Kinetics of Angiogenic Responses in Corneal Transplantation

Myeloid-derived suppressor cells promote allograft survival by suppressing regulatory T cell dysfunction in high-risk corneal transplantation

Highly inflamed and neovascularized corneal graft beds are known as high-risk (HR) environments for transplant survival. One of the primary factors leading to this rejection is reduction in the suppressive function of regulatory T cells (Treg). Our results show that myeloid-derived suppressor cells (MDSC) counteract interleukin-6-mediated Treg dysfunction by expressing interleukin-10. Additionally, MDSC maintain forkhead box P3 stability and their ability to suppress IFN-γ+ Th1 cells. Administering MDSC to HR corneal transplant recipients demonstrates prolonged graft survival via promotion of Treg while concurrently suppressing IFN-γ+ Th1 cells. Moreover, MDSC-mediated donor-specific immune tolerance leads to long-term corneal graft survival as evidenced by the higher survival rate or delayed survival of a second-party C57BL/7 (B6) graft compared to those of third-party C3H grafts observed in contralateral low-risk or HR corneal transplantation of BALB/c recipient mice, respectively. Our study provides compelling preliminary evidence demonstrating the effectiveness of MDSC in preventing Treg dysfunction, significantly improving graft survival in HR corneal transplantation, and showing promising potential for immune tolerance induction.

Dysregulation of Lymphatic Endothelial VEGFR3 Signaling in Disease

Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR3), a receptor tyrosine kinase encoded by the FLT4 gene, plays a significant role in the morphogenesis and maintenance of lymphatic vessels. Under both normal and pathologic conditions, VEGF-C and VEGF-D bind VEGFR3 on the surface of lymphatic endothelial cells (LECs) and induce lymphatic proliferation, migration, and survival by activating intracellular PI3K-Akt and MAPK-ERK signaling pathways. Impaired lymphatic function and VEGFR3 signaling has been linked with a myriad of commonly encountered clinical conditions. This review provides a brief overview of intracellular VEGFR3 signaling in LECs and explores examples of dysregulated VEGFR3 signaling in various disease states, including (1) lymphedema, (2) tumor growth and metastasis, (3) obesity and metabolic syndrome, (4) organ transplant rejection, and (5) autoimmune disorders. A more complete understanding of the molecular mechanisms underlying the lymphatic pathology of each disease will allow for the development of novel strategies to treat these chronic and often debilitating illnesses.

Biological effects of stored platelet-rich plasma eye-drops in corneal wound healing

BACKGROUND/AIMS

This study aimed to assess the efficacy and sterility of stored platelet-rich plasma (PRP) eye-drops for corneal epithelial wound healing compared with those of autologous serum (AS) eye-drops.

METHODS

At our single institution, PRP and AS eye-drops were prepared using peripheral blood obtained from six healthy volunteers and stored at 4°C. Platelet and leucocyte counts and transforming growth factor (TGF)-β1, epidermal growth factor (EGF), and fibronectin levels were assessed during storage for up to 4 weeks. Sterility was assessed by culturing 4-week poststorage samples. PRP, AS, and phosphate-buffered saline (PBS) eye-drop efficacies were compared using corneal epithelial wound healing assays in vitro and in vivo and monitoring wound areas under a microscope every 3 hours.

RESULTS

Higher platelet and lower leucocyte counts were seen in PRP than in whole blood on the day of preparation. After storage, TGF-β1, EGF, and fibronectin levels were significantly higher in PRP than in AS eye-drops. In vitro and in vivo, PRP eye-drops used on the day of preparation significantly promoted corneal epithelial wound healing compared with PBS. Moreover, PRP eye-drops stored for 4 weeks significantly promoted corneal wound healing compared with PBS and AS eye-drops.

CONCLUSION

PRP eye-drops stored at 4°C for 4 weeks promoted corneal epithelial wound healing with higher levels of growth factors than those observed in AS eye-drops, while maintaining sterility, suggesting that this preparation satisfies the unmet medical needs in the treatment of refractory keratoconjunctival epithelial disorders.

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.

A Novel Murine Model of Endothelial Keratoplasty

PURPOSE

The purpose of this study was to establish a murine model of endothelial keratoplasty.

METHODS

Endothelial keratoplasty (EK) was performed using C57BL/6 donor and BALB/c recipient mice. The central endothelium and Descemet membrane were removed from the recipient cornea, and a 1.5-mm posterior lamellar donor graft was made adherent to the recipient cornea with a small amount of viscoelastic. Mice were followed through slitlamp microscopy postoperatively, and OCT was used to assess the cornea and anterior chamber and measure central corneal thickness. Histology and immunohistochemistry were performed to confirm graft adherence and endothelial cell morphology.

RESULTS

Successfully attached EK grafts were visualized in all transplanted animals. Histology and immunostaining confirmed proper graft orientation and adherence, as well as the presence of donor endothelium on transplanted grafts. We observed maximal corneal edema in all animals at day 1 postoperatively which gradually subsided. EK graft survival was 97% at 8 weeks.

CONCLUSIONS

In this study, we describe a novel murine model for EK which we anticipate will enable detailed investigation into the cellular and molecular mechanisms involved in EK pathobiology.

Loss of TRPV4 Cation Channel Inhibition of Macrophage Infiltration and Neovascularization in a Mouse Cornea

Corneal injury-associated inflammation could induce inward-growing neovascularization from the periphery of the tissue. Such neovascularization could cause stromal opacification and curvature disturbance, and both potentially impair visual function. In this study, we determined the effects of the loss of transient receptor potential vanilloid 4 (TRPV4) expression on the development of neovascularization in the corneal stroma in mice by producing a cauterization injury in the central area of the cornea. New vessels were immunohistochemically labeled with anti-TRPV4 antibodies. TRPV4 gene knockout suppressed the growth of such CD31-labeled neovascularization in association with the suppression of infiltration of macrophages and tissue messenger RNA expression of the vascular endothelial cell growth factor A level. Treatment of cultured vascular endothelial cells with supplementation of HC-067047 (0.1 μM, 1 μM, or 10 μM), a TRPV4 antagonist, attenuated the formation of a tube-like structure with sulforaphane (15 μM, for positive control) that modeled the new vessel formation. Therefore, the TRPV4 signal is involved in injury-induced macrophagic inflammation and neovascularization activity by vascular endothelial cells in a mouse corneal stroma. TRPV4 could be a therapeutic target to prevent unfavorable postinjury neovascularization in the cornea.

Piperlongumine alleviates corneal allograft rejection via suppressing angiogenesis and inflammation

Background

Neovascularization and inflammatory response are two essential features of corneal allograft rejection. Here, we investigated the impact of Piperlongumine (PL) on alleviating corneal allograft rejection, primarily focusing on pathological angiogenesis and inflammation.

Methods

A murine corneal allograft transplantation model was utilized to investigate the role of PL in preventing corneal allograft rejection. PL (10 mg/kg) or vehicle was intraperitoneally injected daily into BALB/c recipients from day -3 to day 14. The clinical signs of the corneal grafts were monitored for 30 days. Corneal neovascularization and inflammatory cell infiltration were detected by immunofluorescence staining and immunohistochemistry. The proportion of CD4⁺ T cells and macrophages in the draining lymph nodes (DLNs) was examined by flow cytometry. In vitro, HUVECs were cultured under hypoxia or incubated with TNF-α to mimic the hypoxic and inflammatory microenvironment favoring neovascularization in corneal allograft rejection. Multiple angiogenic processes including proliferation, migration, invasion and tube formation of HUVECs in hypoxia with or without PL treatment were routinely evaluated. The influence of PL treatment on TNF-α-induced pro-inflammation in HUVECs was investigated by real-time PCR and ELISA.

Results

In vivo, PL treatment effectively attenuated corneal allograft rejection, paralleled by coincident suppression of neovascularization and alleviation of inflammatory response. In vitro, PL distinctively inhibited hypoxia-induced angiogenic processes in HUVECs. Two key players in hypoxia-induced angiogenesis, HIF-1α and VEGF-A were significantly suppressed by PL treatment. Also, TNF-α-induced pro-inflammation in HUVECs was hampered by PL treatment, along with a pronounced reduction in ICAM-1, VCAM-1, CCL2, and CXCL5 expression.

Conclusions

The current study demonstrated that PL could exhibit both anti-angiogenic and anti-inflammatory effects in preventing corneal allograft rejection, highlighting the potential therapeutic applications of PL in clinical strategy.

Local and Systemic Injections of Human Cord Blood Myeloid-Derived Suppressor Cells to Prevent Graft Rejection in Corneal Transplantation

Myeloid-derived suppressor cells (MDSCs) are therapeutic agents to prevent graft rejection in organ transplants by modulating inflammation. Herein, the immunosuppressive effect of human cord blood MDSCs on corneal allograft models was confirmed. CB-MDSCs were locally (subconjuctival, 5 × 10⁵) or systemically (intravenous, 1 × 10⁶) injected twice on days 0 and 7. A corneal transplantation model was established using C57BL/6 and BALB/c mice, and corneal graft opacity was measured to evaluate graft rejection up to 6 weeks. Results showed that graft survival in the MDSCs groups increased compared to vehicle groups after 42 days. Systemic and local MDSC administration inhibited the maturation (MHC-II^hi CD11c+) of dendritic cells (DCs) and the differentiation of interferon γ+ CD4+ Th1 in draining lymph nodes (LNs). However, vehicle groups increased the infiltration of CD3+ T cells and F4/80+ macrophages and produced prominent neovascular and lymphatic vessels into the graft site with increased mRNA expression of VEGF-A/C and VEGFR-1/R-3. Local MDSCs administration showed prominent anti-angiogenic/anti-lymphangiogenic effects even at lower MDSCs doses. Thus, CB-MDSCs could relatively suppress the infiltration of pathological T cells/macrophages into the corneas and the migration of mature DCs into draining LNs Therefore, ocular and systemic MDSCs administration showed therapeutic potential for preventing corneal allograft rejection.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Promotion of corneal angiogenesis by sensory neuron-derived calcitonin gene-related peptide

The normal cornea has no blood vessels but has abundant innervation. There is emerging evidence that sensory nerves, originated from the trigeminal ganglion (TG) neurons, play a key role in corneal angiogenesis. In the current study, we examined the role of TG sensory neuron-derived calcitonin gene-related peptide (CGRP) in promoting corneal neovascularization (CNV). We found that CGRP was expressed in the TG and cultured TG neurons. In the cornea, minimal CGRP mRNA was detected and CGRP immunohistochemical staining was exclusively co-localized with corneal nerves, suggesting corneal nerves are likely the source of CGRP in the cornea. In response to intrastromal suture placement and neovascularization in the cornea, CGRP expression was increased in the TG. In addition, we showed that CGRP was potently pro-angiogenic, leading to vascular endothelial cell (VEC) proliferation, migration, and tube formation in vitro and corneal hemangiogenesis and lymphangiogenesis in vivo. In a co-culture system of TG neurons and VEC, blocking CGRP signaling in the conditioned media of TG neurons led to decreased VEC migration and tube formation. More importantly, subconjunctival injection of a CGRP antagonist CGRP8-37 reduced suture-induced corneal hemangiogenesis and lymphangiogenesis in vivo. Taken together, our data suggest that TG sensory neuron and corneal nerve-derived CGRP promotes corneal angiogenesis.

Anti-CD80/86 antibodies inhibit inflammatory reaction and improve graft survival in a high-risk murine corneal transplantation rejection model

We investigated the effects of anti-CD80/86 antibodies in a murine high-risk corneal transplantation rejection model. A mixed lymphocyte reaction (MLR) assay was conducted with anti-CD80/86 antibodies. Inflammatory cytokine levels in the culture supernatant were measured using an enzyme-linked immunosorbent assay. Interferon (IFN)-γ-producing CD4⁺ T cell frequencies in the MLR were assessed using flow cytometry. In vivo, high-risk corneal allograft survival and IFN-γ-producing CD4⁺ T cell frequencies in corneal grafts were assessed with intraperitoneal injection of anti-CD80/86 antibodies compared to phosphate-buffered saline (PBS). RNA-sequencing was performed on corneal grafts 2 weeks post-transplantation. Anti-CD80/86 antibodies significantly decreased T-cell proliferation, IFN-γ⁺-producing CD4⁺ T cell frequencies, and IFN-γ, interleukin (IL)-1β, IL-2, IL-10, and tumor necrosis factor-α production in the MLR compared to PBS injection. Intraperitoneal injection of anti-CD80/86 antibodies significantly prolonged corneal graft survival and decreased IFN-γ⁺-producing CD4⁺ T cell frequencies compared to PBS injection. Gene set enrichment analysis showed that the gene sets mainly enriched in the control group were related to allograft rejection and inflammatory response compared to PBS injection. Anti-CD80/86 antibodies significantly prolonged corneal graft survival by inhibiting T-cell proliferation and inflammatory response.

Femtosecond laser-assisted deep anterior lamellar keratoplasty: A safer option in keratoconus surgery

PURPOSE

To evaluate postoperative safety of femtosecond laser deep anterior lamellar keratoplasty performed with an innovative anvil profile in keratoconus patients.

METHODS

This is a single-center, retrospective cohort study. We reviewed medical records of 89 keratoconus patients that underwent femtosecond laser deep anterior lamellar keratoplasty surgery (46 eyes) and manual deep anterior lamellar keratoplasty (47 eyes). Inclusion criteria required: age > 18 years old, best-corrected visual acuity < 0.3 LogMAR, continuous suture of the graft, postoperative immunomodulant regimen with dexamethasone 0.1% for 6 months and at least 12 months follow-up. Previous eye surgery, hydrops, and other ocular disease were excluded. The main outcome measures were postoperative events: rejections, persistent epithelial defects, and graft failures.

RESULTS

During the follow-up (20 ± 6 months) graft rejection was diagnosed in 0 of femtosecond laser deep anterior lamellar keratoplasty versus 6 (17%) of manual deep anterior lamellar keratoplasty [p 0.027], persistent epithelial defect in 0 of femtosecond laser deep anterior lamellar keratoplasty versus in 4 (11%) of manual deep anterior lamellar keratoplasty [p 0.048] and graft failure occurred in 4 (11%) of manual deep anterior lamellar keratoplasty. The best-corrected visual acuity, after removal of sutures, was better in the femtosecond laser deep anterior lamellar keratoplasty group 0.09 ± 0.08 LogMAR versus 0.16 ± 0.13 LogMAR in manual deep anterior lamellar keratoplasty [p 0.035] group although refractive spherical equivalent and cylinder, topographic average keratometry and cylinder were similar.

CONCLUSIONS

Anvil-shaped femtosecond laser deep anterior lamellar keratoplasty in keratoconus surgery increases safety and readiness of recovery, decreasing the incidence of corneal rejection, epithelial defects, graft failures, and producing better best-corrected visual acuity after removal of sutures.

Loss of miR-673-5p expression in the cornea promotes rat corneal allograft rejection by promoting Th17 cell differentiation mediated by JAK2/STAT3

Background

Cluster of differentiation 4 positive (CD4⁺) T cells play an important role in corneal graft rejection, especially the dynamic balance between regulatory T cells and helper T cells. This study aims to explore the upstream and downstream regulatory mechanisms of Th17 cell differentiation-mediated corneal allograft rejection.

Methods

By establishing rat corneal allograft transplantation model, transcriptome analysis was carried out to screen the differentially expressed genes related to T helper 17 (Th17) cell differentiation, and then cell experiments were used to verify the effect of miR-673-5p/Janus Kinase 2 (JAK2) signal on naïve CD4⁺ T cell differentiation and the proliferation, migration, and tube formation ability of human umbilical vein endothelial cells (HUVECs). Finally, the role of miR-673-5p/JAK2 signal in corneal allograft rejection was verified by animal model in vivo.

Results

The results showed that JAK2/STAT3 signaling activation-mediated Th17 cell differentiation was significantly up-regulated during corneal allograft rejection, and miR-673-5p expression was down-regulated after corneal allograft rejection. Low expression of miR-673-5p promoted Th17 cell differentiation by up-regulating JAK2, and then promoted placental growth factor (PLGF)mediated corneal neovascularization (CNV).

Conclusions

The results of this study suggested that low expression of miR-673-5p is a promoter of corneal allograft rejection. Overexpression of miR-673-5p can improve the survival rate of corneal allografts by inhibiting the differentiation and maturation of Th17 cells mediated by JAK2/STAT3 signaling.

Novel adaptation of a running suture technique in a mouse model of corneal transplantation

Several murine models of corneal transplantation have been developed over the years to study the immunopathological processes that lead to the failure of grafted corneas. In all of them, the classic eight interrupted sutures technique is utilized for transplanting the donor cornea on the host bed. However, in clinical practice, a single continuous suture with a single knot is generally performed for corneal transplantation. Here, we describe the adaptation of the single continuous suture technique in a mouse model of corneal transplantation.

Role of Immune Cell Diversity and Heterogeneity in Corneal Graft Survival: A Systematic Review and Meta-Analysis

Corneal transplantation is one of the most successful forms of solid organ transplantation; however, immune rejection is still a major cause of corneal graft failure. Both innate and adaptive immunity play a significant role in allograft tolerance. Therefore, immune cells, cytokines, and signal-transduction pathways are critical therapeutic targets. In this analysis, we aimed to review the current literature on various immunotherapeutic approaches for corneal-allograft rejection using the PubMed, EMBASE, Web of Science, Cochrane, and China National Knowledge Infrastructure. Retrievable data for meta-analysis were screened and assessed. The review, which evaluated multiple immunotherapeutic approaches to prevent corneal allograft rejection, showed extensive involvement of innate and adaptive immunity components. Understanding the contribution of this immune diversity to the ocular surface is critical for ensuring corneal allograft survival.

Ex Vivo-Induced Bone Marrow-Derived Myeloid Suppressor Cells Prevent Corneal Allograft Rejection in Mice

Purpose

To investigate the effects of ex vivo-induced bone marrow myeloid-derived suppressor cells (BM-MDSCs) on allogeneic immune responses in corneal transplantation.

Methods

Bone marrow cells from C57BL/6J (B6) mice were cultured with IL-6 and GM-CSF for four days. The ex vivo induction of the BM-MDSCs was assessed using flow cytometry, inducible nitric oxide synthase (iNOS) mRNA expression using reverse transcription-quantitative polymerase chain reaction, and nitric oxide (NO) production in allogeneic stimulation. T-cell proliferation and regulatory T-cell (Treg) expansion were investigated on allogeneic stimulation in the presence of ex vivo-induced BM-MDSCs. IFN-γ, IL-2, IL-10, and TGF-β1 protein levels were measured using enzyme-linked immunosorbent assays. After subconjunctival injection of ex vivo-induced BM-MDSCs, the migration of the BM-MDSCs into corneal grafts, allogeneic corneal graft survival, neovascularization, and lymphangiogenesis were assessed using flow cytometry, slit-lamp microscopy, and immunohistochemistry.

Results

The combination of GM-CSF and IL-6 significantly induced BM-MDSCs with increased iNos mRNA expression. The ex vivo-induced BM-MDSCs promoted NO release in allogeneic stimulation in vitro. The ex vivo-induced BM-MDSCs inhibited T-cell proliferation and promoted Treg expansion. Decreased IFN-γ and increased IL-2, IL-10, and TGF-β1 production was observed in coculture of ex vivo-induced BM-MDSCs. Injected ex vivo-induced BM-MDSCs were confirmed to migrate into the grafts. The injected BM-MDSCs also prolonged corneal graft survival and prevented angiogenesis and lymphangiogenesis.

Conclusions

The ex vivo-induced BM-MDSCs have suppressive effects on allogeneic immune responses and prolong corneal allograft survival via the iNOS pathway, indicating that they may be a potential therapeutic tool for corneal transplantation.

Topical administration of the kappa opioid receptor agonist nalfurafine suppresses corneal neovascularization and inflammation

Corneal neovascularization (CNV) causes higher-order aberrations, corneal edema, ocular inflammation, and corneal transplant rejection, thereby decreasing visual acuity. In this study, we investigated the effects of topical administration of the kappa opioid receptor agonist nalfurafine (TRK-820) on CNV. To induce CNV, intrastromal corneal sutures were placed on the corneal stroma of BALB/c mice for 2 weeks. Nalfurafine (0.1 µg/2 μL/eye) was topically administered to the cornea once or twice daily after CNV induction. The CNV score, immune cell infiltration, and mRNA levels of angiogenic and pro-inflammatory factors in neovascularized corneas were evaluated using slit-lamp microscopy, immunohistochemistry, flow cytometry, and polymerase chain reaction. The mRNA expression of the kappa opioid receptor gene Oprk1 was significantly upregulated following CNV induction. Topical administration of nalfurafine twice daily significantly suppressed CNV and lymphangiogenesis, as well as reduced the mRNA levels of angiogenic and pro-inflammatory factors in the neovascularized corneas. Moreover, nalfurafine administration twice daily reduced the numbers of infiltrating leukocytes, neutrophils, macrophages, and interferon-γ-producing CD4⁺ T cells in the neovascularized corneas. In this study, we demonstrated that topical administration of nalfurafine suppressed local CNV in a mouse model along with the activation of KOR, suggesting that nalfurafine may prevent and control CNV in humans.

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.

Corneal angiogenic privilege and its failure

The cornea actively maintains its own avascular status to preserve its ultimate optical function. This corneal avascular state is also defined as "corneal angiogenic privilege", which results from a critical and sensitive balance between anti-angiogenic and pro-angiogenic mechanisms. In our review, we aim to explore the complex equilibrium among multiple mediators which prevents neovascularization in the resting cornea, as well as to unveil the evolutive process which leads to corneal angiogenesis in response to different injuries.

Novel immunotherapeutic effects of topically administered ripasudil (K-115) on corneal allograft survival

Corneal allograft survival is mediated by the variety of immunological reactions and wound healing process. Our aim was to explore the effects of topical administration of ripasudil, a selective Rho-associated coiled-coil protein kinase inhibitor, on corneal allograft survival. Ripasudil was administered to mice thrice a day after allogeneic corneal transplantation. Corneal graft survival, opacity, neovascularization, re-epithelization, immune cell infiltration, and mRNA levels of angiogenic and pro-inflammatory factors in the grafted cornea and draining lymph nodes (dLNs) were evaluated with slit-lamp microscopy, immunohistochemistry, flow cytometry, and polymerase chain reaction. Graft survival was significantly prolonged with lower graft opacity and neovascularization scores in 0.4% and 2.0% ripasudil-treated groups, and mRNA levels of angiogenic and pro-inflammatory factors in ripasudil-treated grafted corneas were reduced. Moreover, 0.4% and 2.0% ripasudil reduced CD45⁺-infiltrated leukocyte frequency, Cd11b and Cd11c mRNA levels, and the frequencies of mature dendritic cells, IFNγ-, and IL-17- producing CD4⁺T cells in the dLNs of recipients. Re-epithelization rate of the grafted cornea was significantly higher in the 0.4% and 2.0% ripasudil groups than in the control. Topically applied ripasudil prolonged graft survival by downregulating neovascularization and inflammation factors, while promoting corneal re-epithelization, suggesting that ripasudil may be useful for suppressing immunological rejection in corneal transplantation.

Topical VEGF-C/D Inhibition Prevents Lymphatic Vessel Ingrowth into Cornea but Does Not Improve Corneal Graft Survival

Vascular endothelial growth factor-C/D (VEGF-C/D) regulates lymphangiogenesis. Ingrowth of lymphatic vessels is negatively associated with corneal transplantation success. In this study, we therefore analyzed the effect local blockade of VEGF-C/D has on inflamed corneas. We used the murine model of suture-induced neovascularization and subsequent high-risk corneal transplantation. Mice were treated with a VEGF-C/D trap prior to transplantation. Topical inhibition of VEGF-C/D significantly reduced lymphatic vessel ingrowth, but increased Macrophage numbers in the cornea. Furthermore, corneal transplantation success was not improved by the topical application of the compound. This study demonstrates that local VEGF-C/D inhibition is insufficient to increases corneal transplantation success, likely due to interaction with immune cells.

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.

Sensory neurons directly promote angiogenesis in response to inflammation via substance P signaling

Blood vessels and nerves travel together to supply most tissues in the body. However, there is a knowledge gap in the mechanisms underlying the direct regulation of angiogenesis by nerves. In the current study, we examined the regulation of angiogenesis by sensory nerves in response to inflammation using the cornea, a normally avascular and densely innervated ocular tissue, as a model. We used desiccating stress as an inflammatory stimulus in vivo and found that sub-basal and epithelial nerve densities in the cornea were reduced in dry eye disease (DED). We established a co-culture system of trigeminal ganglion sensory neurons and vascular endothelial cells (VEC) and found that neurons isolated from mice with DED directly promoted VEC proliferation and tube formation compared with normal controls. In addition, these neurons expressed and secreted higher levels of substance P (SP), a proinflammatory neuropeptide. SP potently promoted VEC activation in vitro and blockade of SP signaling with spantide I, an antagonist of SP receptor Neurokinin-1, significantly reduced corneal neovascularization in vivo. Spantide I and siRNA knockdown of SP abolished the promotion of VEC activation by DED neurons in vitro. Taken together, our data suggested that sensory neurons directly promote angiogenesis via SP signaling in response to inflammation in the cornea.

Variable Responses to Corneal Grafts: Insights from Immunology and Systems Biology

Corneal grafts interact with their hosts via complex immunobiological processes that sometimes lead to graft failure. Prediction of graft failure is often a tedious task due to the genetic and nongenetic heterogeneity of patients. As in other areas of medicine, a reliable prediction method would impact therapeutic decision-making in corneal transplantation. Valuable insights into the clinically observed heterogeneity of host responses to corneal grafts have emerged from multidisciplinary approaches, including genomics analyses, mechanical studies, immunobiology, and theoretical modeling. Here, we review the emerging concepts, tools, and new biomarkers that may allow for the prediction of graft survival.

Regulation of matrix metalloproteinases 2 and 9 in corneal neovascularization

Corneal neovascularization (CNV), a pathological process of angiogenesis, can lead to serious consequences in the cornea. CNV is generally proved to associate with inflammation in the cornea closely, which is mainly elicited by the disruption of equilibrium between angiogenic and antiangiogenic factors. Angiogenic factors including vascular endothelial growth factors (VEGFs), basic fibroblast growth factors (bFGFs), and matrix metalloproteinases (MMPs) are vital factors in the formation of CNV. Especially VEGFs are convinced to be the core angiogenic factors in CNV, and MMPs are proved to exert dual effects on the process. Strikingly, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) are determined to play key roles in the formation of CNV, while the mechanism is still vague. In this review, the latest researches are reviewed to discuss the role of MMP-2 and MMP-9 in CNV, respectively, and some inhibitors of them are presented. We hope to provide a new direction of drug research for CNV.

Regulatory T cells promote corneal endothelial cell survival following transplantation via interleukin-10

The functional competence of corneal endothelial cells (CEnCs) is critical for survival of corneal allografts, but these cells are often targets of the immune response mediated by graft-attacking effector T cells. Although regulatory T cells (Tregs) have been studied for their role in regulating the host's alloimmune response towards the graft, the cytoprotective function of these cells on CEnCs has not been investigated. The aim of this study was to determine whether Tregs suppress effector T cell-mediated and inflammatory cytokine-induced CEnC death, and to elucidate the mechanism by which this cytoprotection occurs. Using 2 well-established models of corneal transplantation (low-risk and high-risk models), we show that Tregs derived from low-risk graft recipients have a superior capacity in protecting CEnCs against effector T cell-mediated and interferon-γ and tumor necrosis factor-α-induced cell death compared to Tregs derived from high-risk hosts. We further demonstrate that the cytoprotective function of Tregs derived from low-risk hosts occurs independently of direct cell-cell contact and is mediated by the immunoregulatory cytokine IL-10. Our study is the first to report that Tregs provide cytoprotection for CEnCs through secretion of IL-10, indicating potentially novel therapeutic targets for enhancing CEnC survival following corneal transplantation.

LncRNAs in ocular neovascularizations

The prevalence of eye diseases worldwide is dramatically increasing and represents a major concern in underdeveloped and developed regions. Ocular diseases, previously associated with a higher depression risk, also impose a substantial economic burden on affected families, thus early detection and/or accurate treatment in order to avoid and prevent blindness should be emphasized. Ocular neovascularization (NV), the leading cause of blindness in a variety of eye diseases, is a pathologic process characterized by the formation, proliferation and infiltration of anomalous, tiny and leaky fragile blood vessels within the eye. Genetics have been suspected to play an important role in the occurrence of eye diseases, with the detection of a numbers of specific gene mutations. Long non-coding RNA (lncRNAs) are novel class of regulatory molecules previously associated with various biological processes and diseases, however the nature of the relation and pathways by which they might contribute to the development of corneal, choroidal and retinal NV have not yet been completely elucidated. In this review, we focus on the regulation and characteristics of lncRNAs, summarize results from ocular NV-related studies and discuss the implication of lncRNAs in ocular NV development.

The purinergic receptor antagonist oxidized adenosine triphosphate suppresses immune-mediated corneal allograft rejection

Adenosine triphosphate (ATP) is released into the extracellular environment during transplantation, and acts via purinergic receptors to amplify the alloimmune response. Here, using a well-established murine model of allogeneic corneal transplantation, we investigated the immunomodulatory mechanisms of the purinergic receptor antagonist oxidized ATP (oATP). Corneal transplantation was performed using C57BL/6 donors and BALB/c hosts. oATP or sterile saline was administered via intraperitoneal injection for 2 weeks postoperatively. Frequencies of CD45⁺ leukocytes, CD11b⁺MHCII⁺ antigen presenting cells (APCs), CD4⁺IFN-γ⁺ effector Th1 cells and CD4⁺Foxp3⁺ regulatory T cells (Tregs) were evaluated by flow cytometry. Slit-lamp microscopy was performed weekly for 8 weeks to evaluate graft opacity and determine transplant rejection. Treatment with oATP was shown to significantly reduce graft infiltration of CD45⁺ leukocytes, decrease APC maturation and suppress effector Th1 cell generation relative to saline-treated control. No difference in Treg frequencies or Foxp3 expression was observed between the oATP-treated and control groups. Finally, oATP treatment was shown to reduce graft opacity and increase graft survival. This report demonstrates that oATP limits the alloimmune response by regulating APC maturation and suppressing the generation of alloreactive Th1 immunity.

Method for selective quantification of immune and inflammatory cells in the cornea using flow cytometry

The cornea serves as a protective surface against the environment (i.e., allergens, pollutants, desiccation and microorganisms) and promotes vision, made possible by corneal transparency. This protocol describes corneal preparation for flow cytometry to assess cells localized in the cornea. Our model details the process, from determining how many corneas are needed in the experiment to corneal excision to digestion and staining of the cornea cells. The simplicity of the model allows for systematic analysis of different corneal mechanisms of immunity, inflammation, angiogenesis and wound healing. In corneal transplantation, residential immune and inflammatory cells are key to the mechanisms that underlie angiogenesis, opacity, and graft rejection. In addition, this model can also elucidate cellular mechanisms mediating corneal graft outcomes and wound healing. Lastly, this model can be used to analyze the efficacy of new medications such as instillation and subconjunctival injections and assess the potential of therapeutic molecules to enhance graft survival and wound healing in vivo.

Pathological conversion of regulatory T cells is associated with loss of allotolerance

CD4+CD25+Foxp3+ Regulatory T cells (Tregs) play a critical role in immune tolerance. The plasticity and functional adaptability of Tregs in an inflammatory microenvironment has been demonstrated in autoimmunity. Here, using a double transgenic mouse model that permits Foxp3 lineage tracing, we investigated the phenotypic plasticity of Foxp3+ Tregs in a well-characterized murine model of corneal transplantation. In order to subvert the normal immune privilege of the cornea and foster an inflammatory milieu, host mice were exposed to desiccating stress prior to transplantation. Treg frequencies and function were decreased following desiccating stress, and this corresponded to decreased graft survival. A fraction of Tregs converted to IL-17+ or IFNγ+ 'exFoxp3' T cells that were phenotypically indistinguishable from effector Th17 or Th1 cells, respectively. We investigated how Foxp3 expression is modulated in different Treg subsets, demonstrating that neuropilin-1- peripherally-derived Tregs are particularly susceptible to conversion to IL-17+/IFNγ+ exFoxp3 cells in response to cues from their microenvironment. Finally, we show that IL-6 and IL-23 are implicated in the conversion of Tregs to exFoxp3 cells. This report demonstrates that the pathological conversion of Tregs contributes to the loss of corneal immune privilege.

Safety and Efficacy of OXB-202, a Genetically Engineered Tissue Therapy for the Prevention of Rejection in High-Risk Corneal Transplant Patients

Due to both the avascularity of the cornea and the relatively immune-privileged status of the eye, corneal transplantation is one of the most successful clinical transplant procedures. However, in high-risk patients, which account for >20% of the 180,000 transplants carried out worldwide each year, the rejection rate is high due to vascularization of the recipient cornea. The main reason for graft failure is irreversible immunological rejection, and it is therefore unsurprising that neovascularization (NV; both pre and post grafting) is a significant risk factor for subsequent graft failure. NV is thus an attractive target to prevent corneal graft rejection. OXB-202 (previously known as EncorStat^®) is a donor cornea modified prior to transplant by ex vivo genetic modification with genes encoding secretable forms of the angiostatic human proteins, endostatin and angiostatin. This is achieved using a lentiviral vector derived from the equine infectious anemia virus called pONYK1EiA, which subsequently prevents rejection by suppressing NV. Previously, it has been shown that rabbit donor corneas treated with pONYK1EiA substantially suppress corneal NV, opacity, and subsequent rejection in an aggressive rabbit model of cornea graft rejection. Here, efficacy data are presented in a second rabbit model, which more closely mirrors the clinical setting for high-risk corneal transplant patients, and safety data from a 3-month good laboratory practice toxicology and biodistribution study of pONYK1EiA-modified rabbit corneas in a rabbit corneal transplant model. It is shown that pONYK1EiA-modified rabbit corneas (OXB-202) significantly reduce corneal NV and the rate of corneal rejection in a dose-dependent fashion, and are tolerated with no adverse toxicological findings or significant biodistribution up to 13 weeks post surgery in these rabbit studies. In conclusion, angiogenesis is a valid target to prevent corneal graft rejection in a high-risk setting, and transplanted genetically modified corneas are safe and well-tolerated in an animal model. These data support the evaluation of OXB-202 in a first-in-human trial.

Therapeutic approaches for corneal neovascularization

Angiogenesis refers to new blood vessels that originate from pre-existing vascular structures. Corneal neovascularization which can lead to compromised visual acuity occurs in a wide variety of corneal pathologies. A large subset of measures has been advocated to prevent and/or treat corneal neovascularization with varying degrees of success. These approaches include topical corticosteroid administration, laser treatment, cautery, and fine needle diathermy. Since the imbalance between proangiogenic agents and antiangiogenic agents primarily mediate the process of corneal neovascularization, recent therapies are intended to disrupt the different steps in the synthesis and actions of proangiogenic factors. These approaches, however, are only partially effective and may lead to several side effects. The aim of this article is to review the most relevant treatments for corneal neovascularization available so far.

Immunophysical analysis of corneal neovascularization: mechanistic insights and implications for pharmacotherapy

The cornea lacks adaptive immune cells and vasculature under healthy conditions, but is populated by both cell types under pathologic conditions and after transplantation. Here we propose an immunophysical approach to describe postoperative neovascularization in corneal grafts. We develop a simple dynamic model that captures not only the well-established interactions between innate immunity and vascular dynamics but also incorporates the contributions of adaptive immunity to vascular growth. We study how these interactions determine dynamic changes and steady states of the system as well as the clinical outcome, i.e. graft survival. The model allows us to systematically explore the impact of pharmacological inhibitors of vascular growth on the function and survival of transplanted corneas and search for the optimal time to initiatetherapy. Predictions from our models will help ongoing efforts to design therapeutic approaches to modulate alloimmunity and suppress allograft rejection.

Decoding Noncoding RNAs: Role of MicroRNAs and Long Noncoding RNAs in Ocular Neovascularization

Ocular neovascularization is a pathological sequel of multiple eye diseases. Based on the anatomical site into which the abnormal neovessels grow, ocular neovascularization can be categorized into corneal neovascularization, choroidal neovascularization, and retinal neovascularization. Each category is intractable, and may lead to blindness if not appropriately treated. However, the current therapeutic modalities, including laser photocoagulation, vitrectomy surgery, and anti-VEGF drugs, raise concerns due to limited efficacy, damage on retinal parenchyma and vasculature, and the patients' unresponsiveness to the treatments. Therefore, the in-depth study on pathogenesis of and the search for novel therapeutic targets to the ocular neovascularization are needed. During the last 10 years or so, a large number of literatures have emerged indicating a critical role of noncoding RNAs, particularly microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), in the pathogenesis and regulation of the ocular neovascularization. This review summarizes the current understanding of the biosynthesis and functions of the miRNAs and lncRNAs, the regulation of the miRNAs and lncRNAs in neovascular eye diseases, as well as the roles of these noncoding RNAs in the disease models of ocular neovascularization, in the hope that it could provide clues for the pathogenesis of and molecular targets to the ocular neovascularization.