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 (C0) 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 C0 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.