Protocol core needle biopsy and histological chronic allograft damage index as surrogate endpoint for Long-Term graft survival

Abstract

Following encouraging results from several single-center studies showing that early histological manifestations of chronic rejection are seen in the graft before a decline in transplant function, we tested this concept in a multicenter study and investigated whether protocol needle biopsy may be used as a surrogate to late graft survival in multicenter renal transplantation trials. During two mycophenolate mofetil trials, 621 representative protocol biopsies were obtained at baseline, 1 year, and 3 years. The samples were coded and evaluated blindly by two pathologists and a Chronic Allograft Damage Index (CADI) score was constructed. At 1 year only 20% of patients had elevated (>1.5 mg/100 mL) serum creatinine, whereas 60% of the biopsies demonstrated an elevated (>2.0) CADI score. The mean CADI score at baseline, 1.3 +/- 1.1, increased to 3.3 +/- 1.8 at 1 year and to 4.1 +/- 2.2 at 3 years. The patients at 1 year were divided into 3 groups, those with CADI <2, between 2 and 3.9, and >4.0, the first two groups having normal (1.4 +/- 0.3 and 1.5 +/- 0.6 mg/dL) and the third group pathological (1.9 +/- 0.8 mg/dL) levels of serum creatinine. At 3 years there were no lost grafts in the "low" CADI group, six lost grafts (4.6%) in the "elevated" CADI group, and 17 lost grafts (16.7%) in the "high" CADI group (P <.001). One-year histological CADI score predicts graft survival even when the graft function is still normal. This observation makes it possible to use CADI as a surrogate endpoint in prevention trials and to identify the patients at risk for intervention trials.