E-Selectin Mediates Immune Cell Trafficking in Corneal Transplantation

Conventional type I migratory CD103+ dendritic cells are required for corneal allograft survival

Corneal transplant rejection primarily occurs because of the T helper 1 (Th1) effector cell-mediated immune response of the host towards allogeneic tissue. The evidence suggests that type 1 migratory conventional CD103+ dendritic cells (CD103+DC1) acquire an immunosuppressive phenotype in the tumor environment; however, the involvement of CD103+DC1 in allograft survival continues to be an elusive question of great clinical significance in tissue transplantation. In this study, we assess the role of CD103+DC1 in suppressing Th1 alloreactivity against transplanted corneal allografts. The immunosuppressive function of CD103+DC1 has been extensively studied in non-transplantation settings. We found that host CD103+DC1 infiltrates the corneal graft and migrates to the draining lymph nodes to suppress alloreactive CD4+ Th1 cells via the programmed death-ligand 1 axis. The systemic depletion of CD103+ DC1 in allograft recipients leads to amplified Th1 activation, impaired Treg function, and increased rate of allograft rejection. Although allograft recipient Rag1 null mice reconstituted with naïve CD4+CD25- T cells efficiently generated peripheral Treg cells (pTreg), the CD103+DC1-depleted mice failed to generate pTreg. Furthermore, adoptive transfer of pTreg failed to rescue allografts in CD103+DC1-depleted recipients from rejection. These data demonstrate the critical role of CD103+DC1 in regulating host alloimmune responses.

The impact of donor diabetes on corneal transplant immunity

Corneal transplantation is the most common form of solid tissue grafting, with an approximately 80% to 90% success rate. However, success rates may decline when donor tissues are derived from patients with a history of diabetes mellitus (DM). To evaluate the underlying immunopathologic processes that cause graft rejection, we used streptozotocin-induced type 1 DM (DM1) and transgenic Lepob/ob type 2 DM (DM2) diabetic murine models as donors and nondiabetic BALB/c as recipients. DM resulted in an increased frequency of corneal antigen-presenting cells (APCs) with an acquired immunostimulatory phenotype. Following transplantation, recipients that received either type of diabetic graft showed increased APC migration and T helper type 1 alloreactive cells, impaired functional regulatory T cells, and graft survival. Insulin treatment in streptozotocin-induced diabetic mice led to an increased tolerogenic profile of graft APC, lower T helper type 1 sensitization, and a higher frequency of functional regulatory T cells with high suppressive capacity, reflected in increased graft survival. We conclude that both DM1 and DM2 in donors can impact corneal APC functional phenotype, rendering the tissue more immunogenic and thereby increasing the risk of graft failure.

An Overview of Corneal Transplantation in the Past Decade

The cornea is a transparent avascular structure located in the front of the eye that refracts light entering the eyes and also serves as a barrier between the outside world and the internal contents of the eye. Like every other body part, the cornea may suffer insult from trauma, infection, and inflammation. In the case of trauma, a prior infection that left a scar, or conditions such as keratoconus that warrant the removal of all or part of the cornea (keratoplasty), it is important to use healthy donor corneal tissues and cells that can replace the damaged cornea. The types of cornea transplant techniques employed currently include: penetrating keratoplasty, endothelial keratoplasty (EK), and artificial cornea transplant. Postoperative failure acutely or after years can result after a cornea transplant and may require a repeat transplant. This minireview briefly examines the various types of corneal transplant methodologies, indications, contraindications, presurgical protocols, sources of cornea transplant material, wound healing after surgery complications, co-morbidities, and the effect of COVID-19 in corneal transplant surgery.

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.

A nanozyme-based competitive electrochemical immunosensor for the determination of E-selectin

A nanozyme-based competitive electrochemical immunosensor has been developed for the quantitative determination of E-selectin, a common adhesion molecule expressed by activated endothelial cells. A glassy carbon electrode modified with poly(azure A) and E-selectin antibody (GCE/PAA/Ab) was prepared. Au-CuO nanocomposite-labeled E-selectin, CD62E-Au-CuO, was synthetized, and it could be captured on GCE/PAA/Ab owing to the immunoreaction. The immobilized nanocomposites on GCE/PAA/Ab/CD62E-Au-CuO acted as nanozymes and were involved in the electrocatalytic process that caused the high cathodic peak current. The assembly of GCE/PAA/Ab/CD62E-Au-CuO was inhibited by E-selectin due to the competitive immunoreaction, which resulted in a decrease of the current signal. The cathodic peak current difference at - 0.35 V vs SCE was proportional to the concentration of E-selectin in the range 0.500-500 ng mL^-1, and the limit of detection was estimated to be 226 pg mL^-1. The cell morphology observation, the cell viability test, and the electrochemical measurement indicate that the injury of human umbilical vein endothelial cells was aggravated, and the release of E-selectin from the injured cells was gradually accelerated when the NaCl content in the growth medium increased.

Blockage of P2X7R suppresses Th1/Th17-mediated immune responses and corneal allograft rejection via inhibiting NLRP3 inflammasome activation

P2X7R is a vital modifier of various inflammatory and immune-related diseases. However, the immunomodulatory effects of P2X7R on corneal allograft rejection remains unknown. Here we showed that P2X7R expression was significantly upregulated in corneal grafts of allogeneic transplant mice. Pharmacological blockage of P2X7R remarkably prolonged graft survival time, and reduced inflammatory cell infiltration in corneal grafts, in particular Th1/Th17 cells. Meanwhile, the frequencies of Th1/Th17 cells in draining lymph nodes were significantly decreased in P2X7R blocked allogeneic mice. Further results showed that the effect of P2X7R on promoting Th1/Th17 mediated immune responses in corneal allograft rejection relied heavily on its activation on the NLRP3/caspase-1/IL-1β axis, while P2X7R blockage could mitigate such activation. Nevertheless, the addition of IL-1β in vivo abrogated the protective effect of P2X7R blockage on promoting corneal graft survival. These findings demonstrate that blockage of P2X7R can substantially alleviate corneal allograft rejection and promote grafts survival, highlighting it as a promising target for preventing or treating corneal allograft rejection.

The NLRP3 inflammasome regulates corneal allograft rejection through enhanced phosphorylation of STAT3

The success of corneal transplantation is limited by allograft rejection, but the pathogenic mechanisms of this disease remain poorly defined. In this study, we showed that the NOD, LRR-and pyrin domain-containing protein3 (NLRP3) inflammasome-mediated interleukin-1β (IL-1β) production exacerbated corneal allograft rejection. Extracellular ATP contributed to the NLRP3 inflammasome-mediated IL-1β release, which in turn was preferentially skewed toward Th17 differentiation via enhanced phosphorylation of STAT3. Pharmacological inhibition of IL-1β/IL-6-STAT3 signaling significantly delayed corneal allograft rejection. Thus, the identification of NLRP3 inflammasome's key role sheds new light on the pathogenesis of corneal allograft rejection and opens a potential new avenue for treating or preventing corneal allograft rejection.

Gene-based Therapeutic Tools in the Treatment of Cornea Disease

BACKGROUND

As one of the main blinding ocular diseases, corneal blindness resulted from neovascularization that disrupts the angiogenic privilege of corneal avascularity. Following neovascularization, inflammatory cells are infiltrating into cornea to strengthen corneal injury. How to maintain corneal angiogenic privilege to treat corneal disease has been investigated for decades.

METHODOLOGY

Local administration of viral and non-viral-mediated anti-angiogenic factors reduces angiogenic protein expression in situ with limited or free of off-target effects upon gene delivery. Recently, Mesenchymal Stem Cells (MSCs) have been studied to treat corneal diseases. Once MSCs are manipulated to express certain genes of interest, they could achieve superior therapeutic efficacy after transplantation.

DISCUSSION

In the text, we first introduce the pathological development of corneal disease in the aspects of neovascularization and inflammation. We summarize how MSCs become an ideal candidate in cell therapy for treating injured cornea, focusing on cell biology, property and features. We provide an updated review of gene-based therapies in animals and preclinical studies in the aspects of controlling target gene expression, safety and efficacy. Gene transfer vectors are potent to induce candidate protein expression. Delivered by vectors, MSCs are equipped with certain characters by expressing a protein of interest, which facilitates better for MSC-mediated therapeutic intervention for the treatment of corneal disease.

CONCLUSION

As the core of this review, we discuss how MSCs could be engineered to be vector system to achieve enhanced therapeutic efficiency after injection.

Mesenchymal Stromal Cells Modulate Corneal Alloimmunity via Secretion of Hepatocyte Growth Factor

Mesenchymal stromal cells (MSCs) are multipotent stem cells that participate in tissue repair and possess considerable immunomodulatory potential. MSCs have been shown to promote allograft survival, yet the mechanisms behind this phenomenon have not been fully defined. Here, we investigate the capacity of MSCs to suppress the allogeneic immune response by secreting the pleiotropic molecule hepatocyte growth factor (HGF). Using an in vivo mouse model of corneal transplantation, we report that MSCs promote graft survival in an HGF‐dependent manner. Moreover, our data indicate that topically administered recombinant HGF (a) suppresses antigen‐presenting cell maturation in draining lymphoid tissue, (b) limits T‐helper type‐1 cell generation, (c) decreases inflammatory cell infiltration into grafted tissue, and (d) is itself sufficient to promote transplant survival. These findings have potential translational implications for the development of HGF‐based therapeutics. stem cells translational medicine2019;8:1030–1040

Pharmacokinetic study of sirolimus ophthalmic formulations by consecutive sampling and liquid chromatography-tandem mass spectrometry

Sirolimus is regarded as one of the most effective immunosuppressants receiving extensive attention over the years, for which the ocular application needs further development in clinical keratoplasty. In order to study the transcorneal absorption effect of ophthalmic administration, there was a need to study the pharmacokinetics of drugs in aqueous humor. In this work, a validated and reliable HPLC-ESI-MS/MS method was established to study the pharmacokinetics of sirolimus nanoformulations in rabbit aqueous humor. The analysis conditions were as follows. Ascomycin was chosen as internal standard. After a simple precipitation extraction procedure, the aqueous humor samples were separated on a XBridge C18 column (4.6 mm × 150 mm, 3.5 μm, Waters Co., USA) with a mobile phase comprised of water (0.1% formic acid and 5 mM ammonium formate) and methanol (0.1% formic acid) at the ratio of 10:90 (v/v). The mass analysis was achieved by positive ionization with multiple reaction monitoring (MRM) mode. The highest response ion pairs m/z at 931.5→864.5 were chosen for sirolimus. The validated results showed that the calibration range was 0.3-100.6 ng/mL with r = 0.9997 (n = 6). The R.S.D. values of the intra- and inter-day precision were less than 11% and the average accuracy values were between 94.73%-100.20%. Besides, for reducing the consumption of rabbits and the variation of the data, we designed a consecutive sampling method in pharmacokinetic study, with only seven rabbits consumed for each formulation. In conclusion, the developed analysis method was more reliable and practical than previously reported experiments. Meanwhile, the validated method was successfully applied to study the pharmacokinetics of sirolimus micelle and sirolimus nanosuspension after ophthalmic administration.

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.

An Experimental Study of Femto-Laser in Assisting Xenograft Acellular Cornea Matrix Lens Transplantation

Background

The aim of this study was to evaluate the feasibility of using a femto-laser in assisting xenograft cornea matrix lens transplantation in correcting ametropia, along with evaluating the effectiveness and predictability of this procedure.

Material/Methods

A corneal matrix pouch was prepared on the right eyes on 8 healthy New Zealand rabbits by a femto-laser that was also employed to perform small incision lenticule extraction (SMILE) on 8 bovine cornea matrix lenses (+6D). A lens was treated acellular and implanted into a right rabbit cornea matrix pouch. Surface inflammation was observed at 1, 2, 4, 8, 12, and 24 weeks after surgery. Anterior ocular segment optical coherence tomography (OCT), corneal topography, retinoscopy, and cornea endothelial cell enumeration were performed.

Results

All the surgeries were successfully performed without any complications. The hyperopia condition of the rabbit eyes transformed into myopia status at an early stage and gradually developed hyperopia. Diopter at 24 weeks after surgery was 1/3 of that before surgery. Central corneal thickness stabilized at 4 weeks after surgery. Anterior segment OCT showed a clear lens edge at early post-operative stage, and blurred edge at 24 weeks later, indicating gradual fusion with the rabbit corneal matrix.

Conclusions

Femto-laser assisted xenograft corneal matrix lens transplantation is safe and effective in correcting ametropia, with satisfactory predictability, thus providing novel choice for correcting ametropia.

Therapeutic approaches for induction of tolerance and immune quiescence in corneal allotransplantation

The cornea is the most commonly transplanted tissue in the body. Corneal grafts in low-risk recipients enjoy high success rates, yet over 50% of high-risk grafts (with inflamed and vascularized host beds) are rejected. As our understanding of the cellular and molecular pathways that mediate rejection has deepened, a number of novel therapeutic strategies have been unveiled. This manuscript reviews therapeutic approaches to promote corneal transplant survival through targeting (1) corneal lymphangiogenesis and hemangiogenesis, (2) antigen presenting cells, (3) effector and regulatory T cells, and (4) mesenchymal stem cells.

Elevated Aqueous Cytokine Levels in Eyes With Ocular Surface Diseases

PURPOSE

To evaluate cytokine and protein levels in the aqueous humor (AqH) of eyes with ocular surface diseases.

DESIGN

Prospective consecutive case series.

METHODS

This study includes 14 patients (aged 62.4 ± 13.7 years) with chronic-phase ocular surface diseases (4 with ocular cicatricial pemphigoid, 5 with chemical burns, 2 with a thermal burn, 2 with Stevens-Johnson syndrome, and 1 with exposure keratitis), 14 matched patients without ocular surface disease (controls with corneal scar), and 30 patients who underwent cataract surgery (healthy controls). AqH samples were collected at the beginning of surgery. AqH levels of cytokines (interleukin [IL]-1α, IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-17A, monocyte chemotactic protein [MCP]-1, interferon [IFN]-α, IFN-γ, macrophage inflammatory protein [MIP]-1α, MIP-1β, P-selectin, E-selectin, soluble-intercellular adhesion molecule [s-ICAM]-1, tumor necrosis factor [TNF]-α, granulocyte-macrophage colony-stimulating factor [GM-CSF], IFN-γ-induced protein [IP]-10) were measured using multiplex beads immunoassays.

RESULTS

The levels of IL-6, IL-10, IL-17A, GM-CSF, E-selectin, P-selectin, and s-ICAM in AqH were significantly elevated in eyes with ocular surface diseases (in pg/mL: 1696 ± 804, 4.0 ± 1.0, 24.3 ± 9.8, 26.0 ± 18.3, 5150 ± 1232, 13122 ± 7219, and 7914 ± 2813, respectively), compared to healthy controls (IL-6: 6.36 ± 0.94, P = .001; IL-10: 1.68 ± 0.04, P = .0006; IL-17A: 3.7 ± 0.2, P = .008; GM-CSF: 2.7 ± 0.3, P = .007; E-selectin: 2093 ± 37, P = .0001; P-selectin: 3658 ± 137, P = .0001; sICAM-1: 1397 ± 119, P = .008). The levels of IL-6, IL-17A, E-selectin, and P-selectin in AqH were significantly higher in eyes with ocular surface diseases compared to those with corneal scar (IL-6: 44.1 ± 15.0, P = .0077; IL-17A: 4.1 ± 0.7, P = .034; E-selectin: 2439 ± 302, P = .039; and P-selectin: 5673 ± 1553, P = .017).

CONCLUSIONS

Multiple AqH cytokine levels were elevated in chronic ocular surface diseases.

Kinetics of Angiogenic Responses in Corneal Transplantation

PURPOSE

To delineate and compare the kinetics of corneal angiogenesis after high-risk (HR) versus low-risk (LR) corneal transplantation.

METHODS

In mice, intrastromal sutures were placed in the recipient graft bed 2 weeks before allogeneic transplantation to induce angiogenesis and amplify the risk of graft rejection. Control (LR) graft recipients did not undergo suture placement, and thus the host bed remained avascular at the time of transplantation. Graft hemangiogenesis and opacity scores were evaluated for 8 weeks by slit-lamp biomicroscopy. Immunohistochemistry was used to measure CD31 (blood vessels) and LYVE-1 (lymphatic vessels) cells.

RESULTS

Biphasic kinetics were observed for hemangiogenesis in both HR and LR transplant recipients using clinical and immunohistochemical assessments. The biphasic kinetics were composed of a rise-fall (phase 1) followed by a second rise (phase 2) in the degree of vessels. Compared with LR recipients, HR recipients showed higher hemangiogenesis (whole cornea and graft) throughout 8 weeks. Analyzing grafts revealed sustained presence of lymphatic vessels in HR recipients; however, lymphatic neovessels regressed in LR recipients 2 weeks posttransplantation. In contrast to HR host beds, the LR host bed microenvironment cannot sustain the growth of lymphatic neovessels in allografts, whereas it can sustain continued hemangiogenesis.

CONCLUSIONS

The sustained presence of lymphatic vessels in HR host beds can facilitate host immunity against allografts and is likely associated with ongoing higher risk of rejection of these grafts in the long term, suggesting that therapeutic interventions targeting inflammation and lymphatic vessels need to be sustained long term in the HR corneal transplant setting.

An Analysis of Trafficking Receptors Shows that CD44 and P-Selectin Glycoprotein Ligand-1 Collectively Control the Migration of Activated Human T-Cells

Selectins guide the traffic of activated T-cells through the blood stream by mediating their tethering and rolling onto inflamed endothelium, in this way acting as beacons to help navigate them to sites of inflammation. Here, we present a comprehensive analysis of E-selectin ligands expressed on activated human T-cells. We identified several novel glycoproteins that function as E-selectin ligands. Specifically, we compared the role of P-selectin glycoprotein ligand-1 (PSGL-1) and CD43, known E-selectin ligands, to CD44, a ligand that has not previously been characterized as an E-selectin ligand on activated human T-cells. We showed that CD44 acts as a functional E-selectin ligand when expressed on both CD4⁺ and CD8⁺ T-cells. Moreover, the CD44 protein carries a binding epitope identifying it as hematopoietic cell E- and/or L-selectin ligand (HCELL). Furthermore, by knocking down these ligands individually or together in primary activated human T-cells, we demonstrated that CD44/HCELL, and not CD43, cooperates with PSGL-1 as a major E-selectin ligand. Additionally, we demonstrated the relevance of our findings to chronic autoimmune disease, by showing that CD44/HCELL and PSGL-1, but not CD43, from T-cells isolated from psoriasis patients, bind E-selectin.

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.

Systemic Immunomodulatory Strategies in High-risk Corneal Transplantation

The cornea is the most commonly transplanted tissue in the body. Although corneal grafts generally have high success rates, transplantation onto inflamed and vascularized host beds, or so-called high-risk corneal transplantation, has a high rate of graft rejection. The management of this high-risk corneal transplantation is challenging and involves numerous measures. One of the key measures to prevent graft rejection in these cases is the use of systemic immunosuppressive agents. In this article, we will review the systemic immunosuppressive agents most commonly used for high-risk corneal transplantation, which include corticosteroids, cysclosporine A, tacrolimus, mycophenolate mofetil, and rapamycin. Benefits, risks, and published data on the use of these medications for high-risk corneal transplantation will be detailed. We will also summarize novel immunoregulatory approaches that may be used to prevent graft rejection in high-risk corneal transplantation.