Local bioactive tumour necrosis factor (TNF) in corneal allotransplantation

Dendrimers in Corneal Drug Delivery: Recent Developments and Translational Opportunities

Dendrimers are biocompatible organic nanomaterials with unique physicochemical properties, making them the focus of recent research in drug delivery. The cornea of the human eye presents a challenge for drug transit due to its inherently impenetrable nature, requiring nanocarrier-mediated targeted drug delivery. This review intends to examine recent advancements in the use of dendrimers for corneal drug delivery, including their properties and their potential for treating various ocular diseases. The review will also highlight the benefit of the novel technologies that have been developed and applied in the field, such as corneal targeting, drug release kinetics, treatments for dry eye disease, antibacterial drug delivery, corneal inflammation, and corneal tissue engineering. The review seeks to provide a comprehensive overview of the current state of research in this field, along with the translational developments in the field of dendrimer-based therapeutics and imaging agents and inspire the potential for future developments and translational opportunities in dendrimers based corneal drug delivery.

Pathophysiology of Corneal Endothelial Cell Loss in Dry Eye Disease and Other Inflammatory Ocular Disorders

PURPOSE

Dry eye disease (DED) and other inflammatory ocular disorders have been reported to be associated with decreased corneal endothelial cell density (CECD), however the mechanism of underlying endothelial cell loss remains unknown.

METHODS

We conducted a comprehensive literature search of English-written publications on dry eye disease, corneal endothelial cell loss, Sjögren's syndrome, and Graft Vs Host Disease (GVHD), to review the effects of DED and other inflammatory ocular surface conditions on CECD.

RESULTS

A total of 78 studies were included in our study. Loss of corneal neurotrophic support, cytotoxic stress, and a heightened immune response, all of which may occur secondarily to a common causative agent such as inflammation, are major contributors to reduced CECD.

CONCLUSION

More studies are needed to determine how the interrelated pathways of altered corneal nerve function and upregulated expression of inflammatory activity influence corneal endothelial cell loss.

Tumor Necrosis Factor-Alpha Disrupts Cx43-Mediated Corneal Endothelial Gap Junction Intercellular Communication

Connexin43 (Cx43)-mediated gap junctions are vital in maintaining corneal endothelium homeostasis. Tumor necrosis factor-alpha (TNF-α) is among the most important inflammatory factors which cause corneal endothelial dysfunction in various eye diseases. However, the effect of TNF-α on Cx43-mediated gap junctions of the corneal endothelium remains undefined. In the current research, we determined the effect of TNF-α on gap junction intercellular communication (GJIC) in rabbit corneal endothelium. To evaluate alterations of GJIC, if any, we treated ex vivo cultured rabbit corneal endothelium with different concentrations of TNF-α (2-20 ng/ml). The localization of Cx43 was analyzed by immunostaining, while RT-qPCR and western blot were used to profile the expression of Cx43 and zonula occludens-1 (ZO-1). The association between ZO-1 and Cx43 was evaluated using immunoprecipitation and double staining. GJIC activity was determined by the scrap loading and dye transfer assay (SLDT). Our data demonstrated that a high concentration of TNF-α (10 ng/ml and 20 ng/ml) disrupts the Cx43 mediated gap junction distribution in rabbit corneal endothelium and suppresses the expression of Cx43 protein. Furthermore, rabbit corneal endothelial GJIC was inhibited due to the decreased association between the ZO-1 and Cx43 proteins. Current results demonstrate that TNF-α inhibits corneal endothelial GJIC via decreasing the association between ZO-1 and Cx43, disrupting the distribution of Cx43, and downregulating the expression of Cx43 protein. This study offers a new theoretical foundation for diagnosing and treating corneal endothelial cell decompensation induced by elevated TNF-α in various eye diseases.

On chaotic dynamics in transcription factors and the associated effects in differential gene regulation

The control of proteins by a transcription factor with periodically varying concentration exhibits intriguing dynamical behaviour. Even though it is accepted that transcription factors vary their dynamics in response to different situations, insight into how this affects downstream genes is lacking. Here, we investigate how oscillations and chaotic dynamics in the transcription factor NF-κB can affect downstream protein production. We describe how it is possible to control the effective dynamics of the transcription factor by stimulating it with an oscillating ligand. We find that chaotic dynamics modulates gene expression and up-regulates certain families of low-affinity genes, even in the presence of extrinsic and intrinsic noise. Furthermore, this leads to an increase in the production of protein complexes and the efficiency of their assembly. Finally, we show how chaotic dynamics creates a heterogeneous population of cell states, and describe how this can be beneficial in multi-toxic environments.

It is becoming clear that the dynamics of transcription factors may be important for gene regulation. Here, the authors study the implications of oscillatory and chaotic dynamics of NF-κB and demonstrate that it allows a degree of control of gene expression and can generate phenotypic heterogeneity.

[Immunosuppressives to prevent rejection reactions after allogeneic corneal transplantation]

In order to prevent rejection of an allogeneic corneal transplant after perforating (high risk) keratoplasty, active agents from different classes of pharmacological substances are used, as with solid organ transplantation. In addition to glucocorticoids, antiproliferative agents, small molecule inhibitors and antibodies, those belonging to the group of macrolides with their many derivatives represent an interesting class of substances in this context. As a supplement to cyclosporin A (CSA) the most successful macrolide in transplantation medicine, animal experiments are currently being carried out to test newer macrolide derivatives, such as sanglifehrin A (SFA). This overview describes the classes of drugs and modes of action of currently administered standard medications in the clinical routine and new developments are presented.

Effects of subconjunctivally injected bevacizumab, etanercept, and the combination of both drugs on experimental corneal neovascularization

OBJECTIVE

To compare the effect of subconjunctivally injected bevacizumab, etanercept and the combination of both drugs on experimental corneal neovascularization in rats.

DESIGN

Experimental study.

PARTICIPANTS

28 male Wistar-Albino rats.

METHODS

Right corneas of rats were cauterized by silver nitrate sticks. Rats were divided randomly and equally into 4 groups so that each group contained 7 subjects. Immediately after the cauterization, 0.05 ml normal saline was injected subconjunctivally in group 1 (control group); 0.05 ml (1.25 mg) bevacizumab was injected subconjunctivally in group 2; 0.05 ml (1.25 mg) etanercept was injected subconjunctivally in group 3; 0.05 ml (1.25 mg) bevacizumab and 0.05 ml (1.25 mg) etanercept was injected subconjunctivally in group 4. The rats were euthanized on the 8th day, and digital photographs were obtained before the eyes were enucleated. The area of corneal neovascularization was calculated from digital photographs. Corneal sections were analyzed by histopathologically.

RESULTS

The burn stimulus score was +1 or higher in all eyes. The difference of the neovascularization score between groups was found to be statistically significant (p = 0.001). The area of corneal neovascularization was 79.8% in group 1, 43.2% in group 2, 54.5% in group 3, and 34.8% in group 4. In group 4, corneal neovascularization was inhibited more than in the other groups. Histologic examination showed that the treatment groups had less neovascularization, inflammation, and fibroblast activity than the control group (p< 0.05).

CONCLUSIONS

Our study has shown that etanercept does have some antiangiogenic and anti-inflammatory effects in treatment of corneal neovascularization. The combination of bevacizumab and etanercept may be a promising approach in the treatment of corneal neovascularization.

Early expression of tumor necrosis factor α and nuclear factor kappa B after Descemet stripping endothelial keratoplasty in rabbits

PURPOSE

To investigate immune rejection after Descemet stripping endothelial keratoplasty (DSEK) compared with that after penetrating keratoplasty (PKP) in New Zealand rabbit eyes and to identify the relationship between tumor necrosis factor alpha (TNF-α) and nuclear factor kappa B (NFκB) and evaluate their involvement in graft rejection.

METHODS

Sixty-nine New Zealand rabbits were divided into 3 groups: group A comprised the control group, which did not undergo either of the procedures; group B underwent DSEK; and group C underwent PKP. Twenty-three Chinese rabbits (46 eyes) were used as donors. The corneal transparency, graft placement, and anterior chamber were observed for 28 days. Blood serum, aqueous humor, and corneal samples were obtained on days 7, 14, 21, and 28 after the procedures. TNF-α levels were measured weekly by double-antibody enzyme-linked immunosorbent assay. NFκB in the cornea was checked by immunofluorescence.

RESULTS

There were no graft rejections in group B. Group C showed a 50% rejection frequency with an increase in both the TNF-α concentrations and NFκB expression observed at 7 days and peak levels observed at 28 days after PKP. TNF-α concentrations did not differ significantly (P > 0.05) between groups B and A. NFκB expression was slightly increased at 7 days and returned to normal levels by day 14 after DSEK.

CONCLUSION

Rabbits with DSEK had a lower rejection rate than rabbits with PKP. NFκB and TNF-α may contribute to the early rejection of corneal allografts.

Cell signaling in regulation of the barrier integrity of the corneal endothelium

The barrier integrity of the corneal endothelium, which is conferred by its tight and adherens junctions, is critical for the maintenance of deturgescence of the corneal stroma. Although characteristically leaky, the barrier integrity restricts fluid leakage into the stroma such that the rate of leak does not exceed the rate of the endothelial active fluid transport directed toward the aqueous humor. At a molecular level, the barrier integrity is influenced by the actin cytoskeleton and microtubules, which are coupled to tight and adherens junctions via a variety of linker proteins. Since the cytoskeleton is affected by Rho family small GTPases and p38 MAP kinase, among others, many pathophysiological stimuli induce plasticity to the cytoskeleton and thereby elicit dynamic regulation of the barrier integrity. This review presents an overview of the impact of several bioactive factors on the barrier integrity of the corneal endothelium through altered actin cytoskeleton and/or disassembly of microtubules. The main focus is on the effect of TNF-α (tumor necrosis factor-α) which is a pro-inflammatory molecule found in the intraocular milieu during allograft rejection and anterior uveitis. This cytokine elicits acute activation of p38 MAP kinase, induces disassembly of microtubules, disrupts the peri-junctional actomyosin ring, and concomitantly breaks down the barrier integrity. These effects of TNF-α could be inhibited by stabilizing the microtubules, co-treating with a selective p38 MAP kinase inhibitor, and elevating intracellular cAMP via A2B receptors or direct exposure to forskolin. Overall, the corneal edema following a potential breakdown of the endothelial barrier integrity can be rescued pharmacologically by inhibiting specific cell-signaling mechanisms.

Elevated cAMP opposes (TNF-alpha)-induced loss in the barrier integrity of corneal endothelium

PURPOSE

Elevated cyclic adenosine monophosphate (cAMP) enhances the barrier integrity of the corneal endothelium and thereby facilitates stromal hydration control, which is necessary for corneal transparency. This study investigates whether elevated cAMP is effective against the tumor necrosis factor-alpha (TNF-alpha)-induced loss of barrier integrity in monolayers of bovine corneal endothelial cells (BCEC).

METHODS

BCEC in primary culture were used for the study. Trans-endothelial electrical resistance (TER), a measure of barrier integrity, was determined by electrical cell-substrate impedance sensing. The changes were also ascertained by measuring paracellular permeability to fluorescein isothiocyanate (FITC)-dextran (10 kDa) across cells grown on porous culture inserts, and by immunofluorescence imaging of the apical junctional complex (AJC). The activation of p38 MAP kinase was assessed using western blotting.

RESULTS

Co-treatment with forskolin, which activates adenylate cyclase, and rolipram, which inhibits cAMP-dependent phosphodiesterase PDE4, reduced the TNF-alpha-induced increase in the flux of FITC-dextran. Similar co-treatment also prevented the TNF-alpha-induced disorganization of zona occludens-1 (ZO-1) and cadherins at the AJC. Co-treatment, as well pre-treatment, with forskolin plus rolipram prevented the TNF-alpha-induced decrease in TER. The influence of the agents was significant after 12 h of exposure to the cytokine. This effect was also mimicked by A2B agonists, adenosine and 5'-N-ethylcarboxamidoadenosine (NECA), which are known to mobilize cAMP in BCEC. Elevated cAMP also inhibited the cytokine-induced activation of p38 MAP kinase, and further blocked the disassembly of microtubules as well as the disruption of the PAMR (peri-junctional actomyosin ring) at the AJC.

CONCLUSIONS

These results suggest that elevated cAMP opposes the TNF-alpha-induced loss in barrier integrity of the corneal endothelium. This effect follows inhibition of the cytokine-induced activation of p38 MAP kinase and its downstream signaling involved in the disruption of AJC and PAMR, as well as the disassembly of microtubules.

Dynamic regulation of barrier integrity of the corneal endothelium

The corneal endothelium maintains stromal deturgescence, which is a prerequisite for corneal transparency. The principal challenge to stromal deturgescence is the swelling pressure associated with the hydrophilic glycosaminoglycans in the stroma. This negative pressure induces fluid leak into the stroma from the anterior chamber, but the rate of leak is restrained by the tight junctions of the endothelium. This role of the endothelium represents its barrier function. In healthy cornea, the fluid leak is counterbalanced by an active fluid pump mechanism associated with the endothelium itself. Although this pump-leak hypothesis was postulated several decades ago, the mechanisms underlying regulation of the balance between the pump and leak functions remain largely unknown. In the last couple of decades, the ion transport systems that support the fluid pump activity have been discovered. In contrast, despite significant evidence for corneal edema secondary to endothelial barrier dysfunction, the molecular aspects underlying its regulation are relatively unknown. Recent findings in our laboratory, however, indicate that barrier integrity (i.e., structural and functional integrity of the tight junctions) of the endothelium is sensitive to remodeling of its peri-junctional actomyosin ring, which is located at the apical junctional complex. This review provides a focused perspective on dynamic regulation of the barrier integrity of endothelium vis-à-vis plasticity of the peri-junctional actomyosin ring and its association with cell signaling downstream of small GTPases of the Rho family. Based on findings to date, it appears that development of specific pharmacological strategies to treat corneal edema in response to inflammatory stress would be possible in the near future.

Barrier dysfunction of the corneal endothelium in response to TNF-alpha: role of p38 MAP kinase

PURPOSE

TNF-alpha is elevated in the cornea and aqueous humor during allograft rejection and anterior uveitis. The authors investigated the involvement of p38 MAP kinase in the TNF-alpha-induced loss of barrier integrity in monolayers of cultured bovine corneal endothelial cells.

METHODS

Transendothelial electrical resistance (TER), a measure of barrier integrity, was determined by electrical cell-substrate impedance sensing. Barrier integrity was further assessed in terms of permeability to FITC dextran. Reorganization of the apical junctional complex (AJC) in response to TNF-alpha was visualized by immunofluorescence. The expression of TNF-alpha receptors was confirmed by RT-PCR. Activation of p38 MAP kinase in response to TNF-alpha was determined by Western blot analysis.

RESULTS

Exposure to TNF-alpha induced a continuous decline in TER that persisted for more than 20 hours. It also led to a significant increase in permeability to FITC dextran. At the AJC, the cytokine caused disassembly of microtubules, disruption of perijunctional actomyosin ring (PAMR), and dislocation of ZO-1 and cadherins. Western blot analysis showed that TNF-alpha also led to the activation of p38 MAP kinase. All these responses to the cytokine were opposed by treatment with SB-203580, a selective p38 MAP kinase inhibitor. TNFR1, but not TNFR2, was expressed in untreated cells with no change in the expression pattern on treatment with the cytokine.

CONCLUSIONS

TNF-alpha breaks down the barrier integrity of corneal endothelium, concomitant with the disruption of PAMR, remodeling of AJC, and disassembly of microtubules. These effects are mediated by transient activation of p38 MAP kinase. Thus, the TNF-alpha-induced barrier dysfunction in the corneal endothelium can be suppressed by inhibitors of p38 MAP kinase and agents downstream of the kinase that affect the cytoskeleton.

Immune mechanisms of corneal allograft rejection

Penetrating keratoplasty has been successfully performed on humans for over 100 years and remains the most common form of solid tissue transplantation. Although corneal allografts enjoy a remarkable degree of immune privilege, immune rejection remains the leading cause of keratoplasty failure. The immunologic basis for corneal allograft rejection was established in animal studies over 50 years ago, yet large gaps remain in our knowledge regarding the cellular and molecular mechanisms of corneal allograft rejection. The enormous redundancy in the mammalian immune system creates a condition that favors the development of multiple independent immune mechanisms that can produce corneal allograft rejection. Although there are few absolute principles, it is certain that the immune rejection of corneal allografts is (1) T cell-dependent, (1) heavily dependent upon CD4(+) T cells, (3) not restricted to either Th1 or Th2 T cell populations, and (4) dependent upon an intact repertoire of resident antigen presenting cells.

Nitrosative Stress and Corneal Transplant Endothelial Cell Death During Acute Graft Rejection

BACKGROUND

Nitrosative stress takes place in endothelial cells (EC) during corneal acute graft rejection. The purpose of this study was to evaluate the potential role of peroxynitrite on corneal EC death.

METHODS

The effect of peroxynitrite was evaluated in vivo. Fifty, 250, and 500 microM in 1.5 microL of the natural or denatured peroxynitrite in 50 microM NaOH, 50 microM NaOH alone, or balanced salt solution were injected into the anterior chamber of rat eyes (n=3/group). Corneal toxic signs after injection were assessed by slit-lamp, in vivo confocal imaging, pachymetry, and EC count. The effect of peroxynitrite was also evaluated on nitrotyrosine and leucocyte elastase inhibitor/LDNase II immunohistochemistry. Human corneas were incubated with peroxynitrite and the effect on EC viability was evaluated. A specific inducible nitric oxide synthase inhibitor (iNOS) was administered systemically in rats undergoing allogeneic corneal graft rejection and the effect on EC was evaluated by EC count.

RESULTS

Rat eyes receiving as little as 50 microM peroxynitrite showed a specific dose-dependent toxicity on EC. We observed an intense nitrotyrosine staining of human and rat EC exposed to peroxynitrite associated with leucocyte elastase inhibitor nuclear translocation, a noncaspase dependent apoptosis reaction. Specific inhibition of iNOS generation prevented EC death and enhanced EC survival of the grafted corneas. However, inhibition of iNOS did not have a significant influence on the incidence of graft rejection.

CONCLUSION

Nitrosative stress during acute corneal graft rejection in rat eyes induces a noncaspase dependent apoptotic death in EC. Inhibition of nitric oxide production during the corneal graft rejection has protective effects on the corneal EC survival.

Tumor necrosis factor antagonists: preliminary evidence for an emerging approach in the treatment of ocular inflammation

The anti-tumor necrosis factor (TNF) monoclonal antibody infliximab and the soluble TNF receptor etanercept inhibit the pleiotropic actions of TNF and are widely used for the treatment of rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), spondyloarthropathies (SpA), Crohn's disease, and psoriasis with an acceptable safety profile. A pathogenetic role of TNF in ocular inflammatory conditions has recently emerged from small trials reporting preliminary results on the efficacy of these agents in patients with noninfectious uveitis, regardless of the origin of the disease. The authors review the published experience, derived mostly from investigator-sponsored trials and uncontrolled case series, on the use of TNF antagonists in approximately 280 patients with various ocular conditions who were inadequately controlled on currently available therapy. These reports suggest that TNF antagonists, mainly infliximab, which may have better efficacy than etanercept, are useful in the treatment of ocular inflammation associated with Adamantiades-Behçet's disease, RA, JIA, SpA, Crohn's, sarcoidosis, and Graves' disease ophthalmopathy. Infliximab was also beneficial in small numbers of patients with idiopathic uveitis or scleritis, birdshot retinochoroiditis, uveitic and diabetic cystoid macular edema, and age-related macular degeneration. The currently available data are nonrandomized and thus preliminary, providing the foundation and justification for randomized trials to assess efficacy and safety. Until such results are available, knowledge regarding the use of anti-TNF regimens in ophthalmology is incomplete. However, the preliminary evidence points to a growing optimism for targeting TNF in patients with ocular inflammation.

Oscillations in the immune system

Oscillations are surprisingly common in the immune system, both in its healthy state and in disease. The most famous example is that of periodic fevers caused by the malaria parasite. A number of hereditary disorders, which also cause periodic fevers, have also been known for a long time. Various reports of oscillations in cytokine concentrations following antigen challenge have been published over at least the past three decades. Oscillations can also occur at the intracellular level. Calcium oscillations following T-cell activation are familiar to all immunologists, and metabolic and reactive oxygen species oscillations in neutrophils have been well documented. More recently, oscillations in nuclear factor kappaB activity following stimulation by tumor necrosis factor alpha have received considerable publicity. However, despite all of these examples, oscillations in the immune system still tend to be considered mainly as pathological aberrations, and their causes and significance remained largely unknown. This is partly because of a lack of awareness within the immunological community of the appropriate theoretical frameworks for describing and analyzing such behavior. We provide an introduction to these frameworks and give a survey of the currently known oscillations that occur within the immune system.

Function of indoleamine 2,3-dioxygenase in corneal allograft rejection and prolongation of allograft survival by over-expression

Indoleamine 2,3-dioxygenase (IDO) suppresses T cell responses by its action in catabolising tryptophan. It is important in maintenance of immune privilege in the placenta. We investigated the activity of IDO in the cornea, following corneal transplantation and the effect of IDO over-expression in donor corneal endothelium on the survival of corneal allografts. IDO expression was analysed and functional activity was quantified in normal murine cornea and in corneas following transplantation as allografts. Low levels of IDO, at both mRNA and protein levels, was detected in the normal cornea, up-regulated by IFN-gamma and TNF. Expression of IDO in cornea was significantly increased following corneal transplantation. However, inhibition of IDO activity in vivo had no effect on graft survival. Following IDO cDNA transfer, murine corneal endothelial cells expressed functional IDO, which was effective at inhibiting allogeneic T cell proliferation. Over-expression of IDO in donor corneal allografts resulted in prolonged graft survival. While, on one hand, our data indicate that IDO may augment corneal immune privilege, up-regulated IDO activity following cytokine stimulation may serve to inhibit inflammatory cellular responses. While increasing IDO mRNA expression was found in allogeneic corneas at rejection, over-expression in donor cornea was found to significantly extend survival of allografts.

Corneal transplantation: the forgotten graft

The most commonly performed transplant is that of the cornea, with 2292 corneal grafts performed in the UK in 2002-03, compared with 1775 renal transplants [1]. In the USA approximately 40 000 transplants are performed every year [2]. However this preponderance is not reflected in the amount of attention given to this transplanted tissue by the scientific community: for example up till now there have been no papers published in the American Journal of Transplantation that have cornea as a key or title word (as determined by a Medline search in December 2003). There are several reasons for this. The first is that corneal grafting is the province of ophthalmologists, who (with notable exceptions) are isolated from the transplant community. The second is that there is a widespread belief that, because of the existence of immune privilege, corneal grafts are not rejected and so there is no need for further research. As we will discuss later, this is incorrect. In this article we will seek to show that study of corneal transplantation is important in its own right, and also that it has lessons for those interested in other forms of allograft.

Prospects for gene therapy in corneal disease

Transfer of cDNA to corneal cells has been accomplished using viral and nonviral vectors. Studies examining the feasibility and optimal methods for vector-mediated gene transfer to the cornea have, as in other tissues, been performed using histochemical or fluorescent marker genes. These have used corneal cells or cell lines in vitro, and whole corneas maintained in ex vivo culture. Gene-based interventions have been examined in specific corneal disorders such as allograft rejection, postexcimer laser scarring, and herpes simplex keratitis using experimental models. As the feasibility of genetic modification of corneal cells has been successfully demonstrated, there is great potential for gene therapy vectors in the treatment of human corneal disease. Continued improvements in vectors for gene transfer will improve the efficacy and safety of gene therapy. In addition to use of cDNA transfer as an alternative to drug or protein treatments in acquired corneal disorders, our expanding knowledge of the genetic basis of inherited corneal disorders will ultimately lead to the development of specific and effective gene therapies in this category of diseases.

Optimal analysis of composite cytokine responses during alloreactivity

The one-way mixed lymphocyte reaction (MLR) is a useful model of the graft-vs.-host (GvH) response that occurs following bone-marrow transplantation (BMT). Previous studies of the MLR have shown high levels of type-1 cytokine production, such as IL-1, IL-6, IFN-gamma and TNF-alpha, but low or undetectable levels of type-2 cytokines, such as IL-4 and IL-10. Here, through establishing optimal conditions for the examination of levels and kinetics of a more definitive panel of type-1/type-2 cytokines (IL-4, IL-5, IL-10 and IL-13, IFN-gamma, TNF-alpha and the soluble IL-4 receptor) we show that, contrary to previously published data, the human alloresponse is truly heterogeneous, resulting in abundant type-2 as well as type-1 cytokine secretion. The kinetics of cytokine levels in the MLR show surprising complexity, suggesting a well-defined regulation as the alloresponse develops over time. Furthermore, each MLR responder:stimulator combination tested produces a composite cytokine profile that is intrinsic to that particular pairing. These combination-specific cytokine responses are reproducible when tested on multiple occasions over time. These data reveal a potential clinical application for the cytokine MLR in selecting donors for BMT with the least inflammatory cytokine profile. Additional analysis of this system reveals that the bulk of cytokine measured is both allospecific and T-cell-derived, with comparatively low levels produced through an autologous mechanism. Interestingly, although most of the cytokine detected is produced by CD45RO+ 'mature/activated' T cells, CD45RA+ 'naive' T cells are responsible for transient early production of IL-4. This novel finding suggests that naive T cells themselves could regulate type-1/type-2 developmental fate through an autocrine IL-4 mechanism.

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.