TNF receptor secretion after ex vivo adenoviral gene transfer to cornea and effect on in vivo graft survival

PURPOSE

To explore the potential for adenovirus-mediated ex vivo gene transfer of a soluble tumor necrosis factor (TNF) receptor and evaluate the effect of transplanting the adenovirally transplanted corneas in vivo.

METHODS

Rabbit corneal segments were transfected with replication-deficient adenovirus (AdTNFR) encoding a soluble TNF receptor fusion protein (TNFR-Ig). Production of TNFR-Ig was measured by using ELISA and bioassay. Corneas were transfected ex vivo with AdTNFR and then transplanted in vivo. Survival of AdTNFR-transfected corneas was compared with that of those treated either with a null vector control adenovirus (Ad0) or nontransfected control corneas.

RESULTS

Ex vivo production of a molecule with TNF blocking bioactivity from AdTNFR-transfected corneas was demonstrated over a period of 4 weeks. Transplanted AdTNFR-transfected corneas showed a marginally increased survival time in vivo over nontransfected control corneas, but a significantly increased survival time over Ad0-treated control corneas. Ad0 treatment of corneal allografts before transplantation had a proinflammatory effect and accelerated the onset of corneal endothelial rejection.

CONCLUSIONS

Adenoviral gene transfer is an effective means of transferring a gene encoding soluble TNFR-Ig to corneal endothelium, and ex vivo production of a biologically active secreted molecule was demonstrated for 4 weeks. However, in vivo, only a marginally increased survival was seen compared with control corneas. The introduction of this transgene using a less immunogenic vector may demonstrate prolongation of corneal allograft survival.

Transferrin receptor-mediated gene transfer to the corneal endothelium

BACKGROUND

The application of gene therapy to prevent allograft rejection requires the development of noninflammatory vectors. We have therefore investigated the use of a nonviral system, transferrin-mediated lipofection, to transfer genes into the cornea with the aim of preventing corneal graft rejection.

METHODS

Rabbit and human corneas were cultured ex vivo and transfected with either lipofection alone or in conjunction with transferrin. The efficiency of transfection, localization, and kinetics of marker gene expression were determined. Strategies to increase gene expression, using chloroquine and EDTA, were investigated. In addition to a marker gene, a gene construct encoding viral interleukin 10 (vIL-10) was transfected and its functional effects were examined in vitro.

RESULTS

Transferrin, liposome, and DNA were demonstrated to interact with each other, forming a complex. This complex was found to deliver genes selectively to the endothelium of corneas resulting in gene expression. Treatment of corneas with chloroquine and EDTA increased the transfection efficiency eight-fold and threefold, respectively. We also demonstrated that constructs encoding vIL-10 could be delivered to the endothelium. Secreted vIL-10 was shown to be functionally active by inhibition of a mixed lymphocyte reaction.

CONCLUSIONS

Our data indicate that transferrin-mediated lipofection is a comparatively efficient nonviral method for delivering genes to the corneal endothelium. Its potential for use in preventing graft rejection is shown by the ability of this system to induce vIL-10 expression at secreted levels high enough to be functional.

Cytokine and chemokine expression kinetics after corneal transplantation

BACKGROUND

Allogeneic rejection is the most common cause of corneal graft failure. The aim of this work was to establish the kinetics of cytokine and chemokine mRNA expression before and after onset of corneal graft rejection.

METHODS

Intracorneal cytokine and chemokine mRNA levels were investigated in the Brown Norway-->Lewis inbred rat model in which rejection onset is observed at 8/9 days after grafting in all animals. Nongrafted corneas and syngeneic (Lewis-->Lewis) corneal transplants were used as controls. Donor and recipient cornea was examined by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) for hypoxyanthine phosphoribosyltransferase (HPRT), CD3, CD25, interleukin (IL)-1beta, IL-1RA, IL2, IL-6, IL-10, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), transforming growth factor (TGF)-beta1, and macrophage inflammatory protein (MIP)-II and by nonquantitative RT-PCR for IL4, IL-5, IL-12 p40, IL-13, TGF-beta2, monocyte chemotactic protein-1 (MCP-1), MIP-1alpha, MIP-1beta, and RANTES (for regulated upon activation normal T cell expressed and secreted).

RESULTS

A biphasic expression of cytokine and chemokine mRNA was found after transplantation. During the early phase (days 3-9), there was an elevation of the majority of the cytokines examined, including IL-1beta, IL-6, IL-10, IL-12 p40, and MIP-II. There was no difference in cytokine expression patterns between allogeneic or syngeneic recipients at this time. In syngeneic recipients, cytokine levels reduced to pretransplant levels by day 13, whereas levels of all cytokines rose after observed rejection onset in the allografts, including TGF-beta1, TGF-beta2, and IL-1RA. The T cell-derived cytokines IL-4, IL-13, and IFN-gamma were detected only during the rejection phase in allogeneic recipients.

CONCLUSIONS

There is an early cytokine and chemokine response to the transplantation process, evident in syngeneic and allogeneic grafts, that probably drives angiogenesis, leukocyte recruitment, and affects leukocyte functions. After an immune response has been generated, allogeneic rejection results in the expression of Th1 cytokines (IL-2, IL-12 p40, IFN-gamma), Th2 cytokines (IL-4, IL-6, IL-10, and IL-13), and antiinflammatory/Th3 cytokines (TGF-beta1/2 and IL-1RA).

Factors leading to lens implant decentration and exchange

PURPOSE

To examine the intra- and post-operative factors leading to posterior chamber intraocular lens (IOL) decentration in patients requiring IOL exchange, and to identify avoidable causes of IOL decentration.

METHODS

Case records of 17 patients who had undergone posterior chamber IOL exchange were examined for: (i) any complication or alteration to the original intended surgical procedure, (ii) IOL type and position at the completion of initial surgery, (iii) IOL position at the time of re-operation.

RESULTS

The decentred lens implants were injected silicone plate-haptic IOLs in 10 patients, small (5.5 mm) optic diameter PMMA IOLs in 4 patients and large (7 mm) optic diameter PMMA IOLs in 3 patients. In all cases, decentration was due to IOL subluxation. Early decentration of the injected lenses was due to IOL implantation in eyes without a continuous capsulorrhexis. In contrast late decentration was due to subluxation associated with capsule fibrosis. Decentration of small optic PMMA IOLs was found to be associated with an anterior capsule tear and haptic malposition in the ciliary sulcus. Decentration of large optic PMMA IOLs was associated with posterior displacement of one haptic through a posterior capsule defect, zonule dehiscence or fixation of one haptic in the sulcus and one in the capsule bag.

CONCLUSION

Clinically significant post-operative subluxation of injected silicone IOLs may be minimised by implanting only into a lens capsule bag with an intact capsulorrhexis. The risk of decentration of small optic PMMA IOLs may be minimised by positioning the haptics at 90 degrees to any capsulorrhexis tear. After cataract surgery complicated by posterior capsule rupture or zonule dehiscence, it is important to assess the remaining capsule support and, where sufficient, implant a large optic diameter posterior chamber IOL in the ciliary sulcus.

Gene delivery to the corneal endothelium

Gene transfer to the corneal endothelium has potential for modulating rejection of corneal grafts. It can also serve as a convenient and useful model for gene therapy of other organs. In this article we review the work carried out in our laboratory using both viral and nonviral vectors to obtain gene expression in the cornea.

Local bioactive tumour necrosis factor (TNF) in corneal allotransplantation

The aim of this study was to examine the kinetic profile of bioactive TNF levels in aqueous humour of rabbit eyes undergoing corneal allograft rejection and to investigate the effect of locally blocking TNF activity after corneal transplantation. In a rabbit corneal transplantation, endothelial allograft rejection was identified and correlated with increase in central graft thickness. Samples of aqueous humour obtained on alternate days following transplantation were tested for TNF mRNA and bioactive TNF protein. To investigate the effect of locally blocking TNF activity in allograft recipients, the fusion protein TNFR-Ig was administered by injections into the anterior chamber after transplantation. Pulsatile increases in levels of this cytokine were found in 14 of 15 allograft recipients. Peaks of TNF bioactivity preceded by varying intervals the observed onset of rejection in allograft recipients. TNF levels were not elevated in aqueous humour from corneal autograft recipient controls or in serum of allografted animals. mRNA levels were elevated before onset of and during clinically observed allograft rejection. In three of seven animals receiving TNFR-Ig injections on alternate days from day 8 to day 16 post-transplant, clear prolongation of corneal allograft survival was demonstrated. Bioactive TNF is present in aqueous humour following rabbit corneal allotransplantation. Rather than correlating directly with endothelial rejection onset, pulsatile peak levels of TNF precede and follow the observed onset of endothelial rejection. Blockade of TNF activity prolongs corneal allograft survival in some animals, indicating that this cytokine may be a suitable target in local therapy of corneal allograft rejection.

Adeno-associated and herpes simplex viruses as vectors for gene transfer to the corneal endothelium

PURPOSE

We examined the efficacy and cytopathogenicity of adeno-associated (AAV) and herpes simplex viruses (HSV) as vectors for gene transfer to corneal endothelial cells (CECs).

METHODS

Recombinant AAV and HSV were examined for their ability to deliver a lacZ histochemical marker gene to whole-thickness rabbit and human corneas ex vivo. Transgene expression was detected with histochemistry and quantified by a colorimetric assay.

RESULTS

Rabbit and human corneas transduced with AAV showed increasing numbers of cells expressing marker gene over a 3- to 4-week period. Using 2.5 x 10(6) or 1.5 x 10(7) infective units for rabbit and human corneal specimens, respectively, approximately 2% of CECs expressed the reporter gene. HSV (10(6) plaque-forming units/specimen) transduced approximately 5% of rabbit and human CECs but showed cytotoxicity. In contrast to the duration of recombinant AAV-mediated lacZ expression, recombinant HSV expression was maximal at day 1 and declined to low levels at day 7.

CONCLUSION

AAV is a promising vector, but its usefulness for corneal transduction is currently limited by the technical difficulties preparing high titres. The HSV vector examined is efficient but needs further genetic modification to prolong transgene expression and reduce its toxicity.

Randomised controlled trial of corticosteroid regimens in endothelial corneal allograft rejection

AIM

To determine whether the addition of systemic corticosteroid to local intensive corticosteroid therapy of endothelial corneal allograft rejection improves outcome.

METHODS

A prospective randomised treatment trial was carried out at a tertiary referral centre. 36 consecutive corneal graft recipients, presenting with a first episode of endothelial graft rejection, received either (i) one intravenous pulse of methylprednisolone 500 mg in addition to local corticosteroid treatment, or (ii) local treatment only. The regimen of local treatment standardised in all cases for the first 24 hours consisted of one subconjunctival betamethasone 2 mg injection and dexamethasone 0.1% drops in the affected eye every hour for 24 hours.

RESULTS

Failure to reverse the graft rejection episode was found in 3/36 (8%) patients. Each of these had been treated with local steroid only. Graft failure from any cause occurred in 9/36 (25%) within 2 years of follow up. No statistically significant difference was found between the two groups with regard to reversal of the graft rejection episode, later recurrence of graft rejection, or graft failure.

CONCLUSIONS

In treatment of graft rejection, additional systemic treatment with 500 mg methylprednisolone yields no significant benefit over intensive local corticosteroid alone. Graft survival following treatment of a rejection episode with local corticosteroid treatment alone is good in those patients without other risk factors for graft failure and much higher than reported previously.

Activated polyamidoamine dendrimers, a non-viral vector for gene transfer to the corneal endothelium

We investigated the efficiency of activated polyamidoamine dendrimers, a new class of nonviral vectors, to transfect rabbit and human corneas in ex vivo culture. In addition to assessing the expression of a marker gene we have demonstrated that this approach can be used to induce the production of TNF receptor fusion protein (TNFR-Ig), a protein with therapeutic potential. Whole thickness rabbit or human corneas were transfected ex vivo with complexes consisting of dendrimers and plasmids containing lacZ or TNFR-Ig genes. Following optimisation 6-10% of the corneal endothelial cells expressed the marker gene. Expression was restricted to the endothelium and was maximal after transfection with 18:1 (w/w) activated dendrimer:plasmid DNA ratio and culture for 3 days. The supernatant of corneas transfected with TNFR-Ig plasmid contained TNFR-Ig protein which was able to inhibit TNF-mediated cytotoxicity in a bioassay. We have therefore shown that activated dendrimers are an efficient nonviral vector capable of transducing corneal endothelial cells ex vivo. They may have applications in gene-based approaches aimed at prevention of corneal allograft rejection or in treatment of other disorders of corneal endothelium.

A new model of orthotopic penetrating corneal transplantation in the sheep: graft survival, phenotypes of graft-infiltrating cells and local cytokine production

BACKGROUND

Orthotopic penetrating keratoplasty in the sheep was developed as an outbred preclinical model to allow correlation of the cellular infiltrate during graft rejection with local production of cytokine mRNA.

METHODS

Penetrating corneal autografts and allografts were performed in Merino sheep. Graft outcome was followed at the slit-lamp. Corneal infiltrates were examined by immunoperoxidase staining on postmortem specimens. Cytokine mRNA was detected by polymerase chain reaction.

RESULTS

Corneal autografts survived indefinitely. Allografts became vascularized and underwent rejection at a median of 20 days postgraft. Both endothelial and epithelial rejection lines were observed. Immunohistochemical staining of rejecting grafts showed up-regulation of major histocompatibility complex class I molecules on corneal graft epithelium, damaged or absent graft endothelium and a marked, predominantly mononuclear cell infiltrate. CD4-positive T cells were observed in the graft within 2 days of the onset of rejection, followed several days later by CD8-positive T cells. Messenger RNA transcripts for interleukin (IL)-2, tumour necrosis factor (TNF)-alpha and IL-10 (but not for interferon (IFN)-gamma or IL-4) were found in autografted corneas. Proportionately, more allografts than autografts contained transcripts for IL-2 and TNF-alpha, and IFN-gamma was detected in three of four allografts.

CONCLUSIONS

Corneal graft rejection in the sheep is macroscopically and histologically similar to human corneal graft rejection. Allografts become infiltrated by both CD4- and CD8-positive T cells and local production of pro-inflammatory cytokines occurs during graft rejection.

Distribution of integrins alpha v beta 5, alpha v beta 3 and alpha v in normal human cornea: possible implications in clinical and therapeutic adenoviral infection

PURPOSE

Integrins are heterodimeric cell surface molecules involved in cell-cell and cell-matrix interactions. Adenoviral entry into human cells has been shown to be dependent on integrins alpha v beta 5 and alpha v beta 3 that promote viral internalisation. We studied the distribution of integrins alpha v beta 5, alpha v beta 3 and the alpha v chain in normal human cornea to investigate possible mechanisms of adenoviral entry to specific corneal cell types.

METHODS

We used immunohistochemistry with monoclonal antibodies to study the distribution of alpha v beta 5, alpha v beta 3 and alpha v in normal human corneas maintained for up to 4 days in corneal storage medium (Optisol) at 4 degrees C (n = 9).

RESULTS

Both alpha v beta 5 and alpha v were present to a variable extent on the corneal epithelium and corneal endothelium of most specimens. In some specimens staining of both alpha v beta 5 and alpha v in the epithelium was graded, with more basal than superficial staining, alpha v beta 3 was not detectable in either the corneal epithelium or the corneal endothelium in those specimens tested.

CONCLUSIONS

The integrin alpha v beta 5 is present on both epithelium and endothelium in the normal human cornea. The role of alpha v integrins in clinical infection and in adenoviral entry for gene transfer is discussed.

Lipid-mediated enhancement of transfection by a nonviral integrin-targeting vector

Nonviral vectors consisting of integrin-targeting peptide/DNA (ID) complexes have the potential for widespread application in gene therapy. The transfection efficiency of this vector, however, has been limited by endosomal degradation. We now report that lipofectin (L) incorporated into the ID complexes enhances integrin-mediated transfection, increasing luciferase expression by more than 100-fold. The transfection efficiency of Lipofectin/Integrin-binding peptide/DNA (LID) complexes, assessed by beta-galactosidase reporter gene expression and X-gal staining, was improved from 1% to 10% to over 50% for three different cell lines, and from 0% to approximately 25% in corneal endothelium in vitro. Transfection complexes have been optimized with respect to their transfection efficiency and we have investigated their structure, function, and mode of transfection. Both ID and LID complexes formed particles, unlike the fibrous network formed by lipofectin/DNA complexes (LD). Integrin-mediated transfection by LID complexes was demonstrated by the substantially lower transfection efficiency of LKD complexes in which the integrin-biding peptide was substituted for K16 (K). Furthermore, the transfection efficiency of complexes was shown to be dependent on the amount of integrin-targeting ligand in the complex. Finally, a 34% reduction in integrin-mediated transfection efficiency by LID complexes was achieved with a competing monoclonal antibody. The role of lipofectin in LID complexes appears, therefore, to be that of a co-factor, enhancing the efficiency of integrin-mediated transfection. The mechanism of enhancement is likely to involve a reduction in the extent of endosomal degradation of DNA.

Lipoadenofection-mediated gene delivery to the corneal endothelium: prospects for modulating graft rejection

BACKGROUND

Gene transfer to the corneal endothelium has potential for the prevention or reversal of corneal allograft rejection. Previous work has examined adenoviral vectors for gene transfer to endothelium. These have a number of theoretical and practical disadvantages, both for experimental and clinical applications. We have therefore used lipoadenofection, in which plasmid DNA is delivered using a combination of liposomes and adenovirus, to transfer marker genes to the cornea.

METHODS

Corneas were obtained from New Zealand White rabbits and cultured ex vivo using standard conditions. The corneas were transfected using either lipofection or lipoadenofection with plasmids encoding marker genes. The efficiency of gene transfer and the location and kinetics of gene expression were determined. We also investigated the delivery of a gene construct containing an inducible promoter that is activated by tumor necrosis factor (TNF), to determine whether expression of the relevant genes could be controlled by exogenous factors such as cytokines.

RESULTS

This study shows that gene expression is limited to the endothelium and that expression is transient. Furthermore, we have shown that expression of a gene controlled by an inducible promoter only occurs when TNF is present.

CONCLUSIONS

These data indicate that lipofection is an efficient method to transfer therapeutic genes to the corneal epithelium, and that it can be used to transfer constructs that utilize an inducible promoter controlled by TNF. As TNF is present in the aqueous humor during allograft rejection, and this is in contact with the corneal endothelium, this has the potential to restrict expression of a therapeutic gene to rejection episodes in the cornea.

Retreatment for significant regression after excimer laser photorefractive keratectomy. A prospective, randomized, masked trial

PURPOSE

Regression, a gradual partial or complete return to the myopic state, remains a common complication of excimer laser photorefractive keratectomy (PRK) and limits the predictability of refractive outcome, especially in high myopia. An estimated 10% to 20% of patients, therefore, request a repeat PRK procedure. This study was designed to provide patient selection criteria and guidelines for successful retreatment.

METHODS

One hundred six patients who had regressed were randomized to 1 of 4 retreatment groups comprising (1) those with minimal haze after their first PRK who received an exact retreatment; (2) those with minimal haze treated with a 50% deliberate overcorrection; (3) those with significant haze (> or = 2+ haze) given an exact retreatment; and (4) those with significant haze who received a 50% overcorrection. A Visx 20/20 laser was used in each case. Mean follow-up after retreatment was 12 months (range, 6-18 months).

RESULTS

Deliberate overcorrection (groups 2 and 4) resulted in a statistically significantly better refractive outcome (P = 0.026 at 6 months). Analysis of variance showed that significant haze after the first PRK was the most important predictor of a poor outcome after retreatment, other factors being high original myopia, marked regression, and loss of best-corrected visual acuity.

CONCLUSIONS

A retreatment PRK procedure for significant regression will reduce residual myopia significantly in the majority of patients, and a deliberate overcorrection (50%) reduces the chance of further regression. However, patients with high myopia who have regressed beyond approximately -3.50 diopters originally and who show significant anterior stromal haze (> 2+) should be retreated only with great caution, because of the risk of further regression, haze, and loss of visual acuity.

Gene transfer to ex vivo stored corneas

PURPOSE

We examined the efficiency and kinetics of recombinant adenovirus vector-mediated gene transfer to rat and rabbit cornea in culture ex vivo.

METHODS

A recombinant replication-defective adenovirus was used to transfer a lacZ marker gene to whole rat and rabbit corneas in culture. Histochemistry was used to localise transgene expression and a colorimetric assay to quantify recombinant protein expression.

RESULTS

After infection with recombinant virus and culture for 3 days, high-efficiency gene transfer was found, with expression in most endothelial cells of both species. Minimal expression was found in other corneal cell types. On histochemistry, longer duration of expression was found in rat than in rabbit endothelium. In both rat and rabbit cornea, highest levels of recombinant protein were found at days 3-7 after incubation with virus, decreasing to low or undetectable levels at 21 days.

CONCLUSION

Adenovirus vectors allow high-efficiency transgene expression in cornea, largely restricted to the endothelial cells of ex vivo cultured cornea. Kinetics of expression differ according to the species of cornea studied, a factor that must be considered if this vector is used in further studies.

Ex vivo adenovirus-mediated gene transfer and immunomodulatory protein production in human cornea

One attractive strategy to prevent or control allograft rejection is to genetically modify the donor tissue before transplantation. In this study, we have examined the feasibility of gene transfer to human corneal endothelium, using a number of recombinant adenovirus constructs. Ex vivo infection of human corneas with adenoviral vectors containing lacZ, under transcriptional control of either cytomegalovirus (CMV) or Rous sarcoma virus (RSV) promoters, provided high-level gene expression, which was largely restricted to endothelium. Expression of the reporter gene persisted at relatively high levels for up to 7 days, followed by a decline to indetectable levels by 28 days. RT-PCR analysis of lacZ transcription showed a similar picture with a short period (3-7 days) of RNA transcription after infection. In contrast, adenoviral DNA persisted for at least 56 days. Subsequently, we examined the expression of a potential therapeutic gene, CTLA-4 Ig fusion protein. Following infection of human corneas with adenoviral vectors encoding CTLA-4 Ig protein, high levels of the fusion protein were detected in corneal culture supernatants for up to 28 days. This protein was functionally active, as determined by binding to B7.1 (CD80)-expressing transfectants. This study suggests that genetic alteration of donor cornea before transplantation is a feasible approach for preventing or controlling allograft rejection. Similar gene-based strategies might also be feasible to prevent rejection of other transplanted tissues or organs.

A method for separation and staining of flat mounts of human corneal endothelium

A technique is described in which sheets of corneal endothelium are removed from human donor corneo-scleral discs. Celloidin solution was applied to the endothelial surface, allowed to dry, peeled off with the attached endothelial cell layer and mounted on a glass slide. Following removal of the celloidin with acetone, this endothelial cell flat mount was then stained with H&E and monoclonal antibodies to cell adhesion molecules. A pilot study of endothelial cell adhesion molecule expression in flat mount preparations of 14 corneas showed constitutive neural cell adhesion molecule (NCAM) expression, but a lower degree of focal expression of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VACM)-1, P/E-selectin and HLA-DR.

Identification and characterization of cells infiltrating the graft and aqueous humour in rat corneal allograft rejection

In a rat model of corneal transplantation, Fischer 344 (RT1(lv1)) rats received orthotopic corneal isografts or Wistar-Furth (RT1(u)) donor allografts. Rejection was observed in 25 of 26 allograft recipients, at a median time of 18 days, with all isografts surviving > 100 days. Flow cytometric analysis of aqueous humour identified cellular infiltration of the aqueous at the time of allograft rejection, in contrast to the acellular aqueous found in isografts at corresponding times following transplantation. A higher proportion of CD8+ than CD4+ cells was found at days 1-3 following rejection, whereas there was a higher proportion of CD4+ cells at days 5-8. No changes in peripheral blood T cell subsets were found at the time of rejection. Immunohistochemical analysis of cells infiltrating recipient iris and grafted cornea undertaken at days 1-2, 4 and 7-10 following onset of rejection, demonstrated inflammatory cells in the graft epithelium, stroma and aggregated on the endothelium. Large numbers of macrophages, T cells (CD4+ > CD8+ at all time points), natural killer (NK) cells and neutrophils were detected in graft tissue at days 1-2 and 4, diminishing after that time. Most infiltrating cells expressed MHC class II antigen, and a smaller number expressed IL-2R. Expression of the co-stimulatory marker B7 was identified in a few cells at day 4 in the region of the graft-host wound. The immune response in graft rejection was characterized at day 4 also by expression of intercellular adhesion molecule-1 (ICAM-1) on endothelial cells of iris and corneal vessels, demonstration of interferon-gamma on mononuclear cells in the peripheral (recipient) cornea, and tumour necrosis factor-alpha on aggregated mononuclear cells on the graft, but not recipient, endothelium. Only sparse cellular infiltrates were found in isograft controls, with inflammation located at the graft-host wound. These findings suggest that inflammatory cells reach a corneal allograft by two routes--from vessels in the peripheral recipient cornea, and from vessels in the recipient iris via the aqueous humour. Different aqueous and intragraft T cell subset proportions were seen early in rejection, although a preponderance of CD4+ cells was found in both aqueous and graft at later times.

Infiltrating inflammatory cell phenotypes and apoptosis in rejected human corneal allografts

PURPOSE

The aim of this study was to survey the histopathological and immunohistochemical features of rejected human corneal allografts.

METHODS

Following graft failure in each case due to rejection, paraffin-embedded specimens of 17 corneal transplants which had been replaced were examined by light microscopy and immunohistochemistry. Specimens were either first (n = 9), second (n = 4) or third (n = 4) grafts and were removed at varying intervals from 4 weeks following documented rejection.

RESULTS

Those grafts which were removed earliest following onset of rejection had the most intense graft inflammatory infiltrates. Immunohistochemical staining showed a high proportion of graft stroma-infiltrating cells expressing leucocyte common antigen, and many of these cells also bore T cell or macrophage markers. Leucocyte-keratocyte apposition and regional loss of keratocytes were observed in all rejection specimens, but not in non-rejected control grafts. In situ end-labelling of DNA double-strand breaks and morphological features identified keratocyte apoptosis in 5 of 12 specimens examined for this phenomenon. Corneal endothelial cells were absent in 7 specimens and present in reduced numbers in the remaining 10 specimens.

CONCLUSIONS

Endothelial cell monolayer attenuation and keratocyte loss are consistent findings in grafts removed subsequent to clinically observed endothelial rejection. Death of donor corneal cells is mediated, at least in part, by apoptosis. The stromal inflammatory infiltrate consists mainly of T lymphocytes and macrophages, which may be responsible for induction of keratocyte apoptosis.

Adenovirus-mediated gene delivery to the corneal endothelium

Genetic manipulation of donor cornea prior to transplantation has the potential to modulate the allogeneic response, as well as the endothelial cell function. This study examined the feasibility of gene transfer to corneal endothelial cells using replication-defective recombinant adenoviral vectors. Adult rabbits corneas were infected with recombinant adenovirus RAd35, containing the Escherichia coli beta-galactosidase (lacZ) gene. Localization of gene transfer was assessed by histochemical staining for beta-galactosidase and recombinant protein production was quantified by a soluble assay. In initial experiments, the efficiency of gene transfer and kinetics of expression were studied ex vivo, using organ culture of transfected corneas. Following coculture of whole corneal fragments with RAd35, high levels of gene expression were evident on days 107, diminishing after that time. Gene transfer was found to be almost entirely restricted to corneal endothelial cells, with scattered expression in epithelial cells. Following these ex vivo studies, genetically modified corneas were transplanted as orthotopic allografts in rabbits. Similar kinetics of gene expression were seen after transplantation as in the ex vivo experiment, with maximal levels of gene expression in endothelial cells on days 1-4 after grafting. Corneal function following transplantation was not affected by the gene transfer, with the corneas attaining clarity within 1 day of grafting, and thereafter showing the expected thinning on ultrasonic pachymetry. In the absence of any immunosuppression, no inflammation was evident in graft recipient eyes, with the exception of allograft rejection in 1 animal 23 days after grafting. In this study we show that gene transfer to nonreplicating corneal endothelial cells is feasible using recombinant adenovirus vectors, and so may have potential application in the setting of corneal transplantation.

Experimental orthotopic corneal xenotransplantation in the rat. Mechanisms of graft rejection

Orthotopic penetrating guinea pig to rat and chicken to rat corneal xenografts were performed to examine the nature of the host response. Guinea pig to rat xenografts failed at a median of day 3 after surgery. A similar but slightly accelerated pattern of failure was seen in guinea pig xenografts performed in prevascularized recipient rat corneas. Chicken to rat xenografts failed at a median of day 2 after grafting. Rat corneal isograft controls survived indefinitely. Corneal endothelial cells were visible by silver staining on the xenografts immediately after operation, which indicates that failure was not due to loss of these cells during surgery. Histopathology and immunoperoxidase staining indicated that xenograft failure in euthymic recipients was characterized by early corneal epithelial and endothelial cell damage, granulocytic infiltration, and hemorrhage from recipient corneal and iris capillaries, followed at 7-14 days by infiltration with T cells, macrophages, and eosinophils. An accelerated pattern of graft failure was also observed in guinea pig grafts into homozygous nude rat recipients, which suggests that preformed anti-donor antibody and complement were responsible for some of the early graft damage. Flow cytometry demonstrated the presence of pre-existing natural antibodies to guinea pig and chicken lymphocytes and erythrocytes, as expected from other studies. Immunohistochemistry showed the presence of rat IgG2a, IgG1, and IgM, but not IgD deposited on grafts in immunocompetent recipients on the first postoperative day. We conclude that orthotopic corneal xenografts undergo substantial accelerated damage mediated by pre-existing antibody, followed at 7-14 days by a cell-mediated response that causes further destruction.

The host response in experimental corneal xenotransplantation

In addressing the worldwide shortage of human donor cornea for transplantation, animal cornea may be a substitute if mechanisms of xenogeneic (cross-species) rejection can be identified and controlled. Xenotransplantation of solid organs is followed by hyperacute rejection with minutes due to humoral graft rejection. In an experimental model corneal xenografts in rats survived for 2-3 days, depending on the phylogenetic disparity of the donor animal. Endothelial injury was the specific cause of graft failure, probably mediated by humoral rejection mechanisms. A later cell-mediated rejection response was seen. The potent humoral response is the most important feature differentiating xenograft from allograft rejection.

Corneal allograft rejection

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Treatment of Acanthamoeba keratitis with polyhexamethylene biguanide

Polyhexamethylene biguanide (PHMB) is a polymeric biguanide disinfectant that has not previously been used in the treatment of infection. Six patients with confirmed Acanthamoeba keratitis were treated with PHMB 0.02%. All patients had uncontrolled keratitis refractory to therapy with multiple conventional antiamebic agents. The rationale for use and the dose of PHMB was determined by in vitro sensitivity testing of the Acanthamoeba corneal isolates to the drugs available for use. Trophozoite forms were sensitive to most agents. Only PHMB was cysticidal at low concentrations in all cases. Sensitivity to the other drugs, including propamidine, showed wide variation. In 5 of 6 cases, complete resolution of inflammation followed the introduction of PHMB. Toxicity to the ocular surface was not evident with PHMB, unlike propamidine or neomycin. The reasons for the treatment failure in one case, despite cyst sensitivity to both PHMB and propamidine, are not clear. PHMB is a promising new treatment for this infection.

In vitro corneal pathogenicity of Acanthamoeba

The comparative cytopathic effects of a keratitis and an environmental isolate of Acanthamoeba were studied on confluent monolayers of human and rabbit corneal cells grown in culture. The presence of cells in culture induced excystment of amoebae to the active trophozoite form. Total destruction of cell monolayers was observed to be similar for both isolates, and dependent on incubation time and amoebic concentration. The relevance of these findings to human and experimental Acanthamoeba keratitis is discussed.

Experimental Acanthamoeba keratitis: II. Immunohistochemical evaluation

In a Wistar rat experimental model of Acanthamoeba keratitis immunohistochemical techniques were used to analyse the host cellular response. The inflammatory cell profile was observed to change at intervals. In tissue sections the cellular response consisted of neutrophils on the first day but predominantly macrophages on the following days. Some T lymphocytes but no B lymphocytes were observed.

Quantitative alterations of the commensal eye bacteria in contact lens wear

A study was performed on the commensal external eye flora in 34 long-term contact lens wearers and a matched control group, in order to identify the effect of lens wear. Samples were taken from the lid margin and conjunctiva by semi-quantitative, and tear film by quantitative methods. Cultured bacteria were identified with particular attention to coagulase-negative staphylococci. No qualitative alteration in the commensal bacteria was found, although lens wearers were found to have a significantly higher number of species at all sites than controls. Significant quantitative changes were identified on the lid margin, with particularly high counts in some lens wearers, and tear film. Increased numbers of bacteria obtained from the conjunctiva were not statistically significant. Quantitative changes in the tear film are thought to be secondary to changes at the lid margin, for which no explanation is apparent.

Experimental Acanthamoeba keratitis: I. Preliminary findings

Experimental Acanthamoeba keratitis was induced in Wistar rats by intrastromal inoculation of Acanthamoeba polyphaga cysts. Keratitis developed in all corneas injected and was characterised by a diffuse granular opacity. The animals were examined for 70 days and a gradual reduction of keratitis was observed. Pathological sections showed liquefactive stromal necrosis and Acanthamoeba localised in deep stroma persisting to 70 days. A brisk inflammatory infiltrate of neutrophils and macrophages was seen in the early days of infection. Severity of keratitis was found to correlate with inflammatory activity in pathological sections. The uses of an animal model of Acanthamoeba keratitis are described.

Acanthamoeba adherence to contact lenses and removal by cleaning agents

The quantitative adherence of a keratitis isolate of Acanthamoeba polyphaga to low- and high-water content non-ionic soft contact lenses and one type of rigid gas-permeable lens was investigated. Adherence of trophozoite and cyst forms of the organism was observed in vitro, and adherent amoebae counted by a plaque assay method following detachment. Trophozoites adhered to all lens types with adherence being statistically significantly greater to high water content soft lenses. Cyst attachment occurred only to the soft lenses but not to gas-permeable lenses, and was significantly higher for the high water content lenses. Attachment of cysts was significantly lower than that of trophozoites to each lens tested. Recommended cleaning procedures using two commercial solutions removed all adherent trophozoites and cysts from lenses. These studies demonstrate (i) that lenses may act as a vector in Acanthamoeba keratitis, particularly for high-water content lenses and trophozoite amoebae, (ii) that lens cleaning agents may prevent keratitis by removing adherent Acanthamoeba.

Contamination of contact lens storage cases by Acanthamoeba and bacteria

In order to identify possible risk factors for microbial keratitis the storage cases for contact lenses of 102 asymptomatic lens wearers were tested for contamination by bacteria and free-living amoebae. Of this group 43 had significant counts of viable bacteria and only 40 had negligible counts. Seven had contamination by acanthamoebae, of whom six also had significant bacterial counts. These results were categorised according to the type of contact lens worn and the lens disinfection method. The high rates of contamination by apathogenic and pathogenic organisms, in particular Acanthamoeba, and the probable support by contaminating bacteria of Acanthamoeba, are discussed.

External eye flora as a nutrient source for Acanthamoeba

Certain bacteria cause excystment of Acanthamoeba from cyst to trophozoite form and are then ingested by migrating trophozoites. We studied the response of Acanthamoeba cysts to inoculation on agar seeded with three types of commensal eye bacteria and Escherichia coli. Amoebae excysted on all bacteria tested, and the migration rate of Acanthamoeba trophozoites on each was compared. Acanthamoeba migrated with equal speed on E. coli and Staphylococcus epidermidis. Migration was observed, but was more slow on Micrococcus and Corynebacterium. Commensal bacteria on the eyelids, conjunctiva and tear film may have a role in pathogenesis of Acanthamoeba keratitis.

Yersinia-induced uveitis in Ireland

A prospective study was undertaken on 54 patients with an apparently idiopathic first attack of acute anterior uveitis. Blood samples were assayed for antibodies to Yersinia enterocolitica and Yersinia pseudotuberculosis, and tested for HLA type. Thirteen patients were found to have serological evidence of recent yersinia infection, eight with Y. enterocolitica and five with Y. pseudotuberculosis. The clinical course of uveitis did not differ from that typically found in HLA-B27 positive patients. Five patients were observed to develop non-ocular inflammation at a variable interval. The means by which eye inflammation follows yersinia infection is discussed in the light of recent theories on pathogenesis of HLA-B27 associated diseases.

Orbital fibrous histiocytoma in an infant

A rare case of fibrous histiocytoma in an infant is described. The tumour appeared to arise in the medial orbit, invading the ethmoid and maxillary sinuses. Surgical and medical management, and the subsequent clinical course in a 11 year follow-up period are described. Histogenesis of this primary mesenchymal tumour is discussed.

Developmental glaucoma in oculocutaneous albinism

A case of oculocutaneous albinism is described in which bilateral Axenfeld's anomaly co-exists. Progressive elevation of intraocular pressure required treatment and this complication has not been reported. Different hypotheses regarding the co-existence of these conditions are reviewed.

Management of intraocular pressure during cardiopulmonary bypass

Intraocular pressure was measured in two groups of patients undergoing cardiopulmonary bypass surgery. A control group received mannitol at the start of bypass in accordance with standard practice; pressure was found to rise by 6.4 mmHg. In a second group of patients mannitol was administered 30 min prior to bypass; pressure elevation of 2.4 mmHg was found. These findings are discussed in relation to other clinical observations during bypass and to ocular morbidity complicating bypass surgery.

Ischaemic optic neuropathy complicating cardiopulmonary bypass

Bilateral anterior ischaemic optic neuropathy occurred in two patients undergoing cardiopulmonary bypass grafting. The causes may have been vasoconstriction of the posterior ciliary arteries by increased circulating angiotensin and diminished ciliary blood flow in the setting of systemic hypotension and elevated intraocular pressure.

Intraocular pressure during cardiopulmonary bypass

Intraocular pressure was measured in 24 patients undergoing elective cardiopulmonary bypass surgery. There was a rapid rise when the bypass circulation began, and this was maintained for about 30 minutes. A simultaneous drop in arterial perfusion pressure and packed cell volume occurred. We suggest that marked haemodilution is responsible for this effect, through increased ocular blood flow and low colloidal osmotic pressure. The possible aetiological significance in relation to ischaemic optic neuropathy complicating cardiopulmonary bypass is discussed.

Sinus histiocytosis with massive lymphadenopathy simulating subacute thyroiditis

A white woman who had sinus histiocytosis with massive lymphoadenopathy (SHML) presented with a painful goiter and tender cervical lymph nodes. She had biochemical evidence of hypothyroidism but remained clinically euthyroid. Histologic examination confirmed SHML in the thyroid and cervical lymph nodes. The disease remitted spontaneously.