Immune privilege of corneal allografts

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Available Therapeutic Options for Corneal Neovascularization: A Review

Corneal neovascularization can impair vision and result in a poor quality of life. The pathogenesis involves a complex interplay of angiogenic factors, notably vascular endothelial growth factor (VEGF). This review provides a comprehensive overview of potential therapies for corneal neovascularization, covering tissue inhibitors of metalloproteinases (TIMPs), transforming growth factor beta (TGF-β) inhibitors, interleukin-1L receptor antagonist (IL-1 Ra), nitric oxide synthase (NOS) isoforms, galectin-3 inhibitors, retinal pigment epithelium-derived factor (PEDF), platelet-derived growth factor (PDGF) receptor inhibitors, and surgical treatments. Conventional treatments include anti-VEGF therapy and laser interventions, while emerging therapies such as immunosuppressive drugs (cyclosporine and rapamycin) have been explored. Losartan and decorin are potential antifibrotic agents that mitigate TGF-β-induced fibrosis. Ocular nanosystems are innovative drug-delivery platforms that facilitate the targeted release of therapeutic agents. Gene therapies, such as small interfering RNA and antisense oligonucleotides, are promising approaches for selectively inhibiting angiogenesis-related gene expression. Aganirsen is efficacious in reducing the corneal neovascularization area without significant adverse effects. These multifaceted approaches underscore the corneal neovascularization management complexity and highlight ideas for enhancing therapeutic outcomes. Furthermore, the importance of combination therapies and the need for further research to develop specific inhibitors while considering their therapeutic efficacy and potential adverse effects are discussed.

Neovascularization against autologous SLET donor grafts despite successful corneal epithelialization and graft adherence

PURPOSE

To report a case of neovascularization against autologous grafts after simple limbal epithelial transplantation (SLET) despite successful corneal epithelialization, as well as its subsequent regression without intervention.

METHODS

A case report and review of the literature.

RESULTS

A 52-year-old woman underwent uncomplicated autologous SLET for asymmetric limbal stem cell deficiency (LSCD) in the left eye. One month after the surgery, the patient had successful adherence of the graft and corneal epithelialization; however, new neovascularization developed in the left eye towards the graft sites. With only a slow taper of topical prednisolone acetate and polymyxin b/trimethoprim, the neovascularization regressed to ghost vessels over the following three months with improvement of her LSCD symptoms and increased clarity of her cornea.

CONCLUSION

The limbus does not enjoy relative immune privilege like other parts of the eye; therefore, autologous limbal stem cell transplantation (along with the minimal immune response generated) is valuable for restoration of the ocular surface. Here, we describe neovascularization against autologous donor grafts despite an otherwise uncomplicated surgery and expected epithelialization course. Inflammation-mediated angiogenesis likely initiated the neovascularization, suggesting that immune mediators of inflammation may be inadvertently part of the graft tissue in bilateral LSCD.

Clinical Applications of Anterior Segment Optical Coherence Tomography: An Updated Review

Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed.

Impaired Immunomodulatory Properties of the Retina from the Inflammatory Environment of the Damaged Eye

The retina represents a highly specialized structure with the primary function to capture a light signal and to convert it into electrical impulses. Any damage or disease of the retina can cause visual impairment. Since retinal degenerative diseases are generally associated with immune cell infiltration, a local inflammatory reaction, and cytokine burn, there is a need for mechanisms to prevent the retina from damage by a deleterious immune reaction. In this study, we show that mouse retinal explants co-cultivated with stimulated spleen cells, inhibit in a dose-dependent manner the activation of T cells, and suppress the production of cytokines interleukin-2, interleukin-10, and interferon-[Formula: see text]. The immunoregulatory properties of the retina were mainly mediated by a paracrine effect since retinal explants, separated by a semipermeable membrane, or supernatants obtained after the cultivation of retinal explants, inhibited the reactivity of immune cells. A model of retinal damage was established by the application of sodium iodate which selectively destroys photoreceptors, as it was demonstrated by a decrease in the number of rhodopsin-positive cells. This process was accompanied by increased infiltration of the retina with cells of the immune system and by a local inflammatory reaction. The pharmacologically damaged retina had significantly decreased the ability to inhibit T cell activation and production of cytokines by immune cells. Overall, the results showed that the retina possesses immunoregulatory properties and inhibits the activation and functions of T cells. However, the immunomodulatory properties of the retina are decreased if the retina is damaged.

Amplified Natural Killer Cell Activity and Attenuated Regulatory T-cell Function Are Determinants for Corneal Alloimmunity in Very Young Mice

BACKGROUND

Corneal transplantation outcomes are generally less favorable in young children compared with adults. The purpose of this study was to determine the immunological mechanisms underlying this difference.

METHODS

A murine model of allogeneic corneal transplantation was used in the study, and graft survival was determined by evaluating opacity scores for 8 wk. Syngeneic transplantation in the very young host served as a surgical control. The frequencies of total and activated natural killer (NK) cells in cornea posttransplantation were kinetically evaluated using flow cytometry. The regulatory T cell (Treg) frequency and function in naive animals were assessed by flow cytometry and in vitro suppression assays, respectively. Finally, graft survival and immune responses were determined in NK cell-depleted, or adult naive Treg-transferred, young hosts.

RESULTS

Corneal allograft survival in the very young recipients was significantly lower than in adult hosts. The frequencies of total NK cells and their interferon gamma-expressing subset in the cornea were significantly higher in the very young mice posttransplantation. In ungrafted mice, frequencies of Treg in draining lymph nodes as well as their capabilities to suppress NK-cell secretion of interferon gamma were lower in the very young compared with adults. In NK cell-depleted or adult Treg--transferred very young recipients, the allograft survival was significantly improved along with the suppressed NK-cell response.

CONCLUSIONS

Our data demonstrate that amplified activity of NK cells, together with lower suppressive function of Treg, contributes to early rejection of corneal allografts in very young graft recipients.

Quiescent innate and adaptive immune responses maintain the long-term integrity of corneal endothelium reconstituted through allogeneic cell injection therapy

This study aims to clarify the immunogenicity in acquired and innate immune responses of cultured human corneal endothelial cells (hCECs) applied for cell injection therapy, a newly established modality for corneal endothelium failures. Thirty-four patients with corneal endothelial failure received injection of allogeneic hCEC suspension into anterior chamber. No sign of immunological rejection was observed in all 34 patients during the 5-8 years postoperative follow-up period. Cell injection therapy was successful in 2 patients treated for endothelial failure after penetrating keratoplasty and one patient with Descemet membrane stripping automated endothelial keratoplasty failure. ELISPOT assays performed in allo-mixed lymphocyte reaction to the alloantigen identical to that on the injected hCECs, elicited sparse IFN-γ-specific spots in the peripheral blood mononuclear cells of patients who received hCEC injection. The therapy generated simple and smooth graft-host junctions without wound stress. The injection of C57BL/6 CECs into the anterior chamber of BALB/c mice, which rejected C57BL/6 corneas 6 weeks ago, induced no sign of inflammatory reactions after the second challenge of alloantigen. Collectively, injection of the hCEC cell suspension in the aqueous humor induces immune tolerance that contributes to the survival of the reconstituted endothelium.

Keratoplasty rejection after messenger RNA vaccine (BNT162b2) for COVID-19

This report shows a case of corneal transplant rejection after vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), short after receiving the BNT162b2 vaccine, in a patient who had undergone keratoplasty more than 20 years ago, with no previous episodes of rejection and no other factor that could lead to the findings on his examinations. After treatment with high doses of topic, oral, and sub-conjunctival corticoids, the patient had a favorable therapeutic response. The signs of corneal transplant rejection must be oriented to the patients and the causing factors actively searched by ophthalmologists so that treatment is rapidly initiated and sequels are avoided. This report raises the question if these events are correlated and whether the patient should receive the second dose of the vaccine against SARS-CoV-2 or not.

Transcriptomic Profiling of Human Limbus-Derived Stromal/Mesenchymal Stem Cells-Novel Mechanistic Insights into the Pathways Involved in Corneal Wound Healing

Limbus-derived stromal/mesenchymal stem cells (LMSCs) are vital for corneal homeostasis and wound healing. However, despite multiple pre-clinical and clinical studies reporting the potency of LMSCs in avoiding inflammation and scarring during corneal wound healing, the molecular basis for the ability of LMSCs remains unknown. This study aimed to uncover the factors and pathways involved in LMSC-mediated corneal wound healing by employing RNA-Sequencing (RNA-Seq) in human LMSCs for the first time. We characterized the cultured LMSCs at the stages of initiation (LMSC−P0) and pure population (LMSC−P3) and subjected them to RNA-Seq to identify the differentially expressed genes (DEGs) in comparison to native limbus and cornea, and scleral tissues. Of the 28,000 genes detected, 7800 DEGs were subjected to pathway-specific enrichment Gene Ontology (GO) analysis. These DEGs were involved in Wnt, TGF-β signaling pathways, and 16 other biological processes, including apoptosis, cell motility, tissue remodeling, and stem cell maintenance, etc. Two hundred fifty-four genes were related to wound healing pathways. COL5A1 (11.81 ± 0.48) and TIMP1 (20.44 ± 0.94) genes were exclusively up-regulated in LMSC−P3. Our findings provide new insights involved in LMSC-mediated corneal wound healing.

Lentivirus-mediated PD-L1 overexpression in bone marrow-derived dendritic cells induces immune tolerance in a rat keratoplasty model

PURPOSE

The side effects of immune suppressants on immune rejection have become increasingly apparent after keratoplasty. To find out new alternative immunotherapy strategies, we studied the role of programmed death-1 (PD-1) and its ligand (PD-L1) co-stimulatory pathway in inducing immune tolerance of rat keratoplasty.

METHODS

The PD-L1 protein was constitutively overexpressed via lentiviral transduction in bone marrow-derived dendritic cells (BMDCs) from rats, then infused via the tail vein into rats before undergoing keratoplasty. Western blot analysis of PD-L1 protein confirmed the effectiveness of lentivirus-mediated. The phenotype of immature BMDC was confirmed by flow cytometry analysis with CD80, CD86, CD11c and MHC-II antibodies. To investigate the mechanism of the immune tolerance induced by BMDCs transfusion, PD-L1, IFN-γ and IL-17 in serum and cell culture supernatant were assessed by ELISA and qPCR.

RESULTS

After LPS stimulation, immature dendritic cells with over-expression of PD-L1 still showed high expression of PD-L1(p < 0.001), and low expression of IL-17 and IFN-γ (p < 0.001), which reduced neovascularization (p < 0.05), and prolonged the survival after corneal implants.

CONCLUSION

Immature DC cells with overexpression of PD-L1 have low ability to activate T cells，which is a potential treatment for avoiding graft rejection by promoting natural immunosuppression. This cellular treatment is expected to reduce the use of immune suppressants and the occurrence of side effects.

Presence of Panel-reactive Antibodies after Penetrating Keratoplasty

PURPOSE

To evaluate the relationship between penetrating keratoplasty (PK) and postoperative PRA level and number of unacceptable antigens.

METHODS

A cross-sectionalstudy was performed on patients with history of PK. Patients with prior solid organ transplantation, pregnancy, or blood transfusion were excluded. These findings were combined with a retrospective review. Patients were grouped by single or multiple PKs. The primary outcome was postoperative PRA level.

RESULTS

Incidence of postoperative PRA elevation and mean peak PRA was higher in the multiple PK group (p = .08 and p = .010, respectively). Mean number of unacceptable antigens was elevated in the multiple PK group (p = .024). There was a moderately positive correlation between number of PK grafts and PRA level (r = 0.629, p = .0002).

CONCLUSIONS

PRA level may be influenced by PKs, with higher PRA associated with increased prior PKs. Further studies are necessary to determine the potential prognostic value.Abbreviations: PK: penetrating keratoplasty; PRA: panel reactive antibodies; OSST: ocular surface stem cell transplantation; LSCD: limbal stem cell deficiency.

Survey of Corneal Surgeons' Attitudes Regarding Keratoplasty Rejection Risk Associated With Vaccinations

PURPOSE

To investigate the attitudes and practice of corneal specialists if patients with keratoplasty sought advice regarding common vaccinations and risk for potential graft rejection.

METHODS

An online questionnaire was posted on the Kera-net listserv and the EuCornea Web site in early 2020. Attitudes toward vaccinations and keratoplasty were obtained. Decision making for common keratoplasty (endothelial keratoplasty, deep anterior lamellar keratoplasty, and penetrating keratoplasty) scenarios at early and late time points was explored regarding the herpes zoster and influenza vaccines.

RESULTS

There were 142 respondents: 51.1% (70/137) specifically advise their patients with keratoplasty to get all vaccinations; 19.7% (27/137) stated clinical experience of a vaccine-associated rejection episode; 42.2% (57/135) were unaware of any such cases; and 64% (27/42) of those concerned would recommend delay if within 3 months of transplant surgery, recent corneal infection, or a recent rejection episode. The 2245 total responses to 18 clinical scenarios demonstrated wide variability in management of grafts in the setting of vaccination. Generally, 45.9% would not alter management, 26.2% would increase frequency of topical steroids, and 22.2% would recommend delay to vaccinations. Increased concern was expressed with recent surgery, live zoster vaccine and higher-risk penetrating keratoplasty scenarios.

CONCLUSIONS

Nearly half of the respondents do not alter management in the setting of keratoplasty and zoster and/or influenza vaccinations. Anecdotal rejection episodes possibly associated with vaccinations were reported by some. Vaccine-related rejection has not been shown in higher-level research, but that has not eliminated clinical concerns. Prospective research into the true vaccine-related risks in keratoplasty is necessary if evidence-based management guidelines are to be developed or definitive reassurance provided.

Evaluation of serum neutrophil-to-lymphocyte ratio in corneal graft rejection after low-risk penetrating keratoplasty

PURPOSE

To evaluate systemic inflammatory parameters in patients with corneal graft rejection after low-risk penetrating keratoplasty.

METHODS

Patients undergoing penetrating keratoplasty with indications of keratoconus, pseudophakic bullous keratopathy, and Fuchs endothelial dystrophy were analyzed retrospectively. Patients who had an endothelial rejection attack within two years post-transplant were included in the rejection group (n = 20), whereas patients with at least two years of post-transplant follow-up without graft rejection or failure were included in the control group (n = 46). All patients' clinical features and preoperative laboratory parameters were obtained from hospital records. The neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio, and platelet-to-lymphocyte ratio of the groups were calculated and compared.

RESULTS

There was no difference between the two groups in terms of age, sex, indication, postmortem time and storage time of grafts, graft diameter, follow-up time, and common systemic diseases (p > 0.05). The NLR was found to be significantly lower in the rejection group when compared with the control group (2.04 ± 1.17, 2.66 ± 0.91, respectively, p = 0.023). There was no significant difference between the groups in terms of MLR and PLR (p = 0.243, p = 0.101, respectively).

CONCLUSIONS

Although a high NLR value, which is an indicator of systemic inflammatory condition, is associated with many ocular diseases, NLR was found to be lower in patients with a rejection episode after transplant surgery when compared with the control group. Further studies are needed to clarify the role of these hematologic parameters in graft rejection.

Characteristics of endothelial corneal transplant rejection following immunisation with SARS-CoV-2 messenger RNA vaccine

AIM

We report two cases of endothelial corneal allograft rejection following immunisation with SARS-CoV-2 messenger RNA (mRNA) vaccine BNT162b2 and describe the implications for management of transplant recipients postvaccination for COVID-19.

METHODS

A 66-year-old woman with Fuchs endothelial corneal dystrophy (FECD) and a unilateral Descemet's membrane endothelial keratoplasty (DMEK) transplant received COVID-19 mRNA vaccine BNT162b2 14 days post-transplant. Seven days later, she presented with symptoms and signs of endothelial graft rejection. An 83-year-old woman with bilateral DMEK transplants for FECD 3 and 6 years earlier developed simultaneous acute endothelial rejection in both eyes, 3 weeks post second dose of COVID-19 mRNA vaccine BNT162b2. Rejection in both cases was treated successfully with topical corticosteroids.

CONCLUSIONS

We believe this is the first report of temporal association between corneal transplant rejection following immunisation against COVID-19 and the first report of DMEK rejection following any immunisation. We hypothesise that the allogeneic response may have been initiated by the host antibody response following vaccination. Clinicians and patients should be aware of the potential of corneal graft rejection associated with vaccine administration and may wish to consider vaccination in advance of planned non-urgent keratoplasties. Patients should be counselled on the symptoms and signs that require urgent review to allow early treatment of any confirmed rejection episode.

"Corneal Nerves, CD11c+ Dendritic Cells and Their Impact on Ocular Immune Privilege"

The eye and the brain have limited capacities for regeneration and as such, immune-mediated inflammation can produce devastating consequences in the form of neurodegenerative diseases of the central nervous system or blindness as a result of ocular inflammatory diseases such as uveitis. Accordingly, both the eye and the brain are designed to limit immune responses and inflammation – a condition known as “immune privilege”. Immune privilege is sustained by physiological, anatomical, and regulatory processes that conspire to restrict both adaptive and innate immune responses.

Keratoplasty for Keratoconus in Young Patients: Demographics, Clinical Features, and Post-transplant Outcomes

PURPOSE

To examine pretransplant findings and outcomes of corneal transplants for keratoconus in children.

DESIGN

Retrospective cohort (national registry) study.

METHODS

Data on all patients aged 16 or younger (n = 170) who had a first transplant for keratoconus between 2003 and 2018 in all corneal transplant centers in the UK were compared to adult patients aged 17 and older (n = 7,191). The influence of demographic variables, pretransplant corneal findings, and transplant type on 2-year visual, rejection-free, and transplant survival outcomes was examined.

RESULTS

Children had poorer pretransplant visual acuity and higher rates of corneal vascularization and ocular surface disease than adults. However, 2-year post-transplant corrected visual acuity reached 20/20 or better in 35% of children compared to 28% of adults (P = .1). Transplant rejection and failure rates were 11% (P = .79) and 3% (P = .31), respectively, for children, which were comparable to rates for adults. Endothelial rejection was reported following penetrating keratoplasty (PK) in 13% of children (10% in adults). Irreversible rejection was not recorded for any transplant in a child. Despite a lack of difference in transplant outcomes, there was a significant age effect in the Cox regression model for transplant rejection, such that for every 5-year increase in age there was a 6% reduction in the hazard of rejection. Transplant survival following anterior lamellar keratoplasty and PK in children was similar.

CONCLUSIONS

Young keratoconus patients have excellent transplant outcomes and visual results comparable to adults. Overall, the hazard of rejection was found to decrease with advancing age. However, in this large cohort of young patients with keratoconus and poor vision, there is no evidence of outcome advantage in delaying transplant until adult years.

Effectiveness of matching human leukocyte antigens (HLA) in corneal transplantation: a systematic review protocol

BACKGROUND

Corneal transplantation is the most frequently performed transplantation in the UK. Despite this, the therapeutic value of matching human leukocyte antigen (HLA) subtypes for transplanted corneas remains controversial. Ocular immune privilege was originally deemed to render matching unnecessary; however, more recently, matching has demonstrated improved outcomes including graft success, amongst others. This systematic review aims to evaluate the effectiveness of major and minor antigen matching on graft outcomes in corneal transplantation.

METHODS

Standard systematic review methodology will be used to identify, select and extract data from observational studies and clinical trials assessing the effects of HLA matching on corneal graft outcomes. Bibliographic databases (Cochrane Library, EMBASE, MEDLINE, Web of Science, Scopus), clinical trial registers, abstract and conference proceedings, in addition to dissertation, thesis and grey literature will be searched. Neither date of publication nor language will be restricted, and non-English articles will be translated where necessary. The primary outcome will be to assess corneal graft success for different degrees of HLA matching/mismatching. The precise end outcome measure varies amongst studies and includes graft rejection, immunoreaction, failure and survival. Therefore, data will be extracted across all relevant outcome parameters and grouped for subsequent statistical tests. Risk of bias assessment will be completed, appropriate to each study design. Study selection, data extraction and risk of bias assessment will be independently completed by two reviewers. Data will be tabulated, and a narrative synthesis presented. Meta-analysis will be performed where there is sufficient homogeneity between studies to warrant its effective completion. Subgroup and sensitivity analysis will be undertaken if appropriate.

DISCUSSION

Many studies have investigated the effectiveness of HLA matching for corneal transplantation. A systematic review is needed to collate and analyse this evidence. Findings of this systematic review may form the basis of evidence-based recommendations on pre-operative HLA typing and matching of corneal grafts for transplantation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO reference CRD42020198882.

Age-related changes in ocular mucosal tolerance: Lessons learned from gut and respiratory tract immunity

The ocular surface is the part of the visual system directly exposed to the environment, and it comprises the cornea, the first refractive tissue layer and its surrounding structures. The ocular surface has evolved to keep the cornea smooth and wet, a prerequisite for proper sight, and also protected. To this aim, the ocular surface is a bona fide mucosal niche with an immune system capable of fighting against dangerous pathogens. However, due to the potential harmful effects of uncontrolled inflammation, the ocular surface has several mechanisms to keep the immune response in check. Specifically, the ocular surface is maintained inflammation-free and functional by a particular form of peripheral tolerance known as mucosal tolerance, markedly different from the immune privilege of intraocular structures. Remarkably, conjunctival tolerance is akin to the oral and respiratory tolerance mechanisms found in the gut and airways, respectively. And also similarly, this form of immunoregulation in the eye is affected by ageing just as it is in the digestive and respiratory tracts. With ageing comes an increased prevalence of immune-based ocular surface disorders, which could be related to an age-related impairment of conjunctival tolerance. The purpose of this review was to summarize the present knowledge of ocular mucosal tolerance and how it is affected by the ageing process in the light of the current literature on mucosal immunoregulation of the gut and airways.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

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.

Gender medicine in corneal transplantation: influence of sex mismatch on rejection episodes and graft survival in a prospective cohort of patients

To evaluate the effect of donor-to-recipient sex mismatched (male donor corneas to female recipients) on the incidence of rejection episodes and failures up to 1 year after corneal transplantation. Prospective observational cohort study, with donor corneas randomly assigned and surgeons blind to the sex of donor. A unique eye bank retrieved and selected the donor corneas transplanted in 4 ophthalmic units in patients with clinical indication for primary or repeated keratoplasty for optical reasons, perforating or lamellar, either anterior or posterior. Rejection episode defined as any reversible or irreversible endothelial, epithelial or stromal sign, with or without development of corneal edema, and graft failure as a permanently cloudy graft or a regraft for any reason detected or acknowledged during a postoperative ophthalmic visit at any time up to 1 year after surgery were recorded.156 (28.6%) patients resulted donor-to-recipient gender mismatched for H-Y antigen (male donor to female recipient). During the 12 months follow-up, 83 (14.7%, 95% CI 12.0-17.9) grafts showed at least 1 rejection episode and 17 (3.2%, 95% CI 2.0-5.0) failed after immune rejection, among 54 (9.6%, 95% CI 7.4-12.3) grafts failed for all causes. No significant differences between matched and mismatched patients were found for cumulative incidence of both rejection episodes (15.2% and 13.5%) and graft failures following rejection (3.2% and 2.6%), respectively. Multivariable analyses showed that H-Y matching either is not a predictive factor for rejection or graft failure nor seems to influence incidence of failures on respect to patient's risk category. The lack of influence of donor-to-recipient mismatched on the rate of rejections and graft failures resulting from this study do not support the adoption of donor-recipient matching in the allocation of corneas for transplantation.

Galectins as Regulators of Corneal Inflammation

The cornea is a transparent avascular tissue on the anterior segment of the eye responsible for providing refractive power and forming a protective barrier against the external environment. Infectious and inflammatory conditions can compromise the structure of the cornea, leading to visual impairment and blindness. Galectins are a group of β-galactoside-binding proteins expressed by immune and non-immune cells that play pivotal roles in innate and adaptive immunity. In this brief review, we discuss how different members of this family of proteins affect both pro-inflammatory and anti-inflammatory responses in the cornea, particularly in the context of infection, transplantation and wound healing. We further describe recent research showing beneficial effects of galectin-targeted therapy in corneal diseases.

[Antiangiogenic therapy in high-risk keratoplasty]

PURPOSE

To analyze the effectiveness and safety of VEGF inhibitor used to improve keratoconus transplant survival in patients with corneal neovascularization as stand-alone and in combination with laser coagulation of ingrowing vessels before keratoplasty.

MATERIAL AND METHODS

The study included 56 patients (56 eyes) with corneal opacifications of various etiology complicated by corneal neovascularization (CNV). The patients were divided into three groups. The 1st group included 27 patients with diffuse CNV who were undergoing an antiangiogenic therapy using anti-VEGF drug, the 2nd group - 14 patients with stem cell CNV who underwent laser coagulation of major corneal vessels combined with subconjunctival administration of drug before keratoplasty; the control group consisted of 15 patients with mixed type CNV who were undergoing conventional treatment without antiangiogenic therapy.

RESULTS

During the follow-up (24.5±4.84 months, 4 to 25 months), transplant rejection reaction was recorded in 7 (23%) patients of the 1^st group, 5 (35%) patients of the 2^nd group and 9 (60%) patients of the control group.

CONCLUSION

Subconjunctival administration of Aflibercept as a stand-alone measure and in combination with laser coagulation of ingrowing vessels may increase the chances of transparent transplant acceptance in high-risk keratoplasty.

Corneal Stem Cells as a Source of Regenerative Cell-Based Therapy

In the past few years, intensive research has focused on corneal stem cells as an unlimited source for cell-based therapy in regenerative ophthalmology. Today, it is known that the cornea has at least two types of stem cells: limbal epithelial stem cells (LESCs) and corneal stromal stem cells (CSSCs). LESCs are used for regeneration of corneal surface, while CSSCs are used for regeneration of corneal stroma. Until now, various approaches and methods for isolation of LESCs and CSSCs and their successful transplantation have been described and tested in several preclinical studies and clinical trials. This review describes in detail phenotypic characteristics of LESCs and CSSCs and discusses their therapeutic potential in corneal regeneration. Since efficient and safe corneal stem cell-based therapy is still a challenging issue that requires continuous cooperation between researchers, clinicians, and patients, this review addresses the important limitations and suggests possible strategies for improvement of corneal stem cell-based therapy.

Microporous Drug Delivery System for Sustained Anti-VEGF Delivery to the Eye

Purpose

To describe a novel microporous drug delivery system (DDS) for sustained anti- vascular endothelial growth factor (VEGF) delivery to the eye and to evaluate its efficacy in a corneal injury model.

Methods

A macro-porous DDS (1.5 × 1.5 × 4 mm) loaded with 2 mg of bevacizumab was implanted subconjunctivally in three Dutch-belted pigmented rabbits after corneal alkali injury (2N NaOH). Three rabbits received sham DDS. Animals were followed for three months and assessed in vivo and ex vivo for corneal neovascularization (NV), epithelial defect, stromal scarring, endothelial cell loss, and expression of angiogenic and inflammatory markers in the cornea and retina.

Results

Anti-VEGF DDS treatment led to complete inhibition of superior cornea NV and complete corneal re-epithelialization by day 58 whereas sham DDS resulted in severe cornea NV and persistent epithelial defect (9%∼12% of total cornea area) through the end of the study. Histologically, anti-VEGF DDS significantly reduced CD45⁺ and F4/80 CD11b⁺ cell accumulation (79%, P < 0.05) in the cornea, ameliorated tumor necrosis factor–α expression (90%, P < 0.05), reduced corneal stromal scarring and prevented corneal endothelial cell loss, as compared to sham DDS. Moreover, anti-VEGF DDS achieved retinal penetration and reduction in retinal VEGF levels at 3 months.

Conclusions

Use of subconjunctival anti-VEGF DDS suppresses cornea NV, inflammation, stromal scarring, prevents endothelial cell loss, and abrogates retinal VEGF upregulation in a rabbit corneal alkali burn model. Moreover, it delivers anti-VEGF antibodies to the retina for three months. This delivery platform could enable antibody therapy of other corneal and retinal vascular pathologies.

Translational Relevance

We describe a method for sustained anti-VEGF delivery to the eye for the treatment of ocular injuries.

Combined specular microscopy and Scheimpflug imaging to improve detection of an upcoming allograft rejection after DMEK

PURPOSE

To assess whether combined analysis of specular microscopy and Scheimpflug imaging improves detection of an upcoming allograft rejection following Descemet membrane endothelial keratoplasty (DMEK).

METHODS

Retrospective analysis of 22 eyes that had developed a clinical proven allograft rejection 28 (±22) months (range: 4-84 months) after DMEK. Specular microscopy and Scheimpflug images routinely made after DMEK were retrospectively analysed for changes in endothelial cell morphology (e.g. nuclear activation), cell density (>10%) and pachymetry (>7%), and/or the presence of subclinical keratic precipitates. The same parameters were evaluated for 22 control eyes matched for age, gender and surgery indication.

RESULTS

A total of 20/22 eyes (91%) showed detectable changes 0.25-75 months before allograft rejection became clinically manifest: 13/22 (59%) showed both specular microscopy and Scheimpflug imaging changes; 5/22 (23%) only had changes on Scheimpflug imaging; and 2/22 (9%) only had specular microscopy changes. In 18/22 (82%) and 14/22 (64%) eyes, subclinical keratic precipitates and endothelial cell morphology changes could be detected, respectively. A total of 11/22 (50%) eyes concurrently showed a >10% drop in endothelial cell density and 4/22 (18%) a >7% pachymetry increase. Of the control eyes, 7/22 (32%) showed changes with specular microscopy but not with Scheimpflug imaging.

CONCLUSIONS

Combined analysis of specular microscopy and Scheimpflug imaging may allow recognizing an upcoming allograft rejection in over 90% of eyes and up to 6 years before rejection becomes clinically manifest. Early recognition of eyes at risk may allow for targeted intensified steroid treatment to prevent endothelial cell damage associated with rejection.

Corneal Nerve Ablation Abolishes Ocular Immune Privilege by Downregulating CD103 on T Regulatory Cells

Purpose

Severing corneal nerves during orthotopic corneal transplantation elicits the elaboration of the neuropeptide substance P (SP), which induces the generation of CD11c+ contrasuppressor (CS) cells. CS cells disable T regulatory cells (Tregs) that are induced when antigens enter the anterior chamber (AC), either by direct injection or by orthotopic corneal transplantation. This study examined the crucial cell surface molecules on Tregs that are adversely affected by CS cells that are generated by severing corneal nerves.

Methods

CS cells were induced by producing shallow 2.0-mm circular incisions in the corneal epithelium in BALB/c mice. CD8+ Tregs were generated by injecting ovalbumin into the AC. The effects of CS cells and SP on the expression and function of two cell surface molecules (CD103 and the receptor of interferon-γ) that are crucial for the induction and function of CD8+ Tregs were analyzed.

Results

SP converted CD11c+, but not CD11c- , dendritic cells (DCs) to CS cells. Severing corneal nerves resulted in a 66% reduction in the expression of CD103 on CD8+ AC-associated immune deviation (ACAID) Tregs, and a 50% reduction in the interferon-γ receptor (IFN-γR). These effects could be mimicked in vitro by coculturing CS cells with CD8+ ACAID Tregs.

Conclusions

The elaboration of SP in response to corneal nerve ablation converts CD11c+ DCs to CS cells. CS cells disable CD8+ ACAID Tregs by downregulating two crucial cell surface molecules, CD103 and IFN-γR, by an SP-dependent pathway. Blocking this pathway may provide a means of restoring ocular immune privilege in corneas subjected to corneal nerve injury.

Evaluation of thrombospondin-1 gene polymorphisms in corneal allograft rejection in Asian Indian patients

Purpose:

To evaluate the frequency and the association of Thrombospondin 1 (THBS1) gene single nucleotide polymorphisms (SNPs) in Asian Indian patients with optical full thickness corneal grafting surgery.

Methods:

Prospective case–control analysis of optical penetrating keratoplasty patients with and without immune rejection and controls for genotyping of 3 THBS1 gene SNPs (rs1478604 A>G; rs2228261 C>T; rs2228262 A>G) by Amplification Refractory Mutation System-Polymerase Chain Reaction (ARMS PCR).

Results:

Among 58 patients [45 with immune allograft rejection (DNA isolation was possible in 38 samples) and 13 without immune corneal allograft rejection] and 65 controls, allele frequencies observed for rs1478604 (A>G) are A: 69.7% and 72.6%, G: 30.2% and 27.3%; for rs2228261 (C>T) are T: 70.2% and 62.3%, C: 29.7% and 37.6%; and for rs2228262 (A>G) A: 97.4% and 98.4%; G 2.5% and 1.5% respectively. Genotype frequencies were rs1478604 (A>G) AA: 57.8% and 59.3%, AG 23.6% and 26.5%; GG 18.4% and 14%; for rs2228261 (C>T) TT: 40.5% and 33.8%, TC: 59% and 56.9%, CC: 0% and 9.2%; for rs2228262 (A>G) AA: 94.8% and 96.8%, AG: 5.1% and 3.1% in rejection and controls respectively. The allele and genotype frequency for the 3 described THSB1 SNPs did not show any difference between the corneal graft immune rejection patients and controls.

Conclusion:

Asian Indian population evaluated for THBS1 gene SNPs by ARMS PCR genotyping in Asian Indian population did not show any genetic association to immune rejection occurrence in our study.

Differential effects of primary disease and corneal vascularisation on corneal transplant rejection and survival

Aims

To investigate the relative risk of pretransplant corneal vascularisation on rate of rejection and graft failure within 5 years of surgery when categorised by indication for transplantation.

We analysed all adults recorded in the UK transplant registry who had a first cornea transplant for keratoconus (KC), pseudophakic bullous keratopathy (PBK) or previous infection (viral/bacterial/fungal/protozoan) between 1999 and 2017. We analysed the number of quadrants of the recipient cornea vascularised before transplant and type of vascularisation, the interval post-transplant to rejection, if any, and the outcome at 5 years post-transplant. Risk factors for rejection and transplant failure were modelled by multivariable risk-adjusted Cox regression.

Results

Corneal vascularisation was recorded in 10%, 25% and 67% of patients with KC, PBK and infection, respectively. Individuals with PBK had an increased hazard of transplant rejection only when there were more than two quadrants of vascularisation (HR 1.5, p=0.004) when either superficial and/or deep vascularisation was present (HR 1.3 and 1.4, respectively, p=0.004). Individuals who had a transplant for previous infection had an increased hazard of rejection with four quadrants of vascularisation (HR 1.6, p=0.003). There was no risk-adjusted increase in transplant failure associated with vascularisation in any group. There was weak evidence of reduction in risk of rejection and/or failure associated with lamellar compared with penetrating transplantation in KC and PBK in vascularised recipient corneas.

Conclusion

Vascularisation is a risk factor for corneal allograft rejection within 5 years. The indication for transplantation has a clinically significant effect on the magnitude of this risk.

Application of corneal injury models in dual fluorescent reporter transgenic mice to understand the roles of the cornea and limbus in angiogenic and lymphangiogenic privilege

The role of the corneal epithelium and limbus in corneal avascularity and pathological neovascularization (NV) is not well understood. To investigate the contributions of the corneal and limbal epithelia in angiogenic and lymphangiogenic privilege, we designed five injury models involving debridement of different portions of the cornea and limbus and applied them to the dual-fluorescence reporter Prox1-GFP/Flt1-DsRed mouse, which permits in vivo imaging of blood and lymphatic vessels via fluorescence microscopy. Debridement of the whole cornea resulted in significant hemangiogenesis (HA) and lymphangiogenesis (LA), while that of the whole limbus yielded minimal corneal HA or LA. Following hemilimbal plus whole corneal debridement, corneal NV occurred only through the non-injured aspect of the limbus. Overall, these results suggest that the integrity of the corneal epithelium is important for (lymph)angiogenic privilege, whereas the limbus does not act as a physical or physiologic barrier to invading vessels. In CDh5-CreERT2VEGFR2lox/PGFD mice, conditional deletion of vascular endothelial growth factor receptor 2 in vascular endothelial cells abolished injury-induced HA and LA, demonstrating the utility of this transgenic mouse line for identifying important factors in the process of neovascularization.

Predictive biomarkers for graft rejection in pig-to-non-human primate corneal xenotransplantation

We investigated the predictive biomarkers for graft rejection in pig-to-non-human primate (NHP) full-thickness corneal xenotransplantation (n = 34). The graft score (0-12) was calculated based on opacity, edema, and vascularization. Scores ≥ 6 were defined as rejection. NHPs were divided into two groups: (a) graft rejection within 6 months; and (b) graft survival until 6 months. In the evaluation of 2-week biomarkers, none of the NHPs showed rejection within 2 weeks and the 34 NHPs were divided into two groups: (a) entire rejection group (n = 16); and (b) survival group (n = 18). In the evaluation of 4-week biomarkers, four NHPs showing rejection within 4 weeks were excluded and the remaining 30 NHPs were divided into two groups: (a) late rejection group (n = 12); and (b) survival group (n = 18). Analysis of biomarker candidates included T/B-cell subsets, levels of anti-αGal IgG/M, donor-specific IgG/M from blood, and C3a from plasma and aqueous humor (AH). CD8⁺ IFNγ⁺ cells at week 2 and AH C3a at week 4 were significantly elevated in the rejection group. Receiver operating characteristic areas under the curve was highest for AH C3a (0.847) followed by CD8⁺ IFNγ⁺ cells (both the concentration and percentage: 0.715), indicating excellent or acceptable discrimination ability, which suggests that CD8⁺ IFNγ⁺ cells at week 2 and AH C3a at week 4 are reliable biomarkers for predicting rejection in pig-to-NHP corneal xenotransplantation.

Comparison Therapeutic Effects of Ciprofloxacin, Silver Nanoparticles and Their Combination in the Treatment of Pseudomonas keratitis in Rabbit: An Experimental Study

Pseudomonas aeruginosa is one of the most common causes of keratitis. The current study was done to evaluate the therapeutic effects of antibacterial combinations with Silver nanoparticles (Ag-NPs) and Ciprofloxacin in experimental Pseudomonas keratitis. Sixty four New Zealand rabbits were prepared. All rabbits were randomly categorized into eight groups (each group containing eight rabbits): Control +, Control -, Ciprofloxacin, Ag-NPs, Ciprofloxacin plus Betamethasone, Ag-NPs plus Betamethasone, Ciprofloxacin plus Ag-NPs, and Ciprofloxacin plus Ag-NPs plus Betamethasone. Twelve hours after bacterial inoculation into the cornea, the eyes were examined daily to evaluate the number of days of ocular discharge and blepharospasm. Also, after 108 and 204 h, first grading of corneal opacity was done and then four rabbits of each groups were euthanized for bacterial count. The results showed that the means of days of blepharospasm, ocular discharge, and bacterial counts (log CFU mL^-1) were significantly different in the treatment groups at 108 and 204 h (P <0.0005, ANOVA). According to Tukey's test, Ciprofloxacin plus Ag-NPs plus Betamethasone group was significantly less than Control +, Ag-NPs, and Ag-NPs plus Betamethasone groups for these variables (P < 0.05). The mean rank of opacity scores was significantly different between treatment groups (P = 0.01, Kruskal-Wallis). Mann-Whitney U-test revealed that Ciprofloxacin plus Ag-NPs plus Betamethasone group had significantly better score than Control +, Ag-NPs, and Ag-NPs plus Betamethasone groups (P < 0.05). It seems Ag-NPs can be an appropriate adjuvant for Ciprofloxacin, but due to the results they can't be an alternative for Ciprofloxacin to treat Pseudomonas keratitis.

Lectin-Glycan Interactions in Corneal Infection and Inflammation

The cornea is an extraordinary component of vision that functions as the principal barrier to pathogens in the eye while allowing light transmission into the retina. Understanding the cellular and molecular mechanisms that maintain homeostasis in this tissue is the subject of intense scientific study given the high prevalence of corneal disease. Over the past decade, the interactions between lectins and glycans on plasma membranes have emerged as important regulatory factors in corneal biology. In particular, members of the galectin family have been shown to bind multiple β-galactoside-containing receptors to regulate immunopathological processes associated with viral and bacterial infection, transplantation, wound healing, dry eye, angiogenesis, and lymphangiogenesis. In this review, we describe the current understanding of how these surface interactions intersect with different pathways to activate unique cellular responses in cornea as well as their potential therapeutic implications.

IFN-γ Regulates the Expression of MICA in Human Corneal Epithelium Through miRNA4448 and NFκB

Purpose

Major histocompatibility complex class I-related chain A (MICA), a non-classical major histocompatibility complex molecule, can stimulate or co-stimulate CD8+ T cells or natural killer (nk) cells, thus affecting cornea allograft survival. This study investigated IFN-γ regulation of MICA expression levels in human corneal epithelium by miRNA4448.

Methods

MICA expression levels in human corneal epithelial cells (HCECs) stimulated with IFN-γ were detected by qRT-PCR and an enzyme-linked immunosorbent assay, and differential miRNA expression levels were measured. qRT-PCR, Western blotting, and immunofluorescence staining revealed nuclear factor kappa B (NFκB)/P65 expression in IFN-γ-treated and miRNA4448-overexpressed HCECs. A luciferase reporter assay was used to predict the interaction between NFκB and MICA. Additionally, HCECs were transfected with MICA plasmid or treated with IFN-γ and NKG2D-mAb and cocultured with NK cells and CD8+ T cells. Cell apoptosis was measured using Annexin V/PI staining. qRT-PCR detected the expression of anti-apoptosis factor Survivin and apoptosis factor Caspase 3 in MICA-transfected and IFN-γ-treated HCECs after co-culturing with NK cells and CD8+ T cells.

Results

IFN-γ (500 ng/ml, 24 h) upregulated MICA expression in HCECs in vitro. Among six differentially expressed microRNAs, miRNA4448 levels decreased the most after IFN-γ treatment. The overexpression of miRNA4448 decreased MICA expression. miRNA4448 downregulated NFκB/P65 expression in IFN-γ-induced HCEC, and it was determined that NFκB/P65 directly targeted MICA by binding to the promotor region. A coculture with NK cells and CD8+ T cells demonstrated that MICA overexpression enhanced HCEC apoptosis, which could be inhibited by NKG2D-mAb. Simultaneously, Survivin mRNA expression decreased and Caspase3 mRNA expression increased upon the interaction between MICA and NK (CD8+ T) cells in HCECs.

Conclusion

IFN-γ enhances the expression of MICA in HCECs by modulating miRNA4448 and NFκB/P65 levels, thereby contributing to HCEC apoptosis induced by NK and CD8+ T cells. This discovery may lead to new insights into the pathogenesis of corneal allograft rejection.

The effects of donor age on organ transplants: A review and implications for aging research

Despite the considerable amount of data available on the effect of donor age upon the outcomes of organ transplantation, these still represent an underutilized resource in aging research. In this review, we have compiled relevant studies that analyze the effect of donor age in graft and patient survival following liver, kidney, pancreas, heart, lung and cornea transplantation, with the aim of deriving insights into possible differential aging rates between the different organs. Overall, older donor age is associated with worse outcomes for all the organs studied. Nonetheless, the donor age from which the negative effects upon graft or patient survival starts to be significant varies between organs. In kidney transplantation, this age is within the third decade of life while the data for heart transplantation suggest a significant effect starting from donors over age 40. This threshold was less defined in liver transplantation where it ranges between 30 and 50 years. The results for the pancreas are also suggestive of a detrimental effect starting at a donor age of around 40, although these are mainly derived from simultaneous pancreas-kidney transplantation data. In lung transplantation, a clear effect was only seen for donors over 65, with negative effects of donor age upon transplantation outcomes likely beginning after age 50. Corneal transplants appear to be less affected by donor age as the majority of studies were unable to find any effect of donor age during the first few years posttransplantation. Overall, patterns of the effect of donor age in patient and graft survival were observed for several organ types and placed in the context of knowledge on aging.

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Data on the effects of donor age upon the outcomes of organ transplantation are an underutilized resource in biogerontology

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We compiled data on the effect of donor age following liver, kidney, pancreas, heart, lung and cornea transplantation

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Older donor age is associated with worse outcomes for all the organs studied

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The donor age from which the negative effects upon survival starts to be significant varies between organs

Activation of human macrophages by human corneal allogen in vitro

Purpose

To study distinct aspects of human monocyte-derived macrophage (MDM) activation by human corneal tissue as a possible initial stage in human corneal allograft rejection.

Methods

Human monocytes were isolated from peripheral blood mononuclear cells (PBMC) and differentiated into MDM. Human corneas with or without endothelium were fragmented using a standardized protocol. MDM were stimulated with human corneal fragments, corneal fragment supernatant, lipopolysaccharide (LPS) or interferon-gamma (IFNγ), and expression profiles for 34 cytokines were determined in MDM-conditioned media using a Luminex bead-based multiplex assay. Data from clinical aqueous humour samples served for comparison and validation. To assess cell recruitment, immunogenicity of corneal endothelial cells (CEC), monocyte survival and differentiation, we applied transwell migration assays, cell viability assays and fluorescence-activated cell sorting, respectively.

Results

Corneal fragments induced MDM to release distinct cytokines into the medium. Media thus conditioned in vitro by stimulated MDM shared cytokine patterns, namely MCP-1, MIP-1α and MIP-1β, with human aqueous humor samples obtained in human corneal allograft rejection. The presence of CEC in tissue fragments used for MDM stimulation attenuated the upregulation of distinct pro-inflammatory chemokines, like MCP-3 and IL-8, reduced the monocyte survival time, and diminished monocyte-to-macrophage differentiation induced by conditioned media. Distinct anti-inflammatory cytokines, like IL-4 and IL-13, were upregulated in the presence of corneal endothelium. Cornea fragment-stimulated MDMs induced recruitment of monocytes from a PBMC pool in a transwell migration model, modulated immune cell viability and promoted further immune cell recruitment and differentiation.

Conclusions

Human macrophages respond to allogenic corneal tissue and generate an inflammatory milieu. This can drive further recruitment of immunocompetent cells and modulate cell survival and differentiation of the cells recruited. These observations are consistent with the hypothesis that macrophages play a significant role in the initiation of corneal transplant rejection. Our data also indicate that distinct aspects of early human corneal transplant rejection can be modelled in vitro.

Potential lymphangiogenesis therapies: Learning from current antiangiogenesis therapies-A review

In recent years, lymphangiogenesis, the process of lymphatic vessel formation from existing lymph vessels, has been demonstrated to have a significant role in diverse pathologies, including cancer metastasis, organ graft rejection, and lymphedema. Our understanding of the mechanisms of lymphangiogenesis has advanced on the heels of studies demonstrating vascular endothelial growth factor C as a central pro-lymphangiogenic regulator and others identifying multiple lymphatic endothelial biomarkers. Despite these breakthroughs and a growing appreciation of the signaling events that govern the lymphangiogenic process, there are no FDA-approved drugs that target lymphangiogenesis. In this review, we reflect on the lessons available from the development of antiangiogenic therapies (26 FDA-approved drugs to date), review current lymphangiogenesis research including nanotechnology in therapeutic drug delivery and imaging, and discuss molecules in the lymphangiogenic pathway that are promising therapeutic targets.

Effect of sorafenib in a murine high risk penetrating keratoplasty model

AIM

To evaluate the effect of sorafenib in murine high risk keratoplasty model.

METHODS

Graft survival, corneal neovascularization, and corneal lymphangiogenesis were compared among the sorafenib, dexamethasone, dimethyl sulfoxide (DMSO), and phosphate buffered saline (PBS) groups following subconjunctival injection in mice that underwent high risk penetrating keratoplasty (HRPK). Real-time polymerase chain reaction was performed to quantify the expression of inflammatory cytokines and vascular endothelial growth factor (VEGF)-A, VEGF-C, vascular endothelial growth factor receptor (VEGFR)-2, VEGFR-3.

RESULTS

The two-month graft survival rate for HRPK was 42.86% in sorafenib group, 37.50% in dexamethasone group, 0 in DMSO group, and 0 in PBS group. Sorafenib significantly increased graft survival compared to the DMSO and PBS group (P<0.05). The sorafenib didn't show significant effect in decreasing neovascularization compared with dexamethsone, DMSO, and PBS group. The sorafenib showed less total lymphangiogenesis than the dexamethasone, DMSO, and PBS group (P=0.011, P<0.001, P<0.001, respectively). The sorafenib group showed reduced expression of VEGF-C, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, VEGFR-2 and VEGFR-3 compared with DMSO group and PBS group (all P<0.05). The sorafenib group didn't show difference in the expression of VEGF-A compared with DMSO, neither with PBS. The sorafenib group showed reduced expression of VEGFR-3 compared with dexamethasone (P=0.051).

CONCLUSION

The subconjunctivally administered sorafenib shows significant anti-lymphangiogenic effect, resulting in increased transplant survival in a murine high risk keratoplasty model. We suggest that a close linkage between decreased VEGF-C/VEGFR-2 and -3 signaling and increased corneal graft survival by sorafenib seems to exist.

Effector and Regulatory T Cell Trafficking in Corneal Allograft Rejection

Corneal transplantation is among the most prevalent and successful forms of solid tissue transplantation in humans. Failure of corneal allograft is mainly due to immune-mediated destruction of the graft, a complex and highly coordinated process that involves elaborate interactions between cells of innate and adaptive immunity. The migration of immune cells to regional lymphoid tissues and to the site of graft plays a central role in the immunopathogenesis of graft rejection. Intricate interactions between adhesion molecules and their counter receptors on immune cells in conjunction with tissue-specific chemokines guide the trafficking of these cells to the draining lymph nodes and ultimately to the site of graft. In this review, we discuss the cascade of chemokines and adhesion molecules that mediate the trafficking of effector and regulatory T cells during corneal allograft rejection.

Low oxygen tension and macromolecular crowding accelerate extracellular matrix deposition in human corneal fibroblast culture

Development of implantable devices based on the principles of in vitro organogenesis has been hindered due to the prolonged time required to develop an implantable device. Herein we assessed the influence of serum concentration (0.5% and 10%), oxygen tension (0.5%, 2% and 20%) and macromolecular crowding (75 μg/ml carrageenan) in extracellular matrix deposition in human corneal fibroblast culture (3, 7 and 14 days). The highest extracellular matrix deposition was observed after 14 days in culture at 0.5% serum, 2% oxygen tension and 75 μg/ml carrageenan. These data indicate that low oxygen tension coupled with macromolecular crowding significantly accelerate the development of scaffold-free tissue-like modules. Copyright © 2016 John Wiley & Sons, Ltd.

New insights into mononuclear phagocyte biology from the visual system

Major advances in mononuclear phagocyte biology have been made but key questions pertinent to their roles in health and disease remain, including in the visual system. One problem concerns how dendritic cells can trigger immune responses from certain tightly regulated immune- privileged sites of the eye. Another, albeit separate, problem involves whether there are functional specializations for microglia versus monocytes in retinal neurodegeneration. In this Review, we examine novel insights in eye immune privilege and, separately, we discuss recent inroads concerning retinal degeneration. Both themes have been extensively studied in the visual system and show parallels with recent findings concerning mononuclear phagocytes in the central nervous system and in the periphery.

Mucosal immune tolerance at the ocular surface in health and disease

The ocular surface is constantly exposed to environmental irritants, allergens and pathogens, against which it can mount a prompt immune response to preserve its integrity. But to avoid unnecessary inflammation, the ocular surface's mucosal immune system must also discriminate between harmless and potentially dangerous antigens, a seemingly complicated task. Despite its unique features, the ocular surface is a mucosal lining, and as such, it shares some homeostatic and pathophysiological mechanisms with other mucosal surfaces. The purpose of this review is to explore the mucosal homeostatic immune function of the ocular surface in both the healthy and diseased states, with a special focus on mucosal immunology concepts. The information discussed in this review has been retrieved by PubMed searches for literature published from January 1981 to October 2016.

Gr-1intCD11b+ myeloid-derived suppressor cells accumulate in corneal allograft and improve corneal allograft survival

We identified the characteristics of myeloid-derived suppressor cells (MDSCs) and investigated their mechanism of induction and their functional role in allograft rejection using a murine corneal allograft model. In mice, MDSCs coexpress CD11b and myeloid differentiation antigen Gr-1. Gr-1⁺CD11b⁺ cells infiltrated allografted corneas between 4 d and 4 wk after surgery; however, the frequencies of Gr-1⁺CD11b⁺ cells were not different between accepted and rejected allografts or in peripheral blood or BM. Of interest, Gr-1^intCD11b⁺ cells, but not Gr-1^hiCD11b⁺ cells, infiltrated the accepted graft early after surgery and expressed high levels of immunosuppressive cytokines, including IL-10, TGF-β, and TNF-related apoptosis-inducing ligand. This population remained until 4 wk after surgery. In vitro, only high dose (>100 ng/ml) of IFN-γ plus GM-CSF could induce immunosuppressive cytokine expression in Gr-1^intCD11b⁺ cells. Furthermore, adoptive transfer of Gr-1^intCD11b⁺ cells reduced T cell infiltration, which improved graft survival. In conclusion, high-dose IFN-γ in allograft areas is essential for development of Gr-1^intCD11b⁺ MDSCs in corneal allografts, and subtle environmental changes in the early period of the allograft can result in a large difference in graft survival.