Association of Blood Donor-derived Cell-free DNA Levels With Banff Scores and Histopathological Lesions in Kidney Allograft Biopsies: Results From an Observational Study.

Background: Donor-derived cell-free DNA (dd-cfDNA) is an emerging biomarker of kidney allograft injury, mainly investigated in the context of rejection. However, the dd-cfDNA dynamics in other graft pathologies merit further investigation.

Methods: In this single-center observational study, we prospectively collected dd-cfDNA at indication biopsies. To evaluate the association between dd-cfDNA and different histological patterns, we correlated absolute and relative dd-cfDNA (thresholds of 50 copies/mL and 0.5%, respectively) with the Banff 2022 lesion scores and the assigned diagnoses.

Results: We examined 151 dd-cfDNA paired biopsies in 131 kidney transplant recipients and found significantly higher absolute dd-cfDNA levels in antibody-mediated rejection (n, median, IQR: 45, 63 copies/mL, 42-89), microvascular inflammation (MVI) without donor-specific antibodies or C4d-deposition (6, 102 copies/mL, 61-134), mixed rejection (8, 140 copies/mL, 77-171), and BK virus-associated nephropathy (6, 213 copies/mL, 83-298) compared with glomerulonephritis (20, 12 copies/mL, 8-18), calcineurin toxicity (19, 10 copies/mL, 7-16), interstitial fibrosis/tubular atrophy (12, 10 copies/mL, 9-16) and normal histology (6, 9 copies/mL, 7-16). In the multivariable analysis, absolute and relative dd-cfDNA correlated with the peritubular capillaritis (ptc), glomerulitis (g), and tubulitis (t) scores. In the receiver operating characteristic analysis, absolute dd-cfDNA showed best discrimination for MVI of any cause (area under the curve [AUC] 0.88, sensitivity 0.71, specificity 0.86, positive predictive value [PPV] 0.76, negative predictive value [NPV] 0.82), followed by antibody-mediated rejection including mixed rejection (AUC 0.85, sensitivity 0.72, specificity 0.83, PPV 0.69, NPV 0.84), and overall rejection (AUC 0.83, sensitivity 0.66, specificity 0.85, PPV 0.76, NPV 0.77). T cell-mediated rejection was only detectable by dd-cfDNA when associated with vascular lesions.

Conclusions: Altogether, we conclude that dd-cfDNA-release is not limited to rejection-related injury phenotypes and is mainly driven by MVI in kidney allografts.