Donor-reactive clonotypes are overrepresented in the urinary T cell repertoire during kidney transplant rejection and show distinct dynamics in the circulation.

In kidney transplantation, the immune response against the graft is mediated by donor-reactive T cells (DRTCs). Urine represents a potentially informative but understudied T cell compartment, particularly during rejection. Here, in a prospective open cohort study recruiting kidney transplantation recipients and collecting urine as well as peripheral blood mononuclear cells, we characterized the urinary and circulating T cell receptor repertoires of 7 patients with rejection and 7 controls, by next-generation sequencing. DRTC populations were defined via mixed lymphocyte reactions performed with peripheral blood mononuclear cells collected both pretransplant and at biopsy. At biopsy, T cell receptor mRNA was found in the urine of all rejectors but only 3 of 7 controls (P = .035). The urinary repertoires were distinct from the circulating repertoires of the respective patients, with 63% ± 19% (mean ± standard deviation) of urinary clonotypes being unique to this compartment. Further, urinary repertoires were consistently and significantly enriched in DRTCs compared to circulation, in both groups. Defining DRTCs at biopsy allowed identification of previously uncaptured clonotypes. Compared to all DRTC clonotypes, those also detected in urine expanded in circulation at an increased rate, from pretransplant to the date of biopsy. The higher abundance of DRTCs in urine highlights its potential for monitoring DRTC dynamics following transplantation.