Increased Immunogenicity and Cause of Graft Loss of Old Donor Kidneys

. Donor age was identified recently as a major factor that determines long-term outcome after transplantation, but the mechanism that is responsible for increased graft loss of old donor kidneys is unknown. The influence of donor age on graft survival was assessed retrospectively in 514 consecutive first cadaveric transplants that were treated with cyclosporine maintenance immunosuppression. Donor age ≥50 yr (relative risk [RR] = 1.7; 95% confidence interval [CI], 1.2 to 2.6), acute rejection (RR = 2.0; 95% CI, 1.3 to 3.0), and type of rejection (RR = 3.3; 95% CI, 2.0 to 5.3) had a significant impact on graft survival. However, when subsets of patients who entered subsequent intervals after transplantation were analyzed, donor age was not an independent predictive factor of graft loss. Donor age (RR = 1.53; 95% CI, 1.19 to 1.98), human leukocyte antigen-DR mismatch (RR = 2.28; 95% CI, 1.78 to 2.92), and recipient age (RR = 1.34; 95% CI, 1.05 to 1.72) were associated significantly with acute rejection episodes. Delayed graft function alone was not associated independently with the occurrence of early acute rejection (RR = 1.24; 95% CI, 0.96 to 1.61). The timing of the rejection episodes of old donor kidneys was not different, and the excess rejection prevalence was attributable entirely to interstitial (grade I) types of rejection. Interstitial rejection episodes in kidneys from old donors had a significant ( P < 0.05) negative impact on graft survival. Beyond the first year, poor renal function and proteinuria were significant risk factors for graft loss, regardless of rejection. Our data fit best the hypothesis that increased graft loss of older donor kidneys results from an increased incidence of acute interstitial rejection episodes in the early posttransplantation months. It is proposed that kidneys from older donors are more immunogenic than kidneys from young donors and that acute rejection episodes result in functional deterioration. Contrary to interstitial rejection in kidneys from younger donors, kidneys from old donors seem to have an impaired ability to restore tissue.