Short communication: 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 biopsy-proven, acute T cell-mediated rejection (aTCMR) with patients without aTCMR.

METHODS: Proximity extension immunoassay (PEA) was used to measure 92 inflammation-related protein concentrations in the pre-rejection and rejection sera of 11 patients with aTCMR and 9 patients without aTCMR. This assay uses two matched oligonucleotide-labelled antibody probes for each protein and PCR 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. Non-hierarchical clustering analysis showed distinct clustering of samples with aTCMR and samples without aTCMR. This clustering was not found in pre-rejection samples (one month after transplantation). In pre-rejection samples, IFN-γ was expressed at a significantly lower level (NPX value median -0.15, IQR: -0.27-0.04) than in samples of patients without rejection (median 0.13, IQR: -0.07-0.15, adjusted p-value=0.00367).

CONCLUSIONS: Targeted proteomic analysis with PEA is a promising minimally invasive technique to diagnose aTCMR in kidney transplant recipients.