The impact of age on rejection in kidney transplantation

The time to failure of a renal allograft is determined by the initial function achieved after transplantation, the number and severity of insults to the graft, and a number of tissue characteristics. The insults a graft usually encounters include ischaemia/reperfusion injury, acute rejection episodes, drug-related nephrotoxicity, hypertension and hyperlipidaemia. Important tissue characteristics include susceptibility to injury and the ability of the tissue to repair damage. Elderly transplant recipients are considered poor immune responders but if a single acute rejection episode occurs this is more likely to significantly shorten graft and patient survival in this age group. Two issues have been identified with the use of old (> 50 years of age) donor kidneys. First, compared with kidneys from younger donors, they have an increased incidence of acute interstitial rejection. Secondly, once a rejection episode occurs, the ability to mount a tissue repair process seems impaired. An explanation for the increased loss of grafts from old donors that have experienced acute rejection episodes is that such kidneys have fewer nephrons that function adequately and that the cumulated effect of damage results in an earlier demise of the graft compared with younger donor kidneys. Alternatively, graft parenchymal cells may undergo premature senescence or aging as a result of multiple injuries and repair. If progressive loss of renal mass or senescence is the mechanism responsible for increased graft loss, then it is expected that grafts from older donors will show a progressive decrease in function over time and that the rate of decline of function will correlate with donor age. We have suggested that increased graft loss of older donor kidneys results from increased incidence of acute rejection episodes in the early post-transplantation months together with a partly impaired ability to repair the tissue. Drug pharmacokinetic parameters are generally little influenced by age. However, the degree to which drugs suppress the immune system, and the extent to which kidneys from older donors are susceptible to the nephrotoxic effects of certain drugs, are unpredictable. There appears to be a more delicate balance between adequate immunosuppression and excess nonimmune toxicity in patients receiving older kidneys. Outcome parameters in elderly renal transplant recipients are currently dominated by increased death from infectious disease and drug-related (cardiovascular) causes. Increased susceptibility to nephrotoxic drugs, and to calcineurin inhibitors in particular, may be related to the increased risk of allograft failure experienced by the elderly as a surrogate for chronic allograft nephropathy.