*Purpose: Elevated donor-derived cell-free DNA (dd-cfDNA) in the presence of HLA donor-specific antibodies (DSA) are shown to correlate with acute antibody-mediated rejection (AMR) in adult and pediatric kidney transplant recipients. A dd-cfDNA result of &gt 1.0% is considered positive for acute rejection but data about changes in dd-cfDNA after AMR treatment in children remain scarce. The objective of our study is to assess the changes in dd-cfDNA over time after therapy of AMR in children with kidney transplant. We report the preliminary results of two patients who participated in the study.

*Methods: This is a longitudinal non-interventional study in children &lt 21 y with biopsy-proven AMR and positive DSA. Our center’s standard therapy for AMR consists of steroids, rituximab, and 3-5 monthly intravenous gamma globulin (IVIG) infusions, then quarterly as necessary. Persistent AMR is treated with additional plasma exchanges and bortezomib. DSA and dd-cfDNA tests were obtained before each IVIG infusion. We calculated the cumulative MFI by adding together the MFI of each single DSA. Statistical analysis used descriptive statistics.

*Results: Two subjects accumulated enough data points to report. Subject 1 is a 14-year-old male who developed AMR 21 months post living unrelated kidney transplant. He was treated initially with steroids, rituximab, and IVIG. A repeat kidney biopsy showed evidence of persistent AMR and was treated with plasma exchange, bortezomib, rituximab, and IVIG (0.7-2 g/kg/dose X 7). He had two biopsies completed. Subject 2 is an 8-year-old male who developed AMR 37 months after a living-related transplant (documented by biopsy) and was treated with steroids, rituximab, and IVIG (1-2 g/kg/doses X 4 ). Creatinine remained stable in both subjects. Repeated measurements of dd-cfDNA and cumulative DSA-MFI were monitored over several months as in the following graphs:

*Conclusions: The dd-cfDNA test is a valuable tool to use after therapy of AMR when combined with HLA-DSA to monitor response to therapy and may preclude the need for a repeat kidney biopsy. Further studies in a larger population are in progress.

« Back to 2021 American Transplant Congress