Long-Term Graft Survival and Decline in Endothelial Cell Density Following Penetrating Keratoplasty with Organ-Cultured Corneas.

INTRODUCTION: Endothelial cell density (ECD) changes long after penetrating keratoplasty (PKP) of organ-cultured corneas have been little studied. We aim to calculate the point when ECD decline stabilises following PKP with organ culture stored corneas. METHODS: This is an observational study of first-ever PKPs and first-ever re-grafts, performed over 17 years under a single surgeon. ECDs were acquired at 3 and 6 months, 1 year post-graft and annually thereafter by specular microscopy. Time-dependent ECD data was fitted to a log-biexponential model. RESULTS: We studied 465 first-ever grafts and 128 re-grafts. Mean recipient age was 59 years (range 0-96 years; SD 22). Median follow-up was 5.7 (range 0.2-17.1) years. Probability of ED at 5 years in first grafts and re-grafts was 4.4% (2.6-7.1%) and 14.8% (8.3-23.2%). In first grafts, ECD loss reached 0.6% per annum at 7.9 (6.2-9.6) years post-operatively. The half-lives of ECD loss during the immediate post-operative period for first grafts, re-grafts, dystrophies, ectasias, and previous ocular surgery are 20.1 (14.9-30.9), 12.8 (6.9-79.4), 19.5 (13.1-37.7), 26.2 (16.2-68), and 11.6 (6.7-41.3) months, respectively. The half-life during this rapid phase of ECD loss has an inverse correlation with graft survival at 10 years (r = - 0.89, p = 0.02). CONCLUSIONS: Rate of endothelial decompensation is higher in first grafts than re-grafts. ECD decline stabilises 7.9 years post-operatively in first grafts but then becomes lower than the physiological loss expected. Further work is needed to verify whether organ-cultured grafts reach physiological levels of ECD loss faster than hypothermically stored grafts.

Recent Advances in Stem Cell Therapy for Limbal Stem Cell Deficiency: A Narrative Review.

Destruction of the limbus and depletion of limbal stem cells (LSCs), the adult progenitors of the corneal epithelium, leads to limbal stem cell deficiency (LSCD). LSCD is a rare, progressive ocular surface disorder which results in conjunctivalisation and neovascularisation of the corneal surface. Many strategies have been used in the treatment of LSCD, the common goal of which is to regenerate a self-renewing, transparent, and uniform epithelium on the corneal surface. The development of these techniques has frequently resulted from collaboration between stem cell translational scientists and ophthalmologists. Direct transplantation of autologous or allogeneic limbal tissue from a healthy donor eye is regarded by many as the technique of choice. Expansion of harvested LSCs in vitro allows smaller biopsies to be taken from the donor eye and is considered safer and more acceptable to patients. This technique may be utilised in unilateral cases (autologous) or bilateral cases (living related donor). Recently developed, simple limbal epithelial transplant (SLET) can be performed with equally small biopsies but does not require in vitro cell culture facilities. In the case of bilateral LSCD, where autologous limbal tissue is not available, autologous oral mucosa epithelium can be expanded in vitro and transplanted to the diseased eye. Data on long-term outcomes (over 5 years of follow-up) for many of these procedures is needed, and it remains unclear how they produce a self-renewing epithelium without recreating the vital stem cell niche. Bioengineering techniques offer the ability to re-create the physical characteristics of the stem cell niche, while induced pluripotent stem cells offer an unlimited supply of autologous LSCs. In vivo confocal microscopy and anterior segment OCT will complement impression cytology in the diagnosis, staging, and follow-up of LSCD. In this review we analyse recent advances in the pathology, diagnosis, and treatment of LSCD.

Coculture techniques for modeling retinal development and disease, and enabling regenerative medicine.

Stem cell-derived retinal organoids offer the opportunity to cure retinal degeneration of wide-ranging etiology either through the study of in vitro models or the generation of tissue for transplantation. However, despite much work in animals and several human pilot studies, satisfactory therapies have not been developed. Two major challenges for retinal regenerative medicine are (a) physical cell-cell interactions, which are critical to graft function, are not formed and (b) the host environment does not provide suitable queues for development. Several strategies offer to improve the delivery, integration, maturation, and functionality of cell transplantation. These include minimally invasive delivery, biocompatible material vehicles, retinal cell sheets, and optogenetics. Optimizing several variables in animal models is practically difficult, limited by anatomical and disease pathology which is often different to humans, and faces regulatory and ethical challenges. High-throughput methods are needed to experimentally optimize these variables. Retinal organoids will be important to the success of these models. In their current state, they do not incorporate a representative retinal pigment epithelium (RPE)-photoreceptor interface nor vascular elements, which influence the neural retina phenotype directly and are known to be dysfunctional in common retinal diseases such as age-related macular degeneration. Advanced coculture techniques, which emulate the RPE-photoreceptor and RPE-Bruch's-choriocapillaris interactions, can incorporate disease-specific, human retinal organoids and overcome these drawbacks. Herein, we review retinal coculture models of the neural retina, RPE, and choriocapillaris. We delineate the scientific need for such systems in the study of retinal organogenesis, disease modeling, and the optimization of regenerative cell therapies for retinal degeneration.

Developing a simple method to enhance the generation of cone and rod photoreceptors in pluripotent stem cell-derived retinal organoids.

Cell replacement therapy is a promising treatment for irreversible retinal cell death in diverse diseases such as Stargardt's disease, age-related macular degeneration, and retinitis pigmentosa. The final impact of all retinal dystrophies is the loss of photoreceptors; hence, there is a pressing need for research into replacement. Seminal work has shown that a simple three-dimensional culture system enables differentiation of human pluripotent stem cells to retinal organoids containing large numbers of photoreceptors developing alongside retinal neurons and Müller glia cells in a laminated structure that resembles the native retina. Despite these promising developments, current protocols show different efficiencies across pluripotent stem cells and result in retinal organoids with a mixture of photoreceptor cells at varying maturation states, along with nonphotoreceptor cell types. In this study, we investigated the impact of stage-specific addition of retinoic acid (RA), 9-cis-retinal, 11-cis-retinal, levodopa (l-DOPA), triiodothyronine (T3), and γ-secretase inhibitor ((2S)-N-[(3,5-Difluorophenyl)acetyl]-l-alanyl-2-phenyl]glycine1,1-dimethylethyl ester2L [DAPT]) in the generation of cone and rod photoreceptors. Our results indicate that addition of RA + T3 during days 90 to 120 of differentiation enhanced the generation of rod and S-cone photoreceptor formation, while the combined addition of DAPT from days 28 to 42 with RA during days 30 to 120 of differentiation led to enhanced generation of L/M-cones at the expense of rods. l-DOPA when added together with RA during days 90 to 120 of differentiation also promoted the emergence of S-cones at the expense of rod photoreceptors. Collectively, these data represent an advance in our ability to direct generation of rod and cone photoreceptors in vitro.

Sensitivity and Specificity of the Neutrophil-lymphocyte Ratio in the Diagnosis of Acute Appendicitis.

OBJECTIVE: Acute appendicitis is a common surgical emergency; however, its misdiagnosis resulting in negative appendicectomy is not uncommon. Novel diagnostic methods will help reduce the rate of negative appendicectomy. We hypothesise that the neutrophil-lymphocyte ratio (NLR) will increase upon peritoneal involvement by inflammation, as it does in severe disease. METHODS: We conducted a retrospective analysis on prospectively collected data for all emergency appendicectomy patients during the study period. We studied blood results at the time of presentation, and histology of the removed appendices. Receiver Operating Characteristics were calculated to classify histologically normal versus inflamed appendices and moderate versus severe disease. Moderate disease was that confined to the sub-serosal layers, while severe disease involved the serosa and beyond. RESULTS: A total of 372 patients underwent emergency appendicectomy, 254 (78.4%) of which subsequently had acute appendicitis on histology. Sixty-five (25.6%) and 189 (74.4%) patients had moderate and severe disease, respectively. The median age was 27 years (range 16-84). In diagnosing acute appendicitis, the cut-off value of the NLR was 4.2, while the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 79.5%, 67.0%, 89.8%, and 47.5%, respectively. In identifying the moderate versus severe disease, the cut-off value was 9.7, while the sensitivity, specificity, PPV and NPV were 71.4%, 53.8%, 85.4% and 43.7%, respectively. CONCLUSIONS: Inflammatory markers are useful adjuncts to history, examination, and radiological investigations in making the diagnosis of appendicitis. However, due to low sensitivity and specificity, they cannot be used alone. Calculation of the NLR has no additional benefit over the neutrophil count in diagnosis, or in distinguishing moderate and severe disease.

The Role of Nerve Growth Factor in Maintaining Proliferative Capacity, Colony-Forming Efficiency, and the Limbal Stem Cell Phenotype.

Nerve growth factor (NGF) has demonstrated great benefit in the treatment of neurotrophic corneal ulcers. There is evidence for multiple modes of action in promoting corneal healing, but only indirect evidence exists for NGF's effects on limbal stem cells (LSCs). Understanding the role of NGF in LSC biology will improve our understanding of paracrine regulation of the limbal niche and the design of stem cell-based therapies for conditions such as LSC deficiency. In this article, we studied the regulation of NGF signaling components during LSC differentiation and the role of NGF in LSC proliferation and maintenance of the stem cell phenotype. LSC differentiation was induced by prolonged (40 day) culture which resulted in a significant increase in cell size, decrease in colony-forming efficiency and expression of putative LSC markers. A protein microarray measuring expression of 248 signaling proteins indicated the low affinity NGF receptor p75NTR to be the most downregulated protein upon differentiation. Further confirmation by Western blotting and real-time quantitative polymerase chain reaction indicated that NGF and p75NTR are expressed in early LSC cultures and downregulated upon differentiation. LSC cultures grown in the presence of anti-NGF antibody showed decreased colony-forming efficiency, DNA replication and expression of putative LSC markers ABCG2 and C/EBPδ. Supplementation of LSC culture medium with NGF extended the life span of LSC cultures in vitro and increased the expression of putative LSC markers ΔNp63α and ABCG2. Taken together, our data indicate that NGF signaling is a key promoter of LSC proliferation, colony-forming efficiency, and a maintainer of the LSC phenotype. Stem Cells 2019;37:139-149.

Defining the optimal cryoprotectant and concentration for cryopreservation of limbal stem cells.

Limbal stem cell (LSC) deficiency causes progressive loss of vision but may be treated by transplant of autologous LSCs. Cryopreservation has the potential to indefinitely extend the lifespan of LSCs allowing re-transplant in case of graft failure. In this study, we aimed to identify the optimal cryoprotectant and cryoprotectant concentration for LSC cultures. Suspension cultures derived from cadaveric corneoscleral rims were cooled to 4 °C with Me2SO, propylene glycol or ethylene glycol at a concentration of 5%, 10% or 15%. Cell tolerance was measured in terms of membrane integrity, colony-forming efficiency and alamarBlue® reduction. Increasing cryoprotectant concentration above 5% reduced membrane integrity, metabolism and colony-forming efficiency. Cryoprotectant choice did not significantly influence these characteristics. Cells demonstrating Side Population were maintained after cryopreservation with 5% propylene glycol in vapour phase liquid nitrogen for 1 week, indicating that cryopreservation of LSCs with relatively low cryoprotectant concentration (5%) has promise in low-temperature eye banking.