Time- and Stimulus-Dependent Characteristics of Innate Immune Cells in Organ-Cultured Human Corneal Tissue

PURPOSE

The pattern of immune cells infiltrating the corneal stroma has been extensively studied in mice, but data on human tissue have been far less elaborate. To further characterize the number and differentiation state of resident immune cells in organ-cultured human corneal tissue, we employed a comprehensive bioinformatic deconvolution (xCell) of bulk RNA-sequencing (RNA-seq) data, immunohistochemistry (IHC), and flow cytometry (FC).

METHODS

A transcriptome-based analysis of immune cell types in human corneal samples was performed. The results were validated by IHC, focusing on the identification of pro-inflammatory (M1) and regulatory (M2) macrophages. A protocol was established to identify these 2 different macrophage populations in human corneal tissue by means of FC. Subsequently, corneal samples in organ culture were differentially stimulated by IL-10, IL-4 & IL-13, or LPS and macrophage populations were evaluated regarding their response to these stimuli. Furthermore, cell survival was analyzed in correlation with time in organ culture.

RESULTS

xCell-based mathematical deconvolution of bulk RNA-seq data revealed the presence of CD8 T cells, Th17 cells, dendritic cells, and macrophages as the predominant immune cell types in organ-cultured human corneal tissue. Furthermore, RNA-seq allowed the detection of different macrophage marker genes in corneal samples, including PTPRC (CD45), ITGAM (CD11b), CD14, and CD74. Our RNA-seq data showed no evidence of a relevant presence of monocytes in human corneal tissue. The presence of different macrophage subtypes was confirmed by IHC. The disintegration and subsequent FC analysis of human corneal samples showed the presence of both M1 (HLA-DR+, CD282+, CD86+, and CD284+) and M2 (CD163+ and CD206+) macrophage subtypes. Furthermore, we found that the total number of macrophages in corneal samples decreased more than the total cell count with increasing tissue culture time. Treatment with IL-10 led to higher total cell counts per cornea and to an increased expression of the M2 marker CD163 (p < 0.05) while expression levels of various M1 macrophage markers were not significantly reduced by interleukin treatment.

CONCLUSIONS

Regarding different macrophage populations, untreated human corneas showed more M1 than M2 macrophages. With increasing organ culture time, these macrophages decreased. In terms of cell dynamics, adding interleukins to the organ culture medium influenced the phenotype of macrophages within the cornea as detected by FC. Modifying the immunomodulatory properties of human grafts appears a promising approach to further reduce the risk of graft rejection in patients. In this context, treatment with interleukins was more effective in upregulating M2 macrophages than in suppressing M1 macrophages in corneal tissue.

Lower risk of graft dislocation applying organ cultured corneas compared with cold short-term cultured corneas during DSAEK surgery

BACKGROUND

To investigate factors that may affect graft dislocation after uneventful Descemet stripping endothelial keratoplasty (DSAEK), with a special focus on different donor cornea storage conditions.

METHODS

All DSAEK surgeries performed during 6 years in our hospital were retrospectively investigated. Patients with previous intraocular surgeries other than cataract extraction were excluded. Donor data (age, gender, death-to-preservation time, cornea storage conditions, graft storage time, and estimated thickness of the graft) and patient information (age, gender, and indication for surgery) were noted.

RESULTS

A total of 26 dislocations (6.6%) out of 394 DSAEK surgeries were found. The dislocation rate was considerably reduced between 2011 and 2016, due to more experienced surgeons. There was a significantly higher dislocation rate with the use of donor corneas stored in cold storage solution (12.7%) compared with organ culture solution (2.5%) (P < 0.001). During the study period, donor corneas stored in cold storage solution and organ culture solution were applied in 158 (40%) and 236 (60%) cases, respectively. There were no differences in recipient age and gender between patients who received corneas from the two storage systems, indicating a random distribution of grafts. In a multivariate analysis, only operation year (reduced rate over the years) and cold storage solution were statistically significantly associated with graft dislocation.

CONCLUSION

This study suggests that the type of storage solution may have a decisive role in graft dislocation in DSAEK surgery.

Prolonged organ culture reduces the incidence of endothelial immune reactions

PURPOSE The number of antigen-presenting cells decreases during organ culture of corneoscleral discs. This might result in a decrease of immune reactions with increasing duration of organ culture. To investigate this hypothesis, we performed a retrospective analysis of all penetrating keratoplasties that were consecutively performed over the last 5 years.PATIENTS AND METHODS All cases of penetrating keratoplasties (n=1006) were divided into two groups, with the division made at the median of the storage time (21 days). These two groups were compared by a Cox proportional hazards survival model regarding the incidence of endothelial immune reactions, clear graft survival, and chronic endothelial cell loss following penetrating keratoplasty considering patient's age, donor's age, and risk situation as co-variates.RESULTS We observed statistically significantly fewer endothelial immune reactions (20.1% (95% confidence interval 15.5-24.5%) after 2 years) in the group with a storage time of more than 21 days compared with the group with a storage time of <21 days (26.5% (95% confidence interval 21.6-31.2%) after 2 years). However, the duration of organ culture did not have a statistically significant effect on clear graft survival or chronic endothelial cell loss.CONCLUSION Our results demonstrate that an increased duration of organ culture leads to a lower incidence of endothelial immune reactions following penetrating keratoplasty. However, we do not recommend increased storage times in general as overall graft survival did not improve. The reason for this apparent paradox may be that the endothelial cell count decreases during storage time.

Matching for Human Leukocyte Antigens (HLA) in corneal transplantation - to do or not to do

As many patients with severe corneal disease are not even considered as candidates for a human graft due to their high risk of rejection, it is essential to find ways to reduce the chance of rejection. One of the options is proper matching of the cornea donor and recipient for the Human Leukocyte Antigens (HLA), a subject of much debate. Currently, patients receiving their first corneal allograft are hardly ever matched for HLA and even patients undergoing a regraft usually do not receive an HLA-matched graft. While anterior and posterior lamellar grafts are not immune to rejection, they are usually performed in low risk, non-vascularized cases. These are the cases in which the immune privilege due to the avascular status and active immune inhibition is still intact. Once broken due to infection, sensitization or trauma, rejection will occur. There is enough data to show that when proper DNA-based typing techniques are being used, even low risk perforating corneal transplantations benefit from matching for HLA Class I, and high risk cases from HLA Class I and probably Class II matching. Combining HLA class I and class II matching, or using the HLAMatchmaker could further improve the effect of HLA matching. However, new techniques could be applied to reduce the chance of rejection. Options are the local or systemic use of biologics, or gene therapy, aiming at preventing or suppressing immune responses. The goal of all these approaches should be to prevent a first rejection, as secondary grafts are usually at higher risk of complications including rejections than first grafts.

The application of autologous serum eye drops in severe dry eye patients; subjective and objective parameters before and after treatment

AIM

To assess the impact of autologous serum (AS) eye drops on the ocular surface of patients with bilateral severe dry eye and to draw a comparison between the clinical and laboratory examinations and the degree of subjective symptoms before and after serum treatment.

MATERIALS AND METHODS

A three-month prospective study was conducted on 17 patients with severe dry eye. AS eye drops were applied a maximum of 12 times a day together with regular therapy. Dry eye status was evaluated by clinical examination (visual acuity, Schirmer test, tear film breakup time, vital staining, tear film debris and meniscus), conjunctival impression cytology (epithelial and goblet cell density, snake-like chromatin, HLA-DR-positive and apoptotic cells) and subjectively by the patients.

RESULTS

The application of AS eye drops led to a significant improvement in the Schirmer test (p < 0.01) and tear film debris (p < 0.05). The densities of goblet (p < 0.0001) and epithelial cells (p < 0.05) were significantly increased, indicating a decrease of squamous metaplasia after AS treatment. A significant decrease (p < 0.05) was found in the number of apoptotic, HLA-DR-positive and snake-like chromatin cells on the ocular surface. A significant improvement was found in all evaluated subjective symptoms. Altogether, the clinical results were improved in 77%, the laboratory results in 75% and the subjective feelings in 63% of the eyes.

CONCLUSIONS

We found that three-month AS treatment led especially to the improvement of ocular surface dryness and damage of the epithelium. The improvement of dry eye after AS treatment correlated well with the clinical, laboratory and subjective findings. From the patients' subjective point of view, the positive effect of AS decreased with time, but still persisted up to three months after the end of therapy.

Effects of preservation time on proliferative potential of human limbal stem/progenitor cells

AIM

To determine the proliferative potential and the maintenance of stem cell activity in stored human limbal tissues, and correlate this with the preservation time, cell viability and the expression of stem cell markers.

METHODS

Thirty limbal rims were split into 4 parts and stored in corneal preservation medium at 4°C for 0, 1, 4, or 7 days. The limbal stem cell and mitotic markers P63, CK19, proliferating cell nuclear antigen (PCNA), and Ki67 were determined by immunohistochemical staining. The proliferative potential of limbal epithelial cells was assessed by cell viability, the ability of generating stratified epithelium, and colony forming assay.

RESULTS

The stored tissues maintained limbal stratified structure to 7 days and exhibited comparable expression level of stem cell and mitotic markers. The proportion of viable cells decreased with the prolonged preservation time, while colony forming efficiency decreased from the 1(st) day and disappeared at the 4(th) day. When inoculated on amniotic membrane, the cells preserved for 1 day formed a stratified epithelium, while the cells from 4 days' preservation formed a discontinuous layer.

CONCLUSION

The colony forming efficiency of limbal epithelial stem/progenitor cells decreased rapidly with the increasing preservation time, while the expression level of markers and capacity of forming epithelial monolayer on amniotic membrane decreased gradually. The limbal epithelial stem cells lost their function earlier than the lost expression level of stem cell markers. This may help us to better choose the appropriate preservation grafts for future limbal stem cell transplantation.