Effect of CXCL-1/KC production in high risk vascularized corneal allografts on T cell recruitment and graft rejection

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.

Use of Post-transplant Cyclophosphamide Treatment to Build a Tolerance Platform to Prevent Liquid and Solid Organ Allograft Rejection

Corneal transplantation (CT) is the most frequent type of solid organ transplant (SOT) performed worldwide. Unfortunately, immunological rejection is the primary cause of graft failure for CT and therefore advances in immune regulation to induce tolerance remains an unmet medical need. Recently, our work and others in pre-clinical studies found that cyclophosphamide (Cy) administered after (“post-transplant,” PTCy) hematopoietic stem cell transplantation (HSCT), i.e., liquid transplants is effective for graft vs. host disease prophylaxis and enhances overall survival. Importantly, within the past 10 years, PTCy has been widely adopted for clinical HSCT and the results at many centers have been extremely encouraging. The present studies found that Cy can be effectively employed to prolong the survival of SOT, specifically mouse corneal allografts. The results demonstrated that the timing of PTCy administration is critical for these CT and distinct from the kinetics employed following allogeneic HSCT. PTCy was observed to interfere with neovascularization, a process critically associated with immune rejection of corneal tissue that ensues following the loss of ocular “immune privilege.” PTCy has the potential to delete or directly suppress allo-reactive T cells and treatment here was shown to diminish T cell rejection responses. These PTCy doses were observed to spare significant levels of CD4⁺ FoxP3⁺ (Tregs) which were found to be functional and could readily receive stimulating signals leading to their in vivo expansion via TNFRSF25 and CD25 agonists. In total, we posit future studies can take advantage of Cy based platforms to generate combinatorial strategies for long-term tolerance induction.

The cornea IV immunology, infection, neovascularization, and surgery chapter 1: Corneal immunology

PURPOSE

of Review: This review offers an informed and up-to-date insight on the immune profile of the cornea and the factors that govern the regulation of such a unique immune environment.

SUMMARY

The cornea is a unique tissue that performs the specialized task of allowing light to penetrate for visual interpretation. To accomplish this, the ocular surface requires a distinct immune environment that is achieved through unique structural, cellular and molecular factors. Not only must the cornea be able to fend off invasive infectious agents but also control the inflammatory response as to avoid collateral, and potentially blinding damage; particularly of post-mitotic cells such as the corneal endothelium. To combat infections, both innate and adaptive arms of the inflammatory immune response are at play in the cornea. Dendritic cells play a critical role in coordinating both these responses in order to fend off infections. On the other side of the spectrum, the ocular surface is also endowed with a variety of anatomic and physiologic components that aid in regulating the immune response to prevent excessive, potentially damaging, inflammation. This attenuation of the immune response is termed immune privilege. The balance between pro and anti-inflammatory reactions is key for preservation of the functional integrity of the cornea.

RECENT FINDINGS

The understanding of the molecular and cellular factors governing corneal immunology and its response to antigens is a growing field. Dendritic cells in the normal cornea play a crucial role in combating infections and coordinating the inflammatory arms of the immune response, particularly through coordination with T-helper cells. The role of neuropeptides is recently becoming more highlighted with different factors working on both sides of the inflammatory balance.

Animal models of high-risk corneal transplantation: A comprehensive review

Over the past century, corneal transplantation has become the most commonly performed allogeneic solid tissue transplantation. Although more than 80% of the corneal transplantations have favorable outcomes, immune-mediated rejection continues to be the major cause of failure in well over 50% of graft recipients that have inflamed and vascularized host beds. Over the past two decades, the progress in our understanding of the immunological pathways that mediate graft rejection has aided in the development of novel therapeutic strategies. In order to successfully test the efficacy of these interventions, it is essential to model the immunological processes occurring as a consequence of corneal transplantation. Herein, we have comprehensively reviewed the established animal models used for replicating the immunopathological processes causing graft rejection in high-risk corneal transplantation settings. We have also discussed the practical and technical differences, as well as biological and immunological variations in different animal models.

Immune reactions after modern lamellar (DALK, DSAEK, DMEK) versus conventional penetrating corneal transplantation

In the past decade, novel lamellar keratoplasty techniques such as Deep Anterior Lamellar Keratoplasty (DALK) for anterior keratoplasty and Descemet stripping automated endothelial keratoplasty (DSAEK)/Descemet membrane endothelial keratoplasty (DMEK) for posterior keratoplasty have been developed. DALK eliminates the possibility of endothelial allograft rejection, which is the main reason for graft failure after penetrating keratoplasty (PK). Compared to PK, the risk of endothelial graft rejection is significantly reduced after DSAEK/DMEK. Thus, with modern lamellar techniques, the clinical problem of endothelial graft rejection seems to be nearly solved in the low-risk situation. However, even with lamellar grafts there are epithelial, subepithelial and stromal immune reactions in DALK and endothelial immune reactions in DSAEK/DMEK, and not all keratoplasties can be performed in a lamellar fashion. Therefore, endothelial graft rejection in PK is still highly relevant, especially in the "high-risk" setting, where the cornea's (lymph)angiogenic and immune privilege is lost due to severe inflammation and pathological neovascularization. For these eyes, currently available treatment options are still unsatisfactory. In this review, we will describe currently used keratoplasty techniques, namely PK, DALK, DSAEK, and DMEK. We will summarize their indications, provide surgical descriptions, and comment on their complications and outcomes. Furthermore, we will give an overview on corneal transplant immunology. A specific focus will be placed on endothelial graft rejection and we will report on its incidence, clinical presentation, and current/future treatment and prevention options. Finally, we will speculate how the field of keratoplasty and prevention of corneal allograft rejection will develop in the future.

Effect of improved preservation solution with methoxy polyethylene glycol succinimidyl propionate on rat cornea

To observe the effect of DMEM/F12 pegylated with methoxy polyethylene glycol succinimidyl propionate (mPEG-SPA) on the biophysical and immune characteristics of the rat cornea preserved in it. Corneal grafts were harvested from Wistar rat and preserved in the DMEM/F12 plus mPEG-SPA, DMEM/F12 without mPEG-SPA, and standard Optisol-GS solution at 4 °C for 14 days, referred as plus-PEG, minus-PEG, and Optisol grafts, respectively. The biophysical properties of those grafts, including transmittance, thickness, water content, and biomechanics were investigated. The survival of those grafts was observed in the high-risk corneal transplantation model. Transmittance and biomechanics did not show any differences among those grafts. Thickness and water content of plus-PEG grafts were slightly improved. Proliferation and activation of lymphocytes were lower while they were incubated with plus-PEG grafts, compared with minus-PEG grafts and Optisol grafts. The mean survival time was significantly prolonged in plus-PEG grafts. DMEM/F12 solution plus mPEG-SPA improved the survival of corneal grafts and maintained the comparative biophysical characteristics of them, compared with the standard preservation solution.

Visualization of Immune Responses in the Cornea

The eye has become a useful site for the investigation and understanding of local and systemic immune responses. The ease of access and transparency of the cornea permits direct visualization of ocular structures, blood vessels, and lymphatic vessels, allowing for the tracking of normal and pathological biological processes in real time. As a window to the immune system, we have used the eye to dissect the mechanisms of corneal inflammatory reactions that include innate and adaptive immune responses. We have identified that the ocular microenvironment regulates these immune responses by recruiting different populations of inflammatory cells to the cornea through local production of selected chemokines. Moreover, crosstalk between T cells and macrophages is a common and crucial step in the development of ocular immune responses to corneal alloantigens. This review summarizes the data generated by our group using intravital fluorescent confocal microscopy to capture the tempo, magnitude, and function of innate and adaptive corneal immune responses.

Effector and Regulatory T Cell Trafficking in Corneal Allograft Rejection

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

Endostatin's emerging roles in angiogenesis, lymphangiogenesis, disease, and clinical applications

BACKGROUND

Angiogenesis is the process of neovascularization from pre-existing vasculature and is involved in various physiological and pathological processes. Inhibitors of angiogenesis, administered either as individual drugs or in combination with other chemotherapy, have been shown to benefit patients with various cancers. Endostatin, a 20-kDa C-terminal fragment of type XVIII collagen, is one of the most potent inhibitors of angiogenesis.

SCOPE OF REVIEW

We discuss the biology behind endostatin in the context of its endogenous production, the various receptors to which it binds, and the mechanisms by which it acts. We focus on its inhibitory role in angiogenesis, lymphangiogenesis, and cancer metastasis. We also present emerging clinical applications for endostatin and its potential as a therapeutic agent in the form a short peptide.

MAJOR CONCLUSIONS

The delicate balance between pro- and anti-angiogenic factors can be modulated to result in physiological wound healing or pathological tumor metastasis. Research in the last decade has emphasized an emerging clinical potential for endostatin as a biomarker and as a therapeutic short peptide. Moreover, elevated or depressed endostatin levels in diseased states may help explain the pathophysiological mechanisms of the particular disease.

GENERAL SIGNIFICANCE

Endostatin was once sought after as the 'be all and end all' for cancer treatment; however, research throughout the last decade has made it apparent that endostatin's effects are complex and involve multiple mechanisms. A better understanding of newly discovered mechanisms and clinical applications still has the potential to lead to future advances in the use of endostatin in the clinic.

Chemokine CXCL-1: activity in the vitreous during proliferative vitreoretinopathy

The aim of this study was to investigate CXCL-1 chemokine levels in the vitreous during rhegmatogenous retinal detachment (RRD) with and without proliferative vitreoretinopathy (PVR) and identify possible correlations with clinical parameters (extent and duration or RRD and PVR grade). Vitreous samples from patients with primary RRD with or without PVR were collected and assayed using a double antibody enzyme-linked immunosorbent assay (ELISA). Eleven vitreous samples from organ donors were employed as a control group. CXCL-1 levels were measured in 35 vitreous samples from 35 RRD patients. Mean CXCL-1 levels (64·82 ± 6·47 pg/ml) were significantly higher (P = 0·048) compared to controls. There was a significant positive correlation between CXCL-1 levels and the extent of the detachment (r = 0·794, P = 0·006). Peak CXCL-1 levels coincided with 3+ quadrant RRD, an interim of 29-60 days' duration and PVR grade B. Increased CXCL-1 levels may be indicative of mild inflammation in the detached retina and the adjacent vitreous. The results of the present study may provide novel insight into the complex interactions taking place during the early and late stages of RRD complicated by PVR.

Clinical correlates of common corneal neovascular diseases: a literature review

A large subset of corneal pathologies involves the formation of new blood and lymph vessels (neovascularization), leading to compromised visual acuity. This article aims to review the clinical causes and presentations of corneal neovascularization (CNV) by examining the mechanisms behind common CNV-related corneal pathologies, with a particular focus on herpes simplex stromal keratitis, contact lenses-induced keratitis and CNV secondary to keratoplasty. Moreover, we reviewed CNV in the context of different types of corneal transplantation and keratoprosthesis, and summarized the most relevant treatments available so far.

Treatment with mPEG-SPA improves the survival of corneal grafts in rats by immune camouflage

We investigated the immune camouflage effects of methoxy polyethylene glycol succinimidyl propionate (mPEG-SPA) on corneal antigens and explored a novel approach for reducing corneal antigenicity, thereby decreasing corneal graft rejection. Importantly, this approach did not alter normal local immunity. Corneal grafts were treated with mPEG-SPA 5KD or 20KD (3% W/V), which could shield major histocompatibility antigen class I molecules (RT1-A) of corneal grafts. Skin grafts of Wistar rats were transplanted to SD rats. Then the splenic lymphocytes were isolated from SD rats. Subsequently, the lymphocytes were co-cultured with autologous corneal grafts or untreated corneal grafts and PEGylated grafts treated with mPEG-SPA 5KD or 20KD obtained from the counterpart skin donors, which were used as autologous control, allogeneic control, mPEG-SPA 5KD group and mPEG-SPA 20KD group, respectively. Lymphocyte proliferation was lower in mPEG-SPA 5KD group and mPEG-SPA 20KD group than in the allogeneic control. SD rats with corneal neovascularisation were used as recipients for high-risk corneal transplantation and were randomly divided into four groups: autologous control, allogeneic control, mPEG-SPA 5KD group and mPEG-SPA 20KD group. The recipients received corneal grafts from Wistar rats. Corneal graft survival was prolonged and graft rejection was reduced in the mPEG-SPA 5KD group and the mPEG-SPA 20KD group compared to the allogeneic control. Thus, we think that mPEG-SPA could immunologically camouflage corneal antigens to prolong corneal grafts survival in high-risk transplantation.

Cytokine deposition alters leukocyte morphology and initial recruitment of monocytes and γδT cells after corneal injury

PURPOSE

An in vivo mouse model reproducibly induces recurrent epithelial erosions in wild-type mice spontaneously 2 weeks after a single 1.5-mm corneal debridement wound made with a dulled blade. When 1.5-mm wounds are made by a rotating burr so that the corneal epithelial basement membrane is removed, corneas heal without developing erosions. Here, we characterize differences in cytokine deposition and changes in leukocytes between 0 and 6 hours after dulled-blade and rotating-burr wounding.

METHODS

BALB/c mice were used to study 1.5-mm corneal wounds made using a dulled blade or a rotating burr. Mice were studied immediately after wounding (0 hour) and at 6 hours in vivo and in vitro in organ culture. Corneas, corneal extracts, and collagenase digests from naïve and wounded mice were used for three-dimensional (3D) confocal imaging, cytokine arrays, and flow cytometry.

RESULTS

Confocal imaging showed CD45, a protein derived from leukocytes, accumulates at the wound edge by 3 and 6 hours after wounding in vivo but not in vitro with more CD45 accumulating after dulled-blade compared with rotating-burr wounds. Morphologic changes occurred in CD45+ leukocytes and higher levels for several cytokines were detected in the stromal wound bed within minutes following dulled-blade wounds. Flow cytometry showed significantly more monocytes (CD45+/CD11b+/Ly6C+) and γδT cells (CD45+/GL3+) recruited into the corneas of mice with dulled-blade wounds by 6 hours.

CONCLUSIONS

Differences in cytokine-driven leukocyte responses are seen after dulled-blade debridement compared with rotating-burr injury.

In vivo downregulation of innate and adaptive immune responses in corneal allograft rejection by HC-HA/PTX3 complex purified from amniotic membrane

PURPOSE

Heavy chain-hyaluronic acid (HC-HA)/PTX3 purified from human amniotic membrane (AM) was previously observed to suppress inflammatory responses in vitro. We now examine whether HC-HA/PTX3 is able to exert a similar effect in vivo, using murine models for keratitis and corneal allograft rejection.

METHODS

The in vitro effect of HC-HA/PTX3 was tested using OTII ovalbumin (OVA) transgenic, purified CD4(+) T cells, or IFN-γ/lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Cytokine production was measured by ELISA, while cell surface markers and cell proliferation were determined by flow cytometry. In vivo effects of HC-HA/PTX3 were analyzed by quantifying the recruitment of enhanced green fluorescence-labeled macrophages and by measuring the expression of arginase 1 (Arg-1), IL-10, and IL-12 in LPS-induced keratitis in the macrophage Fas-induced apoptosis (Mafia) mouse. The effect of corneal allograft survival in a complete major histocompatibility complex (MHC) mismatched mouse model was assessed by grading corneal opacification.

RESULTS

In vitro studies demonstrated that HC-HA/PTX3 significantly enhanced the expansion of FOXP3 T cells and suppressed cell proliferation and protein expression of IFN-γ, IL-2, CD25, and CD69 in activated CD4(+) T cells. Furthermore, immobilized HC-HA/PTX3 significantly upregulated IL-10 gene expression but downregulated that of IL-12 and IL-23 in activated RAW264.7 cells. Finally, in vivo subconjunctival injection of HC-HA/PTX3 significantly prolonged corneal allograft survival, suppressed macrophage infiltration, and promoted M2 polarization by upregulating Arg-1 and IL-10 but downregulating IL-12.

CONCLUSIONS

HC-HA/PTX3 can suppress inflammatory responses in vivo by modulating both innate and adaptive immunity of macrophages and CD4(+) T cells.

Wounding the cornea to learn how it heals

Corneal wound healing studies have a long history and rich literature that describes the data obtained over the past 70 years using many different species of animals and methods of injury. These studies have lead to reduced suffering and provided clues to treatments that are now helping patients live more productive lives. In spite of the progress made, further research is required since blindness and reduced quality of life due to corneal scarring still happens. The purpose of this review is to summarize what is known about different types of wound and animal models used to study corneal wound healing. The subject of corneal wound healing is broad and includes chemical and mechanical wound models. This review focuses on mechanical injury models involving debridement and keratectomy wounds to reflect the authors' expertise.

Azithromycin treatment increases survival of high-risk corneal allotransplants

PURPOSE

To test the therapeutic efficacy of azithromycin (AZM), a macrolide antibiotic for prolonging murine "high-risk" corneal allograft survival.

METHODS

Fully major histocompatibility complex-mismatched corneas were transplanted from C57BL/6 donors to BALB/c recipients with suture-induced vascularized high-risk corneal beds. Recipient mice were either not treated or treated with topical AZM, oral AZM, or both. Evaluation of graft vascularization and clarity was performed in a masked fashion. Lymph nodes were excised and analyzed for CD4, FoxP3, and CD44 by flow cytometry, and for T-cell priming by proliferation and cytokine production in mixed lymphocyte cultures. Corneal whole mounts were evaluated by confocal microscopy.

RESULTS

The incidence of graft rejection in the control group (81.8%) was significantly reduced by AZM treatment (18.2% topical, 21.7% oral, 33.3% topical + oral), although corneal vascularization was not affected by the treatment. The frequency of corneas that retained complete clarity after transplantation was higher in the AZM-treated groups. Reduced graft rejection in the AZM-treated groups was not associated with a reduced allospecific T-cell response or increased frequency of regulatory T cells.

CONCLUSIONS

AZM is effective in prolonging survival of high-risk corneal allografts by an as yet undefined mechanism that does not seem to involve modulation of corneal neovascularization or allospecific T-cell priming.

Allograft survival enhancement using doxycycline in alkali-burned mouse corneas

PURPOSE

To explore the inhibitory effects of doxycycline on allograft rejection in alkali-burned cornea beds.

METHODS

The corneas of BALB/c mice were injured using a 1 mol/l NaOH solution. Following the injury, the corneas from C57BL/6 mice were transplanted into the eyes of BALB/c mice after being randomized into three groups: allogeneic corneal transplantation (group A), topical use of doxycycline after allogeneic corneal transplantation (group B) and syngeneic corneal transplantation (group C). Corneal angiogenesis was examined using whole-mount immunofluorescence, and corneal inflammation was evaluated using inflammation index scoring. The immune rejection of the grafts was examined using a slit lamp. In addition, the expression of vascular endothelial growth factor A and interleukin-1β in the transplanted corneas was examined using a real-time polymerase chain reaction, immunohistochemistry and an enzyme-linked immunosorbent assay.

RESULTS

The outgrowth of the corneal blood vessels in the group A mice was faster than that in the group B and group C mice. The inflammation index levels were highest in the group A mice, intermediate in the group B mice and lowest in the group C mice. Vascular endothelial growth factor and the interleukin-1β protein and mRNA levels decreased dramatically in the group B mice compared with the group A mice (all p-values < 0.01). In addition, the mean survival time in the group B mice (27.00 ± 2.00 days) was significantly longer than that in the group A mice (11.67 ± 1.51 days; p < 0.05).

CONCLUSIONS

Doxycycline may have had a significant role in preventing corneal angiogenesis and inflammation in alkali-burned corneal beds, which resulted in higher allograft survival rates.

The eye: A window to the soul of the immune system

The eye is considered as an immune privileged site, and with good reason. It has evolved a variety of molecular and cellular mechanisms that limit immune responses to preserve vision. For example, the cornea is mainly protected from autoimmunity by the lack of blood and lymphatic vessels, whereas the retina-blood barrier is maintained in an immunosuppressive state by the retinal pigment epithelium. However, there are several scenarios in which immune privilege is altered and the eye becomes susceptible to immune attack. In this review, we highlight the role of the immune system in two clinical conditions that affect the anterior and posterior segments of the eye: corneal transplantation and age-related macular degeneration. Interestingly, crosstalk between the innate and adaptive immune systems is critical in both acute and chronic inflammatory responses in the eye, with T cells playing a central role in combination with neutrophils and macrophages. In addition, we emphasize the advantage of using the eye as a model for in vivo longitudinal imaging of the immune system in action. Through this technique, it has been possible to identify functionally distinct intra-graft motility patterns of responding T cells, as well as the importance of chemokine signaling in situ for T cell activation. The detailed study of ocular autoimmunity could provide novel therapeutic strategies for blinding diseases while also providing more general information on acute versus chronic inflammation.

Concise review: immunological properties of ocular surface and importance of limbal stem cells for transplantation

Cornea transplantation has been considered to be different from other solid organ transplantation because of the assumed immune-privileged state of the anterior chamber of the eye. Three major lines of thought regarding the molecular mechanisms of immune privilege in the eye are as follows: (a) anatomical, cellular, and molecular barriers in the eye; (b) anterior chamber-associated immune deviation; and (c) immunosuppressive microenvironment in the eye. However, cornea transplants suffer allograft rejection when breached by vascularization. In recent developments, cellular corneal transplantation from cultivated limbal epithelial cells has shown impressive advances as a future therapy. The limbal stem cell niche contains stem cells that promote proliferation and migration and have immunosuppressive mechanisms to protect them from immunological reactions. Limbal stem cells are also noted to display an enhanced expression of genes for the antiapoptotic proteins, a property that is imperative for the survival of transplanted tissues. Further investigation of the molecular mechanisms regulating the immune regulation of limbal stem cells is relevant in the clinical setting to promote the survival of whole corneal and limbal stem cell transplantation.

Role of T cell recruitment and chemokine-regulated intra-graft T cell motility patterns in corneal allograft rejection

Keratoplasty is the primary treatment to cure blindness due to corneal opacification. However, immune-mediated rejection remains the leading cause of keratoplasty failure. Here, we utilize an in vivo imaging approach to monitor, track, and characterize in real-time the recruitment of GFP-labeled allo-specific activated (Bonzo) T cells during corneal allograft rejection. We show that the recruitment of effector T cells to the site of transplantation determined the fate of corneal allografts, and that local intra-graft production of CCL5 and CXCL9/10 regulated motility patterns of effector T cells in situ, and correlated with allograft rejection. We also show that different motility patterns associate with distinct in vivo phenotypes (round, elongated, and ruffled) of graft-infiltrating effector T cells with varying proportions during progression of rejection. The ruffled phenotype was characteristic of activated effectors T cells and predominated during ongoing rejection, which associated with significantly increased T cell dynamics within the allografts. Importantly, CCR5/CXCR3 blockade decreased the motility, size, and number of infiltrating T cells and significantly prolonged allograft survival. Our findings indicate that chemokines produced locally within corneal allografts play an important role in the in situ activation and dynamic behavior of infiltrating effector T cells, and may guide targeted interventions to promote graft survival.

Vascular Endothelial Growth Factor Receptor 1 morpholino increases graft survival in a murine penetrating keratoplasty model

PURPOSE

This study sought to determine whether a Vascular Endothelial Growth Factor Receptor 1 (VEGFR1)-specific morpholino (MO) could decrease neovascularization, thereby enhancing murine cornea transplant survival, and if this effect is synergistic with steroid therapy.

METHODS

Graft survival, corneal neovascularization, and corneal lymphangiogenesis were compared among the VEGFR1_MO, STD MO and PBS groups following subconjunctival injection in mice that underwent normal risk penetrating keratoplasty (NR PK) and high-risk penetrating keratoplasty (HR PK). Graft survival, corneal neovascularization, and corneal lymphangiogenesis in groups treated with both VEGFR1_MO and steroid therapy were also analyzed in HR PK.

RESULTS

In NR PK, the VEGFR1_MO decreased angiogenesis, lymphangiogenesis, and increased graft survival compared with the PBS group (P = 0.055, P = 0.003, P = 0.043, respectively). In HR PK, VEGFR1_MO decreased angiogenesis, lymphangiogenesis, and increased graft survival compared with the STD MO (P = 0.000, P = 0.000, P = 0.029, respectively) and PBS groups (P = 0.004, P = 0.002, P = 0.024). In HR PK, when the VEGFR1_MO was combined with steroid therapy, a significant increase in graft survival was seen compared with steroid treatment alone (P = 0.045). The 2-month graft survival rate for HR PK was 27% in the combination group compared with 0% in the triamcinolone only group.

CONCLUSIONS

VEGFR1_MO decreased angiogenesis and lymphangiogenesis, resulting in increased graft survival in both NR PK and HR PK. This beneficial effect is synergistically enhanced with steroid treatment in HR PK.

Immunological disruption of antiangiogenic signals by recruited allospecific T cells leads to corneal allograft rejection

Corneal transplantation is the most common solid organ transplantation. The immunologically privileged nature of the cornea results in high success rates. However, T cell-mediated rejection is the most common cause of corneal graft failure. Using antiangiogenesis treatment to prevent corneal neovascularization, which revokes immune privilege, prevents corneal allograft rejection. Endostatin is an antiangiogenic factor that maintains corneal avascularity. In this study, we directly test the role of antiangiogenic and immunological signals in corneal allograft survival, specifically the potential correlation of endostatin production and T cell recruitment. We report that 75% of the corneal allografts of BALB/c mice rejected after postoperative day (POD) 20, whereas all syngeneic grafts survived through POD60. This correlates with endogenous endostatin, which increased and remained high in syngeneic grafts but decreased after POD10 in allografts. Immunostaining demonstrated that early recruitment of allospecific T cells into allografts around POD10 correlated with decreased endostatin production. In Rag(-/-) mice, both allogeneic and syngeneic corneal grafts survived; endostatin remained high throughout. However, after T cell transfer, the allografts eventually rejected, and endostatin decreased. Furthermore, exogenous endostatin treatment delayed allograft rejection and promoted survival secondary to angiogenesis inhibition. Our results suggest that endostatin plays an important role in corneal allograft survival by inhibiting neovascularization and that early recruitment of allospecific T cells into the grafts promotes destruction of endostatin-producing cells, resulting in corneal neovascularization, massive infiltration of effector T cells, and ultimately graft rejection. Therefore, combined antiangiogenesis and immune suppression will be more effective in maintaining corneal allograft survival.

High-resolution, noninvasive longitudinal live imaging of immune responses

Intravital imaging emerged as an indispensible tool in biological research, and a variety of imaging techniques have been developed to noninvasively monitor tissues in vivo. However, most of the current techniques lack the resolution to study events at the single-cell level. Although intravital multiphoton microscopy has addressed this limitation, the need for repeated noninvasive access to the same tissue in longitudinal in vivo studies remains largely unmet. We now report on a previously unexplored approach to study immune responses after transplantation of pancreatic islets into the anterior chamber of the mouse eye. This approach enabled (i) longitudinal, noninvasive imaging of transplanted tissues in vivo; (ii) in vivo cytolabeling to assess cellular phenotype and viability in situ; (iii) local intervention by topical application or intraocular injection; and (iv) real-time tracking of infiltrating immune cells in the target tissue.

High-risk corneal allografts and why they lose their immune privilege

PURPOSE OF REVIEW

Corneal allografts are routinely performed without HLA typing or systemic immunosuppressive drugs. However, certain conditions create high risks for immune rejection. This review discusses recent insights into the mechanisms that rob the corneal allograft of its immune privilege.

RECENT FINDINGS

Studies in mice have revealed that stimuli that induce new blood vessel growth in the cornea also elicit proliferation of lymph vessels. Lymph vessels facilitate migration of antigen-presenting cells to regional lymph nodes in which they induce alloimmune responses. The presence of blood vessels in the corneal graft bed creates a unique chemokine milieu that stimulates recruitment of sensitized lymphocytes into the corneal allograft. Other data indicate that although corneal allograft survival is closely associated with Foxp3 expression in CD4+CD25+Foxp3+ T regulatory cells (Tregs), reduced expression of Foxp3 in Tregs creates a high risk for graft rejection. Recent evidence indicates that allergic diseases have a profound impact on the immune response and produce a dramatic increase in corneal allograft rejection.

SUMMARY

Understanding the underlying mechanisms that create 'high-risk' hosts may provide important therapeutic targets for restoring immune privilege of corneal allografts and enhancing their survival.

Dendritic cell physiology and function in the eye

The eye and the brain are immunologically privileged sites, a property previously attributed to the lack of a lymphatic circulation. However, recent tracking studies confirm that these organs have good communication through classical site-specific lymph nodes, as well as direct connection through the blood circulation with the spleen. In addition, like all tissues, they contain resident myeloid cell populations that play important roles in tissue homeostasis and the response to foreign antigens. Most of the macrophage and dendritic cell (DC) populations in the eye are restricted to the supporting connective tissues, including the cornea, while the neural tissue (the retina) contains almost no DCs, occasional macrophages (perivascularly distributed), and a specialized myeloid cell type, the microglial cell. Resident microglial cells are normally programmed for immunological tolerance. The privileged status of the eye, however, is relative, as it is susceptible to immune-mediated inflammatory disease, both infectious and autoimmune. Intraocular inflammation (uveitis and uveoretinitis) and corneal graft rejection constitute two of the more common inflammatory conditions affecting the eye leading to considerable morbidity (blindness). As corneal graft rejection occurs almost exclusively by indirect allorecognition, host DCs play a major role in this process and are likely to be modified in their behavior by the ocular microenvironment. Ocular surface disease, including allergy and atopy, also comprise a significant group of immune-mediated eye disorders in which DCs participate, while infectious disease such as herpes simplex keratitis is thought to be initiated via corneal DCs. Intriguingly, some more common conditions previously thought to be degenerative (e.g. age-related macular degeneration) may have an autoimmune component in which ocular DCs and macrophages are critically involved. Recently, the possibility of harnessing the tolerizing potential of DCs has been applied to experimental models of autoimmune uveoretinitis with good effect. This approach has considerable potential for use in translational clinical therapy to prevent sight-threatening disease caused by ocular inflammation.

Decay accelerating factor is essential for successful corneal engraftment

In contrast to immune restrictions that pertain for solid organ transplants, the tolerogenic milieu of the eye permits successful corneal transplantation without systemic immunosuppression, even across a fully MHC disparate barrier. Here we show that recipient and donor expression of decay accelerating factor (DAF or CD55), a cell surface C3/C5 convertase regulator recently shown to modulate T-cell responses, is essential to sustain successful corneal engraftment. Whereas wild-type (WT) corneas transplanted into multiple minor histocompatibility antigen (mH), or HY disparate WT recipients were accepted, DAF's absence on either the donor cornea or in the recipient bed induced rapid rejection. Donor or recipient DAF deficiency led to expansion of donor-reactive IFN-gamma producing CD4(+) and CD8(+) T cells, as well as inhibited antigen-induced IL-10 and TGF-beta, together demonstrating that DAF deficiency precludes immune tolerance. In addition to demonstrating a requisite role for DAF in conferring ocular immune privilege, these results raise the possibility that augmenting DAF levels on donor corneal endothelium and/or the recipient bed could have therapeutic value for transplants that clinically are at high risk for rejection.