Transplant rejection following endothelial keratoplasty and penetrating keratoplasty in the United Kingdom: incidence and survival

Exploring single-cell RNA sequencing as a decision-making tool in the clinical management of Fuchs' endothelial corneal dystrophy

Single-cell RNA sequencing (scRNA-seq) has enabled the identification of novel gene signatures and cell heterogeneity in numerous tissues and diseases. Here we review the use of this technology for Fuchs' Endothelial Corneal Dystrophy (FECD). FECD is the most common indication for corneal endothelial transplantation worldwide. FECD is challenging to manage because it is genetically heterogenous, can be autosomal dominant or sporadic, and progress at different rates. Single-cell RNA sequencing has enabled the discovery of several FECD subtypes, each with associated gene signatures, and cell heterogeneity. Current FECD treatments are mainly surgical, with various Rho kinase (ROCK) inhibitors used to promote endothelial cell metabolism and proliferation following surgery. A range of emerging therapies for FECD including cell therapies, gene therapies, tissue engineered scaffolds, and pharmaceuticals are in preclinical and clinical trials. Unlike conventional disease management methods based on clinical presentations and family history, targeting FECD using scRNA-seq based precision-medicine has the potential to pinpoint the disease subtypes, mechanisms, stages, severities, and help clinicians in making the best decision for surgeries and the applications of therapeutics. In this review, we first discuss the feasibility and potential of using scRNA-seq in clinical diagnostics for FECD, highlight advances from the latest clinical treatments and emerging therapies for FECD, integrate scRNA-seq results and clinical notes from our FECD patients and discuss the potential of applying alternative therapies to manage these cases clinically.

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.

Dropless penetrating keratoplasty using a subconjunctival dexamethasone implant: safety pilot study

BACKGROUND/AIM

Rejection is the main cause of graft failure after penetrating keratoplasty (PK). Its prevention by repeated instillation of steroid eye-drops has not evolved in decades. Poor adherence and discontinuous nature of eye-drop treatment may explain some PK failures. In a rabbit model, we previously demonstrated that a subconjunctival dexamethasone implant was well tolerated and prevented rejection efficiently in the first 5-6 weeks. This clinical trial investigates its tolerance and safety after PK.

METHODS

Single-centre, phase II non-randomised tolerance and safety pilot study (NCT02834260). Designed to analyse the risk of elevated intraocular pressure (IOP), discomfort and resorption time. Fourteen patients with a low rejection risk indication of PK were enrolled between January 2017 and August 2018. The implant was injected in the 12 o'clock position, 5 mm from the limbus, at the end of PK. A steroid eye-drop treatment was planned when implant resorption was complete. Patients were monitored regularly for 12 months: IOP (main outcome measure at 1 month), discomfort and redness scores, implant status, rejection episode and central corneal thickness by optical coherence tomography. An independent data safety monitoring committee verified safety aspects.

RESULTS

No increase in IOP or other adverse event related to the implant was observed. Average resorption time was 6 weeks. The switch to steroid eye-drops was uneventful. One patient, included despite preoperative corneal neovascularisation (unintended protocol deviation) experienced a rejection.

CONCLUSIONS

This is the first proof of concept that dropless immunosuppression is possible after low rejection risk PK.

TRIAL REGISTRATION NUMBER

NCT02834260.

Keratoplasty Registries: Lessons Learned

ABSTRACT

Clinical registries have been developed for decades in the field of ophthalmology, and they are especially well-suited to the study of keratoplasty practices. A comprehensive donor/recipient registry system can provide insight into donor, recipient, and surgical factors associated with immediate and long-term outcomes and adverse reactions. Furthermore, linkage with demographic databases can elucidate relationships with social determinants of health and potentially shape public policy. The vast sample size and multicenter nature of registries enable researchers to conduct sophisticated multivariate or multilayered analyses. In this review, we aim to emphasize the importance of registry data for keratoplasty practice and 1) summarize the structure of current keratoplasty registries; 2) examine the features and scientific contributions of the registries from Australia, the United Kingdom, Singapore, the Netherlands, Sweden, Eye Bank Association of America, and European Cornea and Cell Transplant registries; 3) compare registry-based studies with large single-site clinical studies; 4) compare registry-based studies with randomized control studies; and 5) make recommendations for future development of keratoplasty registries. Keratoplasty registries have increased our knowledge of corneal transplant practices and their outcomes. Future keratoplasty registry-based studies may be further strengthened by record linkage, data sharing, and international collaboration.

Penetrating Keratoplasty: Indications and Graft Survival by Geographic Region

Corneal transplantation, or penetrating keratoplasty (PK), is the most common form of solid-organ transplantation performed worldwide. Here, we evaluated the indications for PK and rates of transplant survival around the world by geographic region. We conducted a literature search of PubMed, MEDLINE, and Google Scholar databases and identified 155 relevant studies from 41 countries published between 1987 and 2021. The most common indications for PK were keratoconus in Europe, Africa, the Middle East, Australia, New Zealand, and Central and South America, bullous keratopathy in North America, and corneal scarring in Asia. The overall global mean graft survival rates at 1-, 2-, 3-, 5-, and 10-years were 88.6%, 81.2%, 78.9%, 72.8%, and 61.2%, respectively. Through this systematic analysis of PK by region, we hope to bring a new perspective to the corneal transplantation literature and to potentially highlight global differences and unmet needs in patient care.

Peripheral blood immune cell profiling of acute corneal transplant rejection

Acute rejection (AR) of corneal transplants (CT) has a profound effect on subsequent graft survival but detailed immunological studies in human CT recipients are lacking. In this multi-site, cross-sectional study, clinical details and blood samples were collected from adults with clinically diagnosed AR of full-thickness (FT)-CT (n = 35) and posterior lamellar (PL)-CT (n = 21) along with Stable CT recipients (n = 177) and adults with non-transplanted corneal disease (n = 40). For those with AR, additional samples were collected 3 months later. Immune cell analysis was performed by whole-genome microarrays (whole blood) and high-dimensional multi-color flow cytometry (peripheral blood mononuclear cells). For both, no activation signature was identified within the B cell and T cell repertoire at the time of AR diagnosis. Nonetheless, in FT- but not PL-CT recipients, AR was associated with differences in B cell maturity and regulatory CD4⁺ T cell frequency compared to stable allografts. These data suggest that circulating B cell and T cell subpopulations may provide insights into the regulation of anti-donor immune response in human CT recipients with differing AR risk. Our results suggest that, in contrast to solid organ transplants, genetic or cellular assays of peripheral blood are unlikely to be clinically exploitable for prediction or diagnosis of AR.

Impact of vaccination on keratoplasty

PURPOSE OF REVIEW

Corneal graft rejection has been reported after coronavirus disease 2019 (COVID-19) vaccination. The purpose of this review is to evaluate the literature regarding corneal graft rejection after vaccination, including rejection rates and risk factors. We aim to create a framework to identify patients who are at higher risk for graft rejection and may warrant consideration of prophylactic interventions.

RECENT FINDINGS

Graft rejection has been reported following administration of mRNA, viral vector, and inactivated whole-virion COVID-19 vaccines. Most cases had additional risk factors associated with rejection. Vaccination increases circulation of proinflammatory cytokines, CD4+ and CD8+ T-cell responses, and antispike neutralizing antibody, all of which may contribute to graft rejection. Two prospective studies have found no relationship between recent vaccination and rejection but 20% of cornea specialists report to have seen a vaccine-associated rejection and 22% recommend delaying vaccination in certain circumstances. Many specialists recommend prophylactic topical corticosteroids before and after vaccination to mitigate rejection risk but there is no evidence to support this practice on a wider scale.

SUMMARY

Our framework identified 96.8% of penetrating keratoplasty patients with vaccine-associated rejection as higher risk. Further research is needed in order to develop evidence-based guidelines.

Enhanced autophagy alleviated corneal allograft rejection via inhibiting NLRP3 inflammasome activity

Autophagy has been reported to be involved in many aspects of innate and adaptive immunity. Manipulating autophagy is recognized as a promising therapeutic approach for treating immunological diseases, including allograft rejection, and graft-versus-host disease. However, whether autophagy was closely associated with the pathogenesis of corneal allograft rejection remains largely unknown. Here, we showed that rapamycin (RAPA)-induced autophagy alleviated corneal allograft rejection. By contrast, blocking autophagic activity using 3-methyladeine (3-MA) aggravated corneal transplantation rejection. Mechanistically, we revealed that the enhanced autophagic turnover by RAPA inhibited NLRP3 inflammasome activity through NLRP3 degradation. While blocking the fusion of autophagosomes with lysosomes by bafilomycin A1(BafA1), the reduced NLRP3 inflammasome activity induced by RAPA was significantly restored, with increased protein levels of NLRP3 and cleaved Casp-1(p10), as well as IL-1β secretion. Moreover, we further revealed that pharmacologically blocking NLRP3 inflammasome signaling prolonged the survival of corneal allografts. Taken together, these findings underscored the critical roles of enhanced autophagy in treating corneal allograft rejection, which provided an alternative intervention strategy to control corneal transplantation rejection.

Objective measurement of adherence to topical steroid medication after penetrating keratoplasty using an electronic monitoring aid: A pilot study

Objectives

Corneal transplantation is the most common transplant worldwide and its success critically depends on the management of corneal graft rejection through topical steroid therapy during the first 12 months after surgery. There is currently no published data on adherence after keratoplasty. This pilot study aims to explore the adherence to topical steroid after penetrating keratoplasty using a smart electronic device.

Methods

Thirty patients undergoing penetrating keratoplasty were included to evaluate the adherence to topical dexamethasone medication for 12 months after surgery. Patients received the usual post-transplantation treatment (topical dexamethasone) and follow-up after surgery (day 15, months 1, 2, 3, 4, 5, 6, 9, and 12). Adherence to treatment was monitored using the KaliJAR device (Kali Care, Santa Clara, CA, USA), which recorded the number of single-dose units (SDU) discarded. At control visits, data recorded by the device were compared to the manually count of SDU. Adherence ratio and individual adherence curve were explored for all patients.

Results

Data from 27 patients showed a high agreement between adherence ratio calculated based on the device data and obtained from manual counting of the discarded SDU (intraclass coefficient correlation of 0.87 [95% CI: 0.738–0.938]). Mean adherence to the treatment over the 12-month study period was 95.2 ± 4%.

Conclusions

Adherence to topical dexamethasone for 12 months after corneal transplantation was high. The connected device was able to record accurately the discarded SDU. This approach would be a particular interest in the early identification and personalized follow-up of poorly adherent patients.

A novel and efficient method to induce allospecific CD8+ memory T lymphocytes

The aim of the current study was to establish a simple method for effectively inducing memory T lymphocytes by the intraperitoneal injection of spleen lymphocytes into mice. In total, 75 mice were divided into the following groups: an injection group administered three doses of spleen lymphocytes (1 × 10⁶, 5 × 10⁶, and 1 × 10⁷ cells), a transplantation group in which a 0.25‐cm² skin section from C57BL/6 mice was transplanted onto the back of the recipient, and a control group in which an equal volume of phosphate‐buffered saline was injected. At 1, 2, or 3 months following transplantation, the following parameters were evaluated: quantity of T lymphocytes, percentage of cluster of differentiation 8⁺ (CD8⁺) memory T cells, and proliferation index of purified CD8⁺ memory T cells. No significant differences among groups were detected at 1 month (p > .05). However, the injection group administered 1 × 10⁶ cells exhibited the highest proportion of CD8⁺ memory T cells among all groups at 2 months, and the proportions of CD8⁺ T cells were higher in the three injection groups than in the skin transplantation and control groups at 3 months. The proportions of memory T cells were higher in the injection groups administered 5 × 10⁶ or 1 × 10⁷ cells than in the skin transplantation and control groups at 3 months. The newly established method effectively induces memory T lymphocytes via the intraperitoneal injection of spleen lymphocytes in vivo and has potential applications in the field of immunotherapy.

Effectiveness of matching human leukocyte antigens (HLA) in corneal transplantation: a systematic review protocol

BACKGROUND

Corneal transplantation is the most frequently performed transplantation in the UK. Despite this, the therapeutic value of matching human leukocyte antigen (HLA) subtypes for transplanted corneas remains controversial. Ocular immune privilege was originally deemed to render matching unnecessary; however, more recently, matching has demonstrated improved outcomes including graft success, amongst others. This systematic review aims to evaluate the effectiveness of major and minor antigen matching on graft outcomes in corneal transplantation.

METHODS

Standard systematic review methodology will be used to identify, select and extract data from observational studies and clinical trials assessing the effects of HLA matching on corneal graft outcomes. Bibliographic databases (Cochrane Library, EMBASE, MEDLINE, Web of Science, Scopus), clinical trial registers, abstract and conference proceedings, in addition to dissertation, thesis and grey literature will be searched. Neither date of publication nor language will be restricted, and non-English articles will be translated where necessary. The primary outcome will be to assess corneal graft success for different degrees of HLA matching/mismatching. The precise end outcome measure varies amongst studies and includes graft rejection, immunoreaction, failure and survival. Therefore, data will be extracted across all relevant outcome parameters and grouped for subsequent statistical tests. Risk of bias assessment will be completed, appropriate to each study design. Study selection, data extraction and risk of bias assessment will be independently completed by two reviewers. Data will be tabulated, and a narrative synthesis presented. Meta-analysis will be performed where there is sufficient homogeneity between studies to warrant its effective completion. Subgroup and sensitivity analysis will be undertaken if appropriate.

DISCUSSION

Many studies have investigated the effectiveness of HLA matching for corneal transplantation. A systematic review is needed to collate and analyse this evidence. Findings of this systematic review may form the basis of evidence-based recommendations on pre-operative HLA typing and matching of corneal grafts for transplantation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO reference CRD42020198882.

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.

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.

Five-Year Graft Survival of Descemet Membrane Endothelial Keratoplasty (EK) versus Descemet Stripping EK and the Effect of Donor Sex Matching

PURPOSE

To determine whether the reduced risk of immunologic rejection with Descemet membrane endothelial keratoplasty (DMEK) results in a 5-year survival advantage relative to Descemet stripping endothelial keratoplasty (DSEK) and to determine whether matching the donor and recipient sex affects the rejection episode and graft survival rates.

DESIGN

Retrospective cohort study.

PARTICIPANTS

Patients with Fuchs' endothelial corneal dystrophy treated with DSEK or DMEK.

METHODS

This study reviewed 2017 consecutive cases (1312 DSEK and 705 DMEK) performed by 13 surgeons between 2003 and 2012 and included the surgeons' first cases. Survival rates were calculated by Kaplan-Meier analysis.

MAIN OUTCOME MEASURES

Immunologic rejection episodes, graft failure or replacement for any reason, and endothelial cell loss.

RESULTS

The 5-year rejection episode rate was lower with DMEK (2.6% vs. 7.9% with DSEK, relative risk, 0.29; 95% confidence interval, 0.16-0.53) despite early reduction of topical corticosteroids in 25% of the DMEK cases. African Americans (n = 46) had a higher risk of rejection episodes than other races (relative risk, 4.4; 95% confidence interval, 2.0-9.6). The cumulative 5-year survival rate was 93% with DSEK and DMEK (P = 0.86). Forty-four DMEK and 69 DSEK grafts failed or were replaced within 5 years, but only 1 DMEK and 4 DSEK failures followed a rejection episode. Rejection episodes increased endothelial cell loss (P = 0.004) but were not a significant risk factor for graft failure within 5 years (P = 0.90). The mean 5-year endothelial cell loss was similar between DMEK (48%±19%) and DSEK (47%±19%) (P = 0.22). Graft rejection episode and survival rates were not significantly influenced by whether the sex of the donor matched that of the recipient (rejection episodes: P = 0.07 for female recipients and P = 0.33 for male recipients; graft survival: P = 0.67 for female recipients and P = 0.17 for male recipients).

CONCLUSIONS

Five-year graft survival was similar between DMEK and DSEK. Although DMEK had a significantly lower risk of immunologic rejection, rejection episodes rarely resulted in graft failure within 5 years with either procedure. Sex matching the donor and recipient provided no survival advantage with DSEK or DMEK.

Progressive idiopathic unilateral corneal endothelial failure of unknown aetiology in phakic eyes

AIM

To describe a cohort of patients with irreversible unilateral bullous keratopathy (BK) of undetermined aetiology.

METHOD

Retrospective, single-centre case series in a tertiary corneal referral centre.

RESULTS

Eleven consecutive patients (nine females; mean age 71.7 years) presented from 1999 to 2009 with acute onset unilateral visual loss. At presentation, the best-corrected visual acuity of the affected eyes was 6/9 or worse with mean central corneal thickness (CCT) of 684 (SD 66) μm. Specular microscopy was not possible in the affected eyes. There was no other ocular pathology in the affected eye. The fellow eye remained normal throughout the study (mean endothelial cell density (ECD) of 1980 (SD 736) cells/mm² and CCT of 536 (SD 34) μm). Topical steroid, antiviral treatments (both topical and systemic) or a combination of both did not yield any improvement. After a mean follow-up of 82.2 months, eight eyes had penetrating keratoplasty (PK). One required two regrafts. Histology showed typical BK features, with endothelial cell (EC) loss and thickened Descemet's membrane (DM). Transmission electron microscopy revealed DM abnormalities in a non-consistent pattern, featuring variable collagen deposition posterior to the non-banded zone. The ECs were degenerated, reduced or absent. Neither viruses nor pseudoexfoliation material was identified.

CONCLUSION

While medical treatment is not beneficial, PK appears to offer good results. Non-guttate Fuchs' corneal endothelial dystrophy merits consideration but it would be unusual to see an exclusively unilateral presentation. DM thickening is reflective of a chronic EC loss but the cause of this loss remains elusive.

Sequential Bilateral Corneal Transplantation and Graft Survival

PURPOSE

To investigate graft survival and rejection following sequential bilateral corneal transplantation.

DESIGN

Retrospective cohort study.

METHODS

The study included patients with Fuchs endothelial dystrophy (FED), pseudophakic bullous keratopathy (PBK), or keratoconus who had undergone a penetrating keratoplasty (PK), endothelial keratoplasty (EK), or deep anterior lamellar keratoplasty (DALK) between 1999 and 2012. The main cohort included patients who had received a first transplant in both eyes for the same indication and a control cohort patients who had undergone a unilateral first corneal transplant. Main outcome measures were graft rejection or failure at 5 years.

RESULTS

A total of 11 822 patients were included, of whom 9335 had a unilateral and 2487 bilateral corneal transplantation. For patients with FED (P < .005) and KC (P = .03) but not PBK (P = .19), a transplant in the second eye was associated with a 50% reduction in risk of graft failure within 5 years in the first eye (FED: hazard ratio [HR] 0.47, 95% confidence interval [CI]: 0.34-0.64; KC: HR 0.50, 95% CI: 0.24-1.02). For FED this was dependent on the type of transplant (EK: HR 0.30, 95% CI: 0.17-0.52; PK: HR 0.61, 95% CI: 0.42-0.88). We found no association between a transplant in the second eye and a rejection episode in the first eye (KC P = .19, FED P = .39, PBK P = .19).

CONCLUSION

For FED and KC, a transplant in the second eye was associated with a reduced risk of graft failure in the first eye, independent of inter-transplant time. For FED this effect was pronounced following an EK in the first eye, where the risk of failure was reduced by 70%.