Targeted Proteomic Analysis Detects Acute T Cell-Mediated Kidney Allograft Rejection in Belatacept-Treated Patients

Background: There is an unmet need for reliable minimally invasive diagnostic biomarkers for immunological allograft monitoring and for the detection of acute kidney transplant rejection. Here, targeted proteomic analysis was applied to compare 92 proteins in sera of belatacept-treated patients who had biopsyproven, acute T-cell–mediated rejection (aTCMR) with patients without aTCMR. Methods: Proximity extension immunoassay was used to measure 92 inflammation-related protein concentrations in the prerejection and rejection sera of 11 patients with aTCMR and 9 patients without aTCMR. This assay uses 2 matched oligonucleotide-labeled antibody probes for each protein and polymerase chain reaction to measure normalized protein expression values. Results: Five proteins (CD5, CD8A, NCR1, TNFRSF4, and TNFRSF9) were expressed significantly higher in samples with aTCMR compared with samples without aTCMR (adjusted P-value , 0.014) and had a good predictive capacity for aTCMR [area under the curve in a receiver–operator curve ranged from 0.83 to 0.91 (P ,0.014)]. These proteins are associated with CD8+ cytotoxic T-cell and NK cell functions. Nonhierarchical clustering analysis showed distinct clustering of samples with aTCMR and samples without aTCMR. This clustering was not found in prerejection samples (1 month after transplantation). In prerejection samples, IFN-g was expressed at a significantly lower level (normalized protein expression value median 20.15, interquartile range: 20.27 to 0.04) than in samples of patients without rejection (median 0.13, interquartile range: 20.07 to 0.15, adjusted P-value = 0.00367). Conclusions: Targeted proteomic analysis with proximity extension immunoassay is a promising minimally invasive technique to diagnose aTCMR in kidney transplant recipients.

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