The effect of ABO blood incompatibility on corneal transplant failure in conditions with low-risk of graft rejection.

PURPOSE: To determine whether corneal graft survival over a 5-year follow-up period was affected by ABO blood type compatibility in participants in the Cornea Donor Study undergoing corneal transplantation principally for Fuchs dystrophy or pseudophakic corneal edema, conditions at low-risk for graft rejection. DESIGN: Multi-center prospective, double-masked, clinical trial. METHODS: ABO blood group compatibility was determined for 1,002 donors and recipients. During a 5-year follow-up period, episodes of graft rejection were documented, and graft failures were classified as to whether or not they were attributable to immunologic rejection. Endothelial cell density was determined by a central reading center for a subset of subjects. RESULTS: ABO donor-recipient incompatibility was not associated with graft failure attributable to any cause including graft failure because of rejection, or with the occurrence of a rejection episode. The 5-year cumulative incidence of graft failure attributable to rejection was 32 (6%) for recipients with ABO recipient-donor compatibility and 12 (4%) for those with ABO incompatibility (hazard ratio, 0.65; 95% confidence interval, 0.33 to 1.25; P = .20). The 5-year incidence for a definite rejection episode, irrespective of whether graft failure ultimately occurred, was 64 (12%) for ABO compatible compared with 25 (8%) for ABO incompatible cases (P = .09). Among clear grafts at 5 years, percent loss of endothelial cells was similar in ABO compatible and incompatible cases. CONCLUSIONS: In patients undergoing penetrating keratoplasty for Fuchs dystrophy or pseudophakic corneal edema, ABO matching is not indicated since ABO incompatibility does not increase the risk of transplant failure attributable to graft rejection.

Outcomes of penetrating keratoplasty in mentally retarded patients with keratoconus.

PURPOSE: Mentally retarded patients with keratoconus who underwent penetrating keratoplasty (PK) were reviewed to determine long-term graft survival outcome. METHODS: This longitudinal retrospective study included 20 mentally retarded patients who underwent PK at the University Hospital of Alicante during the years 1978-2007. Variables included donor corneal study, type and level of mental retardation, demographic data, age at which PK was performed, preoperative ocular and corneal study, surgical technique, histopathologic study, complications, immunological graft rejection, mean suture permanency, corneal endothelium study, and final anatomic and visual outcome. RESULTS: Thirty-nine penetrating keratoplasties were performed on 28 eyes of 20 patients. Mean age at time of surgery was 29.6 years (range 17-54 years). Follow-up ranged from 8 to 324 months, with a mean of 83.93 months. Vernal keratoconjunctivitis, cataract, and posterior capsular opacification were the most frequent complications during follow-up. Fifteen episodes of immunological graft rejection were registered. At the final examination, 23 grafts remain clear and 5 cloudy. Causes of corneal opacification were self-trauma, corneal ulceration, and immunological graft rejection. Four eyes developed ptisis bulbi. CONCLUSIONS: PK is a safe procedure in mild and moderately mentally retarded patients without compulsive ocular patterns. In patients with associated eye rubbing or ocular self-trauma, the election has to be made individually and carefully assuming an additional risk of serious complications. Providing medical education to caregivers is essential for the correct management of these patients.

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.

The new malononitrilamide immunosuppressant FK778 prolongs corneal allograft survival in the rat keratoplasty model.

PURPOSE: Aim of this study was to prove the efficacy and safety of the new malononitrilamide immunosuppressive FK778 in prolonging clear graft survival following allogeneic orthotopic keratoplasty in rats. METHODS: Sixty-seven penetrating keratoplasties were performed using Fisher and Lewis rats as donors and recipients, respectively: group 1 (n=11), allogeneic control without therapy; group 2 (n=12), syngeneic control; group 3 (n=11), mycophenolate mofetil (MMF) 40 mg/kg bodyweight; group 4 (n=12), FK778 5 mg/kg bodyweight; group 5 (n=12), FK778 10 mg/kg bodyweight; and group 6 (n=9), FK778 20 mg/kg bodyweight. Four animals in each group were killed for immunohistological evaluation on day 14. Therapy was administered orally for 18 days. The grafts were evaluated every three days by means of a scoring system including opacity, oedema, and vascularization. Time to rejection was analysed with the Kaplan-Meier survival analysis and compared with the log-rank test. The densities of infiltrating immune cells were compared statistically using the non-parametric Mann-Whitney test. RESULTS: Mean rejection-free graft survival was 11.4 days in group 1 (allogeneic control), 100 days (total follow-up time) in group 2 (syngeneic control), 24.0 days in group 3 (MMF 40 mg/kg), 15.7 days in group 4 (FK778 5 mg/kg), 19.1 days in group 5 (FK778 10 mg/kg), and 25.4 days in group 6 (FK778 20 mg/kg) (P<0.005). CONCLUSIONS: Systemic immunosuppression with FK778 prolongs graft survival in the rat keratoplasty model. FK778's efficacy is comparable with that of MMF in preventing immunologic graft rejection.

[Matching minor transplantation antigens in penetrating keratoplasty]. / Matching von Minor-Transplantationsantigenen in der perforierenden Keratoplastik.

Specific recognition of foreign tissue is a common feature in higher vertebrates. This capability has commonly been ascribed to the human leukocyte antigen (HLA) complex. Recent developments, however, point to an outstanding role of minor H antigens, especially in the context of corneal transplantation. It is likely that the matching of selected minor H antigens will further improve rejection free, clear graft survival following penetrating keratoplasty in the not so distant future.

[Sustained rapamycin drug delivery system in prevention of high risk corneal allograft rejection and neovascularization in rabbits].

OBJECTIVE: To evaluate the immunosuppressive and antiangiogenesis effects of rapamycin drug delivery system (RAPA DDS) in high risk rabbit model of penetrating keratoplasty (PK). METHODS: (1) RAPA DDS preparation: 50 mg of PGLC and 50 mg of RAPA were mixed as a RAPA drug delivery system. (2) High risk rabbit model: Corneal vascularization was induced in 45 New Zealand white rabbits (45 eyes) by passing 5 - 0 silk sutures in corneal stroma in each quadrant. (3) 40 rabbits with corneal neovascularization beyond three quadrants were received a unilateral 7 mm diameter central PK. The 40 were divided into four treatment groups: Group A, control group and received no therapy; Group B, 1 mg PGLC carrier was implanted in the anterior chamber; Group C, 1% RAPA eye drops was applied four times daily; Group D, 0.5 mg RAPA DDS was implanted in the anterior chamber. (4) Postoperative examination: The cornea allografts (opacity, edema and neovascularization) were examined by the slit-lamp biomicroscopy for ninety days. Rejection index (RI) and neovascularization index (NI) of these animal models were recorded. RAPA concentration in the aqueous humor was detected on 2, 4, 8 and 12 weeks in group C and D after surgery; the expressions of IL-2R, MCP-1, Fas/FasL in samples were detected with in situ hybridization; TNF-alpha and VEGF were detected with immuno-histochemical technique three weeks after the operation in all groups. Histochemical method was carried out on the procured specimens of cornea, retina, liver and kidney at ninety days. RESULTS: (1) Allografts rejection: Mean survival times in 4 trial groups were (16.5 +/- 2.5), (16.0 +/- 2.6), (47.1 +/- 13.2), (87.6 +/- 5.8) d respectively (P = 0.000). (2) Corneal neovascularization: Mean NI was 2.4 +/- 0.7, 2.1 +/- 0.5, 0.6 +/- 0.5, 0.3 +/- 0.5 (P = 0.000) 2 weeks after the operation, and the NI value was 3.8 +/- 0.5, 3.8 +/- 0.4, 0.8 +/- 0.7, 0.4 +/- 0.8 (P = 0.000) 12 weeks after the operation in groups A, B, C and D respectively. (3) RAPA concentration in aqueous humor: Mean RAPA concentration in aqueous humor was 10.7, 12.0, 9.2, 7.0 ng/ml in group D in the 2, 4, 8 and 12 weeks after the operation respectively. RAPA can not be detected in group C. (4) Cytokine expression: IL-2R, MCP-1, TNF-alpha and VEGF were overexpression in group A and B, and undetectable in group C and D. Fas and FasL were negative in all groups. (5) No inflammatory cell infiltration was found in retina, liver and kidney tissue ninety days after the surgery. CONCLUSIONS: Sustained RAPA DDS and eyedrops can prolong allograft survival and inhibit cornea neovascularization in rabbit model. However, RAPA DDS is better than eyedrops.

Thiol redox and immune regulation in corneal transplantation.

Penetrating keratoplasty (PKP) is the most common type of clinical grafting performed in humans. Although PKP has emerged as the most successful form of transplantation, PKP in "high-risk" eyes shows high incidence of allograft rejection. The incidence of epithelial rejection after limbal transplantation (LT) is extremely higher and swifter than PKP rejection, and even intensive systemic immunosuppressive therapy is often of no avail. Because failure of corneal grafts is an important cause of blindness, developing new strategies for suppressing graft rejection is a worthy goal for research. Corneal allograft rejection is mainly mediated by the TH1-type immune response, which leads to a delayed-type hypersensitivity reaction. Because the TH2-type immune response regulates the TH1-type immune response, we have successfully elicited allograft survival after both PKP and LT by inducing systemic TH2-type immune responses. Because intracellular thiol redox status of antigen-presenting cells (APC) reportedly regulates TH1/TH2 balance via distinctive cytokine production by APC, we also investigated the effect of modulating macrophage intracellular thiol redox status on corneal allograft survival. These strategies are quite effective in major histocompatibility complex (MHC) matching in mice, although it is believed that MHC matching has no effect on corneal allograft survival according to many rodent studies. Recently, many laboratories are reconsidering HLA matching for allograft survival in human corneal transplantation. It may be possible that MHC matching improves corneal allograft survival in the context of TH1 suppression. We propose that the suppression of the TH1-type immune response and MHC matching together may promote allograft survival in humans.

[The corneal allograft rejection features in CD4 and CD8 knock-out mice].

OBJECTIVE: To study the mechanism and the features of corneal allograft rejection using a model of CD4 and CD8 knock-out mice. METHODS: The mice were divided into three groups with 20 mice in each group. CD4 knock-out mice, CD8 knock-out mice and C57BL/6 mice were used as recipients and BALB/c mice as corneal graft donors. Postoperative evaluation included slit-lamp biomicroscopy and immunohistological studies. The rejection times were recorded and the cytokines in the eye after the surgery were measured at 1 week, 2 weeks and 4 weeks after the transplantation. Thirty mice (each group ten mice) received skin transplantation using BALB/c as donors in the second week after penetrating keratoplasty. The time of skin grafts rejection was recorded and the cornea grafts were inspected when the skin grafts were rejected. RESULTS: The rejection time varied in these three groups. The corneal grafts in CD4 knock-out mice were clear and no rejection occurred > 90 days. The corneal grafts in CD8 knock out mice were rejected at (28 +/- 3) days. The grafts in the control groups were rejected at (14 +/- 2) days (F = 2034, P < 0.01). The skin grafts rejection were recorded at (14 +/- 2), (12 +/- 1), (10 +/- 1) days in CD4 knock-out mice, CD8 knock-out mice and control groups, respectively (F = 42.54, P < 0.01). CONCLUSIONS: CD4 and CD8 knock-out mice are useful models for studying of corneal graft rejection. The cornea allograft rejection after penetrating keratoplasty is mediated primarily by CD(4)(+) T lymphocytes. The CD(8)(+) T lymphocytes also participate in the rejection processes.

Systemic mycophenolate mofetil avoids immune reactions in penetrating high-risk keratoplasty: preliminary results of an ongoing prospectively randomized multicentre study.

Recently, in a monocentre study mycophenolate mofetil (MMF) was demonstrated to be efficacious and safe in penetrating high-risk keratoplasty. Here, preliminary results of a randomized multicentre trial are presented. To date, 86 of 140 scheduled patients undergoing high-risk penetrating keratoplasty have already been randomized into the two study groups: 48 into the MMF group and 38 into the control group. All 86 patients received fluocortolon 1 mg/kg body weight/day, tapered within 3 weeks, and topical prednisolone acetate 1% tapered within 5 months. MMF was administered at a daily oral dose of 2 x 1000 mg for the first 6 postoperative months. Thereafter, MMF was tapered within 2 weeks. The proportion of grafts with immune reactions and side-effects were the main outcome measures. Within an average follow up of 9.2 +/- 6.6 months two patients developed reversible endothelial immune reactions in the MMF group after cessation of MMF application. In the control group, five reversible and three irreversible immune reactions were observed within an average follow up of 10.1 +/- 7.6 months. According to Kaplan and Meier analysis, the ratio of grafts without immune reactions was estimated 89% 1 year postoperatively in the MMF group, in contrast to only 67% in the control group (P = 0.03; log-rank test). Fifteen patients experienced side-effects, especially gastroenterotoxicity, tachycardia, arthralgia or systemic infections. All attributable side-effects were reversible. Systemic MMF may be an effective and safe immune modulating drug in the prophylaxis of immune reactions after penetrating high-risk keratoplasty.

[Clinical study on the endothelial immune rejection after penetrating keratoplasty].

OBJECTIVE: To study the relationship between the grafts transparency and the endothelial immune rejection at different periods after penetrating keratoplasty (PKP). METHODS: A following-up was performed on patients received PKP in Shandong Eye Institute and Hospital between January 1994 and December 1998. A total of 648 cases (648 eyes) were involved in this study, including 444 males (444 eyes) and 204 females (204 eyes). The incidence of endothelial immune rejection and grafts opacification at the time point of 0.5, 1, 3, 6, 9, 12, 18, 24, 36 and 48 months postoperatively was collected. We made two curves to study the relationship between transparence of grafts and endothelial rejection. Relationship between the endothelial immune rejection and the types of corneal diseases before the operation was also analyzed. RESULTS: There was a significant relationship between grafts opacification and the endothelial immune rejection (linear regression and simple correlation, P < 0.01). The rate of rejection decreased after 3 years postoperatively. Inflammatory background was an important factor for the occurrence of endothelial immune rejection and graft opacification. CONCLUSIONS: After PKP, endothelial immune rejection is the critical factor for affecting the grafts transparency. Long-term follow-up of the patients is important for the maintaining of transparency of grafts and to obtain a successful result of the operation.

Topical FK506 as immunoprophylaxis after allogeneic penetrating normal-risk keratoplasty: a randomized clinical pilot study.

The purpose of this study was to evaluate for the first time the efficacy and safety of topical FK506 in patients undergoing penetrating normal-risk keratoplasty in a prospectively randomized clinical trial. Twenty patients were treated with FK506 0.06% three times per day for 6 months postoperatively. An additional 20 patients received five drops of prednisolone acetate 1% tapered within 6 months. All patients received 1 mg/kg bodyweight/day of systemic fluocortolon tapered within 3 weeks postoperatively. Clear graft survival, ratio of immune reactions and side effects were the main outcome measures. One year postoperatively all patients of the FK 506 group were free from immune reactions, in contrast to 84% in the steroid group (Kaplan-Meier values; P = 0.9 in the log rank test). None of the patients developed irreversible graft failure so far. In eight patients of the FK506 group premature withdrawal of the drug was deemed appropriate because of local side effects. FK506 might turn out to become an effective immunoprophylaxis in subjects undergoing penetrating normal-risk keratoplasty. Local discomfort should be further reduced.

[Effects of 1alpha, 25-dihydroxyvitamin D3 on the acute immune rejection and corneal neovascularization in high-risk penetrating keratoplasty in rats].

OBJECTIVE: To investigate the effects of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), a hormone that has immunosuppressive properties, on acute rejection and corneal neovascularization in rat keratoplasty model, so as to assess the therapeutic effects and explore the mechanism of 1,25(OH)(2)D(3) as an immunosuppressant in corneal transplantation. METHODS: High risk corneal transplantation was performed orthotopically in SD rat models of high risk penetrating keratoplasty established by placing three 10-0 nylon sutures in the central corneas for two weeks, with the Wistar rats as the donors. The SD rat models were randomly assigned into 5 groups and treated with 1,25(OH)(2)D(3) at varied concentrations and cyclosporine A (CsA). The expressions of interleukin (IL)-1alpha, tumor necrosis factor (TNF)-alpha, and vascular endothelial growth factor (VEGF) mRNA were detected by in situ hybridization (ISH). RESULTS: 1,25(OH)(2)D(3) significantly suppressed acute graft rejection and inhibited corneal neovascularization as compared with saline. 1,25(OH)(2)D(3) showed better immunomodulatory effects when administered along with CsA in rat corneal allotransplants. ISH study demonstrated that 1,25(OH)(2)D(3) strongly suppressed mRNA and protein expressions of the cytokines IL-1alpha and TNF-but not those of VEGF. CONCLUSION: Topical administration of 1,25(OH)(2)D(3) can be effective in suppressing acute corneal graft rejection by inhibiting the expression of proinflammatory cytokines (IL-1alpha and TNF-alpha).

Role of tumor necrosis factor receptor expression in anterior chamber-associated immune deviation (ACAID) and corneal allograft survival.

PURPOSE: To determine the role of tumor necrosis factor receptors (TNFRs) in corneal allograft rejection. METHODS: Corneal epithelial and endothelial cells were examined by flow cytometry for the expression of TNFRI and TNFRII and their susceptibility to TNF-alpha-induced apoptosis. Corneal allografts from normal and TNFRI and TNFRII knockout (KO) C57BL/6 mice were transplanted to BALB/c hosts, and the fate of the allografts was monitored. C57BL/6 spleen cells were injected into the anterior chamber (AC) of BALB/c mice to induce anterior chamber-associated immune deviation (ACAID) and promote corneal allograft survival. The presence of ACAID suppressor cells in corneal allograft recipients was tested using a local adoptive transfer (LAT) assay. RESULTS: Murine corneal epithelial and endothelial cells expressed TNFRI and TNFRII and were susceptible to TNF-alpha-induced apoptosis, yet corneal allografts from either TNFRI or TNFRII donors did not enjoy a lower incidence of rejection or a prolongation in survival time compared to corneal allografts from normal C57BL/6 donors. Moreover, all 31 of the TNFRII KO corneal grafts were rejected by naïve BALB/c hosts. Rejection of TNFRII KO corneal grafts occurred even though suppressor cells developed in the hosts and inhibited the expression of delayed-type hypersensitivity to donor alloantigens. CONCLUSIONS: Expression of TNFRII on corneal cells conveys a degree of protection against immune rejection of corneal allografts by a mechanism that is independent of ACAID. Moreover, induction of ACAID before the application of TNFRII KO corneal allografts fails to improve survival and does not replace the TNFRII-dependent protective mechanism.

[Immunohistochemical study of in situ CD86 expression in rejected rat corneal graft after penetrating keratoplasty].

OBJECTIVE: To investigate the expression of CD86 co-stimulatory molecules in rejected rat corneal graft in situ after penetrating keratoplasty. METHODS: Rat models of orthotopical corneal transplantation were established, and after the occurrence of graft rejection, immunohistochemical staining was performed on the corneal whole-mounts and the spleen tissue of the recipient rats. RESULTS: CD86(+) cells were detected in the epithelium of the corneal graft during allograft rejection but not in normal cornea. CONCLUSION: In situ expression of costimulatory molecules in the corneal allograft may be related to the acute immune rejection after penetrating keratoplasty.

[Subconjunctival interleukin-1 receptor antagonist inhibits graft rejection following high-risk penetrating keratoplasty in rats].

OBJECTIVE: To observe the roles of subconjunctival administration of interleukin-1 receptor antagonist (IL-1ra) promoting corneal graft survival in rat models of high-risk penetrating keratoplasty. METHODS: Corneal vascularization was induced in 40 Sprague-Dawley rats (40 eyes) by passing 10-0 silk suture through the corneal stroma, and 30 of these rats received corneal grafts from Wistar rats to establish high-risk keratoplasty models and were divided into 3 groups to receive their respective treatment with IL-1ra eye drops (50 microg/ml), 1% CsA eye drops, administered 3 times a day, or no treatment. All the rats were treated by Tobra Dex eye drops and Tropicamid eye drops, 3 times a day for 14 consecutive days after the operation. During the 30-day observation, the survival of the grafts was recorded, and all the grafts were evaluated for signs of rejection. RESULTS: The mean survival times (MST) of the grafts of the treatment groups with IL-1ra and CsA were 12.00+/-1.50 d and 10.44+/-1.13 d respectively, significantly longer than that in the untreated model group (8.00+/-1.25 d, t=0.00, P<0.01), and the difference in the MST between the 2 treatment groups was also significant (t=0.00, P<0.01). CONCLUSION: Treatment with IL-1ra may significantly prolong high-risk corneal allograft survival.

Endotoxin in storage medium of human corneal grafts and clinical course after penetrating normal-risk keratoplasty.

PURPOSE: It is well known that endotoxins in storage medium may stimulate cytokine production and expression of adhesion molecules as well as endothelial damage in human corneal grafts. It has been supposed that endotoxin exposure of corneal grafts may, therefore, cause immune reactions and lead to reduced endothelial cell count after penetrating keratoplasty. It was the purpose of this prospective study to evaluate if this hypothesis is true. METHODS: A consecutive series of 274 samples of sterile organ culture storage medium from 274 human corneal grafts was collected between August 1998 and February 1999 and tested for endotoxin using Limulus amebocyte-lysate assay (LAL) after 7 days of organ culture. Threshold endotoxin level was set at 1.0 U/ml. A total of 161 grafts were transplanted and 113 were discarded. Within the 161 corneas transplanted, 62 were grafted to normal-risk patients and 99 to high-risk patients. Only normal-risk keratoplasty patients were included in the study and followed for at least 10 months. Immune reactions, graft failures, and postoperative endothelial cell counts were recorded. RESULTS: The mean endotoxin level in organ culture medium of all transplanted grafts was 1.07+/-2.96. Mean endotoxin level in organ culture medium of discarded grafts was 1.68+/-5.76, with 71 samples being below and 42 above the threshold of 1.0 U/ml called endotoxin-negative and endotoxin-positive, respectively. In all 36 culture medium samples from the 62 grafts transplanted to the group of normal-risk keratoplasty patients were endotoxin-negative and 26 endotoxin-positive. An influence of endotoxin levels on incidence of immune reactions, graft failure, and postoperative endothelial cell counts could not be revealed in patients with normal-risk keratoplasty. CONCLUSION: Low endotoxin levels in storage medium neither seem to promote immune reactions nor to contribute to postoperative chronic endothelial cell loss in normal-risk keratoplasty patients.

HLA class I/II matching and chronic endothelial cell loss in penetrating normal risk keratoplasty.

OBJECTIVE: Chronic endothelial cell loss of the graft is very common after penetrating keratoplasty. The aetiology of this is unknown. Clinically, non-identifiable immune reactions have been suspected. Recently, we were able to demonstrate that proper human leucocyte antigen (HLA) matching is a suitable means to reduce classical immune reactions in normal risk keratoplasty patients. In this study, we therefore investigated whether HLA-matched grafts also experience less chronic endothelial cell loss. METHODS: A homogenous group of 223 normal risk keratoplasty patients was divided into six groups with different degrees of HLA matching (group 1 with unknown HLA data, group 2 with up to two mismatches, group 3 with three mismatches, group 4 with four mismatches, group 5 with five mismatches and group 6 with six mismatches on the HLA A, B, DR loci). All serological HLA A, B, C and all moleculargenetic HLA DRB, DRQB typings of donors and recipients were performed in a single laboratory accredited by the American Society for Histocompatibility and Immunogenetics. Only patients with at least three postoperative endothelial cell density values were included in the study. The slopes of the regression lines for each individual scatterplot of endothelial cell density values plotted against postoperative time (linear regression, lost cells/mm2/day), and after logarithmic transformation (exponential regression, annual relative loss of cells) were evaluated, respectively. RESULTS: There were no statistically significant differences between the six groups. CONCLUSION: Whereas proper HLA matching at present standards is already a suitable means to reduce identifiable immune reactions and to prolong graft survival even in normal risk keratoplasty patients, the same HLA matching procedures are not effective in reducing the extent of chronic endothelial cell loss. For several reasons this does not yet exclude, however, the possibility that the underlying cause of chronic endothelial cell loss is immunological.

HLA-A, HLA-B and HLA-DR matching reduces the rate of corneal allograft rejection.

PURPOSE: The purpose of this study is to determine the effectiveness of HLA typing in preventing corneal allograft rejection. METHODS: This retrospective single-center study analyzed 459 consecutive HLA-typed patients who underwent perforating keratoplasty (PKP) between 1983 and 2001. Grafts were postoperatively transparent after donor-recipient selection by HLA-A, -B and -DR typing. Patients were divided into a low- and a high-risk group based on their preoperative diagnosis. RESULTS: The estimated 1-, 5- and 10-year graft survival (Kaplan-Meier) was 93, 88 and 67% in low-risk patients and 73, 43 and 38% in high-risk patients. We found a significant correlation between the number of HLA mismatches and the rate of allograft rejections: a donor-recipient match of two or more alleles in HLA-A, -B or -DR reduces the rejection rate by at least 10% in low-risk (10 years after PKP; P<0.04) and 40% in high-risk patients (3 years after PKP; P<0.0001). Especially HLA-B mismatches are important prognostic factors for both low- ( P<0.008) and high-risk patients ( P<0.003). Considering both HLA-B and -DR mismatches significantly reduces the rate of allograft rejection, particularly in high-risk patients ( P<0.0001). Matching on a split typing level offers no significant advantage over broad level matching. CONCLUSION: Clinical results confirm theories developed to explain the function of the HLA (MHC) receptor. The closest possible donor-recipient match of HLA antigens based on broad level typing significantly reduces the rate of allograft rejection and thus improves the prognosis for long-term transparency of corneal grafts in both high- and low-risk patients.

The immune privilege of corneal grafts.

Keratoplasty is the oldest and one of the most successful forms of solid tissue transplantation. In the United States, over 33,000 corneal transplants are performed each year. Unlike other forms of tissue transplantation, keratoplasties are routinely performed without the aid of tissue typing or systemic immunosuppressive drugs. In spite of this, 90% of the first-time corneal transplants will succeed-a condition that demonstrates the immune privilege of keratoplasties. The avascular nature of the corneal allograft bed led many to suspect that corneal grafts were sequestered from the immune apparatus. Although pleasing in its simplicity, this explanation has given way to a more comprehensive hypothesis that embodies multiple, interdependent mechanisms, which promote the long-term survival of corneal allografts. These mechanisms conspire to interrupt the transmission of immunogenic stimuli to peripheral lymphoid tissues; induce the generation of a deviated immune response; and neutralize immune effector elements at the host-graft interface. This paradigm is analogous to a three-legged stool. Disassembly of any one of the three components results in the collapse of immune privilege. Strategies to re-establish corneal immune privilege may have clinical application for high-risk hosts who have rejected previous corneal allografts.

Preliminary findings in corneal allograft rejection in patients with keratoconus.

PURPOSE: Classically, corneal allograft rejection is thought to be a T(H)1-mediated phenomenon. However, T(H)2-mediated allograft rejection has been reported in other transplanted organ systems, including the heart and kidney. We previously reported a form of T(H)2-mediated corneal allograft rejection in a murine model with a T(H)2 immune bias. In this study we sought to determine if there was any evidence for this form of corneal allograft rejection in humans. DESIGN: Experimental study with an interventional case series. METHODS: The clinical records of all keratoconus patients undergoing penetrating keratoplasty at the University of Texas, Southwestern Medical Center from 1994 to 1999 were reviewed. Careful attention was paid to a clinical history of atopy. Atopic patients were selected, because these patients have been shown to have a "T(H)2 immune bias." The corneal graft rejection rate in these patients and the number of repeat corneal transplants performed was determined. The experimental group consisted of patients with a clinical history of atopy and keratoconus who had at least one repeat penetrating keratoplasty for an immunologically rejected corneal transplant. Any patient with evidence of primary allograft failure was excluded from this study. Tissue specimens from these patients were embedded in paraffin, serially sectioned, stained with Giemsa stains, and examined histologically. The control group consisted of patients without a clinical history of allergy (and therefore no T(H)2 immune bias) who underwent corneal transplantation for Fuch corneal endothelial dystrophy, or aphakic/pseudophakic bullous keratopathy. Failed grafts from these control patients were also paraffin embedded, serially sectioned, stained, and examined histologically. The human experimental and control corneal specimens were compared with data obtained in a murine model of T(H)2-mediated corneal allograft rejection. Briefly, full-thickness penetrating C57BL/6ByJ corneal allografts were transplanted onto Balb/cByJ and Balb/c-IFN-gamma(tm1Ts) (Balb/c-IFN-gamma knockout) mice. Additionally, full-thickness Balb/cByJ corneal allografts were transplanted onto C57BL/6ByJ and C57BL/6ByJ-IFN-gamma(tm1Ts) mice. Corneal allograft rejection rates and mean rejection times were calculated and compared between wild-type and interferon gamma (IFN-gamma) knockout hosts. The rejected allografts were examined histologically by the same methods used in the human tissue. RESULTS: There were 84 penetrating keratoplasties performed from 1994 to 1999 for keratoconus. Seven of these 84 patients rejected their corneal grafts. Of the 7 patients who rejected their corneal allografts, 4 had repeat penetrating keratoplasty. Of these 4 repeat corneal allografts, 3 showed eosinophilia when compared with rejected grafts in control patients. Atopic keratoconus patients had a mixed inflammatory cellular infiltrate in the rejected corneal tissue specimen with a significantly greater density of eosinophils (P =.001) compared with patients who did not have a pre-existing T(H)2 bias. The inflammatory infiltrate in these patients without a T(H)2 immune bias was mononuclear. In the murine model, corneal allograft rejection did occur in the absence of IFN-gamma, a critical T(H)1 cytokine in both fully allogeneic donor-host combinations. Histologically, rejection in these ("T(H)2 mice") was characterized by a predominant eosinophilic infiltrate in the rejected graft bed when compared with wild-type animals ("T(H)1 mice") that had a predominantly mononuclear infiltrate in the rejected corneal graft bed. CONCLUSIONS: Preliminary findings show that corneal allograft rejection in patients with a pre-existing T(H)2 phenotype is similar to what is seen in the murine model of T(H)2-mediated corneal allograft rejection. Based on this small sample, it appears that eosinophils may play a role in corneal allograft rejection in this group of patients. However, further study is necessary to determine the importance of these cells in allograft rejection.