Mechanisms of immune privilege in the anterior segment of the eye: what we learn from corneal transplantation

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Role of IL-27 in HSV-1-Induced Herpetic Stromal Keratitis

Herpetic stromal keratitis (HSK) is a painful and vision-impairing disease caused by recurrent HSV-1 infection of the cornea. The virus replication in the corneal epithelium and associated inflammation play a dominant role in HSK progression. Current HSK treatments targeting inflammation or virus replication are partially effective and promote HSV-1 latency, and long-term use can cause side effects. Thus, understanding molecular and cellular events that control HSV-1 replication and inflammation is crucial for developing novel HSK therapies. In this study, we report that ocular HSV-1 infection induces the expression of IL-27, a pleiotropic immunoregulatory cytokine. Our data indicate that HSV-1 infection stimulates IL-27 production by macrophages. Using a primary corneal HSV-1 infection mouse model and IL-27 receptor knockout mice, we show that IL-27 plays a critical role in controlling HSV-1 shedding from the cornea, the optimum induction of effector CD4+ T cell responses, and limiting HSK progression. Using in vitro bone marrow-derived macrophages, we show that IL-27 plays an antiviral role by regulating macrophage-mediated HSV-1 killing, IFN-β production, and IFN-stimulated gene expression after HSV-1 infection. Furthermore, we report that IL-27 is critical for macrophage survival, Ag uptake, and the expression of costimulatory molecules involved in the optimum induction of effector T cell responses. Our results indicate that IL-27 promotes endogenous antiviral and anti-inflammatory responses and represents a promising target for suppressing HSK progression.

Biomedical Applications of Lactoferrin on the Ocular Surface

Lactoferrin (LF) is a first-line defense protein with a pleiotropic functional pattern that includes anti-inflammatory, immunomodulatory, antiviral, antibacterial, and antitumoral properties. Remarkably, this iron-binding glycoprotein promotes iron retention, restricting free radical production and avoiding oxidative damage and inflammation. On the ocular surface, LF is released from corneal epithelial cells and lacrimal glands, representing a significant percentage of the total tear fluid proteins. Due to its multifunctionality, the availability of LF may be limited in several ocular disorders. Consequently, to reinforce the action of this highly beneficial glycoprotein on the ocular surface, LF has been proposed for the treatment of different conditions such as dry eye, keratoconus, conjunctivitis, and viral or bacterial ocular infections, among others. In this review, we outline the structure and the biological functions of LF, its relevant role at the ocular surface, its implication in LF-related ocular surface disorders, and its potential for biomedical applications.

Overview of Corneal Transplantation for the Nonophthalmologist

Corneal transplant is a procedure that aims to replace dysfunctional corneal tissue with a transparent graft and is one of the most widely performed transplant surgeries, but its public and professional awareness is low outside of ophthalmology. Corneal tissue consists of 5 major layers that serve to maintain its structural integrity and refractive shape: the epithelium, Bowman's layer, the stroma, Descemet's membrane, and the endothelium. Failure or irreversible damage to any layer of the cornea may be an indication for corneal transplant, and variants of this procedure may be full thickness or selectively lamellar. Complications related to corneal transplantation may occur anywhere from during surgery to years afterward, including rejection, dehiscence, cataract, and glaucoma. Complications should be managed by an ophthalmologist, but other physicians should be aware of prophylactic medications. Topical immunosuppressants and steroids are effective for preventing and treating rejection episodes, whereas there is little evidence to support the use of systemic immunosuppression. Eye protection is recommended for any corneal transplant recipient. Physicians should counsel patients on corneal donation, especially if outside the United States, where donor tissue is in short supply.

Development of a Nomogram to Predict Graft Survival After Descemet Stripping Endothelial Keratoplasty

BACKGROUND/PURPOSE

The purpose of this study was to analyze Descemet stripping endothelial keratoplasty (DSEK) outcomes and develop a nomogram to compute the probability of 3- and 5-year DSEK graft survival based on risk factors.

STUDY DESIGN/METHODS

The medical records of 794 DSEK procedures between January 1, 2008, and August 1, 2019, were retrospectively reviewed to identify 37 variables. We also evaluated for the presence of corneal graft failure, defined as irreversible and visually significant graft edema, haze, or scarring. Variables were assessed by multivariable Cox models, and a nomogram was created to predict the probability of 3- and 5-year graft survival.

RESULTS

Graft failure occurred in 80 transplants (10.1%). The strongest risk factors for graft failure included graft detachment [hazard ratio (HR) = 4.46; P < 0.001], prior glaucoma surgery (HR = 3.14; P = 0.001), and glaucoma (HR = 2.23; P = 0.018). A preoperative diagnosis of Fuchs dystrophy was associated with a decreased risk of graft failure (HR = 0.47; P = 0.005) compared with secondary corneal edema. Our nomogram has a concordance index of 0.75 (95% confidence interval, 0.69 to 0.81), which indicates that it may predict the probability of graft survival at 3 and 5 years with reasonable accuracy. We also analyzed graft rejection, which occurred in 39 cases (4.9%). The single risk factor found to be significantly associated with graft rejection was prior glaucoma surgery (HR = 2.87; P = 0.008).

CONCLUSIONS

Our nomogram may accurately predict DSEK graft survival after 3 and 5 years based on 4 variables. This nomogram will empower surgeons to share useful data with patients and improve collective clinical decision-making.

[Immune reaction after penetrating keratoplasty depending on graft size and centration]

BACKGROUND

Immune reaction (IR) after penetrating keratoplasty (PKP) is a serious complication with a high risk of graft failure. The aim of this study was to analyze and evaluate the risk factors for IR, in particular, the influence of graft size and centration.

PATIENTS AND METHODS

A total of 2133 patients who underwent PKP between January 2009 and July 2019 were included in this retrospective study. The following endpoints were analyzed: frequency of IR, graft origin, donor and patient age, diagnosis, corneal diameter and ratio of the graft size to the recipient cornea size. In addition, the role of graft centration, with the help of distance measurements of the graft margins to the vascularized limbus at four locations, was investigated in detail.

RESULTS

Overall, 8.25% of patients suffered from IR during the observational period. The frequency of IR was significantly correlated (p < 0.001) with the ratio of the graft size to the recipient cornea size. In addition, a statistically significant correlation was found between the occurrence of IR and a small distance to the limbal margins in the Y‑axis (inferior and superior). In particular, the correlation coefficient was larger at the inferior limbus (p < 0.001).

CONCLUSION

An IR after PKP is a not uncommon complication and is significantly related to graft size and centration. A large graft chosen in relation to the recipient cornea and the proximity of the graft to the vascularized limbus at the inferior and superior sites significantly correlate with the occurrence of IR. These are important risk factors for graft survival, which can be influenced by the corneal microsurgeon and could possibly be further optimized in the future.

Ocular Manifestations in Primary Immunodeficiency Disorders: A Report From the United States Immunodeficiency Network (USIDNET) Registry

BACKGROUND

Few published studies address eye disease in primary immunodeficiency (PID) despite ocular infections and autoimmune disease being known manifestations of immunodeficient states.

OBJECTIVE

Data from the USIDNET Registry provide a resource to study ocular ailments in subjects with PID.

METHODS

Ocular manifestations and patient characteristics were determined using data from 4624 patients with PID enrolled in the US Immunodeficiency Network (USIDNET) Registry.

RESULTS

A total of 519 (11.2%) patients had recorded ocular diseases. Those with autoinflammatory disorders (n = 4 of 7 [57.1%]), intrinsic and innate immunity defects (n = 9 of 44 [20.5%]), and immune dysregulation (n = 27 of 142 [19.0%]) had the highest percentage of ocular diseases for the PID diagnosis category. Of the 67.6% with infections, 85.5% had conjunctivitis. Bacteria (56.2%) and viruses (27.4%) were the most common microorganisms reported, with Staphylococcus (31.7%), Haemophilus (26.8%), and Streptococcus (22.0%) being the most common bacteria isolated. Those with a history of eye infections had lower immunoglobulin levels, lower CD19 B-cell percentages, and a lower number of protective pneumococcal titers. In patients with noninfectious ocular complications, 30.8% had vision changes, with retina (n = 20 [8.0%]), cataract (n = 16 [6.4%]), and nerve diseases (n = 16 [6.4%]) also being common. Many patients with ocular disease had serious sequelae, with 12.7% undergoing eye surgery and 10.6% having a vision-based disability.

CONCLUSIONS

Vision loss and conjunctivitis were the most commonly reported ocular complications and pose large quality-of-life issues. Learning more about ocular disease in PID will increase awareness about the importance of addressing and evaluating for these ailments.

Immunogenetics of the Ocular Anterior Segment: Lessons from Inherited Disorders

Autoimmune and autoinflammatory diseases cause morbidity in multiple organ systems including the ocular anterior segment. Genetic disorders of the innate and adaptive immune system present an avenue to study more common inflammatory disorders and host-pathogen interactions. Many of these Mendelian disorders have ophthalmic manifestations. In this review, we highlight the ophthalmic and molecular features of disorders of the innate immune system. A comprehensive literature review was performed using PubMed and the Online Mendelian Inheritance in Man databases spanning 1973-2020 with a focus on three specific categories of genetic disorders: RIG-I-like receptors and downstream signaling, inflammasomes, and RNA processing disorders. Tissue expression, clinical associations, and animal and functional studies were reviewed for each of these genes. These genes have broad roles in cellular physiology and may be implicated in more common conditions with interferon upregulation including systemic lupus erythematosus and type 1 diabetes. This review contributes to our understanding of rare inherited conditions with ocular involvement and has implications for further characterizing the effect of perturbations in integral molecular pathways.

Transcriptional Profiling Uncovers Human Hyalocytes as a Unique Innate Immune Cell Population

Purpose

To decipher the transcriptional signature of macrophages of the human vitreous, also known as hyalocytes, and compare it to the profiles of other myeloid cell populations including human blood-derived monocytes, macrophages, and brain microglia.

Methods

This study involves a total of 13 patients of advanced age with disorders of the vitreoretinal interface undergoing vitrectomy at the University Eye Hospital Freiburg between 2018 and 2019. Vitreal hyalocytes were analyzed by fluorescence-activated cell sorting (FACS) and isolated as CD45⁺CD11b⁺CX3CR1⁺Mat-Mac⁺ cells using a FACS-based sorting protocol. RNA extraction, library preparation and RNA sequencing were performed and the sequencing data was analyzed using the Galaxy web platform. The transcriptome of human hyalocytes was compared to the transcriptional profile of human blood-derived monocytes, macrophages and brain microglia obtained from public databases. Protein validation for selected factors was performed by immunohistochemistry on paraffin sections from three human donor eyes.

Results

On average, 383 ± 233 hyalocytes were isolated per patient, resulting in 128 pg/μl ± 76 pg/μl total RNA per sample. RNA sequencing revealed that SPP1, FTL, CD74, and HLA-DRA are among the most abundantly expressed genes in hyalocytes, which was confirmed by immunofluorescence for CD74, FTL, and HLA-DRA. Gene ontology (GO) enrichment analysis showed that biological processes such as “humoral immune response,” “leukocyte migration,” and “antigen processing and presentation of peptide antigen” (adjusted p < 0.001) are dominating in vitreal hyalocytes. While the comparison of the gene expression profiles of hyalocytes and other myeloid cell populations showed an overall strong similarity (R² > 0.637, p < 0.001), hyalocytes demonstrated significant differences with respect to common leukocyte-associated factors. In particular, transcripts involved in the immune privilege of the eye, such as POMC, CD46, and CD86, were significantly increased in hyalocytes compared to other myeloid cell subsets.

Conclusion

Human hyalocytes represent a unique and distinct innate immune cell population specialized and adapted for the tissue-specific needs in the human vitreous. Vitreal hyalocytes are characterized by a strong expression of genes related to antigen processing and presentation as well as immune modulation. Thus, hyalocytes may represent an underestimated mediator in vitreoretinal disease and for the immune privilege of the eye.

Plasmacytoid dendritic cells in the eye

Plasmacytoid dendritic cells (pDCs) are a unique subpopulation of immune cells, distinct from classical dendritic cells. pDCs are generated in the bone marrow and following development, they typically home to secondary lymphoid tissues. While peripheral tissues are generally devoid of pDCs during steady state, few tissues, including the lung, kidney, vagina, and in particular ocular tissues harbor resident pDCs. pDCs were originally appreciated for their potential to produce large quantities of type I interferons in viral immunity. Subsequent studies have now unraveled their pivotal role in mediating immune responses, in particular in the induction of tolerance. In this review, we summarize our current knowledge on pDCs in ocular tissues in both mice and humans, in particular in the cornea, limbus, conjunctiva, choroid, retina, and lacrimal gland. Further, we will review our current understanding on the significance of pDCs in ameliorating inflammatory responses during herpes simplex virus keratitis, sterile inflammation, and corneal transplantation. Moreover, we describe their novel and pivotal neuroprotective role, their key function in preserving corneal angiogenic privilege, as well as their potential application as a cell-based therapy for ocular diseases.

Experimental Models for Fungal Keratitis: An Overview of Principles and Protocols

Fungal keratitis is a potentially blinding infection of the cornea that afflicts diverse patient populations worldwide. The development of better treatment options requires a more thorough understanding of both microbial and host determinants of pathology, and a spectrum of experimental models have been developed toward this end. In vivo (animal) models most accurately capture complex pathological outcomes, but protocols may be challenging to implement and vary widely across research groups. In vitro models allow for the molecular dissection of specific host cell–fungal interactions, but they do so without the appropriate environmental/structural context; ex vivo (corneal explant) models provide the benefits of intact corneal tissue, but they do not provide certain pathological features, such as inflammation. In this review, we endeavor to outline the key features of these experimental models as well as describe key technical variations that could impact study design and outcomes.

What Makes Cornea Immunologically Unique and Privileged? Mechanistic Clues from a High-Resolution Proteomic Landscape of the Human Cornea

Success rates of corneal transplantation are particularly high owing to its unique, innate immune privilege derived from a phenomenon known as Anterior Chamber-Associated Immune Deviation (ACAID). Of note, cornea is a transparent, avascular structure that acts as a barrier along with sclera to protect the eye and contributes to optical power. Molecular and systems biology mechanisms underlying ACAID and the immunologically unique and privileged status of cornea are not well known. We report here a global unbiased proteomic profiling of the human cornea and the identification of 4824 proteins, the largest catalog of human corneal proteins identified to date. Moreover, signaling pathway analysis revealed enrichment of spliceosome, phagosome, lysosome, and focal adhesion pathways, thereby demonstrating the protective functions of corneal proteins. We observed an enrichment of neutrophil-mediated immune response processes in the cornea as well as proteins belonging to the complement and ER-Phagosome pathways that are suggestive of active immune and inflammatory surveillance response. This study provides a key expression map of the corneal proteome repertoire that should enable future translational medicine studies on the pathological conditions of the cornea and the mechanisms by which cornea immunology are governed. Molecular mechanisms of corneal immune privilege have broad relevance to understand and anticipate graft rejection in the field of organ transplantation.

Effect of microalbuminuria on corneal endothelium in patients with diabetes without retinopathy

BACKGROUND

The aim of this study was to investigate the effect of microalbuminuria on corneal endothelium in patients with diabetes without retinopathy.

METHODS

This cross-sectional study comprised 100 patients with type 2 diabetes mellitus (DM) without diabetic retinopathy and 92 control subjects without diabetes. Forty-five patients had microalbuminuria and 55 subjects were microalbuminuria negative. Endothelial measurements were obtained using specular microscopy. Endothelial cell density, average area, co-efficient of variation, maximum area, minimum area, hexagonality and corneal thickness were compared between the groups on the basis of microalbuminuria, DM duration and medication, HbA_1c , body mass index, serum lipid and protein profiles, hypertension and hyperlipidaemia diagnosis.

RESULTS

There were no significant differences in age, gender, endothelial cell density, average area, co-efficients of variation, maximum area, minimum area, hexagonality or corneal thickness among the microalbuminuria positive, microalbuminuria negative and control groups (p > 0.05). However, microalbuminuria positive patients had lower high-density lipoprotein levels than the microalbuminuria negative patients (p = 0.042). DM and control groups showed similar endothelial measurements (p > 0.05). Patients with a HbA_1c > 7 per cent (53 mmol/mol) had lower hexagonality value (p = 0.039) than in the subjects with a HbA_1c ≤ 7 per cent. No significant differences were found in endothelial parameters when groups were compared based on DM duration, medication and co-morbidities.

CONCLUSIONS

Microalbuminuria positive and negative patients with DM without retinopathy seem to have similar corneal endothelial measurements with controls. However, patients with a HbA_1c > 7 per cent should be monitored for deterioration in corneal endothelial cell morphology even without diabetic retinopathy, which might be critical prior to anterior segment surgery.

Factors Associated With Graft Rejection in the Cornea Preservation Time Study

PURPOSE

To identify factors related to graft rejection following Descemet stripping automated endothelial keratoplasty (DSAEK) in the Cornea Preservation Time Study (CPTS).

DESIGN

Cohort study within a multicenter randomized clinical trial.

METHODS

A total of 1330 eyes of 1090 subjects undergoing DSAEK were randomized to receive a donor cornea with preservation time (PT) of 0-7 days (n = 675) or 8-14 days (n = 655) and followed for 3 years. Central endothelial cell density (ECD) was determined by a central image analysis reading center. Multivariable Cox models adjusted for PT, recipient diagnosis, and surgeon effect were used to identify factors associated with rejection.

RESULTS

Cumulative probability of definite graft rejection was 3.6% (99% confidence interval 2.5%-5.3%). Younger recipient age was associated with graft rejection (P < .001; hazard ratio: 0.53 [0.33, 0.83] per decade). PT, donor-recipient sex mismatch, recipient diagnosis, recipient race, graft size, discontinuation of topical corticosteroids and immune-modulators, prior immunizations within 3 months, and prior glaucoma surgery were not associated with rejection (P > .01). Among clear grafts with an ECD measurement at baseline and 3 years (n = 913), endothelial cell loss (ECL) was greater in eyes that experienced a rejection episode (n = 27) than in those that did not (n = 886) (48% vs 38%, P = .03). Twelve of 44 eyes (27%) with definite graft rejection subsequently failed, comprising 15% of the 79 failures in the CPTS.

CONCLUSIONS

Graft rejection is uncommon after DSAEK and more likely with younger age, in a study cohort mostly > 50 years old. Rejection increases ECL, but it is not a leading cause of DSAEK failure.

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.

ILDR2 Is a Novel B7-like Protein That Negatively Regulates T Cell Responses

The B7-like protein family members play critical immunomodulatory roles and constitute attractive targets for the development of novel therapies for human diseases. We identified Ig-like domain-containing receptor (ILDR)2 as a novel B7-like protein with robust T cell inhibitory activity, expressed in immune cells and in immune-privileged and inflamed tissues. A fusion protein, consisting of ILDR2 extracellular domain with an Fc fragment, that binds to a putative counterpart on activated T cells showed a beneficial effect in the collagen-induced arthritis model and abrogated the production of proinflammatory cytokines and chemokines in autologous synovial-like cocultures of macrophages and cytokine-stimulated T cells. Collectively, these findings point to ILDR2 as a novel negative regulator for T cells, with potential roles in the development of immune-related diseases, including autoimmunity and cancer.

Angiogenesis and lymphangiogenesis in corneal transplantation-A review

Corneal transplantation has been proven effective for returning the gift of sight to those affected by corneal disorders such as opacity, injury, and infections that are a leading cause of blindness. Immune privilege plays an important role in the success of corneal transplantation procedures; however, immune rejection reactions do occur, and they, in conjunction with a shortage of corneal donor tissue, continue to pose major challenges. Corneal immune privilege is important to the success of corneal transplantation and closely related to the avascular nature of the cornea. Corneal avascularity may be disrupted by the processes of angiogenesis and lymphangiogenesis, and for this reason, these phenomena have been a focus of research in recent years. Through this research, therapies addressing certain rejection reactions related to angiogenesis have been developed and implemented. Corneal donor tissue shortages also have been addressed by the development of new materials to replace the human donor cornea. These advancements, along with other improvements in the corneal transplantation procedure, have contributed to an improved success rate for corneal transplantation. We summarize recent developments and improvements in corneal transplantation, including the current understanding of angiogenesis mechanisms, the anti-angiogenic and anti-lymphangiogenic factors identified to date, and the new materials being used. Additionally, we discuss future directions for research in corneal transplantation.

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.

CD25+CD127+Foxp3- Cells Represent a Major Subpopulation of CD8+ T Cells in the Eye Chambers of Normal Mice

The aim of this study has been to determine whether eye chambers constitute part of the normal migratory pathway of naive CD4⁺ and CD8⁺ T cells in mouse and if natural CD4⁺CD25⁺Foxp3⁺ and CD8⁺CD25⁺Foxp3⁺ regulatory T cells are present within these eye compartments. To this aim, the cells obtained from aqueous humor (AH) of normal mice were phenotyped in terms of the expression CD4, CD8, CD25, CD127 and transcription factor Foxp3. The mean percentage of CD8⁺ T cells in the total AH lymphocyte population was as high as 28.69%; the mean percentage of CD8^high and CD8^low cells in this population was 34.09% and 65.91%, respectively. The presence of cells with the regulatory phenotype, i.e. CD25⁺Foxp3⁺ cells, constituted only 0.32% of CD8⁺ T cell subset. Regarding the expression of CD25, AH CD8⁺ T cells were an exceptional population in that nearly 85% of these cells expressed this molecule without concomitant Foxp3 expression. Despite having this phenotype, they should not be viewed as activated cells because most of them co-expressed CD127, which indicates that they are naive lymphocytes. With regard to the markers applied in the present research, CD8⁺CD25⁺CD127⁺Foxp3^- T cells represent the most numerous subset of AH CD8⁺ cells. The results suggest that eye chambers in mice are an element in the normal migratory pathway of naive CD8⁺ T cells. The study presented herein demonstrated only trace presence of CD4⁺ cells in the eye chambers, as the mean percentage of these cells was just 0.56. Such selective and specific homing of CD8⁺ and CD4⁺ cells to the eye chambers is most clearly engaged in the induction and maintenance of ocular immune privilege.

Progress in Corneal Stromal Repair: From Tissue Grafts and Biomaterials to Modular Supramolecular Tissue-Like Assemblies

Corneal injuries and degenerative conditions have major socioeconomic consequences, given that in most cases, they result in blindness. In the quest of the ideal therapy, tissue grafts, biomaterials, and modular engineering approaches are under intense investigation. Herein, advancements and shortfalls are reviewed and future perspectives for these therapeutic strategies discussed.

Predicting Corneal Graft Rejection by Confocal Microscopy

PURPOSE

This study aims at estimating corneal healing by activated keratocyte (AK) counting with in vivo confocal microscopy after perforating keratoplasty (PK). It assesses the value of AK counting in predicting corneal graft rejection.

METHODS

This prospective single-center observational study included 45 patients who benefited from PK in 2013 and were followed up over 2 years. All were monitored by confocal microscopy at day 1, day 7, and monthly thereafter. The AKs were counted in 5 optical sections in each of the anterior, middle, and posterior stroma. The ability of AKs in predicting the occurrence of corneal rejection was assessed by comparison of AK counts between patients with and without clinical signs of rejection.

RESULTS

In patients with graft rejection, the AK counts increased significantly 2 months before the clinical diagnosis of rejection, whereas it remained stable after 4 months in patients without rejection. In patient with graft rejection, the AK count reached a maximum at the rejection diagnosis and antirejection treatment initiation but decreased significantly 1 month after treatment initiation.

CONCLUSIONS

This study confirmed the predictive value of AK counting in corneal graft rejection. The increase in the AK count allowed predicting graft rejection 2 months before the clinical diagnosis of rejection; it may then be the first sign of subclinical rejection.

Self-Complementary Adeno-Associated Virus Vectors Improve Transduction Efficiency of Corneal Endothelial Cells

Transplantation of a donor cornea to restore vision is the most frequently performed transplantation in the world. Corneal endothelial cells (CEC) are crucial for the outcome of a graft as they maintain corneal transparency and avoid graft failure due to corneal opaqueness. Given the characteristic of being a monolayer and in direct contact with culture medium during cultivation in eye banks, CEC are specifically suitable for gene therapeutic approaches prior to transplantation. Recombinant adeno-associated virus 2 (rAAV2) vectors represent a promising tool for gene therapy of CEC. However, high vector titers are needed to achieve sufficient gene expression. One of the rate-limiting steps for transgene expression is the conversion of single-stranded (ss-) DNA vector genome into double-stranded (ds-) DNA. This step can be bypassed by using self-complementary (sc-) AAV2 vectors. Aim of this study was to compare for the first time transduction efficiencies of ss- and scAAV2 vectors in CEC. For this purpose AAV2 vectors containing enhanced green fluorescent protein (GFP) as transgene were used. Both in CEC and in donor corneas, transduction with scAAV2 resulted in significantly higher transgene expression compared to ssAAV2. The difference in transduction efficiency decreased with increasing vector titer. In most cases, only half the vector titer of scAAV2 was required for equal or higher gene expression rates than those of ssAAV2. In human donor corneas, GFP expression was 64.7±11.3% (scAAV) and 38.0±8.6% (ssAAV) (p<0.001), respectively. Furthermore, transduced cells maintained their viability and showed regular morphology. Working together with regulatory authorities, a translation of AAV2 vector-mediated gene therapy to achieve a temporary protection of corneal allografts during cultivation and transplantation could therefore become more realistic.

The asymmetric protein expression hypothesis - Explaining the unilaterality of HLA-B27-positive acute anterior uveitides

For reasons still unclear, most HLA-B27-positive acute anterior uveitides occur unilaterally. Building upon the growing literature showing that left-right asymmetry exist at the biomolecular and at the cellular levels, we propose a new hypothesis to explain why HLA-B27-positive acute anterior uveitides tend to affect one eye selectively. We postulate that left and right uveal tissue may present quantitatively and qualitatively different proteins to the immune system, capable to trigger an autoimmune response, and that other variables, including anatomical, cellular and molecular barriers, as well as our own eye-derived immunological tolerance and immune suppressive intraocular microenvironment may also be unequally distributed, and impact differently the immune privileges of the left and right eye. These same quantitative and qualitative differences might also explain why HLA-B27-positive acute anterior uveitides can flip-flop between the left and the right eye, after the first attack. By trying to figure out why one eye is targeted by an autoimmune reaction while the other is clinically unaffected, we might be able to better understand how and why an autoimmune reaction starts. Hopefully, this will help us devise better treatments for ocular autoimmune diseases, and contribute to the management of autoinflammatory conditions with a marked asymmetric clinical presentation in other fields.

Gene delivery of a viral anti-inflammatory protein to combat ocular inflammation

Inflammation of the retina is a contributing factor in ocular diseases such as uveitis, diabetic retinopathy, and age-related macular degeneration (AMD). The M013 immunomodulatory protein from myxoma virus has been shown to interfere with the proinflammatory signaling pathways involving both the NLRP3 inflammasome and NF-κB. We have developed and characterized an adeno-associated viral (AAV) vector that delivers a secretable and cell-penetrating form of the M013 protein (TatM013). The expressed TatM013 protein was secreted and blocked the endotoxin-induced secretion of interleukin (IL)-1β in monocyte-derived cells and the reactive aldehyde-induced secretion of IL-1β in retinal pigment epithelium cells. The local anti-inflammatory effects of AAV-delivered TatM013 were evaluated in an endotoxin-induced uveitis (EIU) mouse model after intravitreal injection of mice with an AAV2-based vector carrying either TatM013 fused to a secreted green fluorescent protein (GFP) tag (sGFP-TatM013) or GFP. Expression of the sGFP-TatM013 transgene was demonstrated by fluorescence funduscopy in living mice. In EIU, the number of infiltrating cells and the concentration of IL-1β in the vitreous body were significantly lower in the eyes injected with AAV-sGFP-TatM013 compared with the eyes injected with control AAV-GFP. These results suggest that a virus-derived inhibitor of the innate immune response, when delivered via AAV, could be a generalized therapy for various inflammatory diseases of the eye.

Donor-related risk factors and preoperative recipient-related risk factors for graft failure

PURPOSE

The aim of this study was to evaluate the outcome of penetrating keratoplasties, at the University Eye Hospital, Ludwig-Maximilians-University, Munich, Germany, using organ-cultured donor corneas and to identify preoperative risk factors, which may influence the event of graft failure.

METHODS

In this study, 377 medical records of patients, who underwent penetrating keratoplasty between 2001 and 2011, were reviewed. Organ-cultured donor corneas were obtained from the eye bank, Ludwig-Maximilians-University, Munich, Germany. Donor-related and preoperative recipient-related risk factors for graft failure were analyzed by univariate and multivariate analyses.

RESULTS

Graft failure occurred in 26% of patients. The following preoperative factors were significantly associated with graft failure by multivariate analyses: high donor age, low donor endothelial cell density, high patient age, indications of infectious keratitis, acute perforation of noninfectious keratitis, prior graft failure, chemical burn, trauma, glaucoma-associated corneal decompensation, high-risk graft indications, corneal edema, anterior chamber lens, diabetes mellitus, atopy, and autoimmune diseases.

CONCLUSIONS

This study demonstrated a success rate of 74%, which is consistent with previous studies. Various preoperative recipient-related factors seem to influence the outcome of penetrating keratoplasties, whereas few donor-related factors have a significant association with graft failure.

Ocular herpes: the pathophysiology, management and treatment of herpetic eye diseases

Herpesviruses are a prominent cause of human viral disease, second only to the cold and influenza viruses. Most herpesvirus infections are mild or asymptomatic. However, when the virus invades the eye, a number of pathologies can develop and its associated sequelae have become a considerable source of ocular morbidity. The most common culprits of herpetic eye disease are the herpes simplex virus (HSV), varicella zoster virus (VZV), and cytomegalovirus (CMV). While primary infection can produce ocular disease, the most destructive manifestations tend to arise from recurrent infection. These recurrent infections can wreck devastating effects and lead to irreversible vision loss accompanied by a decreased quality of life, increased healthcare usage, and significant cost burden. Unfortunately, no method currently exists to eradicate herpesviruses from the body after infection. Treatment and management of herpes-related eye conditions continue to revolve around antiviral drugs, although corticosteroids, interferons, and other newer therapies may also be appropriate depending on the disease presentation. Ultimately, the advent of effective vaccines will be crucial to preventing herpesvirus diseases altogether and cutting the incidence of ocular complications.

Cortisol biosynthesis in the human ocular surface innate immune response

Innate immune responses have a critical role in regulating sight-threatening ocular surface (OcS) inflammation. While glucocorticoids (GCs) are frequently used to limit tissue damage, the role of intracrine GC (cortisol) bioavailability via 11-beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in OcS defense, remains unresolved. We found that primary human corneal epithelial cells (PHCEC), fibroblasts (PHKF) and allogeneic macrophages (M1, GM-CSF; M2, M-CSF) were capable of generating cortisol (M1>PHKF>M2>PHCEC) but in corneal cells, this was independent of Toll-like receptor (TLR) activation. While PolyI∶C induced maximal cytokine and chemokine production from both PHCEC (IFNγ, CCL2, CCL3, and (CCL4), IL6, CXCL10, CCL5, TNFα) and PHKF (CCL2, IL-6, CXCL10, CCL5), only PHKF cytokines were inhibited by GCs. Both Poly I∶C and LPS challenged-corneal cells induced M1 chemotaxis (greatest LPS-PHKF (250%), but down-regulated M1 11β-HSD1 activity (30 and 40% respectively). These data were supported by clinical studies demonstrating reduced human tear film cortisol∶cortisone ratios (a biomarker of local 11β-HSD1 activity) in pseudomonas keratitis (1∶2.9) versus healthy controls (1∶1.3; p<0.05). This contrasted with putative TLR3-mediated OcS disease (Stevens-Johnson Syndrome, Mucous membrane pemphigoid) where an increase in cortisol∶cortisone ratio was observed (113.8∶1; p<0.05). In summary, cortisol biosynthesis in human corneal cells is independent of TLR activation and is likely to afford immunoprotection under physiological conditions. Contribution to ocular mucosal innate responses is dependent on the aetiology of immunological challenge.

Short-term azithromycin treatment promotes cornea allograft survival in the rat

Background

Any inflammatory response following corneal transplantation may induce rejection and irreversible graft failure. The purpose of this study is to analyze the anti-inflammatory effect of azithromycin (AZM) following experimental keratoplasty in rats.

Methods

Corneal transplants were performed between Fisher-donor and Lewis-recipient rats. Recipients were postoperatively treated three times daily with AZM, miglyol, ofloxacin or dexamethasone eye drops. As an additional control, AZM was applied following syngeneic keratoplasty. Furthermore, short-term treatments with AZM for seven days perioperatively or with AZM only three days prior to the transplantation were compared to appropriate controls. All transplants were monitored clinically for opacity, edema, and vascularization. Infiltrating CD45⁺, CD4⁺, CD8⁺, CD25⁺, CD161⁺ and CD163⁺ cells were quantified via immunohistochemistry.

Results

AZM significantly promoted corneal graft survival compared with miglyol or ofloxacin treatment. This effect was comparable to topical dexamethasone. No adverse AZM effect was observed. Histology confirmed a significant reduction of infiltrating leukocytes. The short-term application of AZM for three days prior to transplantation or for seven days perioperatively reduced corneal graft rejection significantly compared with the controls.

Conclusions

Along with antibiotic properties, topical AZM has a strong anti-inflammatory effect. Following keratoplasty, this effect is comparable to topical dexamethasone without the risk of steroid-induced adverse effects. Short-term treatment with AZM three days prior to the transplantation was sufficient to promote graft survival in the rat keratoplasty model. We therefore suggest further assessing the anti-inflammatory function of topical AZM following keratoplasty in humans.

Lymphocyte infiltration and activation in iris-ciliary body and anterior chamber of mice in corneal allograft rejection

AIM

To investigate the infiltration and activation of lymphocyte in iris-ciliary body and anterior chamber after allogenic penetrating keratoplasty (PK), for further revealing the role of iris-ciliary body in corneal allograft immune rejection.

METHODS

In the mice models of PK, BALB/C mice received orthotopic isografts (n =35) or C57BL/6 donor allografts (n =25). Grafts were examined daily for 3 weeks by slit-lamp microscopy and scored for opacity. The infiltration of CD4(+) T lymphocyte in iris-ciliary body and anterior chamber was examined by immunohistology and the mRNA of CD80 and CD86 in both cornea graft and iris-ciliary body by RT-PCR was analyzed in allograft recipient at days 3, 6, 10 and the day when graft rejection occurred. Isograft recipients were examined as control at the corresponding time points. Transmission electron microscope was used to study the ultrastructure, especially cell infiltration, of iris-cilary body and corneal graft at day 3, 7 and the day when rejection occurred after allogenic PK.

RESULTS

Rejection was observed in all the allograft recipients followed more than 10 days, at a median time of 15 days (range 12-18 days), but not in any of isografts. CD4(+) T cells were first detected at day 6 after transplantation in limbus and Ciliary body, and then in the stroma of recipient, iris, anterior chamber and corneal allograft with an increased number until graft rejection occurred. CD80 and CD86 mRNA were detected under RT-PCR examination in both graft and iris-ciliary body of allograft recipient, but not in any of isograft recipient. Three days after operation, lymphocytes and monocytes macrophages were visible in iris blood vessels and the anterior chamber, and vascular endothelial cell proliferation and activation were significant under transmission electron microscopy examination. At day 7, corneal endothelial cells became thinner. Lymphocytes and mononuclear macrophages were found with great number in the anterior chamber and adhered to the corneal endothelium. Blood vessels in iris increased and were filled with lymphocytes. And lymphocytes were detected to migrate through endothelial cell gap out of vessels. When allograft rejection occurred, macrophages attached to endothelial cells with large number of lymphocytes and macrophages infiltrating in iris.

CONCLUSION

Lymphocyte infiltration and activation occurred in iris-ciliary body after allogenic PK, and the lymphocytes could migrate from iris blood vessel to the anterior chamber, which might play an important role in corneal allograft immune rejection.

Effect of donor and recipient factors on corneal graft rejection

PURPOSE

To assess the relationship between donor and recipient factors and corneal allograft rejection in eyes that underwent penetrating keratoplasty in the Cornea Donor Study.

METHODS

Overall, 1090 subjects undergoing corneal transplantation for a moderate risk condition (principally Fuchs dystrophy or pseudophakic corneal edema) were followed for up to 5 years. Associations of baseline recipient and donor factors with the occurrence of a probable or definite rejection event were assessed in univariate and multivariate proportional hazards models.

RESULTS

Eyes with pseudophakic or aphakic corneal edema (n = 369) were more likely to experience a rejection event than eyes with Fuchs dystrophy (n = 676) [34% ± 6% vs. 22% ± 4%; hazard ratio = 1.56; 95% confidence interval (CI), 1.21-2.03]. Among eyes with Fuchs dystrophy, a higher probability of a rejection event was observed in phakic posttransplant eyes compared with those that underwent cataract extraction with or without intraocular lens implantation during penetrating keratoplasty (29% vs. 19%; hazard ratio = 0.54; 95% CI, 0.36-0.82). Female recipients had a higher probability of a rejection event than male recipients (29% vs. 21%; hazard ratio = 1.42; 95% CI, 1.08-1.87) after controlling for the effect of preoperative diagnosis and lens status. Donor age and donor recipient ABO compatibility were not associated with rejection.

CONCLUSIONS

There was a substantially higher graft rejection rate in eyes with pseudophakic or aphakic corneal edema compared to that in eyes with Fuchs dystrophy. Female recipients were more likely to have a rejection event than male recipients. Graft rejection was not associated with donor age.

Human corneal endothelial cell expansion for corneal endothelium transplantation: an overview

The monolayer of cells forming the human corneal endothelium is critical to the maintenance of corneal transparency and is not known to regenerate in vivo. Thus, dysfunction of these cells constitutes the most often cited reasons for the 150,000 or so corneal transplants performed yearly. Although current corneal transplantation is more than 90% successful at 1 year, longer term results are not as encouraging with approximately 70% success at 5 years. Nonimmunologic graft failure and allograft endothelial rejection are the main problems. Furthermore, the global shortage of donor corneas greatly restricts several corneal transplantations performed. With advances in understanding corneal endothelial cell biology, it is now possible to cultivate human corneal endothelial cells (HCECs) in vitro, thus providing new opportunities to develop novel tissue-engineered human corneal endothelium. This review will provide an overview of (a) the characteristics of human corneal endothelium; (b) past and present HCECs isolation and culture protocols; (c) various potential carriers for the generation of tissue-engineered corneal endothelium, together with some of the functional studies reported in various animal models; and (d) the current rapid advancements in surgical techniques for keratoplasty. A successful combination of tissue-engineered human corneal endothelium coupled with innovative and groundbreaking surgical procedures will bridge basic research involving cultured HCECs, bringing it from bench to bedside.

IL-17A-dependent CD4+CD25+ regulatory T cells promote immune privilege of corneal allografts

IL-17A is a proinflammatory cytokine that has received attention for its role in the pathogenesis of several autoimmune diseases. IL-17A has also been implicated in cardiac and renal allograft rejection. Accordingly, we hypothesized that depletion of IL-17A would enhance corneal allograft survival. Instead, our results demonstrate that blocking IL-17A in a mouse model of keratoplasty accelerated the tempo and increased the incidence of allograft rejection from 50 to 90%. We describe a novel mechanism by which CD4(+)CD25(+) regulatory T cells (Tregs) respond to IL-17A and enhance corneal allograft survival. Our findings suggest the following: 1) IL-17A is necessary for ocular immune privilege; 2) IL-17A is not required for the induction of anterior chamber-associated immune deviation; 3) Tregs require IL-17A to mediate a contact-dependent suppression; 4) corneal allograft Tregs suppress the efferent arm of the immune response and are Ag specific; 5) Tregs are not required for corneal allograft survival beyond day 30; and 6) corneal allograft-induced Treg-mediated suppression is transient. Our findings identify IL-17A as a cytokine essential for the maintenance of corneal immune privilege and establish a new paradigm whereby interplay between IL-17A and CD4(+)CD25(+) Tregs is necessary for survival of corneal allografts.

IκB kinase β regulates epithelium migration during corneal wound healing

The IKKβ is known to regulate transcription factor NF-κB activation leading to inflammatory responses. Recent gene knockout studies have shown that IKKβ can orchestrate local inflammatory responses and regulate homeostasis of epithelial tissues. To investigate whether IKKβ has an intrinsic role in epithelial cells, we established an in vivo system in the immune privileged corneal epithelium. We generated triple transgenic Krt12^rtTA/rtTAt/tet-O-Cre/Ikkβ^F/F (Ikkβ^ΔCE/ΔCE) mice by crossing the Krt12-rtTA knock-in mice, which express the reverse tetracycline transcription activator in corneal epithelial cells, with the tet-O-Cre and Ikkβ^F/F mice. Doxcycline-induced IKKβ ablation occurred in corneal epithelial cells of triple transgenic Ikkβ^ΔCE/ΔCE mice, but loss of IKKβ did not cause ocular abnormalities in fetal development and postnatal maintenance. Instead, loss of IKKβ significantly delayed healing of corneal epithelial debridement without affecting cell proliferation, apoptosis or macrophage infiltration. In vitro studies with human corneal epithelial cells (HCEpi) also showed that IKKβ was required for cytokine-induced cell migration and wound closure but was dispensable for cell proliferation. In both in vivo and in vitro settings, IKKβ was required for optimal activation of NF-κB and p38 signaling in corneal epithelial cells, and p38 activation is likely mediated through formation of an IKKβ-p38 protein complex. Thus, our studies in corneal epithelium reveal a previously un-recognized role for IKKβ in the control of epithelial cell motility and wound healing.

IL-17 promotes immune privilege of corneal allografts

Corneal allograft rejection has been described as a Th1-mediated process involving IFN-γ production. However, it has been reported that corneal allograft rejection soars in IFN-γ(-/-) mice or mice treated with anti-IFN-γ mAb. Th17 is a recently described IL-17A-producing Th cell population that has been linked to renal and cardiac graft rejection, which was originally thought to be Th1-mediated. We tested the hypothesis that Th17 cells mediate corneal allograft rejection in an IL-17A-dependent fashion and unexpectedly found that depletion of IL-17A increased the incidence of rejection to 90%. We demonstrate that the exacerbated rejection following depletion of IL-17A did not result from a loss of cross-regulation of Th1 cells or exaggerated delayed-type hypersensitivity responses. Instead, inhibition of the Th1 or Th17 cell lineages promoted the emergence of a Th2 cell subset that independently mediated allograft rejection. These findings demonstrate that IL-17A is not required for corneal allograft rejection and may instead contribute to the immune privilege of corneal allografts.