#6709 DONOR-DERIVED CELL-FREE DNA (DD-CDNA) AS A NON-INVASIVE BIOMARKER OF KIDNEY ALLOGRAFT REJECTION IN PEDIATRIC KIDNEY TRANSPLANTATION

Abstract Background and Aims Rejection remains the first cause of allograft loss in pediatric kidney transplant (pkTx) recipients. Detection of rejection currently relies on kTx biopsies performed either because of allograft dysfunction with the risk of late diagnosis or per surveillance protocols allowing early detection of subclinical rejection but resulting in many unnecessary biopsies. Dd-cfDNA was reported as a new non-invasive biomarker with the potential to improve rejection detection and guide biopsy indications. We aim to assess the association of dd-cfDNA levels with biopsy results in a large cohort of pediatric kTx recipients. Method All pediatric kTx patients with at least one dd-cfDNA assessment at the time of a biopsy at a single pediatric transplant center were included. Clinical, biological and histological data were collected from medical reports. Dd-cfDNA were retrospectively measured from plasma samples biobanked at the time of allograft biopsy between 2015 and 2020 or collected in patients who received regular dd-cfDNA testing as part as clinical care between 2021 and 2022. Results 170 cfDNA measurements in 132 pkTx recipients were available at the time of a biopsy, including 100 performed for surveillance. Mean age at biopsy was 16 years with a median time from kTx of 21 [11;38] months. Median eGFR was 62 [48;83] mL/min/1.73 m2, median UPCR 0,21 [0,14;0,36] g/g, and 20% had DSA at the time of the biopsy. Biopsy findings included: 109 normal, 30 borderline, 15 TCMR, 11 AMR and 5 mixed rejections. Median cfDNA level was 0,64 [0,31;1,80] %. We found a strong association between cfDNA levels and active tubule-interstitial and microvascular Banff lesions (Figure 1). cfDNA levels were significantly increased in cases with rejection (Figure 2). Using the proposed cut-off of 0.5%, performances of the test to detect rejection were Se 84%, Spe 51%, PPV 33%, NPV 92%. Among the borderline cases, 17 (57%) had cfDNA>0.5%. Conclusion We confirm in the largest pediatric kTx cohort to date, the association of dd-cfDNA levels with allograft rejection and its potential interest as a non-invasive biomarker in children. Further studies are needed to assess the added value of dd-cfDNA monitoring to the current standard of care and its ability to reduce unnecessary surveillance biopsies and improve outcomes.