Galectin-9-mediated protection from allo-specific T cells as a mechanism of immune privilege of corneal allografts. PLoS One. 2013;8:e63620. [PMID: 23667648 PMCID: PMC3646846 DOI: 10.1371/journal.pone.0063620]

The level of Tim-3+CD8+ T cells can serve as a potential marker for evaluating the severity of acute graft-versus-host disease after haplo-PBSCT

Early and accurate diagnosis of acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation is crucial for the prognosis of patients. This study identified a potential biomarker for the severity of aGVHD after human leukocyte antigen (HLA)-haploidentical peripheral blood hematopoietic stem cell transplantation (haplo-PBSCT). We included 20 healthy subjects and 57 patients who underwent haplo-PBSCT. Of these patients, 22 developed aGVHD after haplo-PBSCT. The results showed that patients with aGVHD had significantly increased levels of Tim-3+/Perforin+/Granzyme B+CD8+ T cells, but significantly decreased Galectin-9. The differences in Galectin-9 and Tim-3+/Granzyme B+CD8+ T cells between grade I-II aGVHD and III-IV aGVHD were also significant. In vitro, the apoptosis of CD8+ T cells from aGVHD patients was significantly increased after Tim-3/Galectin-9 pathway activation, which decreased Granzyme B secretion. As revealed by univariate analysis, the level of Tim-3+CD8+ T cells was a risk factor for severe aGVHD. ROC analysis demonstrated that high levels of Tim-3+CD8+ T cells had a significant diagnostic value for severe aGVHD, with an area under the curve of 0.854 and cut-off value of 14.155%. In conclusion, the binding of Tim-3 with exogenous Galectin-9 can promote apoptosis of CD8+ T cells and affect the secretion of Granzyme B. Tim-3+CD8+ T cells have the potential to serve as immunological markers for assessing the severity of aGVHD after haplo-PBSCT and identifying patients at a higher risk for severe aGVHD.

Tear Fluid Inflammatory Proteome Analysis Highlights Similarities Between Keratoconus and Allergic Conjunctivitis

Purpose

Keratoconus is characterized by the progressive thinning of the cornea, which leads to a cone-like appearance of the eye over time. Although conventionally defined as a noninflammatory condition, a number of recent studies have associated keratoconus (KC) with allergic conjunctivitis (AC) based on clinical parameters. This study aimed to consolidate this association by performing a proteomic analysis of tear fluid from patients with keratoconus and/or allergic conjunctivitis.

Methods

Of 51 patients, 17 were diagnosed with KC, 17 were diagnosed with AC, and 17 were diagnosed with both KC and AC (combined). Nine of 34 patients with KC had a progressive form of the disease. Tear fluid samples (n = 51, one eye per patient) were collected by the Schirmer's strips. Tear proteins were extracted from the Schirmer's strips. Proteomic profiling of 384 inflammatory proteins was assessed by a multiplex proximity extension assay (Olink Explore 384 Inflammation Panel I).

Results

A total of 384 inflammatory proteins were measured. Two hundred seventy-two of the 384 proteins passed stringent data cleaning and were compared among the patient groups. Compared to the 2 other groups, LGALS9 was upregulated uniquely in KC, whereas FGF19, PDGFB, HPCAL1, OSM, and FCAR were downregulated in KC. Similarly, TNFRSF4 and CCL13 were specifically upregulated in AC, whereas ectodysplasin A receptor (EDAR) was uniquely downregulated in AC.

Conclusions

High-throughput proteomic profiling of tear fluid confirms the association between KC and AC on a molecular level and raise the importance of redefining KC as an inflammatory condition.

Immune Checkpoints in Solid Organ Transplantation

Allogenic graft acceptance is only achieved by life-long immunosuppression, which comes at the cost of significant toxicity. Clinicians face the challenge of adapting the patients' treatments over long periods to lower the risks associated with these toxicities, permanently leveraging the risk of excessive versus insufficient immunosuppression. A major goal and challenge in the field of solid organ transplantation (SOT) is to attain a state of stable immune tolerance specifically towards the grafted organ. The immune system is equipped with a set of inhibitory co-receptors known as immune checkpoints (ICs), which physiologically regulate numerous effector functions. Insufficient regulation through these ICs can lead to autoimmunity and/or immune-mediated toxicity, while excessive expression of ICs induces stable hypo-responsiveness, especially in T cells, a state sometimes referred to as exhaustion. IC blockade has emerged in the last decade as a powerful therapeutic tool against cancer. The opposite action, i.e., subverting IC for the benefit of establishing a state of specific hypo-responsiveness against auto- or allo-antigens, is still in its infancy. In this review, we will summarize the available literature on the role of ICs in SOT and the relevance of ICs with graft acceptance. We will also discuss the possible influence of current immunosuppressive medications on IC functions.

Ocular Vascular Diseases: From Retinal Immune Privilege to Inflammation

The eye is an immune privileged tissue that insulates the visual system from local and systemic immune provocation to preserve homeostatic functions of highly specialized retinal neural cells. If immune privilege is breached, immune stimuli will invade the eye and subsequently trigger acute inflammatory responses. Local resident microglia become active and release numerous immunological factors to protect the integrity of retinal neural cells. Although acute inflammatory responses are necessary to control and eradicate insults to the eye, chronic inflammation can cause retinal tissue damage and cell dysfunction, leading to ocular disease and vision loss. In this review, we summarized features of immune privilege in the retina and the key inflammatory responses, factors, and intracellular pathways activated when retinal immune privilege fails, as well as a highlight of the recent clinical and research advances in ocular immunity and ocular vascular diseases including retinopathy of prematurity, age-related macular degeneration, and diabetic retinopathy.

Association of TIM-3 with anterior uveitis and associated systemic immune diseases: a Mendelian randomization analysis

Background

We aimed to investigate the causal association between TIM-3, an immune checkpoint inhibitor, and anterior uveitis (AU), as well as associated systemic immune diseases.

Materials and methods

We performed two-sample Mendelian randomization (MR) analyses to estimate the causal effects of TIM-3 on AU and three associated systemic diseases, namely ankylosing spondylitis (AS), Crohn's disease (CD), and ulcerative colitis (UC). Single-nucleotide polymorphisms (SNPs) associated with AU, AS, CD, and UC were selected as the outcomes: AU GWAS with 2,752 patients with acute AU accompanied with AS (cases) and 3,836 AS patients (controls), AS GWAS with 968 cases and 336,191 controls, CD GWAS with 1,032 cases and 336,127 controls, and UC GWAS with 2,439 cases and 460,494 controls. The TIM-3 dataset was used as the exposure (n = 31,684). Four MR methods, namely, inverse-variance weighting (IVW), MR-Egger regression, weighted median, and weighted mode, were used in this study. Comprehensive sensitivity analyses were conducted to estimate the robustness of identified associations and the potential impact of horizontal pleiotropy.

Results

Our studies show that TIM-3 is significantly associated with CD using the IVW method (OR = 1.001, 95% CI = 1.0002-1.0018, P-value = 0.011). We also found that TIM-3 may be a protective factor for AU although these results lacked significance (OR = 0.889, 95% CI = 0.631-1.252, P-value = 0.5). No association was observed between the genetic predisposition to particular TIM-3 and susceptibility to AS or UC in this study. No potential heterogeneities or directional pleiotropies were observed in our analyses.

Conclusion

According to our study, a small correlation was observed between TIM-3 expression and CD susceptibility. Additional studies in different ethnic backgrounds will be necessary to further explore the potential roles and mechanisms of TIM-3 in CD.

Epigenetic Regulation of Corneal Epithelial Differentiation by TET2

Epigenetic DNA modification by 5-hydroxymethylcytosine (5hmC), generated by the Ten-eleven translocation (TET) dioxygenases, regulates diverse biological functions in many organ tissues, including the mammalian eye. For example, 5hmC has been shown to be involved in epigenetic regulation of retinal gene expression. However, a functional role of 5hmC in corneal differentiation has not been investigated to date. Here, we examined 5hmC and TET function in the human cornea. We found 5hmC highly expressed in MUC16-positive terminally differentiated cells that also co-expressed the 5hmC-generating enzyme TET2. TET2 knockdown (KD) in cultured corneal epithelial cells led to significant reductions of 5hmC peak distributions and resulted in transcriptional repression of molecular pathways involved in corneal differentiation, as evidenced by downregulation of MUC4, MUC16, and Keratin 12. Additionally, integrated TET2 KD RNA-seq and genome-wide Reduced Representation Hydroxymethylation Profiling revealed novel epigenetically regulated genes expressed by terminally differentiated cells, including KRT78, MYEOV, and MAL. In aggregate, our findings reveal a novel function of TET2 in the epigenetic regulation of corneal epithelial gene expression and identify novel TET2-controlled genes expressed in differentiated corneal epithelial cells. These results point to potential roles for TET2 induction strategies to enhance treatment of corneal diseases associated with abnormal epithelial maturation.

TIGIT-Fc Prolongs Corneal Allograft Survival in Mice by Upregulating TIGIT/CD226 Expression and the Proportion of Helios + Foxp3 + Treg Cells

BACKGROUND

Reduction of graft rejection remains key issue for supporting long-term graft retention after corneal transplantation. The relevance of Treg in reduction of corneal allografts rejection has been demonstrated. It has been recently reported that in addition to Foxp3, Helios is also considered to be a marker of activated Treg. Helios + Foxp3 + Treg are considered to be the true immunosuppressive Treg. TIGIT is an immunosuppressive costimulatory molecule that was found to be highly expressed on the surface of Helios + Foxp3 + Treg.

METHODS

In this study, we aimed to explore whether supplementing TIGIT would result in an expansion and activation of Helios + Foxp3 + Treg thus to mediate an immune tolerance following corneal transplantation by administering topically and systemically TIGIT-Fc treatment in murine models.

RESULTS

TIGIT-Fc treatment significantly improved the survival of corneal allograft compared with the control group. TIGIT-Fc treatment increased TIGIT/CD226 expression, the proportion of Helios + Foxp3 + Treg cells and an enhanced ex vivo suppressive effect from peripheral lymph nodes isolated Treg cells. Furthermore, the expression of Helios in corneal grafts was upregulated, whereas expression of CD226 and production of aqueous interferon-γ and VEGF were reduced by TIGIT-Fc treatment.

CONCLUSIONS

TIGIT-Fc treatment could specifically upregulate Helios + Foxp3 + Treg-mediated immune response after allogeneic corneal transplantation via TIGIT/CD226-CD155 pathway which improves the survival of allografts.

The interplay of galectins-1, -3, and -9 in the immune-inflammatory response underlying cardiovascular and metabolic disease

Galectins are β-galactoside-binding proteins that bind and crosslink molecules via their sugar moieties, forming signaling and adhesion networks involved in cellular communication, differentiation, migration, and survival. Galectins are expressed ubiquitously across immune cells, and their function varies with their tissue-specific and subcellular location. Particularly galectin-1, -3, and -9 are highly expressed by inflammatory cells and are involved in the modulation of several innate and adaptive immune responses. Modulation in the expression of these proteins accompany major processes in cardiovascular diseases and metabolic disorders, such as atherosclerosis, thrombosis, obesity, and diabetes, making them attractive therapeutic targets. In this review we consider the broad cellular activities ascribed to galectin-1, -3, and -9, highlighting those linked to the progression of different inflammatory driven pathologies in the context of cardiovascular and metabolic disease, to better understand their mechanism of action and provide new insights into the design of novel therapeutic strategies.

[Anti-inflammatory Strategies by Focusing on the Particularity of Ocular Immunity]

Particularity of ocular immunity is manifested by "Immune privilege". For example, it has been generally known that corneal transplantation is a typically successful organ transplantation compared with other organs. This immune privilege can be explained by "immune-suppressive ocular microenvironment" and "anterior chamber-associated immune deviation, ACAID". This review focused on molecular mechanisms of the "immune-suppressive ocular microenvironment" and "ACAID", so that possible anti-inflammatory strategies could be raised. Especially, in murine ACAID model, anti-inflammatory actions were induced probably through induction of Treg cells. As an anti-inflammatory strategy, anti-inflammatory Treg cells could be induced in vitro. Treg cells that are specifically responsive for a specific antigen can be induced by culturing spleen cells with the antigen and transforming growth factor-β (TGF-β). The induced Treg cells were activated by stimulation with the specific antigen. When the induced Treg cells were adoptively transferred to recipient mice, antigen-induced inflammation was effectively suppressed. The Treg cells may be able to be efficiently induced by eye-based mechanisms. Further analyses of mechanisms underlying the ocular immune privilege can be useful for development of new anti-inflammatory strategies on the eye basis.

Corneal Allografts: Factors for and against Acceptance

Cornea is one of the most commonly transplanted tissues worldwide. However, it is usually omitted in the field of transplantology. Transplantation of the cornea is performed to treat many ocular diseases. It restores eyesight significantly improving the quality of life. Advancements in banking of explanted corneas and progressive surgical techniques increased availability and outcomes of transplantation. Despite the vast growth in the field of transplantation laboratory testing, standards for corneal transplantation still do not include HLA typing or alloantibody detection. This standard practice is based on immune privilege dogma that accounts for high success rates of corneal transplantation. However, the increasing need for retransplantation in high-risk patients with markedly higher risk of rejection causes ophthalmology transplantation centers to reevaluate their standard algorithms. In this review we discuss immune privilege mechanisms influencing the allograft acceptance and factors disrupting the natural immunosuppressive environment of the eye. Current developments in testing and immunosuppressive treatments (including cell therapies), when applied in corneal transplantation, may give very good results, decrease the possibility of rejection, and reduce the need for retransplantation, which is fairly frequent nowadays.

Galectin-9 interacts with PD-1 and TIM-3 to regulate T cell death and is a target for cancer immunotherapy

The two T cell inhibitory receptors PD-1 and TIM-3 are co-expressed during exhausted T cell differentiation, and recent evidence suggests that their crosstalk regulates T cell exhaustion and immunotherapy efficacy; however, the molecular mechanism is unclear. Here we show that PD-1 contributes to the persistence of PD-1+TIM-3+ T cells by binding to the TIM-3 ligand galectin-9 (Gal-9) and attenuates Gal-9/TIM-3-induced cell death. Anti-Gal-9 therapy selectively expands intratumoral TIM-3+ cytotoxic CD8 T cells and immunosuppressive regulatory T cells (Treg cells). The combination of anti-Gal-9 and an agonistic antibody to the co-stimulatory receptor GITR (glucocorticoid-induced tumor necrosis factor receptor-related protein) that depletes Treg cells induces synergistic antitumor activity. Gal-9 expression and secretion are promoted by interferon β and γ, and high Gal-9 expression correlates with poor prognosis in multiple human cancers. Our work uncovers a function for PD-1 in exhausted T cell survival and suggests Gal-9 as a promising target for immunotherapy.

Galectin-9 as a biomarker of disease severity

Galectin-9 (Gal-9) is a β-galactoside binding lectin known for its immunomodulatory role in various microbial infections. Gal-9 is expressed in all organ systems and localized in the nucleus, cell surface, cytoplasm and the extracellular matrix. It mediates host-pathogen interactions and regulates cell signalling via binding to its receptors. Gal-9 is involved in many physiological functions such as cell growth, differentiation, adhesion, communication and death. However, recent studies have emphasized on the elevated levels of Gal-9 in autoimmune disorders, viral infections, parasitic invasion, cancer, acute liver failure, atopic dermatitis, chronic kidney disease, type-2 diabetes, coronary artery disease, atherosclerosis and benign infertility-related gynecological disorders. In this paper we have reviewed the potential of Gal-9 as a reliable, sensitive and non-invasive biomarker of disease severity. Tracking changes in Gal-9 levels and its implementation as a biomarker in clinical practice will be an important tool to monitor disease activity and facilitate personalized treatment decisions.

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.

Increased Galectin-9 expression, a prognostic biomarker of aGVHD, regulates the immune response through the Galectin-9 induced MDSC pathway after allogeneic hematopoietic stem cell transplantation

Galectin-9 (Gal-9) is a β-galactoside-binding soluble lectin family member that exerts its primary biological functions via specific glycoconjugate interactions. Gal-9 expression is closely related to tumor occurrence, development, metastasis and prognosis. In transplant immunology, a high level of Gal-9 expression has been shown to markedly reduce the severity of acute graft rejection and effectively prolong survival time in organ and bone marrow transplantation (BMT) models. The main mechanism of Gal-9-mediated immunoregulation involves the Tim-3/Gal-9 axis in T cells. However, myeloid-derived suppressor cell (MDSC) accumulation in transgenic mice with persistently high Gal-9 expression was observed in a model of lung inflammation, indicating that a potential immunosuppressive mechanism distinct from the Gal-9/Tim-3 axis might exist. In the present study, increased Gal-9 expression and MDSC frequencies before acute graft-versus-host disease (aGVHD) onset were observed in patients who developed aGVHD. Patients with higher Gal-9 expression (≥14.8417 ng/ml) exhibited reduced overall survival and increased cumulative incidences of GVHD at +100 day. We considered the elevated Gal-9 expression before aGVHD onset a secondary inflammatory response. This increase might be part of a negative feedback pathway corresponding to aGVHD pathogenesis. Additionally, a high Gal-9 concentration induced MDSC proliferation in vivo and in vitro. Gal-9-induced MDSCs (G9-MDSCs) suppressed T cell proliferation and activation. An infusion of G9-MDSCs into a graft contributed to the successful control of severe aGVHD and long-term survival in an allogeneic (allo)-BMT mouse model. Thus, we speculated that increased Gal-9 expression after allo-hematopoietic stem cell transplantation is a potential prognostic biomarker of aGVHD. The Gal-9-associated immunosuppressive effects on aGVHD development might occurr through G9-MDSCs and were independent of the Gal-9/Tim-3 axis.

Blockade of costimulatory CD27/CD70 pathway promotes corneal allograft survival

PURPOSE

To determine whether the CD27/CD70 pathway plays a significant role in corneal allograft rejection by investigating the effect of blocking the CD27/CD70 pathway by anti-CD70 antibody on corneal allograft survival.

METHODS

Orthotopic penetrating keratoplasty was performed using C57BL/6 donor grafts and BALB/c recipients. Expression of CD27 and CD70 on rejected cornea was examined by immunohistochemistry. Corneal transplant recipients received intraperitoneal injection of anti-CD70 antibody (FR70) or control rat IgG. Alloreactivity was measured by mixed lymphoid reaction (MLR) in recipients administered control rat IgG and those administered anti-CD70 antibody. Corneal expression of IFN-γ and IL-12 was also examined in both groups. Graft opacity was assessed over an 8-week period and graft survival was evaluated using Kaplan-Meier survival curves. Proportion of CD4⁺CD44⁺ memory T cells in lymph nodes was measured by flow cytometry.

RESULTS

CD4⁺CD27⁺ cells and CD11c⁺CD70⁺ cells were present in rejected cornea. Anti-CD70 antibody administration suppressed alloreactivity in corneal allograft recipients, and inhibited IFN-γ expression in recipient cornea (p < 0.05). Anti-CD70 antibody suppressed opacity score of recipient cornea and prolonged corneal allograft survival (p < 0.05). Proportion of CD4⁺CD44⁺ memory T cells in recipient lymph nodes was reduced by anti-CD70 antibody treatment.

CONCLUSION

The CD27/CD70 pathway plays a significant role in corneal allograft rejection by initiating alloreactive Th1 cells and preserving memory T cells. Anti-CD70 antibody administration prolongs corneal allograft survival indicating the potential therapeutic effect of CD27/CD70 pathway blockade on corneal allograft rejection.

Galectins and their involvement in ocular disease and development

Galectins are carbohydrate binding proteins with high affinity to ß-galactoside containing glycoconjugates. Understanding of the functions of galectins has grown steadily over the past decade, as a result of substantial advancements in the field of glycobiology. Galectins have been shown to be versatile molecules that participate in a range of important biological systems, including inflammation, neovascularisation and fibrosis. These processes are of particular importance in ocular tissues, where a major theme of recent research has been to divert diseases away from pathways which result in loss of function into pathways of repair and regeneration. This review summarises our current understanding of galectins in the context important ocular diseases, followed by an update on current clinical studies and future directions.

Immune Checkpoints Contribute Corneal Immune Privilege: Implications for Dry Eye Associated with Checkpoint Inhibitors

The eye is provided with immune protection against pathogens in a manner that greatly reduces the threat of inflammation-induced vision loss. Immune-mediated inflammation and allograft rejection are greatly reduced in the eye, a phenomenon called 'immune privilege'. Corneal tissue has inherent immune privilege properties with underlying three mechanisms: (1) anatomical, cellular, and molecular barriers in the cornea; (2) an immunosuppressive microenvironment; and (3) tolerance related to regulatory T cells and anterior chamber-associated immune deviation. This review describes the molecular mechanisms of the immunosuppressive microenvironment and regulatory T cells in the cornea that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, it also provides an update on immune checkpoint molecules in corneal and systemic immune regulation, and its relevance for dry eye associated with checkpoint inhibitor therapy.

VISTA Is Crucial for Corneal Allograft Survival and Maintenance of Immune Privilege

Purpose

V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel immune checkpoint receptor and ligand for regulating T cell proliferation and cytokine production. The purpose of the present study was to determine the role of VISTA in the immune privilege of corneal allografts.

Methods

Expression of VISTA mRNA in mouse eyes was assessed with reverse-transcription PCR. Corneas of C57BL/6 mice were orthotopically transplanted into the eyes of BALB/c wild-type recipients treated with anti-VISTA mAb, and graft survival was assessed. A separate set of BALB/c mice treated with anti-VISTA mAb or rat IgG received injection of C57BL/6 splenocytes into the anterior chamber, and induction of allospecific anterior chamber-associated immune deviation (ACAID) was assessed. CD4+ and CD8+ T cells in the spleen were assessed with flow cytometry.

Results

VISTA mRNA was constitutively expressed in the cornea, and the expression of VISTA was localized to CD11b+ cells on the corneal stroma. Survival of allografts treated with anti-VISTA mAb was less than that of the control. ACAID was induced less efficiently in BALB/c mice treated with VISTA mAb. The proportions of CD8+ T cells and CD8+ CD103+ T cells (CD8+ T regulatory cells) in the spleen of BALB/c mice treated with anti-VISTA mAb were significantly lower than those of the control.

Conclusions

VISTA may play an essential role in the acceptance of corneal allografts via involvement with allospecific ACAID, which suppresses T cell infiltration into the cornea.

Assessment of serum Tim-3 and Gal-9 levels in predicting the risk of infection after kidney transplantation

Infection remains a major cause of morbidity and mortality after kidney transplantation (KT). Reliable biomarkers to predict post-transplant infection are lacking. We investigated the predictive performance of pre- and post-transplant levels of T-cell immunoglobulin and mucin domain-3 (Tim-3) and Galectin-9 (Gal-9), two pleiotropic immunomodulatory molecules, in early identification of infection. Serum Tim-3 and Gal-9 were paired measured before and 30 days after transplantation (PTD 30) in 95 KT recipients (KTRs). The decline rates of Tim-3 and Gal-9 were calculated relative to pre-transplant levels. KTRs with infection history had significantly higher levels of PTD 30 Tim-3 and Gal-9, and slower decrease rates of Gal-9 compared to non-infected recipients, while no difference was observed between two groups regarding pre-transplant levels. The AUCs for predicting 1-year post-transplant infection were 0.653 and 0.711 for post-transplant Tim-3 and Gal-9, 0.664 and 0.670 for relative Tim-3 and Gal-9, respectively. After adjusting for potential confounders, PTD 30 Tim-3, Gal-9 and relative Gal-9 remained as independent risk factors for post-transplant infection. Our results suggested that PTD 30 Tim-3 and Gal-9 and relative decrease of Gal-9 were promising predictors for identifying KTRs with high risk of infection, while pre-transplant Tim-3 and Gal-9 showed no predictive power to infection.

Immune privilege in corneal transplantation

Corneal transplantation is the most successful solid organ transplantation performed in humans. The extraordinary success of orthotopic corneal allografts, in both humans and experimental animals, is related to the phenomenon of "immune privilege". Inflammation is self-regulated to preserve ocular functions because the eye has immune privilege. At present, three major mechanisms are considered to provide immune privilege in corneal transplantation: 1) anatomical, cellular, and molecular barriers in the cornea; 2) tolerance related to anterior chamber-associated immune deviation and regulatory T cells; and 3) an immunosuppressive intraocular microenvironment. This review describes the mechanisms of immune privilege that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, and its relevance for the clinic. An update on molecular, cellular, and neural interactions in local and systemic immune regulation is provided. Therapeutic strategies for restoring immune privilege are also discussed.

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.

The Effects of Anti-LAP Monoclonal Antibody Down-regulation of CD4+LAP+ T Cells on Allogeneic Corneal Transplantation in Mice

CD4+latency-associated peptide (LAP)+ T cells are a newly discovered T cell subset with suppressive function on immune responses. In this study, we investigate the role of CD4+LAP+ T cells on mice corneal allograft survival by down-regulating their expression using anti-LAP mAb. We show that a blockage of LAP leads to a decrease in the percentage of T cells expressing CD4+Foxp3+, CD4+GARP+, CD4+LAP+ and CD4+IL-10+ in the lymph nodes and spleens of mice undergoing orthotopic penetrating transplantation of corneal allograft, without affecting corneal graft survival. In addition, higher percentages of CD4+IFN-γ+ and CD4+IL-17A+ T cells in the lymph nodes and spleens, as well as TNF, IFN-γ, IL-17A and IL-6 levels in the aqueous humor, significantly increase in mice with rejected corneal grafts. The expression of TGF-β1 decreases in corneal grafts during corneal rejection period. It is therefore possible that anti-LAP mAb can down-regulate the regulatory T cell subsets with its immunosuppressive effects. The rejection of corneal grafts seems to mainly be associated with the up-regulation of Th1 and Th17 cell subsets in peripheral lymph nodes.

The Balance of Th1/Th2 and LAP+Tregs/Th17 Cells Is Crucial for Graft Survival in Allogeneic Corneal Transplantation

Purpose

CD4+LAP+ T cells are newly discovered regulatory T cells (Tregs). The aim of this study is to investigate the balance of Th1/Th2 and LAP+Tregs/Th17 in mice after allogeneic corneal transplantation.

Methods

A total of 65 mice received orthotopic penetrating transplantation. According to the survival scores of the grafts, the mice were divided into the rejection group and the survival group 3 weeks after transplantation. Th1, Th2, Th17, and regulatory T cells in the ipsilateral drainage lymph nodes and spleens were measured with flow cytometry. The related cytokines in aqueous humor were also analyzed.

Results

The frequencies of Foxp3+Tregs, GARP+Tregs, and LAP+Tregs in the survival group were significantly higher than those in the rejection group. And the expression trend of CD4+LAP+ T cells and CD4+GARP+ T cells was consistent. The level of IFN-γ, TNF, IL-6, and IL-17A markedly increased in aqueous humor during corneal allograft rejection. The ratio of Th1/Th2 and Th17/LAP+Tregs significantly increased in the rejection group at the 3rd week after corneal transplantation.

Conclusion

LAP+Tregs might be regarded as substitute for Foxp3+Tregs. The balance of Th1/Th2 and LAP+Tregs/Th17 is crucial for corneal allograft survival.

Galectin-9: From cell biology to complex disease dynamics

Galectins is a family of non-classically secreted, beta-galactoside-binding proteins that has recently received considerable attention in the spatio-temporal regulation of surface 'signal lattice' organization, membrane dynamics, cell-adhesion and disease therapeutics. Galectin-9 is a unique member of this family, with two non-homologous carbohydrate recognition domains joined by a linker peptide sequence of variable lengths, generating isoforms with distinct properties and functions in both physiological and pathological settings, such as during development, immune reaction, neoplastic transformations and metastasis. In this review, we summarize the latest knowledge on the structure, receptors, cellular targets, trafficking pathways and functional properties of galectin-9 and discuss how galectin-9-mediated signalling cascades can be exploited in cancers and immunotherapies.

Advances in targeting co-inhibitory and co-stimulatory pathways in transplantation settings: the Yin to the Yang of cancer immunotherapy

In the past decade, the power of harnessing T-cell co-signaling pathways has become increasingly understood to have significant clinical importance. In cancer immunotherapy, the field has concentrated on two related modalities: First, targeting cancer antigens through highly activated chimeric antigen T cells (CAR-Ts) and second, re-animating endogenous quiescent T cells through checkpoint blockade. In each of these strategies, the therapeutic goal is to re-ignite T-cell immunity, in order to eradicate tumors. In transplantation, there is also great interest in targeting T-cell co-signaling, but with the opposite goal: in this field, we seek the Yin to cancer immunotherapy's Yang, and focus on manipulating T-cell co-signaling to induce tolerance rather than activation. In this review, we discuss the major T-cell signaling pathways that are being investigated for tolerance induction, detailing preclinical studies and the path to the clinic for many of these molecules. These include blockade of co-stimulation pathways and agonism of coinhibitory pathways, in order to achieve the delicate state of balance that is transplant tolerance: a state which guarantees lifelong transplant acceptance without ongoing immunosuppression, and with preservation of protective immune responses. In the context of the clinical translation of immune tolerance strategies, we discuss the significant challenge that is embodied by the fact that targeted pathway modulators may have opposing effects on tolerance based on their impact on effector vs regulatory T-cell biology. Achieving this delicate balance holds the key to the major challenge of transplantation: lifelong control of alloreactivity while maintaining an otherwise intact immune system.

High-risk corneal allografts: A therapeutic challenge

Corneal transplantation is the most common surgical procedure amongst solid organ transplants with a high survival rate of 86% at 1-year post-grafting. This high success rate has been attributed to the immune privilege of the eye. However, mechanisms originally thought to promote immune privilege, such as the lack of antigen presenting cells and vessels in the cornea, are challenged by recent studies. Nevertheless, the immunological and physiological features of the cornea promoting a relatively weak alloimmune response is likely responsible for the high survival rate in “low-risk” settings. Furthermore, although corneal graft survival in “low-risk” recipients is favourable, the prognosis in “high-risk” recipients for corneal graft is poor. In “high-risk” grafts, the process of indirect allorecognition is accelerated by the enhanced innate and adaptive immune responses due to pre-existing inflammation and neovascularization of the host bed. This leads to the irreversible rejection of the allograft and ultimately graft failure. Many therapeutic measures are being tested in pre-clinical and clinical studies to counter the immunological challenge of “high-risk” recipients. Despite the prevailing dogma, recent data suggest that tissue matching together with use of systemic immunosuppression may increase the likelihood of graft acceptance in “high-risk” recipients. However, immunosuppressive drugs are accompanied with intolerance/side effects and toxicity, and therefore, novel cell-based therapies are in development which target host immune cells and restore immune homeostasis without significant side effect of treatment. In addition, developments in regenerative medicine may be able to solve both important short comings of allotransplantation: (1) graft rejection and ultimate graft failure; and (2) the lack of suitable donor corneas. The advances in technology and research indicate that wider therapeutic choices for patients may be available to address the worldwide problem of corneal blindness in both “low-risk” and “high-risk” hosts.

Comparison of galectin expression signatures in rejected and accepted murine corneal allografts

PURPOSE

Although members of the galectin family of carbohydrate-binding proteins are thought to play a role in the immune response and regulation of allograft survival, little is known about the galectin expression signature in failed corneal grafts. The aim of this study was to compare the galectin expression pattern in accepted and rejected murine corneal allografts.

METHODS

Using BALB/c mice as recipients and C57BL/6 mice as donors, a total of 57 transplants were successfully performed. One week after transplantation, the grafts were scored for opacity by slit-lamp microscopy. Opacity scores of 3+ or greater on postoperative week 4 were considered rejected. Grafted corneas were harvested on postoperative week 4, and their galectin expressions were analyzed by Western blot and immunofluorescence staining.

RESULTS

As determined by the Western blot analyses, galectins-1, 3, 7, 8 and 9 were expressed in normal corneas. Although in both accepted and rejected grafts, expression levels of the 5 lectins were upregulated compared with normal corneas, there were distinct differences in the expression levels of galectins-8 and 9 between accepted and rejected grafts, as both the Western blot and immunofluorescence staining revealed that galectin-8 is upregulated, whereas galectin-9 is downregulated in the rejected grafts compared with the accepted grafts.

CONCLUSIONS

Our findings that corneal allograft rejection is associated with increased galectin-8 expression and reduced galectin-9 expression, support the hypothesis that galectin-8 may reduce graft survival, whereas galectin-9 may promote graft survival. As a potential therapeutic intervention, inhibition of galectin-8 and/or treatment with exogenous galectin-9 may enhance corneal allograft survival rates.

Negative CD4 + TIM-3 signaling confers resistance against cold preservation damage in mouse liver transplantation

Ischemia-reperfusion injury (IRI), an innate immunity-driven local inflammation, remains the major problem in clinical organ transplantation. T cell immunoglobulin and mucin domain (TIM-3)-Galectin-9 (Gal-9) signaling regulates CD4+ Th1 immune responses. Here, we explored TIM-3-Gal-9 function in a clinically relevant murine model of hepatic cold storage and orthotopic liver transplantation (OLT). C57BL/6 livers, preserved for 20 h at 4°C in UW solution, were transplanted to syngeneic mouse recipients. Up-regulation of TIM-3 on OLT-infiltrating activated CD4+ T cells was observed in the early IRI phase (1 h). By 6 h of reperfusion, OLTs in recipients treated with a blocking anti-TIM-3 Ab were characterized by: (1) enhanced hepatocellular damage (sALT levels, liver Suzuki's histological score); (2) polarized cell infiltrate towards Th1/Th17-type phenotype; (3) depressed T cell exhaustion markers (PD-1, LAG3); and (4) elevated neutrophil and macrophage infiltration/activation. In parallel studies, adoptive transfer of CD4+ T cells from naïve WT, but not from TIM-3 Tg donors, readily recreated OLT damage in otherwise IR-resistant RAG(-/-) test recipients. Furthermore, pre-treatment of mice with rGal-9 promoted hepatoprotection against preservation-association liver damage, accompanied by enhanced TIM-3 expression in OLTs. Thus, CD4+ T cell-dependent "negative" TIM-3 costimulation is essential for hepatic homeostasis and resistance against IR stress in OLTs.

Recipient T cell TIM-3 and hepatocyte galectin-9 signalling protects mouse liver transplants against ischemia-reperfusion injury

BACKGROUND & AIMS

By binding to T cell immunoglobulin mucin-3 (TIM-3) on activated Th1 cells, galectin-9 (Gal-9) negatively regulates Th1-type alloimmunity. Although T cells contribute to hepatic ischemia-reperfusion injury (IRI), it is unknown whether negative T cell-dependent TIM-3 co-stimulation may rescue IR-stressed orthotopic liver transplants from innate immunity-driven inflammation.

METHODS

We used wild type (WT) and TIM-3 transgenic (Tg) mice (C57BL/6) as liver donors and recipients in a clinically-relevant model of hepatic cold storage (20 h at 4°C in UW solution) and syngeneic orthotopic liver transplantation (OLT).

RESULTS

Orthotopic liver transplants in WT or TIM-3Tg→TIM-3Tg groups were resistant against IR-stress, evidenced by preserved hepatocellular function (serum ALT levels) and liver architecture (Suzuki's score). In contrast, orthotopic liver transplants in WT or TIM-3Tg→WT groups were susceptible to IRI. TIM-3 induction in circulating CD4+ T cells of the recipient: (1) depressed T-bet/IFN-γ, while amplifying GATA3 and IL-4/IL-10 expression in orthotopic liver transplants; (2) promoted T cell exhaustion (PD-1, LAG-3) phenotype; and (3) depressed neutrophil and macrophage infiltration/function in orthotopic liver transplants. In parallel studies, we documented for the first time that Gal-9, a natural TIM-3 ligand, was produced primarily by and released from IR-stressed hepatocytes, both in vivo and in vitro. Moreover, exogenous recombinant Gal-9 (rGal-9) potentiated liver resistance against IRI by depressing T cell activation and promoting apoptosis of CD4+ T cells.

CONCLUSIONS

Harnessing TIM-3/Gal-9 signalling at the T cell-hepatocyte interface facilitates homeostasis in IR-stressed orthotopic liver transplants. Enhancing anti-oxidant hepatocyte Gal-9 potentiates liver IR-resistance. Negative regulation by recipient TIM-3+CD4+ cells provides evidence for cytoprotective functions of a discrete T cell subset, which should be spared when applying T cell-targeted immunosuppression in transplant recipients.

Fingerprinting of galectins in normal, P. aeruginosa-infected, and chemically burned mouse corneas

PURPOSE

In this study, we aimed to assess whether the expression pattern of galectins is altered in Pseudomonas aeruginosa-infected and chemically burned mouse corneas.

METHODS

Galectin (Gal) fingerprinting of normal, P. aeruginosa-infected, and silver nitrate-cauterized corneas was performed by Western blotting, immunofluorescence staining, and qRT-PCR.

RESULTS

In normal corneas, Gal-1 was distributed mainly in the stroma, Gal-3 was localized mainly in epithelium, and Gal-7, -8, and -9 were detected in both corneal epithelium and stroma. Expression levels of the five galectins were drastically altered under pathological conditions. In both infected and cauterized corneas, overall Gal-3 expression was downregulated, whereas overall Gal-8 and -9 were upregulated. Changes in the expression level of Gal-7, -8, and -9 were distinct in the epithelium of infected and cauterized corneas. Expression of these three galectins was upregulated in corneal epithelium of infected corneas but not in cauterized corneas. Consistent with the changes in protein expression: (1) Gal-7, -8, and -9 mRNA expression was upregulated in cauterized corneas, and (2) Gal-3 mRNA was downregulated and Gal-9 mRNA expression was upregulated in infected corneas.

CONCLUSIONS

Our data demonstrate differential regulation of various members of the galectin family in the course of corneal infection and neovascularization. The emerging functionality of the sugar code of cell surface receptors via endogenous galectins reflect to the pertinent roles of the five tested galectins in the diseases of cornea.

Microglia activity modulated by T cell Ig and mucin domain protein 3 (Tim-3)

Microglia are the main innate immune cells in the central nervous system that are actively involved in maintaining brain homeostasis and diseases. T cell Ig and mucin domain protein 3 (Tim-3) plays critical roles in both the adaptive and the innate immune system and is an emerging therapeutic target for treatment of various disorders. In the brain Tim-3 is specifically expressed on microglia but its functional role is unclear. Here, we showed that Tim-3 was up-regulated on microglia by ATP or LPS stimulation. Tim-3 activation with antibodies increased microglia expression of TGF-β, TNF-α and IL-1β. Blocking of Tim-3 with antibodies decreased the microglial phagocytosis of apoptotic neurons. Tim-3 blocking alleviated the detrimental effect of microglia on neurons and promoted NG2 cell differentiation in co-cultures. Finally, MAPKs namely ERK1/2 and JNK proteins were phosphorylated upon Tim-3 activation in microglia. Data indicated that Tim-3 modulates microglia activity and regulates the interaction of microglia-neural cells.

Murine corneal transplantation: a model to study the most common form of solid organ transplantation

Corneal transplantation is the most common form of organ transplantation in the United States with between 45,000 and 55,000 procedures performed each year. While several animal models exist for this procedure and mice are the species that is most commonly used. The reasons for using mice are the relative cost of using this species, the existence of many genetically defined strains that allow for the study of immune responses, and the existence of an extensive array of reagents that can be used to further define responses in this species. This model has been used to define factors in the cornea that are responsible for the relative immune privilege status of this tissue that enables corneal allografts to survive acute rejection in the absence of immunosuppressive therapy. It has also been used to define those factors that are most important in rejection of such allografts. Consequently, much of what we know concerning mechanisms of both corneal allograft acceptance and rejection are due to studies using a murine model of corneal transplantation. In addition to describing a model for acute corneal allograft rejection, we also present for the first time a model of late-term corneal allograft rejection.

Matricellular proteins in the trabecular meshwork: review and update

Abstract Primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide, and intraocular pressure (IOP) is an important modifiable risk factor. IOP is a function of aqueous humor production and aqueous humor outflow, and it is thought that prolonged IOP elevation leads to optic nerve damage over time. Within the trabecular meshwork (TM), the eye's primary drainage system for aqueous humor, matricellular proteins generally allow cells to modulate their attachments with and alter the characteristics of their surrounding extracellular matrix (ECM). It is now well established that ECM turnover in the TM affects outflow facility, and matricellular proteins are emerging as significant players in IOP regulation. The formalized study of matricellular proteins in TM has gained increased attention. Secreted protein acidic and rich in cysteine (SPARC), myocilin, connective tissue growth factor (CTGF), and thrombospondin-1 and -2 (TSP-1 and -2) have been localized to the TM, and a growing body of evidence suggests that these matricellular proteins play an important role in IOP regulation and possibly the pathophysiology of POAG. As evidence continues to emerge, these proteins are now seen as potential therapeutic targets. Further study is warranted to assess their utility in treating glaucoma in humans.