44 - Absolute Copies may add value to the percentage of donor derived cell free DNA as a marker of acute rejection and graft injury in pediatric kidney Transplantation

Poster Number: 44
Publication Number: 44.349

Vikas Dharnidharka, Washington University in St. Louis School of Medicine, St. Louis, MO, United States; RAJA DANDAMUDI, Washington University School of Medicine in St.Louis., St. Louis, MO, United States; Lujain Jaza, Washington University in St. Louis School of Medicine, balllwin, MO, United States; Leslie Walther, Washington University in St. Louis School of Medicine, St. Louis, MO, United States; Nimisha Sulejmani, CareDx, Brisbane, CA, United States; Kim Clark-Langone, CareDx, Brisbane, CA, United States; Robert N. Woodward, CareDx, Brisbane, CA, United States

Background: Donor‐derived cell‐free DNA (dd‐cf DNA) is a noninvasive peripheral blood biomarker for the monitoring of allograft integrity in kidney transplantation. The % dd-cf DNA is expressed as the percent of donor DNA to total (donor plus recipient) cell free DNA. In children, the size disparity between the allograft and recipient, a lower background cf DNA due to the lower turnover in children, or the higher frequency of primary viral infection after transplantation all can alter % dd-cf DNA.

Objective: In this study, we assessed the test performance of absolute amount of dd-cf DNA, measured in copies per mL of plasma, versus %dd-cf DNA for detecting transplant rejection in pediatric patients.

Design/Methods: In this retrospective single-center observational study, we studied 55 patients who had concurrent 102 dd-cf DNA levels along with kidney biopsies within the three years post-transplant. We included both surveillance biopsies (3-, 6- and 12-months post-transplant) and diagnostic biopsies. We quantified dd-cf DNA in plasma as a % fraction of the total cell-free DNA and absolute dd-cf DNA (copies/ml) by next generation sequencing using a targeted, multiplex PCR-based method for the analysis of single nucleotide polymorphisms (AlloSure, CareDx, Brisbane, CA). Treating each sample as independent, we divided the 102 biopsy samples with concurrent dd-cf DNA levels into two groups (no evidence of rejection vs any rejection including subclinical rejection) and analyzed the data

Results: In patients (n = 23 samples) with biopsy‐proven rejection, median dd‐cf DNA (cp/mL) was 5.5‐fold higher and median % dd‐cf DNA 3.1‐fold higher (89cp/mL; 0.70%, respectively) than medians in stable phase patients (n = 79 samples) without rejection (16 cp/mL; 0.22%).
Receiver operating characteristic analysis showed superior performance of absolute dd‐cfDNA level (AUC = 0.83, Figure panel A) compared to % dd‐cfDNA (AUC = 0.75; Figure panel B).

Conclusion(s): dd-cf DNA, whether measured as a percentage of total or as copies/ml is able to differentiate rejection from no-rejection. Absolute dd‐cf DNA copies (cp/mL) allowed for better discrimination than % dd‐cf DNA of pediatric kidney transplant patients with acute rejection.