Specific immunosuppression of corneal allograft rejection by combination of anti-VLA-4 and anti-LFA-1 monoclonal antibodies in mice

Effector and Regulatory T Cell Trafficking in Corneal Allograft Rejection

Corneal transplantation is among the most prevalent and successful forms of solid tissue transplantation in humans. Failure of corneal allograft is mainly due to immune-mediated destruction of the graft, a complex and highly coordinated process that involves elaborate interactions between cells of innate and adaptive immunity. The migration of immune cells to regional lymphoid tissues and to the site of graft plays a central role in the immunopathogenesis of graft rejection. Intricate interactions between adhesion molecules and their counter receptors on immune cells in conjunction with tissue-specific chemokines guide the trafficking of these cells to the draining lymph nodes and ultimately to the site of graft. In this review, we discuss the cascade of chemokines and adhesion molecules that mediate the trafficking of effector and regulatory T cells during corneal allograft rejection.

Update on the Management of High-Risk Penetrating Keratoplasty

PURPOSE OF REVIEW

In this article, we review the indications and latest management of high-risk penetrating keratoplasty.

RECENT FINDINGS

Despite the immune-privilege status of the cornea, immune-mediated graft rejection still remains the leading cause of corneal graft failure. This is particularly a problem in the high-risk graft recipients, namely patients with previous graft failure due to rejection and those with inflamed and vascularized corneal beds. A number of strategies including both local and systemic immunosuppression are currently used to increase the success rate of high-risk corneal grafts. Moreover, in cases of limbal stem cell deficiency, limbal stem cells transplantation is employed.

SUMMARY

Corticosteroids are still the top medication for prevention and treatment in cases of corneal graft rejection. Single and combined administration of immunosuppressive agents e.g. tacrolimus, cyclosporine and mycophenolate are promising adjunctive therapies for prolonging graft survival. In the future, cellular and molecular therapies should allow us to achieve immunologic tolerance even in high-risk grafts.

Systemic Immunomodulatory Strategies in High-risk Corneal Transplantation

The cornea is the most commonly transplanted tissue in the body. Although corneal grafts generally have high success rates, transplantation onto inflamed and vascularized host beds, or so-called high-risk corneal transplantation, has a high rate of graft rejection. The management of this high-risk corneal transplantation is challenging and involves numerous measures. One of the key measures to prevent graft rejection in these cases is the use of systemic immunosuppressive agents. In this article, we will review the systemic immunosuppressive agents most commonly used for high-risk corneal transplantation, which include corticosteroids, cysclosporine A, tacrolimus, mycophenolate mofetil, and rapamycin. Benefits, risks, and published data on the use of these medications for high-risk corneal transplantation will be detailed. We will also summarize novel immunoregulatory approaches that may be used to prevent graft rejection in high-risk corneal transplantation.

Win 55212-2, a cannabinoid receptor agonist, attenuates leukocyte/endothelial interactions in an experimental autoimmune encephalomyelitis model

Multiple sclerosis (MS) is the most common of the immune demyelinating disorders of the central nervous system (C NS). Leukocyte/endothelial interactions are important steps in the progression of the disease and substances that interfere with these activities have been evaluated as potential therapeutic agents. C annabinoid receptor agonists have been shown to downregulate immune responses and there is preliminary evidence that they may slow the progress of MS. The purpo se of this investigation was to determine how cannabinoid recepto r agonists interfere with leukocyte rolling and adhesion. This was investigated in an experimental autoimmune encephalo myelitis (EAE) model using six to eight week old C 57BL/6 mice. Mouse myelin oligodendrocyte protein and pertussis toxin were used to induce EAE. WIN 55212-2, C B1 and C B2 antagonist were given. By use of in vivo intravital microscopy, leukocyte/endothelial interactio ns were evaluated via a cranial window implanted two days before. The results demonstrated that EAE increases leukocyte rolling and firm adhesion in the brain, and that this increased leukocyte/endothelial interactio n can be attenuated by administration of WIN 55212-2. Furthermore, use of the selective antagonists for the C B1 recepto r (SR 141716A) and the C B2 receptor (SR144528) in this study demonstrated that the cannabinoid’s inhibitory effects on leukocyte/endothelial interactions can be mediated by activating C B2 receptor.

Corneal Allograft Rejection: Immunopathogenesis to Therapeutics

Corneal transplantation is among the most successful solid organ transplants. However, despite low rejection rates of grafts in the ‘low-risk’ setting, rejection can be as high as 70% when grafted into ‘high-risk’ recipient beds. Under normal homeostatic conditions, the avascular cornea provides a unique environment that facilitates immune and angiogenic privilege. An imbalance in pro-inflammatory, angiogenic and lymphangiogenic mediators leads to a breakdown in corneal immune privilege with a consequent host response against the donor graft. Recent developments in lamellar and endothelial keratoplasties have reduced the rates of graft rejection even more, while providing improved visual outcomes. The corneal layer against which an immune response is initiated, largely determines reversibility of the acute episode. While epithelial and stromal graft rejection may be treated with topical corticosteroids with higher success, acute endothelial rejection mandates a more aggressive approach to therapy due to the lack of regenerative capacity of this layer. However, current immunosuppressive regimens come with the caveat of ocular and systemic side effects, making prolonged aggressive treatment undesirable. With the advent of biologics, efficacious therapies with a superior side effect profile are on the horizon. In our review we discuss the mediators of ocular immune privilege, the roles of cellular and molecular immune players in graft rejection, with a focus on human leukocyte antigen and antigen presenting cells. Furthermore, we discuss the clinical risk factors for graft rejection and compare rates of rejection in lamellar and endothelial keratoplasties to traditional penetrating keratoplasty. Lastly, we present the current and upcoming measures of therapeutic strategies to manage and treat graft rejection, including an overview of biologics and small molecule therapy.

Antigen-specific blocking of CD4-specific immunological synapse formation using BPI and current therapies for autoimmune diseases

In this review, we discuss T-cell activation, etiology, and the current therapies of autoimmune diseases (i.e., MS, T1D, and RA). T-cells are activated upon interaction with antigen-presenting cells (APC) followed by a "bull's eye"-like formation of the immunological synapse (IS) at the T-cell-APC interface. Although the various disease-modifying therapies developed so far have been shown to modulate the IS and thus help in the management of these diseases, they are also known to present some undesirable side effects. In this study, we describe a novel and selective way to suppress autoimmunity by using a bifunctional peptide inhibitor (BPI). BPI uses an intercellular adhesion molecule-1 (ICAM-1)-binding peptide to target antigenic peptides (e.g., proteolipid peptide, glutamic acid decarboxylase, and type II collagen) to the APC and therefore modulate the immune response. The central hypothesis is that BPI blocks the IS formation by simultaneously binding to major histocompatibility complex-II and ICAM-1 on the APC and selectively alters the activation of T cells from T(H)1 to T(reg) and/or T(H)2 phenotypes, leading to tolerance.

The mechanisms and consequences of ultraviolet-induced immunosuppression in the skin and eye

Ultraviolet radiation (UVR) of the skin results in immune suppression to antigens encountered shortly after the exposure. The pathways leading to the downregulation in immunity are complex, initiated by chromophores located at the surface of the skin and ending with the generation of immunosuppressive mediators and regulatory cells. Ultraviolet-induced immunosuppression can be considered not only as beneficial, such as in preventing chronic inflammatory responses and allergic and automimmune reactions, but it can also be detrimental, such as in the lack of control of skin tumors and infectious diseases. The eye is an immune privileged site through a wide variety of mechanisms that allow selected immune responses without causing inflammation. The role of UVR in altering immune responses in the eye is not clear and is discussed in relation to photokeratitis, herpetic stromal keratitis, and pterygium.

LFA-1 (CD11a) as a therapeutic target

Leukocyte function associated antigen-1 (LFA-1) was one of the earliest of cell-surface molecules identified by monoclonal antibodies generated against leukocyte immunogens. This integrin heterodimer is perhaps best known as a classic adhesion molecule facilitating the interaction between T cells and antigen-presenting cells. However, varied studies indicate that LFA-1 has multi-faceted roles in the immune response including adhesion, activation and trafficking of leukocyte populations. While there has been long-standing interest in LFA-1 as a therapeutic target for regulating immunity, anti-LFA-1 therapy is still not a first-line indication for any clinical condition. Antagonism of LFA-1 with monoclonal antibodies, either alone or in combination with other agents, can result in regulatory tolerance in vivo. Furthermore, new generation humanized anti-LFA-1 monoclonal antibodies (Efalizumab) show at least modest promise for continued application in clinical trials. Thus, anti-LFA-1 forms a potential, but still largely unexploited, immunotherapy which may find its greatest application as an agent which augments other therapies.

Adhesive functions of both chains of VLA-integrins are not fully conserved across the human-porcine species barrier: implications for xenotransplantation

BACKGROUND

A possible solution to the shortage of organs for transplantation would be the use of swine as source animals. As current immunosuppressive protocols cannot prevent rejection of these organs, super-selective immunosuppression or the induction of donor-specific central tolerance represent two promising approaches. Central tolerance induction involves bone marrow transplantation, and depends on intrathymic deletion of donor reactive host cells by donor antigen-presenting cells. In super-selective immunosuppression, the aim would be to block specific adhesive interactions on one species side only, leaving the other species side unaffected. As both processes depend on the interaction of adhesion molecules with their ligands, we investigated whether the beta1-integrins, which play roles in hematopoiesis as well as in rejection, can successfully interact across the swine-to-human species barrier.

METHODS

We employed static cell-to-extracellular protein and cell-to-cell adhesion assays, using different cell types and monoclonal antibody as well as peptide-fragments to analyze conservation of cross-species adhesive interactions.

RESULTS

We found that porcine and human cells interact differently with their cross-species ligands than their own and that the adhesive function of the beta1-chain does not seem to be fully conserved across the species barrier.

CONCLUSIONS

Integrin functions are not fully conserved across the pig-to-human species barrier. While the development of multi-transgenic pigs, whose integrins interact with human ligands in a more ''human-like'' manner may be necessary to facilitate tolerance induction, these facts give rise to new possibilities concerning super-selective immunosuppression.

The potential of antibody-based immunosuppressive agents for corneal transplantation

Corneal transplantation is a sight-restorative procedure but its success is limited by irreversible graft rejection, which accounts for up to 50 per cent of failures. The normal eye is an immune-privileged site. Multiple mechanisms maintain ocular privilege, including the blood-eye barrier, the lack of blood vessels and lymphatics in the normal cornea, the relative paucity of mature antigen-presenting cells in the central cornea, the presence of immunomodulatory factors in ocular fluids, and the constitutive expressive of CD95L (Fas ligand) within the eye. However, privilege can be eroded by the sequelae of inflammation and neovascularization. Corneal graft rejection in humans is currently suppressed with topical glucocorticosteroids, which are moderately effective. Systemically administered immunosuppressive therapy is of limited efficacy and may be accompanied by unacceptable morbidity. Alternative therapies are needed to improve outcomes. Corneal graft rejection is primarily a cell-mediated response controlled by the CD4+ T cell, and thus CD4 and costimulatory molecule blockade are appealing targets for new therapeutic interventions. A number of monoclonal antibodies have shown promise as immunosuppressants to prolong corneal graft survival in experimental animal models, and may eventually prove to be useful adjuncts to corticosteroids.

Intraocular dexamethasone delivery system for corneal transplantation in an animal model

PURPOSE

To assess the efficacy of a new intraocular biodegradable polymer dexamethasone drug delivery system (DEX DDS) in a high-risk corneal transplantation model.

METHODS

Lewis rats that received orthotopic corneal transplants (Balb/c mice donors) were divided into three groups (six rats in each); group 1 received no treatment and served as controls, group 2 was treated with 0.1% betamethasone eyedrops three times daily for 6 weeks, and group 3 received DEX DDS in the anterior chamber at the time of transplantation.

RESULTS

All grafts in the untreated control group were rejected within 8 days. In the betamethasone eyedrop group, five eyes (83%) were rejected during the 8-week study period. None of the grafts in the DEX DDS group was rejected. The administration of DEX DDS significantly prolonged the survival rate of the corneal grafts (p < 0.001, log-rank test).

CONCLUSION

DEX DDS is effective in suppressing graft rejection in high-risk corneal transplantation.

Inhibition of murine corneal allograft rejection by treatment with antibodies to CD80 and CD86

The purpose of this study was to investigate the role of CD80 and CD86 costimulatory molecules in corneal allograft rejection. Anti-CD80 and anti-CD86 monoclonal antibodies (mAbs) were administered after orthotopic corneal allograft transplantation. Graft rejection was observed by biomicroscopy. Population and localization of CD80(+)and CD86(+)cells in the cornea, cervical lymph nodes, and spleen were examined by flow cytometry and immunohistochemistry. The combined use of anti-CD80 and anti-CD86 mAbs was effective in prolonging corneal allograft survival. In the untreated mice bearing rejected graft, many CD86(+)and CD80(+)cells were found around the host-graft junctional area in the cornea, and CD86(high)cells were found in the cervical lymph node and spleen. In contrast, few CD86(+)or CD80(+)cells were observed in the cornea, cervical lymph node, and spleen from the mice treated with anti-CD80/CD86 mAbs. These results demonstrated a significant role of CD80 and CD86 costimulatory molecules in corneal allograft rejection.

Discordant effects of anti-VLA-4 treatment before and after onset of relapsing experimental autoimmune encephalomyelitis

Initial migration of encephalitogenic T cells to the central nervous system (CNS) in relapsing experimental autoimmune encephalomyelitis (R-EAE), an animal model of multiple sclerosis (MS), depends on the interaction of the alpha4 integrin (VLA-4) expressed on activated T cells with VCAM-1 expressed on activated cerebrovascular endothelial cells. Alternate homing mechanisms may be employed by infiltrating inflammatory cells after disease onset. We thus compared the ability of anti-VLA-4 to regulate proteolipid protein (PLP) 139-151-induced R-EAE when administered either before or after disease onset. Preclinical administration of anti-VLA-4 either to naive recipients of primed encephalitogenic T cells or to mice 1 week after peptide priming, i.e., before clinical disease onset, inhibited the onset and severity of clinical disease. In contrast, Ab treatment either at the peak of acute disease or during remission exacerbated disease relapses and increased the accumulation of CD4(+) T cells in the CNS. Most significantly, anti-VLA-4 treatment either before or during ongoing R-EAE enhanced Th1 responses to both the priming peptide and endogenous myelin epitopes released secondary to acute tissue damage. Collectively, these results suggest that treatment with anti-VLA-4 Ab has multiple effects on the immune system and may be problematic in treating established autoimmune diseases such as MS.

Preservation of donor cornea prevents corneal allograft rejection by inhibiting induction of alloimmunity

To determine whether preservation of the donor cornea prevents allograft rejection, orthotopic corneal transplantation was performed using corneas preserved in storage medium (Optisol-GS((R))). Donor corneas harvested from C3H/He (H-2(k)) mice and B10.D2 (H-2(d)) mice were preserved in storage medium for 0, 3, 7 and 14 days, and then transplanted into the corneal beds of the recipient BALB/c (H-2(d)) mice. Graft survival was determined clinically and histologically. The expression of major histocompatibility complex (MHC) molecules in the preserved corneas was analysed by immunohistochemistry and Western blotting. Donor-specific cytotoxic T lymphocyte (CTL) and delayed-type hypersensitivity (DTH) responses were assessed 3 weeks after grafting. Active suppression of DTH in the recipient mice was also examined 3 weeks after grafting. The survival of 14 day preserved allografts was significantly higher than that of the non-preserved allografts in both MHC and minor histocompatibility (H) antigens, and minor H only disparate combination. The recipients of the preserved allografts failed to induce both CTL and DTH. The active suppression of DTH was not acquired in these recipients. The expression of donor-derived MHC class I antigens was markedly reduced in the corneas after preservation. Preservation of the donor cornea had a remarkable effect on the prevention of corneal allograft rejection. Since the preserved allografts failed to induce donor-specific CTL and DTH, and active suppression of DTH was not acquired in the recipients, the prevention of allo-rejection is due to a failure of allo-sensitization. These results indicate that the reduction of MHC class I antigens and minor H antigens expression in the preserved grafts induces a failure of allo-sensitization and leads to the high rate of acceptance in corneal allografts.

Characterization of cytokine profiles in corneal allograft with anti-adhesion therapy

BACKGROUND

The cytokine profiles of specific immunosuppression after anti-adhesion molecule therapy are unknown in a mouse corneal transplantation model.

METHODS

Orthotopic mouse corneal transplantation was performed using BALB/c (H-2d) mice as recipients and C3H/He (H-2k) mice as donors. Anti-mouse very late antigen-4 and anti-mouse lymphocyte function-associated antigen-1 monoclonal antibodies (each at a dose of 0.25/mg/day) were administered i.p. until day 7. A second corneal transplantation was performed 5 weeks after the first grafting. Delayed hypersensitivity was tested after the second grafting. Corneal cytokine expression was examined immunohistochemically. The cytokine gene transcription level was assessed in the corneas and splenocytes.

RESULTS

All allografts with anti-adhesion molecule therapy survived for 5 weeks. Two weeks after the second grafts in the fellow eye (7 weeks after the first grafts), 50% of the mice with successful grafts bilaterally had low delayed hypersensitivity responses. Low helper T 1 (interferon-gamma and interleukin-2) cytokine gene and protein expression in corneas was observed in monoclonal antibody-treated mice 3 weeks after the first grafting. The mice with successful second grafts showed low corneal T helper 1 cytokine gene and protein expression. High interleukin-4 gene transcription levels in corneas and splenocytes was obtained in both groups in which the grafts were accepted and rejected after the second grafts.

CONCLUSIONS

The cytokine profile to differentiate alloantigen-specific acceptance with anti-adhesion therapy to lymphocyte function-associated antigen-1 and very late antigen-4 molecules from rejection after the second grafting is local and systemic low T helper 1 cytokine in corneal transplantation. High interleukin-4 cytokine expression in corneas and splenocytes is not associated with achievement of tolerance induction.

Recent advances in immunosuppressants

In recent years, a large number of structurally diverse immunosuppressants have been discovered that are effective for the treatment of organ transplantation. Some of them are undergoing clinical trials and may soon enter into routine clinical practice. These compounds are either chemical entities obtained from natural sources/synthetic means or biomaterials such as monoclonal antibodies/gene products/proteins. They have been found to interfere at different stages of T cell activation and proliferation, and can be identified as inhibitors of nucleotide synthesis, growth factor signal transduction and differentiation. Newer strategies involving combination of new agents with traditional immunosuppressants, monoclonal antibodies and gene therapy offer enormous potential, not only for the investigation of mechanisms pertaining to graft rejection, but also for its therapeutic prevention.

Suppression of allograft rejection with anti-alphabeta T cell receptor antibody in rat corneal transplantation

BACKGROUND

Anti-alphabeta T cell receptor monoclonal antibody (R73) has been reported to be a potent immunosuppressant. The suppressive effects of this antibody on allograft rejection after corneal transplantation are unknown.

METHODS

Orthotopic rat penetrating keratoplasty was performed using Lewis rats as recipients and Brown Norway and Fisher rats as donors. The treated groups received R73 intraperitoneally until day 12 after the transplantation. In grafted rats with or without R73 treatment, cytokine expression of the aqueous humor, corneal-infiltrating cells, draining lymph nodes, and splenocytes was determined. Delayed-type hypersensitivity (DTH) responses were compared.

RESULTS

All allografts in the untreated controls of Fisher-to-Lewis or BN-to-Lewis rat combinations were rejected within 14 days. In contrast, indefinite survival rates of the postoperative R73-treated group increased to 86% in the Fisher-to-Lewis and 23% in the Brown Norway-to-Lewis combinations, respectively. Interferon-y, interleukin (IL)-2 (T helper [Th]1), and IL-10 (Th2), but not IL-4 (Th2), expression of the eye and DTH responses in the control group were suppressed in the R73-treated group. Both IL-2 and IL-10 expression after mixed lymphocyte culture in the R73-treated group were significantly lower than those of the naive and untreated control group.

CONCLUSIONS

alphabeta T cell receptor-targeted therapy prevents allograft rejection in rat corneal transplantation as evidenced by suppression of DTH responses. The cytokine profile after R73 treatment was characterized by low interferon-gamma, IL-2, and IL-10, and high IL-4 expression.

Cytokine profiles of aqueous humor and graft in orthotopic mouse corneal transplantation

BACKGROUND

Cytokine profile is a key in understanding the mechanisms of allograft rejection. Cytokine expression in the aqueous humor and the correlation between the aqueous humor cells and corneal infiltrating cells are not fully understood in corneal transplantation.

METHODS

Orthotopic mouse corneal transplantation was performed using BALB/c (H2d) mice as recipients, and C3H/He (H2k) and BALB/c mice as donors for allografts and isografts, respectively. Immunocytochemistry was performed on aqueous humor cells. Corneal graft was studied immunohistochemically. Cytokine gene expressions of the cells infiltrating the aqueous humor and corneal grafts were determined by the semiquantitative reverse transcription and polymerase chain reaction method.

RESULTS

Interferon-gamma, interleukin (IL)-2, IL-4, and IL-10 were detected in the cells infiltrating the aqueous humor and corneal grafts at both the protein and gene expression levels. T helper 1 (Th1) cytokine expressions at the protein level, however, were consistently predominant in the rejected allografts compared to those of Th2 cytokines. The cytokine and surface marker profiles of the cells in the aqueous humor corresponded well to those of the cells infiltrating the corneal grafts. Cytokine protein and mRNA expression levels in the aqueous humor decreased rapidly.

CONCLUSIONS

Allorejection in corneal transplantation is Th1 cytokine-predominant. Infiltrating cells do not express Th2 cytokine so much in allograft rejection, as compared with Th1 cytokine. The cell infiltration patterns of the aqueous humor were well correlated with those of the cornea.