Integration of intragraft transcriptomics and urinary cytokines identifies CXCL10 and FasL signature in subclinical acute rejection.

Subclinical acute rejection (SCAR) in kidney transplantation, defined by histologic lesions without clinical dysfunction, remains a major cause of allograft injury and is currently detectable only by invasive protocol biopsies. We conducted a multicenter study in which transcriptomic profiling of Formalin-Fixed, Paraffin-Embedded biopsies from SCAR and control patients revealed a distinct signature with upregulation of NFKBIZ, TNFSF14, SLAMF8, and CD247, validated by qRT-PCR and immunohistochemistry but not detectable in urine. Focusing on secreted cytokines, CXCL10 and FasL emerged as candidate urinary biomarkers and were first measured in 12 SCAR patients and 12 controls, showing a significant increase in SCAR. Validation in an independent cohort of 86 kidney transplant recipients, after excluding patients with confounders, confirmed higher CXCL10 and FasL levels in SCAR. When combined as a composite biomarker signature (CXCL10 + FasL), ROC analysis yielded an AUC of 0.711 (95% CI, 0.549–0.874), with 50% sensitivity and 84% specificity at the optimal cutoff. In the still poorly studied context of SCAR, this work is a proof-of-concept approach linking intragraft transcriptomics to urinary cytokine levels. Our findings support the utility of urinary CXCL10 and FasL in assisting clinicians in identifying patients who may benefit from further evaluation, including consideration of a graft biopsy, thereby contributing to improved long-term allograft outcomes.