BACKGROUND: Age limits for transplantation have expanded significantly in the last 20 years, with a 5-fold increase in the number of older adults receiving kidney transplants (KT). However, much remains to be known about the immune system of older adults, both in comparison to younger adults and also in response to various immunosuppression regimens. The goal of this study was to compare rates of acute rejection in older and younger KT recipients, and to evaluate changes in acute rejection rates over time.

METHODS: We studied 254,410 KT recipients (27,380 aged ≥65 at the time of KT) as reported to SRTR between 1990-2011. Risk of acute rejection treated in the first post-KT year was compared between older (≥65) and younger (18-65) recipients, and over time, using adjusted modified Poisson regression.

RESULTS: Overall, 17.5% of KT recipients were treated for acute rejection in the first year (18.2% of younger recipients and 11.0% of older recipients, P<0.001). Although the rejection rates improved over time for both groups, the rates were consistently lower in older KT recipients (P<0.001).

Older KT recipients had almost half the risk of rejection as younger recipients (RR=0.60, 95%CI: 0.58-0.62, P<0.001), independent of other recipient, donor, and transplant factors.

CONCLUSION: In both older and younger KT recipients, 1-year rejection has improved over time. Older KT recipients are at a decreased risk of rejection independent of recipient, donor, and transplant factors. This is consistent with theories of immune senescence with aging and should inform patient selection and immunosuppression regimen decision-making.

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