Dynamic kinetics of graft-derived cell-free DNA and personalized tacrolimus target ranges for acute rejection monitoring in pediatric liver transplantation

Introduction Acute rejection remains the most common complication during the early post-transplantation period for pediatric patients. Given the limitations of current diagnostic strategies, there is an urgent need to develop accurate and noninvasive biomarkers for allograft monitoring. Tacrolimus-based immunosuppression represents the cornerstone regimen following liver transplantation. However, for pediatric patients, current evidence remains insufficient to establish well-defined therapeutic target ranges for personalized tacrolimus therapy in pediatric patients. We investigated perioperative graft-derived cell-free DNA (GcfDNA) kinetics in pediatric recipients to establish the utility of GcfDNA for monitoring acute rejection and to explore the tacrolimus target concentration range in this population. Methods Forty children (age ≤ 3 years) with biliary atresia who underwent liver transplantation were enrolled. All received a tacrolimus-based immunosuppressive regimen on postoperative day (POD) 1 and were followed for at least 1 month. GcfDNA levels were measured by droplet digital PCR. Results GcfDNA (%) declined significantly during the first month. Median percentages on POD 1, 7, 14, 21, and 28 were 41.40%, 12.93%, 6.86%, 5.95%, and 3.23%, respectively. The acute rejection group maintained higher GcfDNA levels, with significant differences observed at POD 14, 21, and 28 ( P < 0.001). GcfDNA (%) was strongly correlated with rejection activity index score (r = 0.854, P < 0.001). In this exploratory single-center analysis, receiver operating characteristic (ROC) curve analysis identified an optimal GcfDNA cutoff of 10.21% for predicting acute rejection, with an area under the curve (AUC) of 0.757 (95% CI: 0.691–0.823, P < 0.001). The optimal tacrolimus trough concentration (C 0 ) threshold was 7.75 ng/mL (AUC = 0.732, 95% CI: 0.655–0.810, P < 0.001). Conclusion We suggest that GcfDNA may serve as a potential biomarker for acute rejection monitoring in pediatric liver transplantation, with an exploratory predictive cutoff value of 10.21% identified in this single-center cohort. Our findings also tentatively point to a minimal effective tacrolimus C 0 of 7.75 ng/mL within the first month post-transplantation, alongside an upper safety limit of 10 ng/mL that is primarily grounded in published peer-reviewed literatures. These thresholds, however, were optimized against stable grafts rather than the full spectrum of graft injury and require multicenter validation before clinical adoption.