Non-Invasive Tool to Distinguish Between Acute Rejection and Stable Graft Function Using Urinary mRNA Signature Reflecting Allograft Status in Kidney Transplantation

Abstract Background: Urine has been regarded as the best resource based on the assumption that urine can directly reflect the state of the allograft or ongoing injury in kidney transplantation. Previous studies, suggesting the usefulness of urinary mRNA as a biomarker of acute rejection, imply that urinary mRNA mirrors the transcriptional activity of the kidneys. Methods: We absolutely measured 14 data-driven candidate genes using quantitative PCR without pre-amplification in the cross-sectional specimens collected from Korean kidney transplant patients. We developed a clinical application model adopting urinary mRNAs for allograft rejection using a binary logistic regression and finally verified its usefulness in a large-scale validation group.Results: We measured the candidate genes in 103 training samples. Expression of 8/14 genes were significantly different between acute rejection and stable graft function with normal pathology and long-term graft survival. Also, CXCL9 was distinctly expressed in allografts with acute rejection in in situ hybridization analysis. This result, consistent with the qPCR result, implies that urinary mRNA could reflect the magnitude of allograft injury. We developed AR prediction model by differently combined mRNAs and the area under the curve (AUC) of the model was 0.89 in training set. The model was validated in 391 independent samples, and the AUC of the model was 0.84 with a fixed manner. In addition, the decision curve analysis indicated a range of reasonable threshold probabilities for biopsy. Conclusions. Therefore, we suggest urinary mRNA signature may serve as a non-invasive monitoring tool of acute rejection and intragraft immune injury.