Introduction: The objective of this study was to explore immunological causes of inferior graft survival in renal transplant recipients during late adolescence and young adulthood  in comparison to other age categories.
Methods: This study is part of the multicentre cohort study Adolesce-NT and investigates the relationship between T cell subsets and pubertal stage in patients with end-stage renal failure, renal transplant recipients and healthy controls.
Participants, with age 8 to 30 years at time of inclusion, were divided in a pre-transplantation, post-transplantation and healthy control group. Exclusion criteria: no informed consent, pubertas praecox, prior treatment with immunomodulating agents. Patients had two study visits one year apart, healthy controls had one study visit. Participants were classified as pre-pubertal, early pubertal, late pubertal or post-pubertal according to skeletal age, Tanner stage, testis volume and timing of menarche.
Using 8-color flow cytometry, mean cell counts of recent thymic emigrants (CD4+CD31+CD62Lhi and CD8+CD31+CD62Lhi) and naïve and memory T cells (CD4+ and CD8+ Temro, Temra and Tcm) were determined.
Results: In total 267 participants were included in the analysis. The increased numbers of recent thymic emigrants showed a trend towards a higher thymic T cell output during the late pubertal period in both patient groups compared other age groups (pre-transplantation group p=0.053, post-transplantation group p=0.054). Memory T cells showed a higher cell count during the post-pubertal stage, being CD8+ Temra in the pre-transplantation group (p=0.014) and CD4+ Temro in the healthy control group (p=0.027) compared to other age groups.
Conclusion: The current study shows a trend towards a more active immune system during the late pubertal and post-pubertal stage in transplant patients. These observations form an important starting point to further explore the possible causes of the poorer kidney transplant survival during late adolescence and early adulthood.