*Purpose: Adolescence (age 13-17 years) has been identified as a high-risk age interval for pediatric kidney transplant recipients, with accelerated rates of late acute rejection and premature allograft failure due in part to medication non-adherence. The purpose here was to identify additional determinants of kidney transplant outcomes in a diverse cohort of adolescents and young adults (age ≥ 18 years) that were transplanted as children.

*Methods: This study contains an interim analysis of an ongoing retrospective cohort study of pediatric kidney transplants performed from 01/2005-12/2015, with clinical follow-up records extending up to 15 years post-transplant. We accumulated clinical, demographic, histology, and outcomes data from time spent in our pediatric transplant program and after transition to an adult program. The primary endpoint was a triple composite of late acute rejection, death-censored graft failure, or death with a functioning allograft. Secondary endpoints included each component of the primary endpoint and subclinical rejection, defined as a 3- or 6-month surveillance biopsy with borderline changes, T cell-mediated rejection, or antibody-mediated rejection.

*Results: We retrospectively evaluated 158 children transplanted at a median (IQR) age of 12 (5-16) years, of which 46% were of black race, 66% were male, and 65% had deceased donors. The majority (>90%) received basiliximab induction and tacrolimus/MMF/prednisone maintenance. Surveillance biopsies were obtained in 72% of patients, with 33% having subclinical rejection and over half of these cases occurring in adolescents and young adults. The composite endpoint occurred in 63 (40%) of patients at a median of 4 years post-transplant, including 35% with late acute rejection, 20% with allograft failure, and 4% with death. Of those meeting the composite endpoint, 46 (72%) were adolescents or young adults. Black race (67% vs. 32%), de novo DSA (79% vs. 21%), and subclinical rejection (56% vs. 23%) were all significantly more prevalent in the group that met the primary endpoint (P<0.01 for all). Importantly, the majority of episodes of late acute rejection or graft failure and nearly half of all deaths occurred in young adulthood, after a typical age of transition to an adult program.

*Conclusions: For pediatric kidney transplant recipients, the accelerated risk for poor long-term outcomes in adolescence persists into young adulthood. This highlights the ongoing need for improvements in transition programs and precision assays for monitoring allograft injury in this high-risk population.

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