Effect of combinations of antiviral drugs on herpes simplex encephalitis.

2-Phenylamino-6-oxo-9-(4-hydroxybutyl)purine (HBPG) is a thymidine kinase inhibitor that prevents encephalitic death in mice caused by herpes simplex virus (HSV) types 1 and 2, although its potency is somewhat less than that of acyclovir (ACV). The present study was undertaken to determine the effect of combinations of HBPG and either ACV, phosphonoformate (PFA), or cidofovir (CDF) against HSV encephalitis. BALB/c mice were given ocular infections with HSV-1 or HSV-2, and treated twice daily intraperitoneally for five days with HBPG, alone or in combination with ACV, PFA, or CDF. Animals were observed daily for up to 30 days, and the day of death of each was recorded. All of the combinations showed additivity, and the combination of HBPG + ACV appeared to be synergistic, ie, protected more mice against HSV-1 encephalitis compared with each drug given alone. Delay of treatment with HBPG for up to two days was still effective in preventing HSV-2 encephalitis. The combination of the thymidine kinase inhibitor HBPG and the antiherpes drug ACV may have synergistic activity against HSV encephalitis. The development of a potent and safe combination therapy for the prevention and/or treatment of HSV infection of the central nervous system can improve the outcome of this infection in humans.

Efficacy of a helicase-primase inhibitor in animal models of ocular herpes simplex virus type 1 infection.

PURPOSE: The aim of this study was to evaluate the effect of BAY 57-1293, a helicase-primase inhibitor, on herpes simplex virus type 1 (HSV-1) reactivation in mice and its efficacy on established disease in rabbits. METHODS: BALB/c mice latent for McKrae-strain HSV-1 were reactivated via heat stress, treated with BAY 57-1293, and their corneas were swabbed for virus or the trigeminal ganglia (TG) obtained for quantification of viral DNA. New Zealand white rabbits were infected and treated topically or orally in comparison with trifluridine or valacyclovir. RESULTS: Oral BAY 57-1293 suppressed reactivation in HSV-1-infected mice and reduced the viral load in TG up to four orders of magnitude. In the rabbits, the therapeutic efficacies of topical BAY 57-1293 and trifluridine were similar. Once-daily oral BAY 57-1293 was significantly more effective than valacyclovir and as effective as twice a day topical trifluridine. CONCLUSIONS: BAY 57-1293 may be more effective than valacyclovir, without the cytotoxicity or potential healing retardation seen with trifluridine. Oral BAY 57-1293 may be a substitute for eye drops as an effective treatment for herpetic keratitis and might be useful in treating stromal keratitis and iritis, as well as preventing recurrences of ocular herpes.

Blockade of the 4-1BB (CD137)/4-1BBL and/or CD28/CD80/CD86 costimulatory pathways promotes corneal allograft survival in mice.

To explore the roles of 4-1BB (CD137) and CD28 in corneal transplantation, we examined the effect of 4-1BB/4-1BB ligand (4-1BBL) and/or CD28/CD80/CD86 blockade on corneal allograft survival in mice. Allogeneic corneal transplantation was performed between two strains of wild-type (WT) mice, BALB/c and C57BL/6 (B6), and between BALB/c and B6 WT donors and various gene knockout (KO) recipients. Some of the WT graft recipients were treated intraperitoneally with agonistic anti-4-1BB or blocking anti-4-1BBL monoclonal antibody (mAb) on days 0, 2, 4 and 6 after transplantation. Transplanted eyes were observed over a 13-week period. Allogeneic grafts in control WT B6 and BALB/c mice treated with rat immunoglobulin G showed median survival times (MST) of 12 and 14 days, respectively. Allogeneic grafts in B6 WT recipients treated with anti-4-1BB mAb showed accelerated rejection, with an MST of 8 days. In contrast, allogeneic grafts in BALB/c 4-1BB/CD28 KO and B6 CD80/CD86 KO recipients had significantly prolonged graft survival times (MST, 52.5 days and 36 days, respectively). Treatment of WT recipients with anti-4-1BB mAb resulted in enhanced cellular proliferation in the mixed lymphocyte reaction and increased the numbers of CD4(+) CD8(+) T cells, and macrophages in the grafts, which correlated with decreased graft survival time, whereas transplant recipients with costimulatory receptor deletion showed longer graft survival times. These results suggest that the absence of receptors for the 4-1BB/4-1BBL and/or CD28/CD80/CD86 costimulatory pathways promotes corneal allograft survival, whereas triggering 4-1BB with an agonistic mAb enhances the rejection of corneal allografts.

ICP0 antagonizes Stat 1-dependent repression of herpes simplex virus: implications for the regulation of viral latency.

BACKGROUND: The herpes simplex virus type 1 (HSV-1) ICP0 protein is an E3 ubiquitin ligase, which is encoded within the HSV-1 latency-associated locus. When ICP0 is not synthesized, the HSV-1 genome is acutely susceptible to cellular repression. Reciprocally, when ICP0 is synthesized, viral replication is efficiently initiated from virions or latent HSV-1 genomes. The current study was initiated to determine if ICP0's putative role as a viral interferon (IFN) antagonist may be relevant to the process by which ICP0 influences the balance between productive replication versus cellular repression of HSV-1. RESULTS: Wild-type (ICP0+) strains of HSV-1 produced lethal infections in scid or rag2-/- mice. The replication of ICP0- null viruses was rapidly repressed by the innate host response of scid or rag2-/- mice, and the infected animals remained healthy for months. In contrast, rag2-/- mice that lacked the IFN-alpha/beta receptor (rag2-/- ifnar-/-) or Stat 1 (rag2-/- stat1-/-) failed to repress ICP0- viral replication, resulting in uncontrolled viral spread and death. Thus, the replication of ICP0- viruses is potently repressed in vivo by an innate immune response that is dependent on the IFN-alpha/beta receptor and the downstream transcription factor, Stat 1. CONCLUSION: ICP0's function as a viral IFN antagonist is necessary in vivo to prevent an innate, Stat 1-dependent host response from rapidly repressing productive HSV-1 replication. This antagonistic relationship between ICP0 and the host IFN response may be relevant in regulating whether the HSV-1 genome is expressed, or silenced, in virus-infected cells in vivo. These results may also be clinically relevant. IFN-sensitive ICP0- viruses are avirulent, establish long-term latent infections, and induce an adaptive immune response that is highly protective against lethal challenge with HSV-1. Therefore, ICP0- viruses appear to possess the desired safety and efficacy profile of a live vaccine against herpetic disease.

Evidence that spontaneous reactivation of herpes virus does not occur in mice.

BACKGROUND: Some species, including humans and rabbits, exhibit periodic viral reactivation and shed infectious virus at the infected end organ. Mice may be an exception, because spontaneous shedding of infectious virus rarely, if ever, occurs. However, spontaneous molecular reactivation, i.e., the expression of a few viral genes and the synthesis of the viral glycoproteins coded for by these genes, has been reported. This finding has prompted the assumption that molecular reactivation is an indicator of reactivation and the production of infectious virus. The goal of this study was to differentiate between viral gene expression during latency and the episodic production of infectious virus in mice. RESULTS: Viral reactivation and infection were not seen in herpes simplex virus type 1 (HSV-1) latent ganglion graft recipient BALB/c scid or immunocompetent BALB/c mice, which survived the 65-day observation period with no evidence of viral infection although the immunocompetent mice developed cellular and humoral immunity to HSV-1. In contrast, BALB/c scid recipients of ganglia containing reactivating virus invariably developed a local and, subsequently, systemic viral infection and died within 14 days. Immunocompetent BALB/c mice that received ganglion grafts containing reactivating virus survived the infection and became immune to the virus. Trigeminal ganglia removed from scid and immunocompetent recipient graft sites 5, 14, and 28 days after transplantation contained latent virus and viable neurons. CONCLUSION: The results suggest that, within the limits of detection of the experiments, spontaneous episodic production of immunogenic viral antigens but not of infectious virus occurs in mouse neural ganglia during latency.

Re-evaluating the role of natural killer cells in innate resistance to herpes simplex virus type 1.

BACKGROUND: Interferon-gamma acts to multiply the potency with which innate interferons (alpha/beta) suppress herpes simplex virus type 1 (HSV-1) replication. Recent evidence suggests that this interaction is functionally relevant in host defense against HSV-1. However, it is not clear which WBCs of the innate immune system, if any, limit HSV-1 spread in an IFN-gamma dependent manner. The current study was initiated to determine if natural killer (NK) cells provide innate resistance to HSV-1 infection, and if so to determine if this resistance is IFN-gamma-dependent. RESULTS: Lymphocyte-deficient scid or rag2(-/-) mice were used to test four predictions of the central hypothesis, and thus determine if innate resistance to HSV-1 is dependent on 1. NK cell cytotoxicity, 2. NK cells, 3. WBCs, or 4. the IFN-activated transcription factor, Stat 1. Loss of NK cell cytotoxic function or depletion of NK cells had no effect on the progression of HSV-1 infection in scid mice. In contrast, viral spread and pathogenesis developed much more rapidly in scid mice depleted of WBCs. Likewise, loss of Stat 1 function profoundly impaired the innate resistance of rag2(-/-) mice to HSV-1. CONCLUSION: Lymphocyte-deficient mice possess a very tangible innate resistance to HSV-1 infection, but this resistance is not dependent upon NK cells.

Inhibition of herpes simplex virus thymidine kinases by 2-phenylamino-6-oxopurines and related compounds: structure-activity relationships and antiherpetic activity in vivo.

Derivatives of the herpes simplex thymidine kinase inhibitor HBPG [2-phenylamino-9-(4-hydroxybutyl)-6-oxopurine] have been synthesized and tested for inhibitory activity against recombinant enzymes (TK) from herpes simplex types 1 and 2 (HSV-1, HSV-2). The compounds inhibited phosphorylation of [3H]thymidine by both enzymes, but potencies differed quantitatively from those of HBPG and were generally greater for HSV-2 than HSV-1 TKs. Changes in inhibitory potency were generally consistent with the inhibitor/substrate binding site structure based on published X-ray structures of HSV-1 TK. In particular, several 9-(4-aminobutyl) analogues with bulky tertiary amino substituents were among the most potent inhibitors. Variable substrate assays showed that the most potent compound, 2-phenylamino-9-[4-(1-decahydroquinolyl)butyl]-6-oxopurine, was a competitive inhibitor, with Ki values of 0.03 and 0.005 microM against HSV-1 and HSV-2 TKs, respectively. The parent compound HBPG was uniquely active in viral infection models in mice, both against ocular HSV-2 reactivation and against HSV-1 and HSV-2 encephalitis. In assays lacking [3H]thymidine, HBPG was found to be an efficient substrate for the enzymes. The ability of the TKs to phosphorylate HBPG may relate to its antiherpetic activity in vivo.

Inhibition of cyclooxygenase 2 synthesis suppresses Herpes simplex virus type 1 reactivation.

Recurrent herpes virus infection, in which the virus reactivates from the nervous system and causes painful lesions in peripheral tissues, is a significant clinical problem. Our recent studies showing that the amount of cyclooxygenase 2 (COX-2) in the trigeminal ganglia of heat-stressed untreated mice is higher than the amount in heat-stressed mice treated with the COX-2 inhibitor, celecoxib, have indicated that the prostaglandin synthesis pathway--and in particular COX-2--may be an intermediate in the pathway to herpes viral reactivation. To further study this process, we infected the corneas of mice using topical application to a lightly scratched epithelium and waited 30 days for Herpes simplex virus type 1 (HSV-1) latency to be established in the trigeminal ganglia. Prior to the induction of viral reactivation, the mice were treated orally with celecoxib. Treated and untreated mice were induced to undergo reactivation by immersion in 43 degrees C water for 10 min. The shedding of virus at the ocular surface was determined by culturing ocular swabs with indicator cells. The presence of infectious virus in the trigeminal ganglion was evaluated by incubating ganglion homogenates with indicator cells and observing for cytopathic effect. Celecoxib treatment significantly suppressed viral reactivation when given prophylactically by the gastrointestinal route. The numbers of corneas and ganglia containing infectious virus were significantly lower in the celecoxib-treated animals, compared to the placebo-treated mice. These experiments demonstrate that a selective COX-2 inhibitor can suppress hyperthermic stress-induced herpes viral reactivation in the nervous system. It may be possible to use COX-2 inhibitors to prevent viral reactivation in high-risk patients by drug prophylaxis.

Corneal epithelial cell growth over tethered-protein/peptide surface-modified hydrogels.

In this study, we investigated the corneal epithelial cell growth rate and adhesion to novel hydrogels with (1) extracellular matrix proteins [fibronectin, laminin, substance P, and insulin-like growth factor-1 (IGF-1)] and (2) peptide sequences [RGD and fibronectin adhesion-promoting peptide (FAP)] tethered to their surface on poly(ethylene glycol) (PEG) chains. The growth rate to confluence of primary rabbit cornea epithelial cells was compared for plain polymethacrylic acid-co-hydroxyethyl methacrylate (PHEMA/MAA) hydrogels, PHEMA/MAA hydrogels coated with extracellular matrix proteins or peptides, and PHEMA/MAA hydrogels with tethered extracellular matrix proteins or peptides on the surface. The development of focal adhesions by the epithelial cells grown on the surfaces was determined by F-actin staining. Little to no epithelial cell growth occurred on the plain hydrogel surfaces throughout the 15-day culture period. Of the coated hydrogels, only the fibronectin-coated surfaces showed a significant increase in cell growth compared to plain hydrogels (p < 0.009). However, even these surfaces reached a maximum of only 20% confluence. Laminin, fibronectin adhesion-promoting peptide (FAP), and fibronectin/laminin (1:1) tether-modified hydrogels all achieved 100% confluence by the end of the culture period, although the rates at which confluence was reached differed. F-actin staining showed that focal adhesions were formed for the laminin, FAP, and fibronectin/laminin tether-modified surfaces. The results support the hypothesis that tethering certain extracellular matrix proteins and/or peptides to the hydrogel surface enhances epithelial cell growth and adhesion, compared with that seen for protein-coated or plain hydrogel surfaces.

Acetylsalicylic acid reduces viral shedding induced by thermal stress.

PURPOSE: To investigate the effect of acetylsalicylic acid on ocular shedding of herpes simplex virus type 1 (HSV-1). MATERIALS AND METHODS: Mice that were latent for the McKrae strain of HSV-1 were treated with acetylsalicylic acid, a nonspecific inhibitor of cyclooxygenases, either prophylactically or at the time of heat stress-induced viral reactivation. The effect of the drug on viral shedding in the tear film, infectious virus in the cornea and trigeminal ganglion, and viral DNA in the cornea and trigeminal ganglion was determined. RESULTS: Acetylsalicylic acid inhibited heat stress-induced shedding of virus in the tears and reduced the numbers of corneal and trigeminal ganglion homogenates containing virus. Intraperitoneal therapeutic and oral prophylactic plus therapeutic treatments were similar in their ability to inhibit reactivation. CONCLUSIONS: The results indicate that a cyclooxygenase inhibitor such as acetylsalicylic acid can reduce recurrent viral infection in mice. These findings may implicate prostaglandins as agents in the viral reactivation process and suggest that therapy to suppress viral reactivation using nontoxic inhibitors of prostaglandin synthesis may be effective in humans.

Effect of acyclovir on thermal stress-induced herpesvirus reactivation.

PURPOSE: Acyclovir has been shown to be effective in preventing recurrent herpes simplex virus lesions of the genitalia and oral labia. The purpose of the current study was to determine the effect of acyclovir on the appearance of infectious virus in the peripheral nervous system and in an end organ, the eye. MATERIALS AND METHODS: Mice latent for the McKrae strain of herpes simplex virus type 1 were given 3.5 mg/ml acyclovir in their drinking water. Control animals received water without drug. Acyclovir treatment was continued for 4 successive days. On the third day, the mice were subjected to a brief period of hyperthermic stress to induce viral reactivation. Twenty-four hours after stress induction, swabs of the ocular surface and homogenates of the cornea and trigeminal ganglia were analyzed for the presence of infectious herpes simplex virus type 1 and viral DNA. RESULTS: Acyclovir treatment significantly decreased the frequency of infectious virus in the ocular tear film and the cornea but not in the trigeminal ganglion. The corneal homogenates of acyclovir-treated animals contained smaller amounts of viral DNA compared with untreated controls, whereas the amounts of viral DNA in the trigeminal ganglia of acyclovir-treated and untreated animals were similar. CONCLUSIONS: These results suggest that oral administration of acyclovir, at least at the dose used in this study, is effective in modestly reducing viral replication in peripheral tissues such as the eye but is not effective in inhibiting viral reactivation and viral DNA synthesis in the peripheral nervous system in mice subjected to induction of reactivation by hyperthermic stress.

Herpesvirus infection of ICAM-1-deficient mice.

PURPOSE: To determine the effect of ICAM-1 deficiency on viral infection of the cornea. MATERIALS AND METHODS: Wild-type and intercellular adhesion molecule 1 (ICAM-1)-deficient mice were infected with the RE strain of herpes simplex virus type 1 (HSV-1). Corneal swabs and trigeminal ganglia were obtained and analyzed for infectious virus. Corneas and trigeminal ganglia were evaluated for signs of inflammation by immunohistochemical staining and for interferon-gamma (IFN-gamma)-producing cells by enzyme-linked immunospot assay (ELISPOT). Serum anti-HSV-1 antibody titers were determined by enzyme-linked immunosorbent assay (ELISA). RESULTS: Viral titers in corneal swabs from the wild-type and ICAM-1-deficient mice were not significantly different during the 21-day study. Infectious virus was present in the trigeminal ganglia of wild-type and ICAM-1-deficient mice through day 6 after infection. Serum anti-HSV-1 antibody titers were significantly higher in wild-type mice 6 days after infection, compared with ICAM-1-deficient mice; by day 8 and thereafter, however, antibody titers were not significantly different. Production of interferon gamma was greater in trigeminal ganglion cells from wild-type mice stimulated with interleukin 12 and interleukin 18 on days 4, 6, and 8 after infection compared with cells from ICAM-1-deficient mice. Histopathologic analysis of corneal and ganglion sections from wild-type and ICAM-1-deficient mice showed no significant differences in the time-course of appearance or the intensity of the inflammatory infiltrate. Immunohistochemical staining for CD3(+) T-lymphocytes and CD11b(+) neutrophils and macrophages demonstrated equivalent numbers of these cells in the corneas and trigeminal ganglia of wild-type and ICAM-1-deficient mice. CONCLUSIONS: The results of these experiments indicate that ICAM-1 deficiency has only a modest effect on viral infection of the cornea and the development of an acquired immune response.

CD137-deficient mice have reduced NK/NKT cell numbers and function, are resistant to lipopolysaccharide-induced shock syndromes, and have lower IL-4 responses.

CD137, a member of the TNF superfamily, is involved in T cell and NK cell activation and cytokine production. To establish its in vivo role in systems dependent on NK and NKT cells, we studied the response of CD137-/- mice to LPS-induced shock, tumor killing, and their IL-4-controlled Th2 responses. In both high and low dose shock models, all the CD137-deficient mice, but none of the wild-type BALB/c mice, survived. After injection of LPS/2-amino-2-deoxy-D-galactose (D-gal), CD137-/- mice had reduced serum cytokine levels and substantially impaired liver IFN-gamma and TNF-alpha mRNA levels. Phenotypic analysis of mononuclear cells revealed fewer NK and NKT cells in the CD137-/- mice. The knockout mice did not generate a rapid IL-4 response after systemic T cell activation, or effective Ag-specific Th2 responses. In addition, both in vitro and in vivo NK-specific cytolytic activities were reduced. These findings suggest that CD137-directed NK/NKT cells play an important role in the inflammatory response leading to the production of proinflammatory cytokines, LPS-induced septic shock, and tumor killing, as well as IL-4-dependent Th2 responses.

Re-evaluating natural resistance to herpes simplex virus type 1.

It is often stated that individuals of a species can differ significantly in their innate resistance to infection with herpes simplex virus type 1 (HSV-1). Three decades ago Lopez reported that C57BL/6 mice could survive a 5,000-fold-higher inoculum of HSV-1 given intraperitoneally than mice of the A or BALB/c strain (Nature 258:152-153, 1975). Susceptible strains of mice died of encephalitis-like symptoms, suggesting that viral spread to the central nervous system was the cause of death. Although Lopez's study documented that C57BL/6 mice were resistant to the development of HSV-1 encephalitis and mortality, the resistance of C57BL/6 mice to other steps of the HSV-1 infection process was not assessed. The results of the present study extend these observations to clarify the difference between resistance to (i) HSV-1 pathogenesis, (ii) HSV-1 replication, (iii) HSV-1 spread, and (iv) the establishment of latent HSV-1 infection. Although C57BL/6 mice are more resistant to HSV-1 pathogenesis than BALB/c mice, the results of the present study establish that HSV-1 enters, replicates, spreads, and establishes latent infections with virtually identical efficiencies in C57BL/6 and BALB/c mice. These observations raise questions about the validity of the inference that differences in natural resistance are relevant in explaining what differentiates humans with recurrent herpetic disease from the vast majority of asymptomatic carriers of HSV-1 and HSV-2.

Distribution of thrombospondin-4 in the bovine eye.

PURPOSE: The purpose of this study was to analyze the distribution of thrombospondin-4 (TSP-4) in the bovine eye. METHODS: Anterior and posterior segments of the bovine eyes were sectioned and stained by the indirect immunofluorescence method with an anti-TSP-4 antibody. The tissues were analyzed by reverse-transcription-polymerase chain reaction (RT-PCR) to determine where the TSP-4 mRNA is produced. RESULTS: Immunohistochemical staining for TSP-4 indicated the presence of TSP-4 in the cornea (epithelium, basement membrane, and keratocytes), conjunctiva (epithelium and stroma), aqueous ducts, sclera, iris (stroma), ciliary processes and muscle, trabecular meshwork, Bruch's membrane, retina, lamina cribrosa, and optic nerve, and in all blood vessel walls. TSP-4 mRNA was expressed by the cells in all structures. CONCLUSIONS: TSP-4 is widely distributed in the bovine eye where it may play a role in the functions of basement membranes in various tissues. It is abundant in the trabecular and uveo-scleral pathways and may play a role in the regulation of aqueous outflow resistance.

Effect of immunosuppression on gene expression in the HSV-1 latently infected mouse trigeminal ganglion.

PURPOSE: To determine alterations in expression of genes in herpes simples virus (HSV)-1 latently infected mouse trigeminal ganglia (TGs), after treatment with cyclophosphamide and dexamethasone. METHODS: Scarified corneas of female BALB/c mice were inoculated with HSV-1 strain McKrae. Four weeks after inoculation, cyclophosphamide and dexamethasone were intravenously injected to induce HSV-1 reactivation. Uninfected mice were also treated with the immunosuppressants. Four groups of animals were studied: uninfected, not treated; uninfected, drug treated; latently infected, not treated; and latently infected, drug treated. PolyA+ mRNA from the TGs of each group was reverse transcribed, labeled with 32P, incubated on a 1185-gene array membrane, and analyzed by phosphorimaging. As a comparison and to confirm microarray results, semiquantitative RT-PCR was also performed for selected genes. RESULTS: The immunosuppressive drugs significantly increased expression of two genes (calpactin 1 light chain and guanine nucleotide-binding protein alpha-stimulating polypeptide [GNAS]) in the ganglia of uninfected mice compared with those in untreated uninfected mice. Ten genes were shown to be significantly increased in the latent TGs of mice treated with immunosuppressants compared with latently infected untreated mice. These genes were prostaglandin E2 receptor EP4 subtype (PTGER4), insulin promoter factor 1 (IPF1), glutathione S-transferase mu2, cyclin D2, peripherin, plasma glutathione peroxidase, methyl CpG-binding protein 2, retinal S-antigen, ErbB2 proto-oncogene, and GNAS. Eight genes were shown to be significantly decreased in the HSV-1 latent TGs treated with the drugs, compared with untreated latently infected mice. These genes were peripheral myelin protein 22, decorin, transcription factor AP-1, dystroglycan 1, myelin protein zero, mitogen-activated protein kinase 3, prothymosin beta 4, and brain lipid-binding protein. The results obtained by semiquantitative RT-PCR were similar to those obtained by microarray analysis. CONCLUSIONS: Those genes with expression altered by immunosuppressive drug treatment may play an important role in ocular HSV-1 recurrence. Changes in expression of genes in the prostaglandin pathway, a transcription factor, and an enzyme in the cell cycle are considered especially important in HSV-1 reactivation by immunosuppression and are reviewed.

Experimental corneal allograft rejection.

The major findings regarding corneal allograft rejection in experimental animals are reviewed. The principal anatomic and biological feature of the cornea that determines the immunologic privilege of this tissue is its avascularity. The surgical trauma of transplantation compromises the immunologic privilege, putting corneal allografts at risk for immune rejection. During the past 50 yr, rabbits, rats, and mice have been used extensively in the study of the process of immunologically mediated corneal allograft rejection. It is clear that the inflammation and neovascularization of the graft that occurs following transplantation predisposes a corneal allograft to the classic cell-mediated immune rejection response. The antigenicity of cornea cells has been studied and has been found to be significantly lower compared to other cells and tissues. Rejection of acorneal allograft is acell-mediated process directed against major histocompatibility complex antigens involving both CD4+ T helper cells and CD8+ cytotoxic cells. The prevention of corneal allograft rejection depends on the development of topically applied compounds that can prevent inflammation and vascularization and inhibit the activation of T lymphocytes. Considerable progress has been made using immunomodulators, including blocking antibodies and soluble coreceptor blocking agents such as CTLA4-Ig. Combinations of antiangiogenic agents and immunomodulators hold great promise for preventing corneal allograft rejection in patients.