Collaborative Corneal Transplantation Studies (CCTS)

Approximately 20 percent of corneal transplant patients, about 6,000 per year, face donor tissue rejection at rates of up to 60 percent because of corneal vascularization or prior graft rejection. Histocompatibility antigen matching and/or crossmatching may have offered these patients an improved chance for successful outcome.

The Collaborative Corneal Transplantation Studies Group conducted two controlled, double-masked studies addressing distinct scientific questions about donor-recipient histocompatibility matching. The Crossmatch Study was a randomized study assessing the effectiveness of crossmatching in preventing graft rejection among high-risk patients with lymphocytotoxic antibodies. The Antigen Matching Study was a prospective, double-masked, observational study of the effectiveness of HLA-A, -B, and -DR donor-recipient matching in high-risk patients who had no lymphocytotoxic antibodies.

Six clinical centers recruited high-risk patients and collaborated with their local eye banking and organ procurement agencies in procuring donor corneal tissue. For each of the two studies, a total of 400 patients were sought. Blood samples from each enrolled patient were sent to the local CCTS tissue typing laboratory for HLA typing, and serum samples were sent to the Central Laboratory to be screened for preformed lymphocytotoxic antibodies. Depending on the results of the testing, patients were entered into the Crossmatch Study or the Antigen Matching Study.

As corneal donors became available, donor blood samples were HLA typed at the local laboratories and crossmatched against all CCTS patients who awaited transplantation. Results of the testing were entered in a national, 24-hour computerized allocation system operated by the United Network for Organ Sharing (UNOS). Patients in the Crossmatch Study received a cornea from either a positively crossmatched donor or a negatively crossmatched donor. Patients in the Antigen Matching Study received a cornea with 0 to 6 matched antigens.

Transplant patients were followed intensively during the first months after surgery. The number of clinic visits was tapered to 2 during the third and final year of followup, resulting in a total of 17 postoperative visits. Irreversible failure of the corneal allograft due to all causes was the primary outcome variable in both studies. Allograft reaction episodes, irreversible failure due to rejection, and visual acuity were secondary outcome variables.

Males and females age 10 years or older with two to four quadrants of corneal stroma vascularization or a history of allograft rejection in the eye considered for surgery were eligible for both studies in the CCTS.

Patients must have been willing to participate in 3 years of followup. No one was eligible for the CCTS who had a condition that would greatly increase the risk of nonrejection graft failure, such as xerophthalmia or severe exposure keratopathy. Also excluded were patients with systemic diseases or with medication usage that might alter their immune response.