The Collaborative Corneal Transplantation Studies (CCTS) were designed to evaluate the effect of donor-recipient histocompatibility matching and crossmatching on the survival of corneal transplants in high-risk patients. Corneas were allocated to the 419 patients in the double-masked Antigen Matching Study on the basis of serologically defined HLA-A, -B and HLA-DR antigen match. ABO blood group compatibility was determined but not used for recipient selection. The 37 patients in the Crossmatch Study were randomly assigned to receive a cornea from either a positively or negatively crossmatched donor. All patients received topical steroid therapy according to a standard protocol. Matching for HLA-A, -B and HLA-DR antigens had no effect on overall graft survival, the incidence of irreversible rejection, or the incidence of rejection episodes. At 3 years after surgery, the estimated proportion of eyes with graft failure was 41% for the ABO-incompatible group and 31% for the ABO-compatible group (relative risk, 1.43; 95% confidence interval, 1.00 to 2.06). The estimated proportion of eyes with failure from rejection by 3 years was 30% for the ABO-incompatible group and 16% for the ABO-compatible group (relative risk, 1.98; 95% confidence interval, 1.25 to 3.13). The positive group in the Crossmatch Study had fewer graft failures, rejection failures, and rejection episodes than the negative group; however, these differences were not statistically significant. These studies demonstrate that, for high-risk patients who are immunosuppressed by topical steroid therapy and followed up according to the CCTS protocol: (1) neither HLA-A, -B nor HLA-DR antigen matching substantially reduces the likelihood of corneal graft failure; (2) a positive donor-recipient crossmatch does not dramatically increase the risk of corneal graft failure; and (3) ABO blood group matching, which can be achieved with relatively little effort and expense, may be effective in reducing the risk of graft failure.

To the Editor. —The principal investigators of the Collaborative Corneal Transplantation Studies (CCTS), a National Eye Institute-sponsored multicentered clinical trial of histocompatibility matching in high-risk keratoplasty, have received several inquires regarding our position on recommendations for tissue matching and sharing of typed tissue. We believe that the available data do not, at this time, allow us to determine whether histocompatibility matching improves the prognosis for penetrating keratoplasty in high-risk recipients. Available data do not allow us to determine whether histocompatibility matching, if effective, should be based on HLA-A matches, HLA-B matches, HLA-DR matches, or ABO matches. It is the purpose of the CCTS to address these and other questions. The CCTS is a masked, prospective, randomized clinical trial. Consequently, none of the investigators is aware of the degree of tissue match that any of his patients receive. Data are reviewed biannually by the CCTS Data and Safety Monitoring Committee. At