Discussion
Together, our proof-of-principle results demonstrate that BLI-based urinary CXCL9 detection has potential as a point-of-care noninvasive biomarker to diagnose and guide therapy for ACR in kidney transplantation recipients.
Methods
We developed a biolayer interferometry (BLI)-based assay to rapidly measure urinary CXCL9 in <1 hour. We validated this new assay versus standard ELISA in 86 urine samples from kidney transplantation recipients with various diagnoses. We then used BLI to analyze samples from 56 kidney transplantation recipients, including 46 subjects who experienced an acute rise in serum creatinine associated with biopsy-proven ACR (n = 22), subclinical rejection (n = 15), or no infiltrates (n = 9), and 10 stable kidney transplantation recipients with surveillance biopsies. To assess its usefulness in detecting adequacy of therapy we serially measured serum creatinine and urinary CXCL9 in 6 subjects after treatment for ACR, and correlated the
Results
BLI accurately and reproducibly detected urinary CXCL9 in <1 hour. BLI-based results showed that urinary CXCL9 was >200 pg/ml in subjects with ACR and ≤100 pg/ml in subjects with stable kidney function without cellular infiltrates. In samples obtained after treatment for ACR, BLI CXCL9 measurements detected biopsy-proven intragraft infiltrates despite treatment-induced reduction in serum creatinine.