An adverse matching effect for the HLA-B locus in corneal transplantation

Tacrolimus (FK506) in the management of high-risk corneal and limbal grafts

OBJECTIVE

To assess the efficacy and side effects of tacrolimus in the management of patients with high-risk corneal and limbal grafts.

DESIGN

Noncomparative case series.

PARTICIPANTS

Seventeen patients (23 grafts) were treated with tacrolimus; 15 patients (20 host corneas) had two or more quadrants of stromal vascularization, 6 patients had stem cell deficiency, and 6 patients had glaucoma. Seven patients had received one previous graft, six patients had two previous grafts, and four patients had three previous grafts.

INTERVENTION

Patients with high-risk corneal and limbal grafts were treated with systemic tacrolimus at a mean optimum dosage of 4.4 mg daily (range, 2-12 mg daily).

MAIN OUTCOME MEASURES

Graft survival, visual acuity.

RESULTS

No patient has had irreversible graft rejection while receiving tacrolimus. The follow-up period ranges from 12 to 46 months, with a mean of 24 months. Three patients have had reversible graft rejection associated with low tacrolimus levels. Nine patients have stopped treatment; two had reversible rejection within 2 months of stopping, and five grafts remain clear. The other four patients stopped treatment because of graft failure, which was not considered to be rejection related. Eight patients remain on treatment, and all have clear grafts.

CONCLUSIONS

Tacrolimus (FK506) is effective in prevention of rejection in patients with high-risk corneal and limbal grafts.

HLA-A and -B alleles in cornea donors as risk factors for graft rejection

We determined the human leucocyte antigen (HLA)-A, -B and -DR allele frequencies in recipients and donors of 115 cornea transplants, for recipients who developed graft rejection and those who did not. No difference in HLA allele frequencies of the recipients was found. The frequencies of the HLA-A26, -B35 and -B44 alleles in cornea donors were increased in recipients who developed graft failure. The detrimental effect on corneal graft survival of these alleles was significant (p < 0.001). No such effect was observed in renal transplantation. Corneal graft survival was similar when one or two A26, B35 or B44 alleles were present on the donor cornea. The negative effect was similar in magnitude to the previously reported negative effect of an HLA-B locus match between donor and recipient. When both a B-locus match and an A26, B35 or B44 allele were present, the negative effect on graft survival was twice as strong, indicating that different immune mechanisms are responsible for these phenomena.

The histo-blood group ABO system and tissue transplantation

In general, one might expect that ABO incompatibility of donor and recipient would be important to some degree if viability of the transplanted allograft is important for graft incorporation and function. This is true for some recipients of organs. However, ABO incompatibility appears to play a minor role, if any, in the clinical success of viable cornea and viable skin allografts. Even though A and B antigens may be present on the transplanted tissue, other factors that can contribute include the strength of the immune response, the avidity of the antibody, and the dose of the antigen presented, which may vary from donor to donor. Although A and B antigens are present on endothelium, the use of ABO-incompatible heart valves is successful, as they carry out their mechanical function by using the strength of the connective tissue rather than the viability of the donor endothelium. The presence, immunogenicity, and significance of A and B antigens in human vessel transplants have not been well studied. With the more commonly transplanted tissue, such as bone and tendon, posttransplant success does not depend on cellular viability or ABO compatibility.