Donor-Derived Cell-Free DNA in Plasma as a Non-Invasive Marker of Graft Rejection in Liver Transplant Recipients: A Review

Abstract

Rejection after liver transplantation is confirmed by biopsy, an invasive procedure with its own sampling error. Donor DNA circulating in recipient lasma offers a measurement of graft injury that can be repeated as often as a blood test. The accuracy is good; the threshold at which it becomes a decision is not settled. Objectives: To review the published evidence on donor-derived cell-free DNA as a marker of graft rejection after liver transplantation: how it is measured, what accuracy it achieves against biopsy, how it compares with liver function tests, and why thresholds differ so widely between studies. Material and Methods: Narrative review of prospective cohort studies, assay validation reports, cross-organ comparisons and methodological papers indexed in PubMed and the major transplantation and clinical chemistry journals. Studies were eligible if they reported the performance of donor-derived cell-free DNA against a defined rejection endpoint in transplant recipients, or the analytical basis of its measurement. No new patient data were
generated; every estimate quoted is one published by the original investigators. Results: In a prospective multicentre cohort of 115 adult recipients across three centres, graft-derived cell-free DNA measured by droplet digital polymerase chain reaction discriminated rejection with sensitivity of 90.3 per cent (95% CI 74.2-98.0) and specificity of 92.9 per cent (95% CI 89.3-95.6) at a threshold of 10 per cent, outperforming conventional liver function tests on the same samples. In paediatric recipients a threshold of 28.7 per cent
gave an area under the curve of 0.878 (95% CI 0.753-0.954), with positive and negative predictive values of 80 and 92.3 per cent. Serial measurement detected rising concentrations before graft dysfunction was apparent on liver enzymes, and the marker performs comparably in kidney, heart and lung transplantation. Conclusion: Donor-derived cell-free DNA detects graft injury earlier and more specifically than liver function tests, and does so without biopsy. Its principal weakness is that it reports injury rather than its cause, and no threshold has been agreed across studies, with published cut-offs differing almost threefold. Abbreviations: dd-cfDNA – Donor-Derived Cell-Free DNA, GcfDNA – Graft-Derived Cell-Free DNA, cfDNA – Cell-Free DNA, LTx – Liver Transplantation, ddPCR – Droplet Digital Polymerase Chain Reaction, SNP – Single Nucleotide Polymorphism, LFT – Liver Function Test, TCMR – T Cell-Mediated Rejection, AMR – Antibody-Mediated Rejection, AUC – Area Under the Receiver Operating Characteristic Curve, PPV – Positive Predictive Value, NPV – Negative Predictive Value.