Keratocyte apoptosis and failure of corneal allografts

TNF-α Inhibitors for the Management of Intractable Corneal Melt: Report of Three Cases and Review of the Literature

OBJECTIVE

To report three consecutive cases with noninfectious corneal melting, whose disease progression could only be halted with tumor necrosis-α (TNF-α) inhibitor infusion, with a review of the relevant literature.

MATERIALS AND METHODS

Patients with toxic epidermal necrolysis, severe alkaline burn, and Sjögren syndrome had experienced severe corneal melting following penetrating keratoplasty, Boston type 1 keratoprosthesis implantation or spontaneously, respectively. Topical autologous serum eye-drops, medroxyprogesterone, and acetylcysteine formulations; frequent nonpreserved lubrication; systemic tetracyclines and vitamin-C supplements; topical and systemic steroids and steroid-sparing agents; surgical approaches including amniotic membrane transplantation, tectonic graft surgery; and tarsorraphy failed to alter the disease courses.

RESULTS

Upon consultation with the rheumatology clinic, TNF-α inhibitor infliximab (Remicade; Centocor Ortho Biotech Inc, Horsham, PA) 5 mg/kg infusion was planned for each patient. After 0-, 2-, and 6-week doses, monthly infusion at the same dose was maintained for 12 months because of severe and intractable course of their diseases. Each case showed dramatic improvements in corneal melts; and sterile vitritis in the eye with Boston keratoprosthesis responded, as well.

CONCLUSIONS

Inhibiting TNF-α-mediated expression of matrix metalloproteinases responsible for collagen breakdown should be considered in refractory cases, as a means of globe salvage.

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.

The Use of Digital Microscopy to Compare the Thicknesses of Normal Corneas and Ex Vivo Rejected Corneal Grafts with a Focus on the Descemet's Membrane

Objective

To compare the thickness of corneal layers, specifically the Descemet's membrane (DM), in normal corneas and in failed grafts due to rejection (FGRs) using the digital histopathology and to propose a model for the measurement of corneal layers using this method.

Methods

This is a prospective, cross-sectional study performed at the MUHC-McGill University Ocular Pathology & Translational Research Laboratory (McGill University, Montreal, Canada). Histopathological sections of 25 normal human corneas and 40 FGRs were fully digitalized and examined. Inclusion criteria: samples diagnosed as normal corneas or FGRs, from patients older than 18 years of age. Exclusion criteria: histopathological sections without adequate tissue or missing epidemiological information. For each sample, the thicknesses of the epithelium, stroma, and DM were acquired. From a perpendicular plane of reference, two central measurements and two nasal and two temporal peripheral measurements were obtained.

Results

There were differences between the normal and FGR groups in the mean central thickness of the epithelium (p < 0.001), the nasal and temporal stromal regions (p < 0.001), and of the DM in the nasal and temporal regions (p < 0.001). Compared with the extremities of the sample (nasal and temporal), the mean thickness of the DM in normal corneas was lower in the central region (p < 0.001), and this difference was not found in the FGR group.

Conclusions

Normal corneas have a thinner epithelium in the central region than the FGR group. In addition, the stroma and DM thicknesses of the nasal and temporal periphery were significantly higher in normal corneas than in those from the FGR group. The digital microscopy protocol applied in this study may be useful for further research studies regarding cornea and other tissues.

MicroRNAs in the cornea: Role and implications for treatment of corneal neovascularization

With no safe and efficient approved therapy available for treating corneal neovascularization, the search for alternative and effective treatments is of great importance. Since the discovery of miRNAs as key regulators of gene expression, knowledge of their function in the eye has expanded continuously, facilitated by high throughput genomic tools such as microarrays and RNA sequencing. Recently, reports have emerged implicating miRNAs in pathological and developmental angiogenesis. This has led to the idea of targeting these regulatory molecules as a therapeutic approach for treating corneal neovascularization. With the growing volume of data generated from high throughput tools applied to study corneal neovascularization, we provide here a focused review of the known miRNAs related to corneal neovascularization, while presenting new experimental data and insights for future research and therapy development.

Effects of Adipose-derived Mesenchymal Stem Cell Exosomes on Corneal Stromal Fibroblast Viability and Extracellular Matrix Synthesis

Background

Corneal stromal cells (CSCs) are components of the corneal endothelial microenvironment that can be induced to form a functional tissue-engineered corneal endothelium. Adipose-derived mesenchymal stem cells (ADSCs) have been reported as an important component of regenerative medicine and cell therapy for corneal stromal damage. We have demonstrated that the treatment with ADSCs leads to phenotypic changes in CSCs in vitro. However, the underlying mechanisms of such ADSC-induced changes in CSCs remain unclear.

Methods

ADSCs and CSCs were isolated from New Zealand white rabbits and cultured in vitro. An Exosome Isolation Kit, Western blotting, and nanoparticle tracking analysis (NTA) were used to isolate and confirm the exosomes from ADSC culture medium. Meanwhile, the optimal exosome concentration and treatment time were selected. Cell Counting Kit-8 and annexin V-fluorescein isothiocyanate/propidium iodide assays were used to assess the effect of ADSC- derived exosomes on the proliferation and apoptosis of CSCs. To evaluate the effects of ADSC- derived exosomes on CSC invasion activity, Western blotting was used to detect the expression of matrix metalloproteinases (MMPs) and collagens.

Results:

ADSCs and CSCs were successfully isolated from New Zealand rabbits. The optimal concentration and treatment time of exosomes for the following study were 100 μg/ml and 96 h, respectively. NTA revealed that the ADSC-derived exosomes appeared as nanoparticles (40-200 nm), and Western blotting confirmed positive expression of CD9, CD81, flotillin-1, and HSP70 versus ADSC cytoplasmic proteins (all P < 0.01). ADSC-derived exosomes (50 μg/ml and 100 μg/ml) significantly promoted proliferation and inhibited apoptosis (mainly early apoptosis) of CSCs versus non-exosome-treated CSCs (all P < 0.05). Interestingly, MMPs were downregulated and extracellular matrix (ECM)-related proteins including collagens and fibronectin were upregulated in the exosome-treated CSCs versus non-exosome-treated CSCs (MMP1: t = 80.103, P < 0.01; MMP2: t = 114.778, P < 0.01; MMP3: t = 56.208, P < 0.01; and MMP9: t = 60.617, P < 0.01; collagen I: t = -82.742, P < 0.01; collagen II: t = -72.818, P < 0.01; collagen III: t = -104.452, P < 0.01; collagen IV: t = -133.426, P < 0.01, and collagen V: t = -294.019, P < 0.01; and fibronectin: t = -92.491, P < 0.01, respectively).

Conclusion:

The findings indicate that ADSCs might play an important role in CSC viability regulation and ECM remodeling, partially through the secretion of exosomes.

MicroRNA-122 ameliorates corneal allograft rejection through the downregulation of its target CPEB1

Transplant rejection is a major cause of corneal transplantation failure. MicroRNAs (miRNAs) are a family of small RNAs that regulates gene expression in a sequence-specific manner. miRNAs have recently been shown to have important roles in human organ transplantation, but reports of miRNAs directly associated with corneal transplantation rejection remain limited. To investigate the role of miRNAs during corneal allograft rejection, we established a mouse penetrating keratoplasty model and used microarrays to screen for differentially expressed miRNAs. Our results revealed that the expression of miR-122 was significantly decreased in the allogeneic group. Consistent with this result, the expression of cytoplasmic polyadenylation element-binding protein-1 (CPEB1), a direct target of miR-122, was significantly increased. Further analysis demonstrated that miR-122 inhibited inflammatory cytokine-induced apoptosis in corneal keratocytes through the downregulation of its target CPEB1. We also found that increased miR-122 expression significantly reduced the risk of corneal transplantation rejection. Thus, our results indicate that miR-122 is an important miRNA associated with corneal graft rejection and can be used as a therapeutic target for the prevention of immune rejection after keratoplasty.

Role of Human Corneal Stroma-Derived Mesenchymal-Like Stem Cells in Corneal Immunity and Wound Healing

Corneal tissue regeneration is of crucial importance for maintaining normal vision. We aimed to isolate and cultivate human corneal stroma-derived mesenchymal stem-like cells (CSMSCs) from the central part of cadaver corneas and study their phenotype, multipotency, role in immunity and wound healing. The isolated cells grew as monolayers in vitro, expressed mesenchymal- and stemness-related surface markers (CD73, CD90, CD105, CD140b), and were negative for hematopoietic markers as determined by flow cytometry. CSMSCs were able to differentiate in vitro into fat, bone and cartilage. Their gene expression profile was closer to bone marrow-derived MSCs (BMMSCs) than to limbal epithelial stem cells (LESC) as determined by high-throughput screening. The immunosuppressive properties of CSMSCs were confirmed by a mixed lymphocyte reaction (MLR), while they could inhibit proliferation of activated immune cells. Treatment of CSMSCs by pro-inflammatory cytokines and toll-like receptor ligands significantly increased the secreted interleukin-6 (IL-6), interleukin-8 (IL-8) and C-X-C motif chemokine 10 (CXCL-10) levels, as well as the cell surface adhesion molecules. CSMSCs were capable of closing a wound in vitro under different stimuli. These cells thus contribute to corneal tissue homeostasis and play an immunomodulatory and regenerative role with possible implications in future cell therapies for treating sight-threatening corneal diseases.

Predicting Corneal Graft Rejection by Confocal Microscopy

PURPOSE

This study aims at estimating corneal healing by activated keratocyte (AK) counting with in vivo confocal microscopy after perforating keratoplasty (PK). It assesses the value of AK counting in predicting corneal graft rejection.

METHODS

This prospective single-center observational study included 45 patients who benefited from PK in 2013 and were followed up over 2 years. All were monitored by confocal microscopy at day 1, day 7, and monthly thereafter. The AKs were counted in 5 optical sections in each of the anterior, middle, and posterior stroma. The ability of AKs in predicting the occurrence of corneal rejection was assessed by comparison of AK counts between patients with and without clinical signs of rejection.

RESULTS

In patients with graft rejection, the AK counts increased significantly 2 months before the clinical diagnosis of rejection, whereas it remained stable after 4 months in patients without rejection. In patient with graft rejection, the AK count reached a maximum at the rejection diagnosis and antirejection treatment initiation but decreased significantly 1 month after treatment initiation.

CONCLUSIONS

This study confirmed the predictive value of AK counting in corneal graft rejection. The increase in the AK count allowed predicting graft rejection 2 months before the clinical diagnosis of rejection; it may then be the first sign of subclinical rejection.

Infliximab after Boston Keratoprosthesis in Stevens-Johnson Syndrome: An Update

PURPOSE

To report our experience using intravenous infliximab for the treatment of tissue melt after Boston keratoprosthesis (B-KPro) types I and II in patients with autoimmune disease.

METHODS

Case series.

RESULTS

We identified four patients who were treated with intravenous infliximab in the context of tissue melt after B-KPro. Stevens-Johnson syndrome-associated corneal blindness was the primary surgical indication for B-KPro implantation in all patients. Two patients received a B-KPro type I and two patients received a B-KPro type II. The patients received intravenous infliximab for skin retraction around B-KPro type II, melting of the carrier graft or leak. Treatment resulted in a dramatic decrease in inflammation and, in some cases, arrest of the melting process. Cost and patient adherence were limiting factors to pursuing infliximab therapy. In addition, one patient developed infusion reactions.

CONCLUSIONS

Intravenous infliximab may be considered as globe- and sight-saving therapy for tissue melt after B-KPro.

Gene therapy in corneal transplantation

Corneal transplantation is the most commonly performed organ transplantation. Immune privilege of the cornea is widely recognized, partly because of the relatively favorable outcome of corneal grafts. The first-time recipient of corneal allografts in an avascular, low-risk setting can expect a 90% success rate without systemic immunosuppressive agents and histocompatibility matching. However, immunologic rejection remains the major cause of graft failure, particularly in patients with a high risk for rejection. Corticosteroids remain the first-line therapy for the prevention and treatment of immune rejection. However, current pharmacological measures are limited in their side-effect profiles, repeated application, lack of targeted response, and short duration of action. Experimental ocular gene therapy may thus present new horizons in immunomodulation. From efficient viral vectors to sustainable alternative splicing, we discuss the progress of gene therapy in promoting graft survival and postulate further avenues for gene-mediated prevention of allogeneic graft rejection.

Initial in vitro investigation of the human immune response to corneal cells from genetically engineered pigs

PURPOSE

To compare the in vitro human humoral and cellular immune responses to wild-type (WT) pig corneal endothelial cells (pCECs) with those to pig aortic endothelial cells (pAECs). These responses were further compared with CECs from genetically engineered pigs (α1,3-galactosyltransferase gene-knockout [GTKO] pigs and pigs expressing a human complement-regulatory protein [CD46]) and human donors.

METHODS

The expression of Galα1,3Gal (Gal), swine leukocyte antigen (SLA) class I and class II on pCECs and pAECs, with or without activation by porcine IFN-γ, was tested by flow cytometry. Pooled human serum was used to measure IgM/IgG binding to and complement-dependent cytotoxicity (CDC) to cells from WT, GTKO, and GTKO/CD46 pigs. The human CD4(+) T-cell response to cells from WT, GTKO, GTKO/CD46 pigs and human was tested by mixed lymphocyte reaction (MLR).

RESULTS

There was a lower level of expression of the Gal antigen and of SLA class I and II on the WT pCECs than on the WT pAECs, resulting in less antibody binding and reduced human CD4(+) T-cell proliferation. However, lysis of the WT pCECs was equivalent to that of the pAECs, suggesting more susceptibility to injury. There were significantly weaker humoral and cellular responses to the pCECs from GTKO/CD46 pigs compared with the WT pCECs, although the cellular response to the GTKO/CD46 pCECs was greater than to the human CECs.

CONCLUSIONS

These data provide the first report of in vitro investigations of CECs from genetically engineered pigs and suggest that pig corneas may provide an acceptable alternative to human corneas for clinical transplantation.

Histopathological study of delayed regraft after corneal graft failure

PURPOSE

To evaluate the histopathological features of corneal graft failures over time.

METHODS

A single-center retrospective analysis was performed on corneal specimens diagnosed as corneal graft failure retrieved from The Henry C. Witelson Ophthalmic Pathology Laboratory and Registry (Montreal, Canada) over a 9-year period. The corneal buttons were divided into 3 different groups according to the time between the diagnosis of corneal graft failure and regraft. Corneal specimens obtained during keratoplasty were subjected to hematoxylin and eosin and periodic acid-Schiff. Five different histopathological findings were evaluated in each specimen.

RESULTS

Overall, the most common histopathological finding was endothelial decompensation (97.2%). Subepithelial pannus (38.9%), vessels in the corneal stroma (11.1%), and anterior synechiae (2.8%) were the other present findings. The inflammatory reaction was considered discrete in 83.3% of the cases. The only significant histopathological finding correlated with time was the presence of vessels in the corneal stroma (P = 0.0092).

CONCLUSIONS

Corneal neovascularization, represented by the presence of vessels in the corneal stroma, was the only histopathological finding correlated with time. Because it is a known factor of poor prognosis, our findings strongly support that early regraft has higher chances of success.

Graft failure IV. Immunologic mechanisms of corneal transplant rejection

Corneal transplantation is the oldest and the most common form of solid tissue transplantation in humans. Immunologic graft rejection is one of the main causes of short and long-term graft failure. Rejection involves donor tissue recognition and destruction by allo-specific immune cells of the recipient. This review outlines (1) the immunobiology of transplantation, with reference to ocular immune privilege, (2) factors that confer "high-risk" status to a graft and (3) the pathophysiologic mechanisms of corneal transplant rejection.

Adipose-derived stem cells are a source for cell therapy of the corneal stroma

Most corneal diseases affect corneal stroma and include immune or infectious diseases, ecstatic disorders, traumatic scars, and corneal dystrophies. Cell-based therapy is a promising therapeutic approach to overcome the current disadvantages of corneal transplantation. We intended to search for a cell source to repopulate and regenerate corneal stroma. We investigated the ability of human processed lipoaspirate derived (PLA) cells to regenerate corneal stroma in experimental animals. In the first set of experiments, we tested the biosafety and immunogenicity of human PLA stem cells transplanted into the corneal stroma of rabbits. No immune response was elicited even though we used immune-competent animals. PLA cells survived up to 10 weeks post-transplant, maintained their shape, and remained intermingled in the stroma without disrupting its histological pattern. Interestingly, transparency was preserved even 10 weeks after the transplant, when PLA cells formed a discontinuous layer in the stroma. In the second set of experiments, regeneration of the corneal stroma by PLA cells was assessed, creating a niche by partial ablation of the stroma. After 12 weeks, human cells were disposed following a multilayered pattern and differentiated into functional keratocytes, as assessed by the expression of aldehyde-3-dehydrogenase and cornea-specific proteoglycan keratocan. Based on our results, we believe that adipose-derived adult stem cells can be a cell source for stromal regeneration and repopulation in diseased corneas. The low health impact of the surgical procedure performed to obtain the PLA cells provides this cell source with an additional beneficial feature for its possible future autologous use in human patients.

Corneal graft rejection is accompanied by apoptosis of the endothelium and is prevented by gene therapy with bcl-xL

Corneal transplants normally enjoy a high percentage of survival, mainly because the eye is an immune-privileged site. When allograft failure occurs, it is most commonly due to rejection, an immune-mediated reaction that targets the corneal endothelium. While the exact mechanism by which the endothelium is targeted is still unknown, we postulate that corneal endothelial cell loss during allograft failure is mediated by apoptosis. Furthermore, because corneal endothelial cells do not normally regenerate, we hypothesize that suppressing apoptosis in the graft endothelium will promote transplant survival. In a murine model of transplantation, TUNEL staining and confocal microscopy showed apoptosis of the graft endothelium occurring in rejecting corneas as early as 2 weeks posttransplantation. We found that bcl-xL protected cultured corneal endothelial cells from apoptosis and that lentiviral delivery of bcl-xL to the corneal endothelium of donor corneas significantly improved the survival of allografts. These studies suggest a novel approach to improve corneal allograft survival by preventing apoptosis of the endothelium.

Keratocyte and subbasal nerve density after penetrating keratoplasty

PURPOSE

To determine central keratocyte and subbasal nerve densities after penetrating keratoplasty (PK) in clear grafts and in grafts with late endothelial failure (LEF).

METHODS

Ninety-nine clear grafts of 74 patients and 21 grafts with LEF in 19 patients were examined by confocal microscopy at 1 to 31 years after PK. Keratocyte density and number of keratocytes in a full-thickness column of stroma with frontal area of 1 mm(2) were determined from images. Subbasal nerve fiber bundle density was measured in the central cornea as the visible length of nerve per frame area. Comparisons were made to normal corneas.

RESULTS

Full-thickness keratocyte density in clear grafts (22,101 +/- 3,799 cells/mm(3), mean +/- SD, n = 99) was lower than in normal corneas (26,610 +/- 3,683 cells/mm(3), n = 63, P < .001) but did not differ from grafts with LEF (21,268 +/- 3,298 cells/mm(3), n = 12, P = .47). The number of keratocytes in clear grafts (10,325 +/- 1,708 cells, n = 99) was lower than in normal corneas (11,466 +/- 1,503 cells, n = 63, P < .001) but did not differ from grafts with LEF (10,778 +/- 1,760 cells, n=12, P = .39). Median subbasal nerve density in clear grafts (150 microm/mm(2), n = 94) was lower than in normal corneas (7,025 microm/mm(2), n = 76, P < .001), and nerve recovery correlated with time after PK (r = 0.36, P < .001, n = 94).

CONCLUSIONS

Keratocyte density and number of keratocytes are decreased in penetrating grafts compared to normal corneas, but not compared to grafts with LEF. Subbasal nerve density does not recover to normal through 30 years after PK.