applications. Identifying the challenges that delimit activities to supplement the donor corneal pool derived from acellular scaffolds allowed us to hypothesize a model for keratoprosthesis applications derived from livestock combining 3D printing and decellularization.

Safety Evaluation of Far-UV-C Irradiation to Epithelial Basal Cells in the Corneal Limbus

Basal cells in the corneal limbus play an important role in the turnover cycle because they are the source of all cells that constitute the corneal epithelium. We examined the penetration depth of ultraviolet (UV) light in the corneal limbus and assessed the safety of Far-UV-C on stem cells in the basal area of the corneal limbus. Rats were irradiated with UV at peaks of 207, 222, 235, 254 and 311 nm while under anesthesia. The UV penetration depth in the rat corneal limbal epithelium was wavelength dependent: 311 nm UV-B and 254 nm UV-C reached the basal cells of the epithelium, and 235 nm radiation reached the middle area; however, 207 and 222 nm UV-C reached only the superficial layer of the epithelium. Porcine cornea, which is similar to the human eye in size and structure, were irradiated with 222 and 254 nm UV-C. As in rats, 222 nm UV-C reached only the superficial layer of the porcine corneal limbal epithelium. These results indicate that Far-UV-C, such as radiation of wavelengths of 207 and 222 nm, could not reach corneal epithelial stem cells, i.e. the cells remained intact. It is unlikely that the turnover of the corneal epithelium is obstructed or disrupted by exposure to Far-UV-C.

A Composite System Based upon Hydroxypropyl Cyclodextrins and Soft Hydrogel Contact Lenses for the Delivery of Therapeutic Doses of Econazole to the Cornea, In Vitro

Fungal keratitis, a disease in which the cornea becomes inflamed due to an invasive fungal infection, remains difficult to treat due in part to limited choices of available treatments. Topical eye drops are first-line treatment, but can be ineffective as low levels of drug reach the target site due to precorneal losses and the impenetrability of the cornea. The aim of this study was to determine the corneal delivery of econazole using a novel topical enhancement approach using a composite delivery system based upon cyclodextrins and soft hydrogel contact lenses. Excess econazole nitrate was added to hydroxypropyl-α-cyclodextrin (HP-α-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) solutions, and the solubility determined using HPLC. Proprietary soft hydrogel contact lenses were then impregnated with saturated solutions and applied to freshly enucleated porcine eyeballs. Econazole nitrate ‘eye drops’ at the same concentrations served as the control. After 6 h, the corneas were excised and drug-extracted, prior to quantification using HPLC. Molecular dynamic simulations were performed to examine econazole−HP-β-CD inclusion complexation and dissociation. The minimum inhibitory concentration (MIC) of econazole was determined against four fungal species associated with keratitis, and these data were then related to the amount of drug delivered to the cornea, using an average corneal volume of 0.19 mL. The solubility of econazole increased greatly in the presence of HP-β-CD and more so with HP-α-CD (p < 0.001), with ratios >> 2. Hydrogel contact lenses delivered ×2.8 more drug across the corneas in comparison to eye drops alone, and ×5 more drug delivered to the cornea when cyclodextrin was present. Molecular graphics demonstrated dynamic econazole release, which would create transient enhanced drug concentration at the cornea surface. The solution-only drops achieved the least satisfactory result, producing sub-MIC levels with factors of ×0.81 for both Fusarium semitectum and Fusarium solani and ×0.40 for both Scolecobasidium tshawytschae and Bipolaris hawaiiensis. All other treatments delivered econazole at > MIC for all four fungal species. The efficacies of the delivery platforms evaluated were ranked: HP-α-CD contact lens > HP-β-CD contact lens > contact lens = HP-α-CD drops > HP-β-CD drops > solution-only drops. In summary, the results in this study have demonstrated that a composite drug delivery system based upon econazole−HP-β-CD inclusion complexes loaded into contact lenses can achieve significantly greater corneal drug delivery with the potential for improved clinical responses.

Critical media attributes in E-beam sterilization of corneal tissue

When ionizing irradiation interacts with a media, it can form reactive species that can react with the constituents of the system, leading to eradication of bioburden and sterilization of the tissue. Understanding the media's properties such as polarity is important to control and direct those reactive species to perform desired reactions. Using ethanol as a polarity modifier of water, we herein generated a series of media with varying relative polarities for electron beam (E-beam) irradiation of cornea at 25 kGy and studied how the irradiation media's polarity impacts properties of the cornea. After irradiation of corneal tissues, mechanical (tensile strength and modulus, elongation at break, and compression modulus), chemical, optical, structural, degradation, and biological properties of the corneal tissues were evaluated. Our study showed that irradiation in lower relative polarity media improved structural properties of the tissues yet reduced optical transmission; higher relative polarity reduced structural and optical properties of the cornea; and intermediate relative polarity (ethanol concentrations = 20-30% (v/v)) improved the structural properties, without compromising optical characteristics. Regardless of media polarity, irradiation did not negatively impact the biocompatibility of the corneal tissue. Our data shows that the absorbed ethanol can be flushed from the irradiated cornea to levels that are nontoxic to corneal and retinal cells. These findings suggest that the relative polarity of the irradiation media can be tuned to generate sterilized tissues, including corneal grafts, with engineered properties that are required for specific biomedical applications. STATEMENT OF SIGNIFICANCE: Extending the shelf-life of corneal tissue can improve general accessibility of cornea grafts for transplantation. Irradiation of donor corneas with E-beam is an emerging technology to sterilize the corneal tissues and enable their long-term storage at room temperature. Despite recent applications in clinical medicine, little is known about the effect of irradiation and preservation media's characteristics, such as polarity on the properties of irradiated corneas. Here, we have showed that the polarity of the media can be a valuable tool to change and control the properties of the irradiated tissue for transplantation.

Paracrine activity of adipose derived stem cells on limbal epithelial stem cells

Limbal stem cells deficiency (LSCD) is an eye disease caused by the loss of stem cells in the corneal limbus as a succession of an injury due physical, biological, or chemical agents. Current therapies of LSCD are focused on the transplantation of donor corneas or tissue equivalents produced from autologous limbal stem cells. Every year there are waiting millions of patients for the cornea transplantation all over the world and the list is growing due to the relatively low number of cornea donors. On the other hand, the transplantation of tissue or cells into the recipient’s body is associated with the higher risk of possible side effects. The possibility of the application of an indirect treatment using the properties of the paracrine activity of stem cells, would be beneficial for the patients with transplant failures. This study was to evaluate the paracrine effect of mesenchymal stem cells derived from adipose tissue (ADSC) on the viability of limbal epithelial stem cells (LESC). The paracrine effect was assessed by treating LESC with conditioned medium collected from ADSC culture. Cell viability, cytotoxicity, apoptosis and proliferation were evaluated using in vitro assays in standard conditions and induced inflammation. After the exposure to the examined conditions, the expression of genes related to pro- and anti- inflammatory factors was evaluated and compared to the secretion of selected cytokines by ELISA test. Moreover, the changes in LESC phenotype were assessed using of phenotype microarrays. Our findings suggest that paracrine activity of ADSC on LESC promotes its proliferation and has a potential role in mitigation of the adverse impact of inflammation induced by lipopolysaccharide.

The use of acellular porcine corneal stroma xenograft (BioCorneaVet™ ) for the treatment of deep stromal and full thickness corneal defects: A retrospective study of 40 cases (2019-2021)

OBJECTIVE

To document the effectiveness and outcome of corneal grafting using acellular porcine corneal stroma (APCS) for veterinary use (BioCorneaVet^™ ) to restore corneal integrity in dogs.

METHODS

A review of medical records of patients that underwent keratoplasty with APCS graft to repair deep corneal defects, descemetoceles, and perforations between 2019 and 2021 was carried out. Only animals with intact dazzle reflex, consensual PLR before the surgery and a minimum follow-up of four weeks were considered for the study, with forty dogs (1 eye each) meeting the inclusion criteria.

RESULTS

Brachycephalic breeds were the most frequently represented, and 20 right eyes and 20 left eyes were affected with 25 perforations, 8 descemetoceles, and 9 deep stromal defects (1 eye had both perforation and descemetocele). Most of the patients had concurrent ocular diseases or had undergone previous surgery on the other eye. Two different thickness of xenograft was used (300 or 450 µm), and the diameter ranged from 3 to 10 mm. Postoperative complications included mild to severe corneal vascularization, partial dehiscence, melting, and glaucoma. Follow-up time ranged from 28 to 797 days (mean: 233 days). Ocular integrity was maintained in 37/40 cases (92.5%), and vision was preserved in 36 cases (90%).

CONCLUSION

The use of APCS (BioCorneaVet^™ ) is an effective surgical treatment for deep stromal defects, descemetocele, and perforations in dogs, providing a good tectonic support and preserving anatomical integrity and vision. The cosmetic appearance was considered good in all the cases and continued to improve with time.

Association of Federal Regulations in the United States and Canada With Potential Corneal Donation by Men Who Have Sex With Men

Question

Regarding federal policy in the United States that prohibits corneal donation by men who have had sex with another man (MSM) in the preceding 5 years (or 12 months in Canada), what is the association of these policies with the supply of donated corneas?

Findings

These policies were associated with the disqualification of an estimated 1558 to 3217 corneal donations by otherwise eligible MSM donors in the United States and Canada in 2018.

Meaning

With reliable modern HIV testing and with many countries experiencing severe corneal shortages, these federal policies may be decreasing the availability of vision-restoring surgery, suggesting these policies should be reevaluated in light of current scientific evidence.

Importance

Federal policy in the United States prohibits corneal donation by men who have had sex with another man (MSM) in the preceding 5 years, whereas Canada enforces a 12-month ban. The potential consequences of these policies on corneal donations should be evaluated.

Objective

To estimate the number of potential corneal donations associated with MSM deferral policies in the United States and Canada.

Design, Setting, and Participants

A nonvalidated telephone survey study was conducted of all 65 eye banks in the United States and Canada to investigate how many potential corneal donors were disqualified in 2018 because of federal MSM restrictions. Published demographic data were also used to arrive at a separate estimate. Survey data were gathered from May 2019 to February 2020.

Main Outcomes and Measures

Eye banks were asked if they keep records of referrals disqualified specifically because of the federal MSM restrictions and, if so, how many referrals they disqualified in 2018 owing to MSM status.

Results

Fifty-four of 65 eye banks (83%) responded to the survey, with 30 eye banks reporting they do not keep specific records of MSM deferrals. The remaining 24 eye banks reported disqualifying 360 referrals in 2018 because of MSM status, equating to 720 corneas. The 24 eye banks accounted for 46.2% of corneal donations in the United States and Canada in 2018, yielding an estimate of approximately 1558 corneas rejected that year because of MSM status. A separate estimate using published MSM demographic data indicates that up to 3217 potential corneal donations may have been disqualified in 2018 because of these federal policies.

Conclusions and Relevance

Findings suggest that between 1558 and 3217 corneal donations were disqualified in 2018 because of federal regulations prohibiting corneal donation by men who have had sex with another man in the preceding 5 years in the United States or 1 year in Canada. With modern virologic testing that is reliable within days of HIV exposure and given the global shortage of corneal tissue, these policies should be reevaluated using current scientific evidence to increase the availability of vision-restoring surgery worldwide.

Gene Expression Profile of Vascular Endothelial Growth Factors (VEGFs) and Platelet-derived Growth Factors (PDGFs) in the Normal Cornea

BACKGROUND/AIM

Angiogenic growth factors expression is not known in the normal cornea. The aim was to study corneal gene expression profile of VEGF and PDGF pathways influencing the avascular state of cornea.

MATERIALS AND METHODS

cDNA synthesis was performed from mRNA extracted from five fresh pig corneas followed by cDNA synthesis and analysis of VEGF and PDGF pathways by TaqMan Array gene expression profile.

RESULTS

Normal pig cornea lacks VEGFR2 and VEGFR3 gene expression. MK2 and AKT1 genes were significantly overexpressed (p=0.000684, p=0.050995, respectively). Six PDGF pathway genes were overexpressed: TIAM1 (p=0.047), PIK3CA (p=0.00005), IKBKG (p=0.000006), PAK4 (p=0.034), RAC1 (p=0.000006 and PTGS2, p=0.00375). PDGF A was up-regulated, but not with a statistical significance (p=0.79911), while PDGFRα was down-regulated and PDGFRβ was not expressed.

CONCLUSION

Normal cornea avascularity is given by growth factor receptors down-regulation. Rapid corneal neovascularisation is induced by activation of the main angiogenic growth factors that induce angiogenic cascade and vessel recruitment.

Ten-Year Follow-up of Lamellar Keratoplasty Treatment With Acellular Porcine Corneal Stroma: A Case Report

PURPOSE

To report a 10-year follow-up case of the first lamellar keratoplasty treatment with acellular porcine corneal stroma (APCS).

METHODS

A 62-year-old woman was diagnosed with a fungal corneal ulcer and received lamellar keratoplasty treatment with APCS in 2010. The 10-year follow-up results were evaluated by slit lamp biomicroscopy, anterior segment optical coherence tomography, in vivo confocal microscopy, and corneal biomechanics analysis.

RESULTS

The APCS graft maintained good biocompatibility and physical properties in transparency, stromal regeneration, elasticity, and deformation resistance. However, some disadvantages were observed, including a protracted course to eventual clearing, a decreased thickness, corneal depositions, sparsely distributed neural fibers, and low stiffness.

CONCLUSIONS

This case indicated that APCS remains stable over a 10-year follow-up period. APCS can serve as a functional stromal surrogate where donor human corneal tissue is unavailable.

Combined blockade of complement C5 and TLR co-receptor CD14 synergistically inhibits pig-to-human corneal xenograft induced innate inflammatory responses

Inadequate supplies of donor corneas have evoked an escalating interest in corneal xenotransplantation. However, innate immune responses contribute significantly to the mechanism of xenograft rejection. We hypothesized that complement component C5 and TLR co-receptor CD14 inhibition would inhibit porcine cornea induced innate immune responses. Therefore, we measured cytokine release in human blood, induced by three forms of corneal xenografts with or without inhibitors. Native porcine cornea (NPC) induced interleukins (IL-1β, IL-2, IL-6, IL-8, IL-1ra), chemokines (MCP-1, MIP-1α, MIP-1β) and other cytokines (TNF, G-CSF, INF-γ, FGF-basic). Decellularized (DPC) and gamma-irradiated cornea (g-DPC) elevated the release of those cytokines. C5-blockade by eculizumab inhibited all the cytokines except G-CSF when induced by NPC. However, C5-blockade failed to reduce DPC and g-DPC induced cytokines. Blockade of CD14 inhibited DPC-induced cytokines except for IL-8, MCP-1, MIP-1α, and G-CSF, while it inhibited all of them when induced by g-DPC. Combined blockade of C5 and CD14 inhibited the maximum number of cytokines regardless of the xenograft type. Finally, by using the TLR4 specific inhibitor Eritoran, we showed that TLR4 activation was the basis for the CD14 effect. Thus, blockade of C5, when combined with TLR4 inhibition, may have therapeutic potential in pig-to-human corneal xenotransplantation. STATEMENT OF SIGNIFICANCE: Bio-engineered corneal xenografts are on the verge of becoming a viable alternative to allogenic human-donor-cornea, but the host's innate immune response is still a critical barrier for graft acceptance. By overruling this barrier, limited graft availability would no longer be an issue for treating corneal diseases. We showed that the xenograft induced inflammation is initiated by the complement system and toll-like receptor activation. Intriguingly, the inflammatory response was efficiently blocked by simultaneously targeting bottleneck molecules in the complement system (C5) and the TLR co-receptor CD14 with pharmaceutical inhibitors. We postulate that a combination of C5 and CD14 inhibition could have a great therapeutic potential to overcome the immunologic barrier in pig-to-human corneal xenotransplantation.

Corneal stromal mesenchymal stem cells: reconstructing a bioactive cornea and repairing the corneal limbus and stromal microenvironment

Corneal stroma-derived mesenchymal stem cells (CS-MSCs) are mainly distributed in the anterior part of the corneal stroma near the corneal limbal stem cells (LSCs). CS-MSCs are stem cells with self-renewal and multidirectional differentiation potential. A large amount of data confirmed that CS-MSCs can be induced to differentiate into functional keratocytes in vitro, which is the motive force for maintaining corneal transparency and producing a normal corneal stroma. CS-MSCs are also an important component of the limbal microenvironment. Furthermore, they are of great significance in the reconstruction of ocular surface tissue and tissue engineering for active biocornea construction. In this paper, the localization and biological characteristics of CS-MSCs, the use of CS-MSCs to reconstruct a tissue-engineered active biocornea, and the repair of the limbal and matrix microenvironment by CS-MSCs are reviewed, and their application prospects are discussed.

Toward electron-beam sterilization of a pre-assembled Boston keratoprosthesis

PURPOSE

To evaluate the effects of electron-beam (E-beam) irradiation on the human cornea and the potential for E-beam sterilization of Boston keratoprosthesis (BK) devices when pre-assembled with a donor cornea prior to sterilization.

METHODS

Human donor corneas and corneas pre-assembled in BK devices were immersed in recombinant human serum albumin (rHSA) media and E-beam irradiated at 25 kGy. Mechanical (tensile strength and modulus, and compression modulus), chemical, optical, structural, and degradation properties of the corneal tissue after irradiation and after 6 months of preservation were evaluated.

RESULTS

The mechanical evaluation showed that E-beam irradiation enhanced the tensile and compression moduli of human donor corneas, with no impact on their tensile strength. By chemical and mechanical analysis, E-beam irradiation caused a minor degree of crosslinking between collagen fibrils. No ultrastructural changes due to E-beam irradiation were observed. E-beam irradiation slightly increased the stability of the cornea against collagenase-induced degradation and had no impact on glucose diffusion. The optical evaluation showed transparency of the cornea was maintained. E-beam irradiated corneal tissues and BK-cornea pre-assembled devices were stable for 6 months after room-temperature preservation.

CONCLUSIONS

E-beam irradiation generated no detrimental effects on the corneal tissues or BK-cornea pre-assembled devices and improved native properties of the corneal tissue, enabling prolonged preservation at room temperature. The pre-assembly of BK in a donor cornea, followed by E-beam irradiation, offers the potential for an off-the-shelf, ready to implant keratoprosthesis device.

The porcine corneal surface bacterial microbiome: A distinctive niche within the ocular surface

Purpose

The ocular surface microbiome has been described as paucibacterial. Until now, studies investigating the bacterial community associated with the ocular surface through high-throughput sequencing have focused on the conjunctiva. Conjunctival samples are thought to reflect and be representative of the microbiome residing on the ocular surface, including the cornea. Here, we hypothesized that the bacterial community associated with the corneal surface was different from those of the inferonasal and superotemporal conjunctival fornices, and from the tear film.

Methods

Both eyes from 15 healthy piglets were sampled using swabs (inferonasal fornix, superotemporal fornix, and corneal surface, n = 30 each) and Schirmer tear test strips (STT, n = 30). Negative sampling controls (swabs and STT, n = 2 each) and extraction controls (n = 4) were included. Total DNA was extracted and high-throughput sequencing targeting the 16S rRNA gene was performed. Bioinformatic analyses included multiple contamination-controlling steps.

Results

Corneal surface samples had a significantly lower number of taxa detected (P<0.01) and were compositionally different from all other sample types (Bray-Curtis dissimilarity, P<0.04). It also harbored higher levels of Proteobacteria (P<0.05), specifically Brevundimonas spp. (4.1-fold) and Paracoccus spp. (3.4-fold) than other sample types. Negative control STT strip samples yielded the highest amount of 16S rRNA gene copies across all sample types (P<0.05).

Conclusions

Our data suggests that the corneal surface provides a distinct environmental niche within the ocular surface, leading to a bacterial community compositionally different from all other sample types.

Corneal xenotransplantation: Where are we standing?

The search for alternatives to allotransplants is driven by the shortage of corneal donors and is demanding because of the limitations of the alternatives. Indeed, current progress in genetically engineered (GE) pigs, the introduction of gene-editing technology by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9, and advanced immunosuppressants have made xenotransplantation a possible option for a human trial. Porcine corneal xenotransplantation is considered applicable because the eye is regarded as an immune-privileged site. Furthermore, recent non-human primate studies have shown long-term survival of porcine xenotransplants in keratoplasty. Herein, corneal immune privilege is briefly introduced, and xenogeneic reactions are compared with allogeneic reactions in corneal transplantation. This review describes the current knowledge on special issues of xenotransplantation, xenogeneic rejection mechanisms, current immunosuppressive regimens of corneal xenotransplantation, preclinical efficacy and safety data of corneal xenotransplantation, and updates of the regulatory framework to conduct a clinical trial on corneal xenotransplantation. We also discuss barriers that might prevent xenotransplantation from becoming common practice, such as ethical dilemmas, public concerns on xenotransplantation, and the possible risk of xenozoonosis. Given that the legal definition of decellularized porcine cornea (DPC) lies somewhere between a medical device and a xenotransplant, the preclinical efficacy and clinical trial data using DPC are included. The review finally provides perspectives on the current standpoint of corneal xenotransplantation in the fields of regenerative medicine.

Corneal Stroma Regeneration: New Approach for the Treatment of Cornea Disease

Corneal grafting is one of the most common forms of human tissue transplantation. The corneal stroma is responsible for many characteristics of the cornea. For these reasons, an important volume of research has been made to replicate the corneal stroma in the laboratory to find an alternative to classical corneal transplantation techniques.There is an increasing interest today in cell therapy of the corneal stroma using induced pluripotent stem cells or mesenchymal stem cells since these cells have shown to be capable of producing new collagen within the host stroma and even to improve its transparency.The first clinical experiment on corneal stroma regeneration in advanced keratoconus cases has been reported and included. Fourteen patients were randomized and enrolled into 3 experimental groups: (1) patients underwent implantation of autologous adipose-derived adult stem cells alone, (2) patients received decellularized donor corneal stroma laminas, and (3) patients received implantation of recellularized donor laminas with adipose-derived adult stem cells. Clinical improvement was detected with all cases in their visual, pachymetric, and topographic parameters of the operated corneas.Other recent studies have used allogenic SMILE implantation lenticule corneal inlays, showing also an improvement in different visual, topographic, and keratometric parameters.In the present report, we try to summarize the available preclinical and clinical evidence about the emerging topic of corneal stroma regeneration.

Deep anterior lamellar keratoplasty with cross-linked acellular porcine corneal stroma to manage fungal keratitis

PURPOSE

To evaluate the effects of deep anterior lamellar keratoplasty (DALK) with cross-linked acellular porcine corneal stroma (APCS) and post-operative topical tacrolimus treatment in patients with fungal keratitis.

METHODS

This multicenter prospective study involved 25 cases of fungal keratitis that were treated by DALK with cross-linked APCSs and post-operative topical tacrolimus from December 2013 to November 2014 at the Wenzhou Eye Hospital and the Henan provincial Eye Hospital. Signs of post-operative inflammation, corneal reepithelialization, corneal neovascularization, and graft rejection were assessed, and best corrected visual acuity (BCVA), intraocular pressure (IOP), and APCS graft transparency were monitored for the 12-month follow-up period.

RESULTS

All 25 patients underwent DALK without Descemet's membrane perforation. Corneal epithelium recovered completely in 17 patients in the first week, and APCS grafts maintained transparency in 18 patients at 1-year follow-up. The mean BCVA significantly improved from 2.16 ± 0.32 (LogMAR) at baseline to 1.56 ± 0.70 at 1-week (P < .001), 0.95 ± 0.57 at 1-month (P < .001), and 0.70 ± 0.51 at 3-month follow-ups (P < .001). The BCVA kept stable at 6-month and 12-month follow-ups. Post-operative topical tacrolimus alleviated the ciliary injection, except in one case which acute stromal rejection occurred. One patient developed fungal reinfection and underwent penetrating keratoplasty. Graft rejection occurred in three patients. No case was noted with graft splitting, elevated IOP or tacrolimus intolerance.

CONCLUSIONS

DALK using cross-linked APCS combining topical tacrolimus treatment is safe and effective in managing fungal keratitis. It may ameliorate the shortage of corneal donation globally.

Corneal Xenotransplantation: Anterior Lamellar Keratoplasty

Corneal transplantation for the treatment of corneal blindness is challenging in many countries due to the shortage of graft procurement. Xenocorneal transplantation is an interesting alternative to explore despite immunologic rejection, which mainly involves endothelial cells. As anterior lamellar keratoplasty, when indicated, shows less immunologic reaction, we developed and describe below a pig-to-non-human-primate model of anterior lamellar corneal xenograft. This model can be used to assess the efficacy of corneas from genetically modified pigs.

Are Corneal Patients Accepting the Transplantation? The Cases of University of Gondar, Tertiary Eye Care and Training Center, Ethiopia

Background

For so long, corneal diseases have been known as one of the leading causes to blindness in the global. This blindness might be due to failure to accept the corneal transplantation. Therefore, this study aimed to determine the prevalence and the root challenges for corneal transplantation acceptance at the University of Gondar tertiary eye care and training center, Ethiopia.

Methods

An institution-based cross-sectional study was conducted among patients who had an indication for corneal transplantation at the University of Gondar tertiary eye care and training center since January 1, 2017, up to October 30, 2018. A structured questionnaire was used to collect the data and entered into Epi-Info 7 software and analyzed using SPSS version 20. Simple logistic regression was used to identify the associated factors of corneal transplantation acceptance. Associations between outcome and exposure variables were expressed by the adjusted odds ratio with a 95% confidence interval and p value <0.05.

Result

A total of 116 patients with a mean age of 51 (±21) years participated in the study. The overall acceptance level of corneal transplantation was only 38.8% (95% CI: 29.93, 47.66). Patients with poor knowledge [AOR = 2.41; 95% CI: 1.90, 6.48] and an unfavorable attitude [AOR = 6.33; 95% CI: 2.42, 16.54] were significantly associated with the acceptance of corneal transplantation.

Conclusion

The study revealed that the corneal transplantation acceptance level was very low. Hence, the government and other concerned stakeholders should give due emphasis to the awareness creation and behavior change communication strategies to increase the acceptance level of corneal transplantation.

Long-term survival of full-thickness corneal xenografts from α1,3-galactosyltransferase gene-knockout miniature pigs in non-human primates

BACKGROUND

We aimed to investigate (a) the long-term survival of corneal grafts from α1,3-galactosyltransferase gene-knockout miniature (GTKOm) pigs in non-human primates as a primary outcome and (b) the effect of anti-CD20 antibody on the survival of corneal grafts from GTKOm pigs as a secondary outcome.

METHODS

Nine rhesus macaques undergoing full-thickness corneal xenotransplantation using GTKOm pigs were systemically administered steroid, basiliximab, intravenous immunoglobulin, and tacrolimus with (CD20 group) or without (control group) anti-CD20 antibody.

RESULTS

Graft survival was significantly longer (P = .008) in the CD20 group (>375, >187, >187, >83 days) than control group (165, 91, 72, 55, 37 days). When we compared the graft survival time between older (>7- month-old) and younger (≤7-month-old) aged donor recipients, there was no significant difference. Activated B cells were lower in the CD20 group than control group (P = .026). Aqueous humor complement C3a was increased in the control group at last examination (P = .043) and was higher than that in the CD20 group (P = .014). Anti-αGal IgG/M levels were unchanged in both groups. At last examination, anti-non-Gal IgG was increased in the control group alone (P = .013).

CONCLUSIONS

The GTKOm pig corneal graft achieved long-term survival when combined with anti-CD20 antibody treatment. Inhibition of activated B cells and complement is imperative even when using GTKO pig corneas.

Application of benzonase in preparation of decellularized lamellar porcine corneal stroma for lamellar keratoplasty

This study was to develop anovel and efficient method using endonuclease (benzonase) to preparedecellularized lamellar porcine corneal stroma (DLPCS). The DLPCS was preparedfrom native lamellar porcine corneal stroma (NLPCS) and was treated with 1000 U/ml benzonase for 5hours. We conducted the following measurements and animal transplantation tocompare DLPCS and NLPCS. The residual DNA was decreased significantly from 367.13 ± 19.96 ng/mg to 15.41 ± 0.65 ng/mg after treatment of benzonase by the detection of fluorescentnucleic acid stain. The residual benzonase was also less than detection limit.There was no significant difference in light transmittance of DLPCS comparedwith NLPCS. The extracts of DLPCS did not inhibit cell proliferation of human cornealepithelial cells, mouse fibroblast (L‐929) and African green monkey kidney cell(Vero cell). The DLPCS was transplanted into the corneas of rabbit by lamellarkeratoplasty. There was no corneal melting and graft rejection been observedwithin 12 months. The images demonstrated that the repairment of corneal nervesand keratocytes of DLPCS were in indentical shape and reflection compared withnormal cornea, and no obvious inflammatory cells were observed postoperation, byin vivo confocal microscopy. We provided novel evidence that the application ofbenzonase may improve the quality of DLPCS.

Finding an Optimal Corneal Xenograft Using Comparative Analysis of Corneal Matrix Proteins Across Species

Numerous animal species have been proposed as sources of corneal tissue for obtaining decellularized xenografts. The selection of an appropriate animal model must take into consideration the differences in the composition and structure of corneal proteins between humans and other animal species in order to minimize immune response and improve outcome of the xenotransplant. Here, we compared the amino-acid sequences of 16 proteins present in the corneal stromal matrix of 14 different animal species using Basic Local Alignment Search Tool, and calculated a similarity score compared to the respective human sequence. Primary amino acid structures, isoelectric point and grand average of hydropathy (GRAVY) values of the 7 most abundant proteins (i.e. collagen α-1 (I), α-1 (VI), α-2 (I) and α-3 (VI), as well as decorin, lumican, and keratocan) were also extracted and compared to those of human. The pig had the highest similarity score (91.8%). All species showed a lower proline content compared to human. Isoelectric point of pig (7.1) was the closest to the human. Most species have higher GRAVY values compared to human except horse. Our results suggest that porcine cornea has a higher relative suitability for corneal transplantation into humans compared to other studied species.

Clinical efficacy of therapeutic keratoplasty using corneal xenografts in patients with corneal ulcers

Objective. to assess the clinical efficacy of keratoplasty using a corneal xenograft in patients with corneal ulcers of various etiologies. Methods. A total of 46 patients (49 eyes) with complicated corneal ulcers (perforated or with impending perforation) have been operated. Freeze-dried corneal xenografts have been used for keratoplasty. Results. Our results showed that postoperative period after xenogeneic keratoplasty in patients with corneal ulcers was uneventful and the transplant underwent gradual resorption. In all patients with non-infected corneal erosions, ulcers healed completely and corneal fistulas were fully closed. The implanted corneal xenograft undergoes complete resorption between 2 to 3 months. Conclusions. Given the shortages of donor material, the demonstrated efficacy of using corneal xenografts in patients with complicated corneal ulcers requiring therapeutic keratoplasty allows recommending corneal xenografts for wide use to relieve inflammation and to preserve the eye.

Anatomic Studies of the Miniature Swine Cornea

The domestic swine eye resembles the human eye both anatomically and physiologically. Xenotransplantation of the swine cornea to humans in need of full keratoplasty shows promise as a potential therapeutic strategy to restore vision in individuals with advanced corneal disease, especially those residing in developing nations. That said, we characterized the morphology of corneas from miniature swine, which are smaller in size, easier to handle, and more cost-effective compared to domestic swine. Eyes (N = 15) were harvested from miniature swine from different age groups: 1 month (N = 3), 2 month (N = 3), 4 month (N = 3), 8 month (N = 3), as well as 24 month old adult domestic swine (N = 3). They were immediately submerged in fixative and processed for histological examination at the light and transmission electron microscopic level. Gross anatomic measurements of the cornea were significantly less (P value ≤ 0.05) in miniature swine versus domestic swine. Corneal strata exhibited morphological characteristics similar to the domestic swine cornea. Adult miniature swine corneas show similar overall corneal thickness at 8 months of age versus domestic swine. Miniature swine exhibit similar corneal morphology with the domestic pig and humans, with the exception of Bowman's layer, which is absent in pigs. Therefore, miniature pigs may be a useful resource of corneal tissue for humans in need of full keratoplasty, as well as serve as a large eye model for ophthalmology residents to develop surgical skills and for development and testing of ocular therapeutic strategies that translate to humans. Anat Rec, 301:1955-1967, 2018. © 2018 Wiley Periodicals, Inc.

Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 Gene Editing Technique in Xenotransplantation

Genetically modified pigs have been considered favorable resources in xenotransplantation. Microinjection of randomly integrating transgenes into zygotes, somatic cell nuclear transfer, homologous recombination, zinc finger nucleases, transcription activator-like effector nucleases, and most recently, clustered regularly interspaced short palindromic repeats-cas9 (CRISPR/Cas9) are the techniques that have been used to generate these animals. Here, we provide an overview of the CRISPR approaches that have been used to modify genes which are vital in improving xenograft survival rate, including cytidine monophosphate-N-acetylneuraminic acid hydroxylase, B1,4N-acetylgalactosaminyltransferase, isoglobotrihexosylceramide synthase, class I MHC, von Willebrand factor, C3, and porcine endogenous retroviruses. In addition, we will mention the importance of potential candidate genes which could be targeted using CRISPR/Cas9.

Comparative efficacy of anti-CD40 antibody-mediated costimulation blockade on long-term survival of full-thickness porcine corneal grafts in nonhuman primates

Porcine corneas may be good substitutes for human corneas in donor shortage. Therefore, we evaluated the efficacy and safety of an anti-CD40 antibody-based regimen compared with an anti-CD20 antibody-based regimen on the survival of full-thickness corneas in pig-to-rhesus xenotransplant. Thirteen Chinese rhesuses underwent full-thickness corneal xenotransplant. Six were administered anti-CD40 antibody, and the others were administered anti-CD20 antibody, basiliximab, and tacrolimus. Graft survival and changes in lymphocyte, donor-specific and anti-Galα1,3Galβ1,4GlcNAc-R (αGal) antibody, and aqueous complement levels were evaluated. Treatment with the anti-CD40 antibody (>511, >422, >273, >203, >196, 41 days) and anti-CD20 antibody (>470, 297, >260, >210, >184, 134, >97 days) resulted in long-term survival of grafts. In the anti-CD20 group, the number of activated B cells was significantly lower than that in the anti-CD40 group, and the level of aqueous complements at 6 months was significantly higher than the preoperative level. There were no differences in the levels of T cells or donor-specific and anti-αGal antibodies between the 2 groups. In the anti-CD20 group, 3 primates had adverse reactions. In conclusion, both the anti-CD40 antibody- and the anti-CD20 antibody-based protocols were effective for the long-term survival of full-thickness corneal xenografts, but the anti-CD40 antibody-based treatment had fewer adverse effects.

Protocol for the first clinical trial to investigate safety and efficacy of corneal xenotransplantation in patients with corneal opacity, corneal perforation, or impending corneal perforation

BACKGROUND

Xenotransplantation using fresh porcine corneas has been suggested as a feasible alternative to overcome the shortage of human donor corneas. Successful long-term survival of grafts without evidence of xenozoonosis in clinically applicable pig-to-non-human primate corneal transplantation model has brought researchers close to human clinical trials. Accordingly, we aimed to prepare a clinical trial protocol to conduct the first corneal xenotransplantation.

METHODS

We developed the clinical trial protocol based on international consensus statement on conditions for undertaking clinical trials of corneal xenotransplantation developed by the International Xenotransplantation Society. Detailed contents of the protocol have been modified with reference to comments provided by ophthalmologists and multidisciplinary experts, including an infectionist, an organ transplantation specialist, a clinical pharmacologist, a neuropsychiatrist, a laboratory medicine doctor, and a microbiologist.

RESULTS

Two patients with bilateral legal corneal blindness (best-corrected visual acuity ≤20/200 in the better eye and ≤20/1000 in the candidate eye) or with (impending) corneal perforation will be enrolled. During the screening period, participants and their family members will have two separate deep consideration periods before signing informed consent forms. Each patient will undergo corneal xenotransplantation using fresh corneas from Seoul National University miniature pigs. Commercially available immunosuppressants will be administered and systemic infection prophylaxis will be performed according to the program schedule. After transplantation, each patient will be monitored at a specialized clinic to investigate safety up to 2 years and efficacy up to 1 year.

CONCLUSIONS

A detailed clinical trial protocol for the first corneal xenotransplantation reflecting the global guidelines is provided.

Modulation of Macrophage Phenotype, Maturation, and Graft Integration through Chondroitin Sulfate Cross-Linking to Decellularized Cornea

Decellularized corneas obtained from other species have gained intense popularity in the field of tissue engineering due to its role to serve as an alternative to the limited availability of high-quality donor tissues. However, the decellularized cornea is found to evoke an immune response inspite of the removal of the cellular contents and antigens due to the distortion of the collagen fibrils that exposes certain antigenic sites, which often lead to graft rejection. Therefore, in this study we tested the hypothesis that cross-linking the decellularized corneas with chondroitin sulfate may help in restoring the distorted conformationation changes of fibrous matrix and thus help in reducing the occurrence of graft rejection. Cross-linking of the decellularized cornea with oxidized chondroitin sulfate was validated by ATR-FTIR analysis. An in vitro immune response study involving healthy monocytes and differentiated macrophages with their surface marker analysis by pHrodo red, Lysotracker red, ER tracker, and CD63, LAMP-2 antibodies confirmed that the cross-linked decellularized matrices elicited the least immune response compared to the decellularized ones. We implanted three sets of corneal scaffolds obtained from goat, i.e., native, decellularized, and decellularized corneas conjugated with chondroitin sulfate into the rabbit stroma. Histology analysis, three months after implantation into the rabbit corneal stromal region, confirmed the restoration of the collagen fibril conformation and the migration of cells to the implanted constructs, affirming proper graft integration. Hence we conclude that the chondroitin sulfate cross-linked decellularized corneal matrix may serve as an efficient alternative to the allograft and human cadaveric corneas.

Endothelial Wound Repair of the Organ-Cultured Porcine Corneas

PURPOSE

To assess whether injured porcine endothelium of small and large corneoscleral disc differ in its reparative/regenerative capacity under various conditions of organ culture storage.

MATERIAL AND METHODS

166 paired porcine corneas were trephined to obtain tissues with diameter 12.0 mm and 17.5 mm (with area neighboring endothelial periphery). In tested discs, central endothelium was mechanically wounded. Density of live endothelial cells (LECD), percentage of dead cells (%DC), coefficient of variation and cell hexagonality were assessed in central and paracentral endothelium following 5- or 9-day incubation in medium with 2% or 10% fetal bovine serum. The parameters were assessed also in fresh and intact cultured discs. Dead endothelial cells (EC) were visualized by trypan blue, cell borders by Alizarin Red S dye. Endothelial imprints were immunoassayed for the proliferation marker Ki-67 and the nucleolar marker fibrillarin.

RESULTS

In fresh corneas, the LECD/mm² (mean ± standard deviation) were 3998.0 ± 215.4 (central area) and 3888.2 ± 363.1 (paracentral area). Only the length of storage had significant effect on wound repair. Lesion was repaired partially after 5-day and fully after 9-day cultivation. After 9-day storage in medium with 10% serum, the mean LECD detected in small discs were 2409.4 ± 881.8 (central area) and 3949.5 ± 275.5 (paracentral area) and in large discs the mean LECD were 2555.0 ± 347.0 (central area) and 4007.5 ± 261.2 (paracentral area). Ki-67 showed cell proliferation associated with healing of EC of both large and small corneas.

CONCLUSIONS

The lesions were completely repaired within 9 days of storage. Presence of the area, where stem cells appear to be located, contributes to stimulation of endothelial reparation less than serum concentration and time of culture. Both cell migration and proliferation contribute to the wound repair.

Porcine Endogenous Retrovirus (PERV) - Molecular Structure and Replication Strategy in the Context of Retroviral Infection Risk of Human Cells

The xenotransplantation of porcine tissues may help overcome the shortage of human organs for transplantation. However, there are some concerns about recipient safety because the risk of porcine endogenous retrovirus (PERV) transmission to human cells remains unknown. Although, to date, no PERV infections have been noted in vivo, the possibility of such infections has been confirmed in vitro. Better understanding of the structure and replication cycle of PERVs is a prerequisite for determining the risk of infection and planning PERV-detection strategies. This review presents the current state of knowledge about the structure and replication cycle of PERVs in the context of retroviral infection risk.

Xenotransplantation-the current status and prospects

Introduction

There is a continuing worldwide shortage of organs from deceased human donors for transplantation into patients with end-stage organ failure. Genetically engineered pigs could resolve this problem, and could also provide tissues and cells for the treatment of conditions such as diabetes, Parkinson's disease and corneal blindness.

Sources of data

The current literature has been reviewed.

Areas of agreement

The pathobiologic barriers are now largely defined. Research progress has advanced through the increasing availability of genetically engineered pigs and novel immunosuppressive agents. Life-supporting pig kidneys and islets have functioned for months or years in nonhuman primates.

Areas of controversy

The potential risk of transfer of a pig infectious microorganism to the recipient continues to be debated.

Growing points

Increased attention is being paid to selection of patients for initial clinical trials.

Areas timely for developing research

Most of the advances required to justify a clinical trial have now been met.

Biomaterials-enabled cornea regeneration in patients at high risk for rejection of donor tissue transplantation

The severe worldwide shortage of donor organs, and severe pathologies placing patients at high risk for rejecting conventional cornea transplantation, have left many corneal blind patients untreated. Following successful pre-clinical evaluation in mini-pigs, we tested a biomaterials-enabled pro-regeneration strategy to restore corneal integrity in an open-label observational study of six patients. Cell-free corneal implants comprising recombinant human collagen and phosphorylcholine were grafted by anterior lamellar keratoplasty into corneas of unilaterally blind patients diagnosed at high-risk for rejecting donor allografts. They were followed-up for a mean of 24 months. Patients with acute disease (ulceration) were relieved of pain and discomfort within 1–2 weeks post-operation. Patients with scarred or ulcerated corneas from severe infection showed better vision improvement, followed by corneas with burns. Corneas with immune or degenerative conditions transplanted for symptom relief only showed no vision improvement overall. However, grafting promoted nerve regeneration as observed by improved touch sensitivity to near normal levels in all patients tested, even for those with little/no sensitivity before treatment. Overall, three out of six patients showed significant vision improvement. Others were sufficiently stabilized to allow follow-on surgery to restore vision. Grafting outcomes in mini-pig corneas were superior to those in human subjects, emphasizing that animal models are only predictive for patients with non-severely pathological corneas; however, for establishing parameters such as stable corneal tissue and nerve regeneration, our pig model is satisfactory. While further testing is merited, we have nevertheless shown that cell-free implants are potentially safe, efficacious options for treating high-risk patients.

A biomaterial implant supports the regeneration of severely damaged corneas in patients at high risk for rejecting conventional transplantation. An international team from Canada, China, India, Sweden, Ukraine and United Kingdom used mini-pigs to confirm the safety of implanting cell-free corneas made from recombinant human collagen and a synthetic lipid, before examining the effects of implantation on human vision in seven patients. The implants were well-tolerated and led to significant vision improvement in patients with damaged corneas due to infection. Furthermore, within two weeks of surgery the implants had relieved pain. Over two years, sensitivity to touch improved, suggesting an ability to promote nerve regeneration. This study supports the use of animal models to test biomaterials designed for medical applications and describes a safe and promising option for treating patients that not treatable by conventional corneal transplantation.

Transplantation and Alternatives to Treat Autoimmune Diseases

Transplantation is considered as one of the methods for the treatment of autoimmune diseases. There are different sorts of transplantation which improved the situation for the cure of different kinds of autoimmune diseases. Cord blood transplantation is favored over other transplant techniques. The propelled treatments incorporate interferon administrative elements and mesenchymal stromal cells for the management of immune system issue particularly in the treatment of rheumatoid joint inflammation. According to the studies conducted, it was proven that cord blood/UC mesenchymal cells along with DMARDs, without consistent organization expanded the level of administrative regulatory T-cells of the peripheral blood which might be a protected and huge technique for the treatment of patients experiencing rheumatoid joint inflammation. This review article focusses on different organ transplantation and alternative methods to treat autoimmune condition like rheumatoid arthritis. Using 3D printing and artificial intelligence are some of the recent trends that may be used for the management of autoimmune diseases.

Comprehensive evaluation of decellularized porcine corneal after clinical transplantation

Corneal disease is the second most common blinding disease in the world. The shortage of cornea donors has become the greatest challenge in curing corneal disease. Decellularized porcine corneas have the potential to be clinically applied as a substitute for human cornea in lamellar keratoplasty. Porcine corneas will help relieve the cornea donor shortage. To comprehensively evaluate the characteristics of the grafts and the effect of the decellularized porcine cornea on the host cornea after clinical transplantation, we assessed the microstructure of the transplanted decellularized porcine corneal tissues. Through the analysis of the microstructure of the tissues by H&E staining, TEM and immunofluorescence of anti-human vimentin, anti-pig vimentin,IL-1, IL-2, IL-3, IL-6, IL-8, INF-γ, and TNF-α immunofluorescence staining, we found that despite the slight rejection that occurred, the porcine cornea has good biocompatibility and can provide a scaffold for cell growth. Genetic analysis using Solexa sequencing of the samples showed that decellularized porcine corneas cannot affect genes in patients' corneas. Decellularized porcine corneas are effective biological materials for use in corneal transplantation.

Corneal blindness and current major treatment concern-graft scarcity

According to World Health Organization, the global prevalence of blindness in 2010 was 39 million people, among which 4% were due to corneal opacities. Often, the sole resort for visual restoration of patients with damaged corneas is corneal transplantation. However, despite rapid developments of surgical techniques, instrumentations and immunosuppressive agents, corneal blindness remains a prevalent global health issue. This is largely due to the scarcity of good quality corneal grafts. In this review, the causes of corneal blindness, its major treatment options, and the major contributory factors of corneal graft scarcity with potential solutions are discussed.

Long-term safety from transmission of porcine endogenous retrovirus after pig-to-non-human primate corneal transplantation

BACKGROUND

The risk of xenozoonosis mainly by porcine endogenous retrovirus (PERV) has been considered as one of the main hurdles in xenotransplantation and therefore should be elucidated prior to the clinical use of porcine corneal grafts. Accordingly, an investigation was performed to analyze the infectivity of PERVs from porcine keratocytes to human cells, and the long-term risk of transmission of PERVs was determined using pig-to-non-human primate (NHP) corneal transplantation models.

METHODS

The infectivity of PERVs from the SNU miniature pig keratocytes was investigated by coculture with a human embryonic kidney cell line. Twenty-two rhesus macaques underwent xenocorneal transplantation as follows: (i) group 1 (n=4): anterior lamellar keratoplasty (LKP) with freshly preserved porcine corneas, (ii) group 2 (n=5): anterior LKP with decellularized porcine corneas followed by penetrating keratoplasty (PKP) with allografts, (iii) group 3 (n=3): PKP under steroid-based immunosuppression, (iv) group 4 (n=4): PKP under anti-CD154 antibody-based immunosuppression, (v) group 5 (n=4): deep anterior LKP with freshly preserved porcine corneas under anti-CD40 antibody-based immunosuppression, and (vi) group 6 (n=2): PKP under anti-CD40 antibody-based immunosuppression. Postoperative blood samples were serially collected, and tissue samples were obtained from thirteen different organs at the end of each experiment. The existence of PERV DNA and RNA was investigated using PCR and RT-PCR.

RESULTS

Using two independent in vitro infectivity tests, neither PERV pol nor pig mitochondrial cytochrome oxidase II was detected after 41 and 92 days of coculture, respectively. After xenocorneal transplantation, a total of 257 serial peripheral blood mononuclear cell samples, 34 serial plasma samples, and 282 tissue samples were obtained from the NHP recipients up to 1176 days post-transplantation. No PERV transmission was evident in any samples.

CONCLUSIONS

Within the limits of this study, there is no evidence to support any risk of PERV transmission from porcine corneal tissues to NHP recipients, despite the existence of PERV-expressing cells in porcine corneas.

Expansion and cryopreservation of porcine and human corneal endothelial cells

Impairment of the corneal endothelium causes blindness that afflicts millions worldwide and constitutes the most often cited indication for corneal transplants. The scarcity of donor corneas has prompted the alternative use of tissue-engineered grafts which requires the ex vivo expansion and cryopreservation of corneal endothelial cells. The aims of this study are to culture and identify the conditions that will yield viable and functional corneal endothelial cells after cryopreservation. Previously, using human umbilical vein endothelial cells (HUVECs), we employed a systematic approach to optimize the post-thaw recovery of cells with high membrane integrity and functionality. Here, we investigated whether improved protocols for HUVECs translate to the cryopreservation of corneal endothelial cells, despite the differences in function and embryonic origin of these cell types. First, we isolated endothelial cells from pig corneas and then applied an interrupted slow cooling protocol in the presence of dimethyl sulfoxide (Me₂SO), with or without hydroxyethyl starch (HES). Next, we isolated and expanded endothelial cells from human corneas and applied the best protocol verified using porcine cells. We found that slow cooling at 1 °C/min in the presence of 5% Me₂SO and 6% HES, followed by rapid thawing after liquid nitrogen storage, yields membrane-intact cells that could form monolayers expressing the tight junction marker ZO-1 and cytoskeleton F-actin, and could form tubes in reconstituted basement membrane matrix. Thus, we show that a cryopreservation protocol optimized for HUVECs can be applied successfully to corneal endothelial cells, and this could provide a means to address the need for off-the-shelf cryopreserved cells for corneal tissue engineering and regenerative medicine.

Anti-CD40 antibody-mediated costimulation blockade promotes long-term survival of deep-lamellar porcine corneal grafts in non-human primates

BACKGROUND

Corneal xenotransplantation is an effective solution for the shortage of human donor corneas, and the porcine cornea may be a suitable candidate for the donor cornea because of its optical similarity with humans. However, it is necessary to administer additional immunosuppressants to overcome antigenic differences. We aimed to investigate the feasibility of porcine corneas with anti-CD40 antibody-mediated costimulation blockade in a clinically applicable pig-to-non-human primate corneal xenotransplantation model.

METHODS

Five Chinese rhesus macaques underwent deep-lamellar corneal transplantation using clinically acceptable sized (7.5 mm diameter) porcine corneal grafts. The anti-CD40 antibody was intravenously administered on a programmed schedule. Graft survival, central corneal thickness, and intraocular pressure were evaluated. Changes in effector and memory T and B cell subsets and anti-αGal and donor-specific antibodies were investigated in the blood, and the changes in complement levels in the aqueous humor and blood were evaluated. Memory cell profiles in the anti-CD40 antibody-treated group were compared with those from the anti-CD154 antibody-treated group or rejected controls presented in our previous report. The changes in anti-αGal, non-αGal, and donor-specific antibodies after 6 months were compared with baseline values.

RESULTS

Anti-CD40 antibody-mediated costimulation blockade resulted in the successful survival of xenocorneal grafts (>389, >382, >236, >201, and >61 days), with 80% reaching 6 months of survival. Injection of anti-CD40 antibody considerably reduced the infiltration of inflammatory cells into the grafts and significantly blocked the complement response in the aqueous humor (P=.0159, Mann-Whitney U test). Systemic expansion of central or effector memory T cells was abrogated in the anti-CD40 antibody-treated primates compared with those in the rejected controls (P<.05, Mann-Whitney U test) or those in the anti-CD154 antibody-treated primates (P>.05, Mann-Whitney U test). The levels of anti-αGal, non-αGal, and donor-specific antibodies at 6 months were not significantly increased compared with baseline levels (P>.05, Wilcoxon signed rank test).

CONCLUSIONS

An anti-CD40 antibody-mediated blockade appears to be effective immunosuppressive approach for porcine corneal deep-lamellar xenotransplantation in primates.

The potentiating effect of hTFPI in the presence of hCD47 reduces the cytotoxicity of human macrophages

BACKGROUND

In pig-to-human xenotransplantation, hyperacute rejection of pig organs could be overcome by the production of α1,3-galactosyltransferase knockout pigs. However, macrophage-mediated acute rejection is another obstacle that needs to be overcome. Among the various candidate genes involved in acute rejection, CD47 inhibits monocyte/macrophage-mediated phagocytosis by identifying the CD47 signal regulatory protein alpha (SIRP-α) as self/non-self. Tissue factor pathway inhibitor (TFPI) is involved in the regulation of the coagulation pathway and is able to bind to another ligand of CD47, thrombospondin-1 (TSP-1). When TSP-1 binds to CD47, phagocytosis in macrophages is increased.

METHODS

The 2A peptide system was used to establish pig kidney cells (PK15) simultaneously expressing human CD47 and human TFPI, and they were cultured with activated THP-1 cells. After staining with 7-aminoactinomycin D, flow cytometry analysis was carried out. TFPI siRNA analysis and recombinant human TFPI (rhTFPI) treatment were performed to determine the potentiating effect of TFPI on pig cells for activated THP-1 cells in the presence of CD47. Related inflammatory cytokines produced by activated THP-1 cells were analyzed using qPCR and Western blot technique. In addition, the tyrosine phosphorylation level of SIRP-α in activated THP-1 cells was analyzed using immunoprecipitation and Western blot.

RESULTS

hCD47/hTFPI-PK15 cells survived better than hCD47-PK15, hTFPI-PK15, or normal PK15 cells on cytotoxicity tests using activated THP-1 cells. TSP-1, derived from these activated THP-1 cells, served as a mediator for this enhancing effect, and it also played a role in activated adherent peripheral blood mononuclear cells (PBMCs). The tyrosine phosphorylation level of SIRP-α in activated THP-1 cells was further increased in the case of co-expression of CD47/TFPI than in individual non-expression or expression of CD47 or TFPI alone.

CONCLUSIONS

When hCD47 was expressed, the expression of hTFPI leaded to tyrosine phosphorylation of SIRP-α in activated THP-1 cells via hTSP-1 inhibition, and consequently, it might improve the effect of hCD47-SIRP-a signaling.

Development of retrocorneal membrane following pig-to-monkey penetrating keratoplasty

Recent reports of long-term survival after wild-type (WT) pig-to-monkey corneal xenotransplantation are encouraging. We experienced the rapid development of retrocorneal membranes, a rare complication after corneal allotransplantation (although seen in infants and young children). The original specific aim of the study was to determine the factors associated with successful (young) pig corneal transplantation in monkeys. However, when it was obvious that retrocorneal membranes rapidly developed, our aims became to determine the factors involved in its development after both WT and Genetically engineered (GE ) pig corneal xenotransplantation and to investigate the characteristics of the retrocorneal membrane. Rhesus monkeys were recipients of penetrating keratoplasty using WT and GE pigs (n=2, respectively, 1-3 months old). Local/systemic steroids were administered for 3 months. Grafts were evaluated by slit lamp for corneal transparency, edema, and neovascularization. Hematoxylin and eosin, Masson trichrome staining, and immunohistochemical analysis were performed. Gal staining was also carried out to distinguish the origin of the membrane. All penetrating keratoplasty recipients developed fibrous retrocorneal membranes in the early post-transplantation period, regardless of whether the graft was from a WT or GE pig. There were no features of rejection, with no cell infiltrate in the graft or anterior chamber during the three-month follow-up. There was no difference in the clinical course between the two groups (WT or GE corneas). Immunohistochemistry indicated that the retrocorneal membranes were CK negative, α-SMA positive, and vimentin positive, suggesting that they were of fibrous (keratocytic) origin. Also, the membrane was Gal positive, suggesting that it is derived from pig cornea. Following pig-to-monkey corneal xenotransplantation, we report that retrocorneal membranes are derived from donor pig keratocytes. Prevention of retrocorneal membranes will be necessary to achieve successful corneal xenotransplantation.

Construction of a Corneal Stromal Equivalent with SMILE-Derived Lenticules and Fibrin Glue

The scarcity of corneal tissue to treat deep corneal defects and corneal perforations remains a challenge. Currently, small incision lenticule extraction (SMILE)-derived lenticules appear to be a promising alternative for the treatment of these conditions. However, the thickness and toughness of a single piece of lenticule are limited. To overcome these limitations, we constructed a corneal stromal equivalent with SMILE-derived lenticules and fibrin glue. In vitro cell culture revealed that the corneal stromal equivalent could provide a suitable scaffold for the survival and proliferation of corneal epithelial cells, which formed a continuous pluristratified epithelium with the expression of characteristic markers. Finally, anterior lamellar keratoplasty in rabbits demonstrated that the corneal stromal equivalent with decellularized lenticules and fibrin glue could repair the anterior region of the stroma, leading to re-epithelialization and recovery of both transparency and ultrastructural organization. Corneal neovascularization, graft degradation, and corneal rejection were not observed within 3 months. Taken together, the corneal stromal equivalent with SMILE-derived lenticules and fibrin glue appears to be a safe and effective alternative for the repair of damage to the anterior cornea, which may provide new avenues in the treatment of deep corneal defects or corneal perforations.

Photodynamic inactivation of multidrug-resistant Staphylococcus aureus by chlorin e6 and red light (λ=670nm)

Multidrug-resistant Staphylococcus aureus (MDR-SA) are a frequent cause of antibiotic treatment refractory bacterial corneal infections. Photodynamic therapy (PDT) is being discussed as a putative treatment option to cure this type of bacterial infection. Here we tested the in vitro susceptibility of a set of 12 clinically derived MDR-SA isolates with differing genetic backgrounds and antibiotic resistance profiles against photodynamic inactivation (PDI) by the porphyrin chlorin e6 (Ce6) and red light (λ=670nm). All tested clinical isolates displayed a 5-log10 reduction in viable cells by Ce6 and red light, when cells were preincubated with the photosensitizer at concentrations ≥128μM for 30min in the dark, and a subsequent irradiation with light at λ=670nm (power density: 31mW/cm(2), absorbed dose: 18,6J/cm(2)) was applied. Similarly, cells of the laboratory strain Newman required the same Ce6 pre-incubation and light dose for a 5-log10 reduction in cell viability. Inactivation of crtM in strain Newman, which interferes with pigment production in S. aureus, rendered the mutant more susceptible to this PDT procedure, indicating that the level of resistance of S. aureus to this therapy form is affected by ability of the pathogen to produce the carotenoid pigment staphyloxanthin. Incubation of freshly explanted porcine corneas with a 0.5% Ce6 gel demonstrated that the photosensitizer can diffuse into and accumulate within the stroma of the cornea in concentrations found to be sufficient to yield a 5-log10 reduction of the S. aureus cell pool in vitro. These data suggest that PDI with Ce6 and red light might be a promising new option for the treatment of MDR-SA induced corneal infections.