VEGF-trap aflibercept significantly improves long-term graft survival in high-risk corneal transplantation. Transplantation. 2015;99:678-686. [PMID: 25606789 DOI: 10.1097/tp.0000000000000512]

Corneal Graft Rejection: Is It Reflected in Peripheral Immune Cells? Results of a Prospective Multicenter Study (VISICORT)

BACKGROUND

Allogeneic graft rejection is the leading cause of graft failure in corneal transplantation (CT) despite the immune privilege of the anterior chamber and corneal bed. The ability to identify patients at higher risk of acute rejection before or after CT could have a major impact on the clinical management of these patients.

METHODS

To address this important issue, a multicenter European cohort of low-risk (n = 142) and high-risk (n = 102) CT recipients was established, and the immune system was evaluated in detail in peripheral blood mononuclear cells and plasma before and 6 and 12 mo posttransplantation. Eleven patients in the low-risk group and 11 in the high-risk group experienced acute rejection.

RESULTS

Mass spectrometry analysis of plasma showed a high similarity in composition between patients with and without acute rejection, regardless of their preexisting clinical risk. Pretransplant and longitudinal immune cell analysis of peripheral blood mononuclear cells using deconvolution of transcriptomic profiling and high-dimensional flow cytometry revealed a lack of immune-related biomarkers associated with acute rejection.

CONCLUSIONS

Our results indicate that the immune response leading to acute rejection of CT is unlikely to be detected in the peripheral blood and suggest that analysis of compartments in close proximity to the cornea is more likely to yield clinically applicable predictive biomarkers.

Immunology in corneal transplantation-From homeostasis to graft rejection

Immunology depends on maintaining a delicate balance within the human body, and disruptions can result in conditions such as autoimmune diseases, immunodeficiencies, and hypersensitivity reactions. This balance is especially crucial in transplantation immunology, where one of the primary challenges is preventing graft rejection. Such rejection can lead to organ failure, increased patient mortality, and higher healthcare costs due to the limited availability of donor tissues relative to patient needs. Xenotransplantation, like using porcine corneas for human transplants, offers a potential solution to the donor tissue shortage but faces substantial immunological rejection issues. To prevent rejection in both allo- and xenotransplantation, a deep understanding of how the body maintains immunological balance is essential, particularly since achieving tolerance to non-self tissues is considered the "holy grail" of the field. The cornea, the most frequently transplanted solid organ, has a high acceptance rate due to its immune-privileged status and serves as an ideal model for studying graft rejection mechanisms that disrupt tolerance. However, multiple immune pathways complicate our understanding of these mechanisms. This review examines the rejection mechanisms in corneal transplantation, identifying key cells involved and potential therapeutic strategies to induce and maintain immunological tolerance in both allo- and xenografts across various transplants.

VEGFR3 pathway in corneal transplantation

PURPOSE

Corneal transplantation, a common procedure in ophthalmology, faces challenges in high-risk (HR) cases due to inflammation and vascularization of the host bed, leading to graft rejection. Despite advancements in surgical techniques and therapeutics, preventing rejection in HR cases remains elusive. This study investigates the role of the vascular endothelial-derived growth factor (VEGF)-C/D-VEGFR3 pathway in corneal transplantation, focusing on its impact on inflammation and immune response.

METHODS

In this study, 42 eyes of 42 patients were evaluated, 24 of whom underwent corneal transplantation, with follow-up visits at 90, 180 and 360 days post-transplantation. Clinical assessments included visual acuity, corneal oedema, endothelial cell count and vascularization. Molecular analyses were performed to measure VEGFR3, VEGF-C, VEGF-D, VEGF-A and inflammatory markers.

RESULTS

Results revealed a distinct pattern of VEGF-C/D and VEGFR3 expression in HR versus low-risk (LR) transplants, correlating with inflammatory markers and clinical outcomes. In HR cases, elevated VEGFR3 expression was associated with increased inflammatory markers (Intercellular Adhesion Molecule 1 (ICAM-1) and Human Leukocyte Antigen - DR isotype (HLA-DR)) and graft rejection risk.

CONCLUSION

These findings underscore the importance of understanding the VEGF-C/D-VEGFR3 pathway in modulating immune responses and inflammation in corneal transplantation, particularly in HR cases. Targeting this pathway could offer novel therapeutic avenues to mitigate inflammation and improve graft survival. Further research is warranted to elucidate the underlying mechanisms and validate these findings, potentially enhancing transplant outcomes, especially in HR patients.

Subconjunctival aflibercept inhibits corneal angiogenesis and VEGFR-3+CD11b+ cells

PURPOSE

This study aimed to investigate the effects of subconjunctival injection of aflibercept, a soluble protein decoy for VEGFR-1 and VEGFR-2, on corneal angiogenesis and VEGFR-expressing CD11b+ cells in a mouse model of suture-induced corneal neovascularization.

METHODS

Corneal neovascularization was induced in BALB/c mice by placing three sutures on the cornea. Immediately after surgery, either 200 µg aflibercept (5 µL) or an equal volume of phosphate-buffered saline (PBS) was administered into the subconjunctival space. Seven days after later, corneal new vessels were quantified through clinical examination and measurement of the CD31-stained area in corneal flat mounts. The levels of pro-angiogenic and inflammatory markers in the cornea were evaluated using RT-qPCR. The percentages of VEGFR-2+CD11b+ cells and VEGFR-3+CD11b+ cells were analyzed in the cornea, blood, and draining cervical lymph nodes (DLNs) using flow cytometry.

RESULTS

Subconjunctival injection of aflibercept significantly reduced the growth of corneal new vessels compared to subconjunctival PBS injection. The mRNA levels of Cd31, vascular growth factors (Vegfc and Angpt1), and pro-angiogenic/inflammatory markers (Tek/Tie2, Mrc1, Mrc2, and Il6) in the cornea were downregulated by subconjunctival aflibercept. Also, the percentage of VEGFR-3+CD11b+ cells in the cornea, blood, and DLNs was decreased by aflibercept, whereas that of VEGFR-2+CD11b+ cells was unaffected.

CONCLUSION

Subconjunctival aflibercept administration inhibits inflammatory angiogenesis in the cornea and reduces the numbers of cornea-infiltrating and circulating VEGFR-3+CD11b+ cells.

Inhibiting corneal transplantation rejection via lymphatic vessel ligation in a novel murine model

The lymphatic system is a crucial contributor to allograft rejection after corneal transplantation. However, no surgical procedures for the central pathway where conjunctival lymphatic vessels converge have been investigated. Therefore, we aimed to establish a murine model of lymphatic vessel ligation and evaluate its inhibitory effect on corneal allograft rejection. A tracer was used to visualise lymphatic vessels, and complications were evaluated. A surgical technique was developed to block the lymphatic vessels. Corneas from C57BL/6 mice were transplanted into BALB/c mice divided into two groups-one with and one without lymphatic vessel ligation, to evaluate their effects on allograft rejection. Graft opacity scores were evaluated for 8 weeks, and immunohistochemistry was used to quantify angiogenesis and lymphangiogenesis. 20% trypan blue used as a tracer showed clear inflow with no complications. The two sutures and cyanoacrylate glue combination demonstrated a blocking effect after 25 days and was thus used for lymphatic ligation. Three and nine out of fourteen eyes showed rejection at 8 weeks post-surgery in the lymphatic vessel ligation and control groups, respectively. Furthermore, neovascularisation and lymphangiogenesis significantly decreased in the lymphatic vessel ligation group. Overall, we present a novel therapeutic strategy for 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.

Combination Nanomedicine Strategy for Preventing High-Risk Corneal Transplantation Rejection

High-risk (HR) corneal transplantation presents a formidable challenge, with over 50% of grafts experiencing rejection despite intensive postoperative care involving frequent topical eyedrop administration up to every 2 h, gradually tapering over 6-12 months, and ongoing maintenance dosing. While clinical evidence underscores the potential benefits of inhibiting postoperative angiogenesis, effective antiangiogenesis therapy remains elusive in this context. Here, we engineered controlled-release nanomedicine formulations comprising immunosuppressants (nanoparticles) and antiangiogenesis drugs (nanowafer) and demonstrated that these formulations can prevent HR corneal transplantation rejection for at least 6 months in a clinically relevant rat model. Unlike untreated corneal grafts, which universally faced rejection within 2 weeks postsurgery, a single subconjunctival injection of the long-acting immunosuppressant nanoparticle alone effectively averted graft rejection for 6 months, achieving a graft survival rate of ∼70%. Notably, the combination of an immunosuppressant nanoparticle and an anti-VEGF nanowafer yielded significantly better efficacy with a graft survival rate of >85%. The significantly enhanced efficacy demonstrated that a combination nanomedicine strategy incorporating immunosuppressants and antiangiogenesis drugs can greatly enhance the ocular drug delivery and benefit the outcome of HR corneal transplantation with increased survival rate, ensuring patient compliance and mitigating dosing frequency and toxicity concerns.

New targets of nascent lymphatic vessels in ocular diseases

Recent advancements in the field of endothelial markers of lymphatic vessels and lymphangiogenic factors have shed light on the association between several ocular diseases and ocular nascent lymphatic vessels. The immune privilege of corneal tissue typically limits the formation of lymphatic vessels in a healthy eye. However, vessels in the eyes can potentially undergo lymphangiogenesis and be conditionally activated. It is evident that nascent lymphatic vessels in the eyes contribute to various ocular pathologies. Conversely, lymphatic vessels are present in the corneal limbus, ciliary body, lacrimal glands, optic nerve sheaths, and extraocular muscles, while a lymphatic vasculature-like system exists in the choroid, that can potentially cause several ocular pathologies. Moreover, numerous studies indicate that many ocular diseases can influence or activate nascent lymphatic vessels, ultimately affecting patient prognosis. By understanding the mechanisms underlying the onset, development, and regression of ocular nascent lymphatic vessels, as well as exploring related research on ocular diseases, this article aims to offer novel perspectives for the treatment of such conditions.

Effector T Cells Promote Fibrosis in Corneal Transplantation Failure

Purpose

To evaluate whether fibrosis contributes to corneal transplant failure and to determine whether effector CD4+ T cells, the key immune cells in corneal transplant rejection, play a direct role in fibrosis formation.

Methods

Allogeneic corneal transplantation was performed in mice. Graft opacity was evaluated by slit-lamp biomicroscopy, and fibrosis was assessed by in vivo confocal microscopy. Expression of alpha-smooth muscle actin (α-SMA) in both accepted and failed grafts was assessed by real-time PCR and immunohistochemistry. Frequencies of graft-infiltrating CD4+ T cells, neutrophils, and macrophages were assessed using flow cytometry. In vitro, MK/T-1 corneal fibroblasts were co-cultured with activated CD4+CD25- effector T cells isolated from corneal transplant recipient mice, and α-SMA expression was quantified by real-time PCR and ELISA. Neutralizing antibody was used to evaluate the role of interferon gamma (IFN-γ) in promoting α-SMA expression.

Results

The majority of failed grafts demonstrated clinical signs of fibrosis which became most evident at week 6 after corneal transplantation. Failed grafts showed higher expression of α-SMA as compared to accepted grafts. Flow cytometry analysis showed a significant increase in CD4+ T cells in failed grafts compared to accepted grafts. Co-culture of activated CD4+CD25- effector T cells with corneal fibroblasts led to an increase in α-SMA expression by fibroblasts. Inhibition of IFN-γ in culture significantly suppressed this increase in α-SMA expression as compared to immunoglobulin G control.

Conclusions

Fibrosis contributes to graft opacity in corneal transplant failure and is mediated at least in part by effector CD4+ T cells via IFN-γ.

Human mesenchymal stem cells derived from adipose tissue showed a more robust effect than those from the umbilical cord in promoting corneal graft survival by suppressing lymphangiogenesis

BACKGROUND

Mesenchymal stem cells (MSCs) have shown promising potential in allograft survival. However, few reports have focused on comparing the immunosuppressive capacity of MSCs from different sources and administered via different routes in inhibiting transplant rejection. Moreover, virtually nothing is known about the role of MSCs in the regulation of graft neovascularization and lymphangiogenesis. In this study, we compared the efficacy of human adipose MSCs (hAD-MSCs) and human umbilical cord MSCs (hUC-MSCs) in vitro and in corneal transplantation models to explore the underlying molecular mechanisms and provide a powerful strategy for future clinical applications.

METHODS

hAD-MSCs and hUC-MSCs were generated, and their self-renewal and multi-differentiation abilities were evaluated. The inhibitory effect of human MSCs (hMSCs) was examined by T-cell proliferation assays with or without transwell in vitro. Two MSCs from different sources were separately adoptively transferred in mice corneal transplantation (5 × 105 or 1 × 106/mouse) via topical subconjunctival or intravenous (IV) routes. Allograft survival was evaluated every other day, and angiogenesis and lymphomagenesis were quantitatively analyzed by immunofluorescence staining. The RNA expression profiles of hMSCs were revealed by RNA sequencing (RNA-seq) and verified by quantitative real-time PCR (qRT‒PCR), western blotting or ELISA. The function of the differentially expressed gene FAS was verified by a T-cell apoptosis assay.

RESULTS

hAD-MSCs induced stronger immunosuppression in vitro than hUC-MSCs. The inhibitory effect of hUC-MSCs but not hAD-MSCs was mediated by cell-cell contact-dependent mechanisms. Systemic administration of a lower dose of hAD-MSCs showed better performance in prolonging corneal allograft survival than hUC-MSCs, while subconjunctival administration of hMSCs was safer and further prolonged corneal allograft survival. Both types of hMSCs could inhibit corneal neovascularization, while hAD-MSCs showed greater superiority in suppressing graft lymphangiogenesis. RNA-seq analysis and confirmation experiments revealed the superior performance of hAD-MSCs in allografts based on the lower expression of vascular endothelial growth factor C (VEGF-C) and higher expression of FAS.

CONCLUSIONS

The remarkable inhibitory effects on angiogenesis/lymphangiogenesis and immunological transplantation effects support the development of hAD-MSCs as a cell therapy against corneal transplant rejection. Topical administration of hMSCs was a safer and more effective route for application than systemic administration.

Management and prevention of corneal graft rejection

The management of an episode of corneal graft rejection (CGR) is primarily by corticosteroids. Immunomodulators are useful for long-term immunosuppression and in dealing with cases of high-risk (HR) corneal grafts. The classical signs of CGR following penetrating keratoplasty (PKP) include rejection line, anterior chamber (AC) reaction, and graft edema. However, these signs may be absent or subtle in cases of endothelial keratoplasty (EK). Prevention of an episode of graft rejection is of utmost importance as it can reduce the need for donor cornea significantly. In our previous article (IJO_2866_22), we had discussed about the immunopathogenesis of CGR. In this review article, we aim to discuss the various clinical aspects and management of CGR.

AA, Kulkarni V, Oh Y, Xia S, Ding Z, Han H, Anders N, Rudek MA, Chow W, Stark W, Ensign LM, Hanes J, Xu Q. Six-month effective treatment of corneal graft rejection

Topical corticosteroid eye drop is the mainstay for preventing and treating corneal graft rejection. While the frequent topical corticosteroid use is associated with risk of intraocular pressure (IOP) elevation and poor patient compliance that leads to graft failure and the requirement for a repeated, high-risk corneal transplantation. Here, we developed dexamethasone sodium phosphate (DSP)-loaded dicarboxyl-terminated poly(lactic acid) nanoparticle (PLA DSP-NP) formulations with relatively high drug loading (8 to 10 weight %) and 6 months of sustained intraocular DSP delivery in rats with a single dosing. PLA DSP-NP successfully reversed early signs of corneal rejection, leading to rat corneal graft survival for at least 6 months. Efficacious PLA DSP-NP doses did not affect IOP and showed no signs of ocular toxicity in rats for up to 6 months. Subconjunctival injection of DSP-NP is a promising approach for safely preventing and treating corneal graft rejection with the potential for improved patient adherence.

Lymphangiogenesis Guidance Mechanisms and Therapeutic Implications in Pathological States of the Cornea

Corneal lymphangiogenesis is one component of the neovascularization observed in several inflammatory pathologies of the cornea including dry eye disease and corneal graft rejection. Following injury, corneal (lymph)angiogenic privilege is impaired, allowing ingrowth of blood and lymphatic vessels into the previously avascular cornea. While the mechanisms underlying pathological corneal hemangiogenesis have been well described, knowledge of the lymphangiogenesis guidance mechanisms in the cornea is relatively scarce. Various signaling pathways are involved in lymphangiogenesis guidance in general, each influencing one or multiple stages of lymphatic vessel development. Most endogenous factors that guide corneal lymphatic vessel growth or regression act via the vascular endothelial growth factor C signaling pathway, a central regulator of lymphangiogenesis. Several exogenous factors have recently been repurposed and shown to regulate corneal lymphangiogenesis, uncovering unique signaling pathways not previously known to influence lymphatic vessel guidance. A strong understanding of the relevant lymphangiogenesis guidance mechanisms can facilitate the development of targeted anti-lymphangiogenic therapeutics for corneal pathologies. In this review, we examine the current knowledge of lymphatic guidance cues, their regulation of inflammatory states in the cornea, and recently discovered anti-lymphangiogenic therapeutic modalities.

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.

Inhibitory effect of anti-Scg3 on corneal neovascularization: a preliminary study

BACKGROUND

Corneal neovascularization (CNV) is an important disease that causes blindness. Secretogranin III (Scg3) has emerged as a new influencing factor of neovascularization. This study analyzed the Scg3 antibody's inhibitory effect on CNV and and explored its preliminary mechanism.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with Scg3 and anti-Scg3. Cell proliferation, wound healing migration and tube formation assays were performed. Healthy adult New Zealand rabbits were randomly selected to be alkali burned and establish the corneal neovascularization (CNV) model. The rabbits were randomly divided into 3 groups (the high concentration group, low concentration group and control group). Different doses of anti-Scg3 and PBS were administered to the rabbits. Clinical examinations, immunostaining, quantitative real-time polymerase chain reaction (qPCR) and western blotting analyses were performed postoperatively.

RESULTS

In the in vitro study, the Scg3 antibody mixture inhibited Scg3-induced endothelial cell proliferation and angiogenesis. In the in vivo study, significant CNV was observed in the control group. Confocal microscopy also revealed considerable active neovascularization in the control group. There was no obvious CNV growth in the high concentration group. Additionally, CD31, LYVE1 and CD45 expression was significantly inhibited after treatment with a high concentration of Scg3 antibody. The qPCR and western blotting analyses revealed that the levels of ERK in the low concentration group and high concentration group were higher than those in the control group at 7 days and 14 days. The levels of VEGF in the control group were significantly increased compared with those in the high concentration group. In all three groups, the levels of Akt were not significantly different at any time point.

CONCLUSION

The expression of Scg3 could affect the growth of HUVECs in vitro. Treatment with a high concentration (0.5 µg/mL) of Scg3 antibody reduced the inflammatory response and inhibited the growth of corneal neovascularization after corneal alkali burn injury in rabbits. The MEK/ERK pathway might play an important role in the inhibitory effect of anti-Scg3.

Ocular Drug Delivery: Advancements and Innovations

Ocular drug delivery has been significantly advanced for not only pharmaceutical compounds, such as steroids, nonsteroidal anti-inflammatory drugs, immune modulators, antibiotics, and so forth, but also for the rapidly progressed gene therapy products. For conventional non-gene therapy drugs, appropriate surgical approaches and releasing systems are the main deliberation to achieve adequate treatment outcomes, whereas the scope of “drug delivery” for gene therapy drugs further expands to transgene construct optimization, vector selection, and vector engineering. The eye is the particularly well-suited organ as the gene therapy target, owing to multiple advantages. In this review, we will delve into three main aspects of ocular drug delivery for both conventional drugs and adeno-associated virus (AAV)-based gene therapy products: (1) the development of AAV vector systems for ocular gene therapy, (2) the innovative carriers of medication, and (3) administration routes progression.

Posttransplant VEGFR1R2 Trap Eye Drops Inhibit Corneal (Lymph)angiogenesis and Improve Corneal Allograft Survival in Eyes at High Risk of Rejection

Purpose

To assess whether topical application of VEGFR1R2 Trap after corneal transplantation can impair corneal (lymph)angiogenesis and promote murine corneal allograft survival in eyes at high risk of rejection.

Methods

We used the murine model of suture-induced neovascularization and subsequent keratoplasty in eyes at high risk of rejection, which is an established model for local drug application. After transplantation, the mice were treated with either VEGFR1R2 Trap (aflibercept) or human IgG Fc as eye drops for 2 weeks (three times/d). Deposition of VEGFR1R2 Trap in corneal tissue was detected by immunohistochemistry. Two and 8 weeks after transplantation, corneal (lymph)angiogenesis was assessed morphometrically. Dendritic cells (DCs) and regulatory T cells (Tregs) in the draining lymph nodes (dLNs) were examined by flow cytometry. Allograft survival was determined by corneal graft opacity scores.

Results

Topically applied VEGFR1R2 Trap penetrated into corneal host and graft stroma after keratoplasty in eyes at high risk of rejection. Additional postsurgical corneal hemangiogenesis (P < 0.0001) and lymphangiogenesis (P < 0.01) as well as infiltrating CD45⁺ leukocytes (P < 0.001) and macrophages (P < 0.01) were significantly reduced in the VEGFR1R2 Trap group compared to controls. VEGFR1R2 Trap eye drops significantly decreased the frequency of total CD11c⁺ DCs (P < 0.01), as well as activated CD11c⁺MHC II⁺ DCs (P < 0.01) and CD11c⁺CD40⁺ DCs (P < 0.05). In contrast, the frequency of CD200R⁺ regulatory DCs (P < 0.05) and Tregs in dLNs (P < 0.01) was enhanced. Moreover, long-term allograft survival was also improved (P < 0.05).

Conclusions

Temporary, topical application of VEGFR1R2 Trap after corneal transplantation can achieve sufficient anti-VEGF activity, inhibit additional (lymph)angiogenesis, and significantly improve corneal allograft survival in eyes at high risk of rejection.

Translational Relevance

VEGFR1R2 Trap eye drops after transplantation present a new therapeutic option for patients undergoing corneal transplantation and are at high risk of graft rejection.

Preincubation of donor tissue with a VEGF cytokine trap promotes subsequent high-risk corneal transplant survival

AIMS

Pathological neovascularisation of the host bed and the transplant itself is the main risk factor for graft rejection after corneal transplantation. This study aims to prevent this process by preincubation of the corneal donor tissue ex vivo with an antivascular endothelial growth factor (VEGF) cytokine trap blocking additional postsurgical hemangiogenesis and lymphangiogenesis to promote high-risk graft survival.

METHODS

The donor tissue was preincubated with a VEGFR1R2 cytokine trap for 24 hours prior to murine high-risk corneal transplantation (human IgG Fc was used as the control). The distribution of VEGFR1R2 Trap in the cornea was investigated by immunohistochemistry. Corneas were excised to quantify the blood vessels (BVs) and lymphatic vessels (LVs) and draining lymph nodes (dLNs) were harvested to analyse the phenotype of dendritic cells (DCs) and T cells at week 1, 2 and 8 post-transplantation. Graft survival was compared between preincubation with VEGFR1R2 Trap and human IgG Fc in high-risk recipients.

RESULTS

VEGFR1R2 Trap was present in the graft for at least 2 weeks after surgery and additionally diffused into the corneal recipient. BVs, LVs and macrophages in the whole cornea were significantly decreased 1-week and 2-week post-transplantation (p<0.05). In dLNs the frequency of CD11c+DCs was significantly reduced, whereas CD200R+ regulatory DCs were significantly increased after keratoplasty (p<0.05). Furthermore, long-term high-risk graft survival was significantly improved (p<0.01).

CONCLUSIONS

Preincubation of corneal donor tissue with a VEGFR1R2 cytokine trap can significantly promote subsequent high-risk corneal transplant survival and thereby opens new treatment avenues for high-risk corneal transplantation.

The role of lymphangiogenesis in cardiovascular diseases and heart transplantation

Cardiac lymphangiogenesis plays an important physiological role in the regulation of interstitial fluid homeostasis, inflammatory, and immune responses. Impaired or excessive cardiac lymphatic remodeling and insufficient lymph drainage have been implicated in several cardiovascular diseases including atherosclerosis and myocardial infarction (MI). Although the molecular mechanisms underlying the regulation of functional lymphatics are not fully understood, the interplay between lymphangiogenesis and immune regulation has recently been explored in relation to the initiation and development of these diseases. In this field, experimental therapeutic strategies targeting lymphangiogenesis have shown promise by reducing myocardial inflammation, edema and fibrosis, and improving cardiac function. On the other hand, however, whether lymphangiogenesis is beneficial or detrimental to cardiac transplant survival remains controversial. In the light of recent evidence, cardiac lymphangiogenesis, a thriving and challenging field has been summarized and discussed, which may improve our knowledge in the pathogenesis of cardiovascular diseases and transplant biology.

Corneal Lymphangiogenesis: Current Pathophysiological Understandings and Its Functional Role in Ocular Surface Disease

The cornea is a transparent and avascular tissue that plays a central role in light refraction and provides a physical barrier to the external environment. Corneal avascularity is a unique histological feature that distinguishes it from the other parts of the body. Functionally, corneal immune privilege critically relies on corneal avascularity. Corneal lymphangiogenesis is now recognized as a general pathological feature in many pathologies, including dry eye disease (DED), corneal allograft rejection, ocular allergy, bacterial and viral keratitis, and transient corneal edema. Currently, sizable data from clinical and basic research have accumulated on the pathogenesis and functional role of ocular lymphangiogenesis. However, because of the invisibility of lymphatic vessels, ocular lymphangiogenesis has not been studied as much as hemangiogenesis. We reviewed the basic mechanisms of lymphangiogenesis and summarized recent advances in the pathogenesis of ocular lymphangiogenesis, focusing on corneal allograft rejection and DED. In addition, we discuss future directions for lymphangiogenesis research.

Efficacious, safe, and stable inhibition of corneal neovascularization by AAV-vectored anti-VEGF therapeutics

Corneal neovascularization (CoNV) leads to visual impairment, affecting over 1.4 million people in the United States per year. It is caused by a variety of pathologies, such as inflammation, hypoxia, and limbal barrier dysfunction. Injection of the anti-vascular endothelial growth factor (VEGF) drug KH902 (conbercept) can inhibit CoNV but requires repeated dosing that produces associated side effects, such as cornea scar. To explore more efficacious and long-lasting treatment of CoNV, we employed recombinant adeno-associated virus (rAAV)2 and rAAV8 vectors to mediate KH902 expression via a single intrastromal injection and investigated its anti-angiogenic effects and safety in both alkali-burn- and suture-induced CoNV mouse models. Our results showed that rAAV-mediated KH902 mRNA expression in the cornea was sustained for at least 3 months after a single intrastromal injection. Moreover, the expression level of rAAV8-KH902 far exceeded that of rAAV2-KH902. A single-dose rAAV8-KH902 treatment at 8 × 10⁸ genome copies (GCs) per cornea dramatically inhibited CoNV for an extended period of time in mouse CoNV models without adverse events, whereas the inhibition of CoNV by a single intrastromal administration of the conbercept drug lasted for only 10−14 days. Overall, our study demonstrated that the treatment of CoNV with a single dose of rAAV8-KH902 via intrastromal administration was safe, effective, and long lasting, representing a novel therapeutic strategy for CoNV.

Ocular surface angiography: from neovessels to neoplasia

The ocular surface vascular system plays a key role in corneal and conjunctival inflammatory, infectious and neoplastic pathology. Angiographic vessel analysis using intravenous dyes and optical coherence tomography technology allow both the quantitative and functional assessment of conjunctival vasculature and corneal neovessels. Based on a thorough understanding of vascular alterations in ocular surface disease, angiographic assessment facilitates the clinical management of corneal neovascularisation, the grading of ocular surface inflammation and the identification of tumour angiogenesis in dysplastic or malignant lesions. This review summarises key aspects of the clinical application of corneal and conjunctival angiography as presented at the 2021 virtual Bowman Club meeting.

Lymphatic Trafficking in the Eye: Modulation of Lymphatic Trafficking to Promote Corneal Transplant Survival

(Lymph)angiogenesis into the cornea prior to and after corneal transplantation is a critical risk factor for allograft rejection. Lymphatic vessels even more than blood vessels seem important in mediating immune responses, as they facilitate allograft sensitization in the draining lymph nodes. Thus, the concept of modulating lymphatic trafficking to promote corneal graft survival seems promising. A variety of approaches has been developed to inhibit progressive lymphangiogenesis in experimental settings. Recently, additionally to pharmacological approaches, clinically available techniques such as UVA-based corneal collagen crosslinking and fine needle diathermy were reported to be effective in regressing lymphatic vessels and to experimentally promote graft survival. Clinical pilot studies also suggest the efficacy of blocking antigen presenting cell trafficking to regional lymph nodes by regressing corneal lymphatic vessels to enhance allograft survival in high-risk eyes. In this article, we will give an overview of current strategies to modulate lymphatic trafficking with a special focus on recently reported strategies, which may be easy to translate into clinical practice. This novel concept of temporary, pretransplant regression of lymphatic vessels at the site of transplantation to promote subsequent corneal transplant survival ("lymphangioregressive preconditioning") may also be applicable to other transplantation sites later.

Microporous Drug Delivery System for Sustained Anti-VEGF Delivery to the Eye

Purpose

To describe a novel microporous drug delivery system (DDS) for sustained anti- vascular endothelial growth factor (VEGF) delivery to the eye and to evaluate its efficacy in a corneal injury model.

Methods

A macro-porous DDS (1.5 × 1.5 × 4 mm) loaded with 2 mg of bevacizumab was implanted subconjunctivally in three Dutch-belted pigmented rabbits after corneal alkali injury (2N NaOH). Three rabbits received sham DDS. Animals were followed for three months and assessed in vivo and ex vivo for corneal neovascularization (NV), epithelial defect, stromal scarring, endothelial cell loss, and expression of angiogenic and inflammatory markers in the cornea and retina.

Results

Anti-VEGF DDS treatment led to complete inhibition of superior cornea NV and complete corneal re-epithelialization by day 58 whereas sham DDS resulted in severe cornea NV and persistent epithelial defect (9%∼12% of total cornea area) through the end of the study. Histologically, anti-VEGF DDS significantly reduced CD45⁺ and F4/80 CD11b⁺ cell accumulation (79%, P < 0.05) in the cornea, ameliorated tumor necrosis factor–α expression (90%, P < 0.05), reduced corneal stromal scarring and prevented corneal endothelial cell loss, as compared to sham DDS. Moreover, anti-VEGF DDS achieved retinal penetration and reduction in retinal VEGF levels at 3 months.

Conclusions

Use of subconjunctival anti-VEGF DDS suppresses cornea NV, inflammation, stromal scarring, prevents endothelial cell loss, and abrogates retinal VEGF upregulation in a rabbit corneal alkali burn model. Moreover, it delivers anti-VEGF antibodies to the retina for three months. This delivery platform could enable antibody therapy of other corneal and retinal vascular pathologies.

Translational Relevance

We describe a method for sustained anti-VEGF delivery to the eye for the treatment of ocular injuries.

High-risk Corneal Transplantation: Recent Developments and Future Possibilities

Human corneal transplantation (keratoplasty) is typically considered to have superior short- and long-term outcomes and lower requirement for immunosuppression compared to solid organ transplants because of the inherent immune privilege and tolerogenic mechanisms associated with the anterior segment of the eye. However, in a substantial proportion of corneal transplants, the rates of acute rejection and/or graft failure are comparable to or greater than those of the commonly transplanted solid organs. Critically, while registry data and observational studies have helped to identify factors that are associated with increased risk of corneal transplant failure, the extent to which these risk factors operate through enhancing immune-mediated rejection is less clear. In this overview, we summarize a range of important recent clinical and basic insights related to high-risk corneal transplantation, the factors associated with graft failure, and the immunological basis of corneal allograft rejection. We highlight critical research areas from which continued progress is likely to drive improvements in the long-term survival of high-risk corneal transplants. These include further development and clinical testing of predictive risk scores and assays; greater use of multicenter clinical trials to optimize immunosuppressive therapy in high-risk recipients and robust clinical translation of novel, mechanistically-targeted immunomodulatory and regenerative therapies that are emerging from basic science laboratories. We also emphasize the relative lack of knowledge regarding transplant outcomes for infection-related corneal diseases that are common in the developing world and the potential for greater cross-pollination and synergy between corneal and solid organ transplant research communities.

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.

Immunomodulatory Strategies Targeting Dendritic Cells to Improve Corneal Graft Survival

Even though the cornea is regarded as an immune-privileged tissue, transplantation always comes with the risk of rejection due to mismatches between donor and recipient. It is common sense that an alternative to corticosteroids as the current gold standard for treatment of corneal transplantation is needed. Since blood and lymphatic vessels have been identified as a severe risk factor for corneal allograft survival, much research has focused on vessel regression or inhibition of hem- and lymphangiogenesis in general. However, lymphatic vessels have been identified as required for the inflammation's resolution. Therefore, targeting other players of corneal engraftment could reveal new therapeutic strategies. The establishment of a tolerogenic microenvironment at the graft site would leave the recipient with the ability to manage pathogenic conditions independent from transplantation. Dendritic cells (DCs) as the central player of the immune system represent a target that allows the induction of tolerogenic mechanisms by many different strategies. These strategies are reviewed in this article with regard to their success in corneal transplantation.

Role of Endogenous Regulators of Hem- And Lymphangiogenesis in Corneal Transplantation

Under normal conditions, the cornea, being the transparent “windscreen” of the eye, is free of both blood and lymphatic vessels. However, various diseases of the eye, like infections, can interfere with the balance between promoting and inhibiting factors, which leads to ingrowth of blood and lymphatic vessels. The newly formed lymphatic vessels increase the risk of graft rejection after subsequent corneal transplantation. Corneal transplantation is one of the most commonly performed transplantations worldwide, with more than 40,000 surgeries per year in Europe. To date, various anti-hem- and anti-lymphangiogenic treatment strategies have been developed specifically for the corneal vascular endothelial growth factor (VEGF) pathway. Currently, however, no treatment strategies are clinically available to specifically modulate lymphangiogenesis. In this review, we will give an overview about endogenous regulators of hem- and lymphangiogenesis and discuss potential new strategies for targeting pathological lymphangiogenesis. Furthermore, we will review recently identified modulators and demonstrate that the cornea is a suitable model for the identification of novel endogenous modulators of lymphangiogenesis. The identification of novel modulators of lymphangiogenesis and a better understanding of the signaling pathways involved will contribute to the development of new therapeutic targets for the treatment of pathological lymphangiogenesis. This, in turn, will improve graft rejection, not only for the cornea.

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.

Tocilizumab promotes corneal allograft survival in rats by modulating Treg-Th17 balance

AIM

To examine the therapeutic effects of tocilizumab on experimental corneal transplantation and its effect on Treg/Th17 balance.

METHODS

Allograft corneal graft was performed between host Sprague Dawley and Wistar donor rats. The rats were randomly divided into four groups: normal, autograft, allograft, and allograft treated with tocilizumab. Kaplan-Meier was performed to draw the survival curve. The protein levels of interleukin-17A (IL-17A), vascular endothelial growth factor (VEGF), and forkhead box protein 3 (Foxp3) were measured by immunohistochemistry. The mRNA levels of IL-17A, VEGF, retinoid-related orphan receptor gammat (RORγt), interleukin-6 (IL-6) and Foxp3 were detected by reverse transcription real-time polymerase chain reaction (RT-PCR). The Treg and Th17 cells were investigated by flow cytometry.

RESULTS

The survival time of tocilizumab group was (24±1.27d) longer than that of allograft group (10±0.55d). Moreover, immunohistochemical examination revealed that IL-17A and VEGF protein levels in the allograft group were significantly higher than that of tocilizumab group (P<0.01), while Foxp3 levels in the allograft group was significantly lower than that of the tocilizumab treated group (P<0.001). Flow cytometry showed that the number of Th17 cells in allograft group was significantly higher than that in tocilizumab group (P<0.001). Meanwhile, the number of Tregs was significantly lower than in tocilizumab group (P<0.001). Simultaneously, Foxp3 mRNA expression level in corneal tissues of tocilizumab treated group was significantly higher than other groups (P<0.001).

CONCLUSION

These findings suggest that tocilizumab may promote corneal allograft survival, possibly by modulating Treg-Th17 balance.

Long-term survival of full-thickness corneal xenografts from α1,3-galactosyltransferase gene-knockout miniature pigs in non-human primates

BACKGROUND

We aimed to investigate (a) the long-term survival of corneal grafts from α1,3-galactosyltransferase gene-knockout miniature (GTKOm) pigs in non-human primates as a primary outcome and (b) the effect of anti-CD20 antibody on the survival of corneal grafts from GTKOm pigs as a secondary outcome.

METHODS

Nine rhesus macaques undergoing full-thickness corneal xenotransplantation using GTKOm pigs were systemically administered steroid, basiliximab, intravenous immunoglobulin, and tacrolimus with (CD20 group) or without (control group) anti-CD20 antibody.

RESULTS

Graft survival was significantly longer (P = .008) in the CD20 group (>375, >187, >187, >83 days) than control group (165, 91, 72, 55, 37 days). When we compared the graft survival time between older (>7- month-old) and younger (≤7-month-old) aged donor recipients, there was no significant difference. Activated B cells were lower in the CD20 group than control group (P = .026). Aqueous humor complement C3a was increased in the control group at last examination (P = .043) and was higher than that in the CD20 group (P = .014). Anti-αGal IgG/M levels were unchanged in both groups. At last examination, anti-non-Gal IgG was increased in the control group alone (P = .013).

CONCLUSIONS

The GTKOm pig corneal graft achieved long-term survival when combined with anti-CD20 antibody treatment. Inhibition of activated B cells and complement is imperative even when using GTKO pig corneas.

Regression of corneal neovascularization: Adiponectin versus bevacizumab eye drops

PURPOSE

Comparing the effect of adiponectin versus bevacizumab in decreasing corneal neovascularization.

METHODS

This study was conducted on 30 eyes of 30 New Zealand Albino male rabbits. Corneal neovascularization was induced by a single 7-0 silk suture 2 mm long and 1 mm in front of the limbus for 2 weeks. Rabbits were randomly divided into three groups of adiponectin (20 µg/mL), bevacizumab (5 mg/mL) and artificial tears. The treatments continued up to 14 days.

RESULTS

At the end of 14 days, the average length of vessels in rabbits treated with adiponectin, bevacizumab and control groups decreased from 2.12 ± 0.32 mm to 0.89 ± 0.46 mm (57.68% ± 19.98%) (P < 0.001), 2.30 ± 0.41 mm to 1.30 ± 0.58 mm (42.49% ± 27.17%) (P = 0.048) and from 2.12 ± 0.44 mm to 1.81 ± 0.42 mm (14.81% ± 5.64%) (P = 0.112), respectively. The length of vessels decreased 57.68% ± 19.98% and 42.49% ± 27.17% in adiponectin versus bevacizumab groups, respectively (P = 0.527). The average surface area of vessels in rabbits treated with adiponectin, bevacizumab and control groups reduced from 5.02 ± 1.50 mm² to 1.40 ± 0.75 mm² (70.64% ± 17.76%) (P < 0.001) 0.34 ± 1.1 mm² to 2.80 ± 1.04 mm² (48.24% ± 19.23%) (P = 0.039) and 5.12 ± 2.92 mm² to 4.4 ± 2.55 mm² (14.68% ± 4.19%) (P = 0.117). Mean surface area of vascularization decreased 70.64% ± 17.76% and 48.24% ± 19.23% in adiponectin versus bevacizumab, respectively (P = 0.013).

CONCLUSIONS

The results of this study suggest that topical adiponectin can decrease recent corneal neovascularization.

Local VEGF-A blockade modulates the microenvironment of the corneal graft bed

The microenvironment plays an important role in several immunological processes. Vascular endothelial growth factor-A (VEGF-A) not only regulates angiogenesis, but is known as a modulator of the immune microenvironment. Modulating the site of transplantation might be beneficial for subsequent transplant survival. In this study, we therefore analyzed the effect that a local blockade of VEGF-A in the inflamed cornea as the graft receiving tissue has on the immune system. We used the murine model of suture-induced neovascularization and subsequent high-risk corneal transplantation, which is an optimal model for local drug application. Mice were treated with VEGFR1/R2 trap prior to transplantation. We analyzed corneal gene expression, as well as protein levels in the cornea and serum on the day of transplantation, 2 and 8 weeks later. Local VEGF depletion prior to transplantation increases the expression of pro-inflammatory as well as immune regulatory cytokines only in the corneal microenvironment, but not in the serum. Furthermore, local VEGFR1/R2 trap treatment significantly inhibits the infiltration of CD11c+ dendritic cells into the cornea. Subsequent increased corneal transplantation success was accompanied by a local upregulation of Foxp3 gene expression. This study demonstrates that locally restricted VEGF depletion increases transplantation success by modulating the receiving corneal microenvironment and inducing tolerogenic mechanisms.

Differential effects of primary disease and corneal vascularisation on corneal transplant rejection and survival

Aims

To investigate the relative risk of pretransplant corneal vascularisation on rate of rejection and graft failure within 5 years of surgery when categorised by indication for transplantation.

We analysed all adults recorded in the UK transplant registry who had a first cornea transplant for keratoconus (KC), pseudophakic bullous keratopathy (PBK) or previous infection (viral/bacterial/fungal/protozoan) between 1999 and 2017. We analysed the number of quadrants of the recipient cornea vascularised before transplant and type of vascularisation, the interval post-transplant to rejection, if any, and the outcome at 5 years post-transplant. Risk factors for rejection and transplant failure were modelled by multivariable risk-adjusted Cox regression.

Results

Corneal vascularisation was recorded in 10%, 25% and 67% of patients with KC, PBK and infection, respectively. Individuals with PBK had an increased hazard of transplant rejection only when there were more than two quadrants of vascularisation (HR 1.5, p=0.004) when either superficial and/or deep vascularisation was present (HR 1.3 and 1.4, respectively, p=0.004). Individuals who had a transplant for previous infection had an increased hazard of rejection with four quadrants of vascularisation (HR 1.6, p=0.003). There was no risk-adjusted increase in transplant failure associated with vascularisation in any group. There was weak evidence of reduction in risk of rejection and/or failure associated with lamellar compared with penetrating transplantation in KC and PBK in vascularised recipient corneas.

Conclusion

Vascularisation is a risk factor for corneal allograft rejection within 5 years. The indication for transplantation has a clinically significant effect on the magnitude of this risk.

Impact of co-blocking the costimulatory signals on immune-related genes after high-risk rabbit corneal allograft using 2nd-generation DNA sequencing technology

The aim of this study was to evaluate the impact and mechanism of co-blocking of costimulatory signals CD28-B7-CD40-CD40L during immune allograft rejection. Forty-eight recipient rabbits were prepared as a high-risk corneal allograft model. After surgery, the animals were randomly divided into: control group, MR1 group, anti-B7 group, and co-blocking group (n=12, each group). Subconjunctival injection was first performed on the allograft surgery day until post-surgery day five. Four weeks later, or when immune rejection occurred, the cornea was sampled to detect and analyze the gene spectrum. The survival time in the co-blocking group was significantly longer than that in the other three groups (p < 0.05). Gene expression analysis revealed that the expression of genes associated with immune rejection, interleukin (IL)-1α, IL-1β, intercellular cell adhesion molecule-1, and IL-2 was down-regulated in the co-blocking group, while IL-10 was up-regulated, but the changes in nuclear factor-κB and interferon-γ were not significant. In conclusion, the co-blocking of costimulatory signals can significantly reduce genes that promote corneal allograft rejection. The inhibition of corneal allograft rejection gene expression was significantly enhanced. These gene expression results can explain the conclusion of previous work at the genetic level.

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.

Collagen-Chitosan- Glycerol-HPMC Composite as Cornea Artificial Candidate

The number of blindness is tend to be increased year by year. One of the blindness cause is cornea ulcer.The cause of cornea ulcer is bacteria, fungi, and herpes simplex virus. Cornea transplantation is the only treatment which could widely accepted for blindness. Transplant by donor network becomes the only treatment that is acceptable on a large for blindness. However, treatment donor transplants have many shortcomings in complications post surgery such as host response, donor limitations, incompatibility and the length of time healing. As technology develops, there are many corneal substitutes based on natural ingredients derived from collagen or their derivatives because they promise better properties in biocompatibility. The aim of research are to conduct the synthesis and characterization of collagen- chitosan- glycerol - HPMC as artificial cornea such functional cluster test, cytotoxycity test, morphological test and antibacterial test. Based on functional cluster test, there are functional groups of all components of composite materials. While from cytotoxicity test, all samples have a percentage of living cells above 85%. The morphology test is showed that the pore size of sample B with composition collagen-chitosan-glycerol-HPMC is in accordance with the standard pore size for keratoprothesis. Sample A (collagen-chitosan-glycerol) and sample B (collagen-chitosan-glycerol-HPMC) have strong antibacterial properties.Biocomposite of collagen-chitosan-glycerol could be considered as artificial cornea due to the proximity with the corneal characteristics.

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.

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

Protective Effect of TLR4 Ablation against Corneal Neovascularization following Chemical Burn in a Mouse Model

PURPOSE

To determine whether Toll-like receptor 4 knockout protects mice from corneal neovascularization following chemical injury compared to wild-type (WT) mice.

METHODS

A chemical burn (75% silver nitrate, 25% potassium nitrate) was created under anesthesia in the central right cornea of 32 WT and 31 Toll-like receptor 4 knockout mice. Corneal neovascularization was evaluated at 3, 4, 6, 8, 10, and 35 days after injury using digital photography, fluorescein angiography, gelatin perfusion with fluorescence vascular imaging, immunofluorescence staining, and molecular analysis.

RESULTS

There was no significant between-group difference in relative corneal burn area at 10 days after injury (39.0 ± 2.4% vs. 38.8 ± 9.8%, respectively). Neovascularization was detected in all corneas in vivo and perfusion was detected by fluorescence vascular imaging, reaching maximum area on day 10. The relative area of neovascularization was significantly smaller in the knockout than the WT mice on days 6 (33.3 ± 4.2% vs. 46.8 ± 7.4%, respectively, p = 0.005) and 8 (36.6 ± 1.1% vs. 52.2 ± 6.4%, respectively, p = 0.027), although neovascularization was intensive in both groups. In line with the immunostaining findings of angiogenesis and inflammatory infiltration of damaged corneas, molecular analysis (performed on day 3) revealed elevated expression levels of angiogenesis-related genes (vascular endothelial growth factor, VEGFR2, VEGFR1) and inflammation-related genes (CD45 and TGFβ1) in the WT mice. The knockout mice had higher TNF-α expression than the WT mice.

CONCLUSION

In a mouse corneal chemical burn model, lack of Toll-like receptor 4 expression did not completely inhibit angiogenesis, but did have a relative effect to reduce neovascularization as compared to the WT.

The atypical chemokine receptor-2 does not alter corneal graft survival but regulates early stage of corneal graft-induced lymphangiogenesis

Purpose

To re-evaluate the role of the atypical chemokine receptor-2 (ACKR2) in corneal graft rejection and investigate the effect of ACKR2 on inflammation-associated lymphangiogenesis using murine orthotopic corneal transplantation.

Methods

Corneal grafts were performed and evaluated in the settings of syngeneic, allogeneic and single antigen (HY-antigen) disparity pairings. Corneal vessels were quantified in whole mounts from WT, ACKR2^−/− and F4/80^−/−ACKR2^−/− mice that received syngeneic or allogeneic grafts using anti-CD31 and anti-Lyve-1 antibodies.

Results

Syngeneic corneal grafts in WT and ACKR2^−/− mice were 100% accepted. Fully histo-incompatible allogeneic grafts were rapidly rejected (100%) with similar tempo in both WT and ACKR2^−/− hosts. Around 50% of single-antigen (HY) disparity grafts rejected at a slow but similar tempo (60 days) in WT and ACKR2^−/− mice. Prior to grafting, F4/80^−/−ACKR2^−/− mice had lower baseline levels of limbal blood and lymphatic vessels compared to ACKR2^−/− mice. Syngeneic grafts, but not allogeneic grafts, in ACKR2^−/− and F4/80^−/−ACKR2^−/− mice induced higher levels of lymphatic sprouting and infiltration of Lyve-1⁺ cells during the early (3d) post-graft (pg) stage but lymphatic density was similar to WT grafted mice by 7d pg.

Conclusions

Our results indicate that the chemokine scavenger receptor, ACKR2, has no role to play in the survival of allogeneic grafts. A minor role in regulation of lymphangiogenesis in the early stage of wound healing in syngeneic grafts is suggested, but this effect is probably masked by the more pronounced lymphangiogenic inflammatory response in allogeneic grafts. No additional effect was observed with the deletion of the resident macrophage gene, F4/80.

Current and emerging therapies for corneal neovascularization

The cornea is unique because of its complete avascularity. Corneal neovascularization (CNV) can result from a variety of etiologies including contact lens wear; corneal infections; and ocular surface diseases due to inflammation, chemical injury, and limbal stem cell deficiency. Management is focused primarily on the etiology and pathophysiology causing the CNV and involves medical and surgical options. Because inflammation is a key factor in the pathophysiology of CNV, corticosteroids and other anti-inflammatory medications remain the mainstay of treatment. Anti-VEGF therapies are gaining popularity to prevent CNV in a number of etiologies. Surgical options including vessel occlusion and ocular surface reconstruction are other options depending on etiology and response to medical therapy. Future therapies should provide more effective treatment options for the management of CNV.

Effect of High VEGF-C mRNA Expression on Achievement of Complete Remission in Adult Acute Myeloid Leukemia

Although vascular endothelial growth factor-C (VEGF-C) is known to be expressed in acute myeloid leukemia (AML) blasts, the relevance of VEGF-C in the clinical setting remains to be fully explored. We examined the effect of VEGF-C on achievement of complete remission (CR) in adult de novo AML and immune cell population profiles according to VEGF-C mRNA expression. In comparison of VEGF-C expression between the no-CR and CR groups, the CR group showed a trend toward higher levels of plasma VEGF-C (P = .088), whereas mRNA expression of VEGF-C was downregulated (P = .008). Next, patients with continuous data for VEGF-C were divided into two groups (low vs. high) by a ROC curve analysis. The low- versus high-level groups for plasma VEGF-C (RR of 0.20, P = .030), mRNA expression of VEGF-C (RR of 18.75, P = .003), and the ratio of plasma level to mRNA expression (RR of 0.05, P = .007) were potential predictors of CR on univariate analysis. After adjusting for potential clinical factors including genetic group, multivariate analyses revealed that high VEGF-C mRNA expression was an independent risk factor for failure of induction chemotherapy. Furthermore, patients with high VEGF-C mRNA expression had a lower frequency of NKT and CD8+ cells and showed a trend for a lower frequency of NK cells. These results suggest that interruption of VEGF-C signaling might be a potential therapeutic target for antileukemic treatment in AML patients.

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.

Comparative immunological study of penetrating and anterior lamellar keratoplasty in a murine model

In lamellar keratoplasty, the diseased part of a cornea is replaced while the healthy tissue remains lamellar keratoplasty has the advantage of better graft survival compared to penetrating keratoplasty (PK). We compared the immunological responses to PK and anterior lamellar keratoplasty (ALK) in a murine model. PK or ALK was performed using C57BL/6 donor grafts and BALB/c recipients, and graft opacity was assessed to evaluate graft rejection up to 8 weeks. We evaluated the immunological responses in both groups, which were not clinically considered as graft failure on postoperative day 21. PK mice showed reduced clinical graft survival compared to ALK mice. The mRNA expression of inflammatory mediators, such as IL-1β, IFN-γ, and granzyme B, in grafted corneas of PK mice, was significantly increased compared to the levels in ALK mice at postoperative day 21. PK led to a higher delayed-type hypersensitivity response and IFN-γ secretion in an in vitro T cell assay from draining lymph nodes (LNs), as compared to ALK. Furthermore, PK showed increased angiogenesis and lymphangiogenesis in grafted corneas compared to ALK and led to greater infiltration of CD3⁺ T cells into grafted corneas and increased frequencies of mature antigen presenting cells (APC; MHC-II^highCD11c + cells) and IL-12 + dendritic cells (DCs) in the draining LNs of transplanted mice. In conclusion, PK results in increased graft rejection compared to ALK through relatively increased neovascularization and lymphangiogenesis, which can induce infiltration of pathologic T cells and mature APC migration into grafted corneas and draining LNs.

Angiogenesis and lymphangiogenesis in corneal transplantation-A review

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

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.

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.