Non-Invasive Biomarkers for Kidney Transplant Monitoring: A Comprehensive Review

Kidney transplant rejection presents a clinical challenge, requiring an accurate and timely diagnosis. While kidney graft biopsy remains the gold standard, its inherent limitations motivate the need for noninvasive diagnosis. This review comprehensively examines emerging non-invasive biomarkers for the monitoring of kidney allograft, specifically donor-derived cell-free DNA (dd-cfDNA), gene expression profiling (GEP), microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), chemokines, and DNA methylation patterns. We review their underlying biological principles and discuss their diagnostic accuracy, clinical applications, and limitations in the current available evidence. Donor-derived cfDNA, a promising predictor of allograft injury, shows particular utility in detecting antibody-mediated rejection (ABMR), lacking however for standardization concerning its cutoff. Gene expression profiling provides insights into immune responses, with various gene signatures developed for detecting subclinical and acute rejection. MicroRNAs and long non-coding RNAs demonstrate potential as tissue-specific biomarkers of injury and rejection, yet face challenges in standardization and clinical translation. Chemokines like urinary CXCL9 and CXCL10 exhibit diagnostic and prognostic value for acute rejection. Furthermore, DNA methylation patterns offer a novel approach to identify cell-specific cfDNA and reflect cell death processes within transplanted organs. The integration of these diverse biomarkers, potentially augmented by artificial intelligence platforms, holds immense promise for improving diagnostic precision, minimizing the need for biopsies, and enabling personalized immunosuppression strategies, which would improve long-term graft survival.