Identification of Urinary Exosomal <scp>microRNAs</scp> Associated With Subclinical Acute T‐Cell‐Mediated Rejection in Kidney Transplant Recipients

This study aimed to evaluate the diagnostic utility of urinary exosomal microRNAs (miRNAs) in subclinical rejection following kidney transplantation by comparing miRNA expression profiles in urinary exosomes between patients with no evidence of rejection and patients with subclinical T-cell-mediated rejection (sc-TCMR), as confirmed by protocol kidney biopsies performed 3 months after transplantation. To elucidate these differences, a comprehensive miRNA expression analysis was conducted using microarray profiling. Consequently, 38 urinary exosomal miRNAs were detected, among which three were upregulated and five were downregulated in patients with sc-TCMR. To further evaluate the diagnostic value of these miRNAs, quantitative real-time PCR analysis was performed using urinary exosomes collected at the time of protocol biopsy from 70 kidney transplant recipients. This analysis confirmed that miR-5100 and miR-7975 were differentially expressed in patients with sc-TCMR at the time of the 12-month protocol biopsy. Importantly, miR-7975 demonstrated the ability to distinguish among three groups-no evidence of rejection, borderline changes, and sc-TCMR-with high diagnostic accuracy, as indicated by an area under the receiver operating characteristic curve of 0.825. In vitro, exposure of proximal tubular epithelial cells to transforming growth factor-beta 1 resulted in a reduction in miR-7975 expression within urinary exosomes, implicating these cells as a potential source of exosomal miR-7975. Collectively, these findings suggest that urinary exosomal miR-7975 may serve as a promising noninvasive biomarker for diagnosing and monitoring sc-TCMR, offering valuable insights for future research and clinical applications.