Increased Plasma Levels of Graft-Derived Cell-Free DNA Correlate With Rejection in Solid Organ Transplant Recipients.: Abstract# 594

Purpose: Circulating graft-derived cell-free DNA (cfDNA) isolated from plasma is a potential biomarker of acute cellular rejection in organ transplant recipients. We sought to investigate if plasma levels of either total or graft-derived cfDNA correlate with clinically proven rejection in heart transplant recipients and kidney transplant recipients. Methods: 118 samples from 76 subjects with heart transplants from the CARGO and CARGOII studies and 72 samples from 38 subjects with kidney transplants were selected for this cohort study. Rejection status was determined by graft biopsy. Levels of total cfDNA were determined by quantitative real-time PCR (qRT-PCR) using assays for HBA, HBB, 18S and PDCD1 genes. Investigation of the value of graft-derived cfDNA took advantage of the gender difference in female recipients with a graft from a male donor. Proportions of graft-derived cfDNA relative to total cfDNA were determined in these subjects by qRT-PCR using an assay for the male-specific TSPY-1 gene. Results: Levels of total cfDNA are not different between stable transplant recipients and subjects with biopsy-confirmed rejection (both heart and kidney). Heart transplant recipients have higher levels of total cfDNA compared to kidney transplant recipients and non-transplant healthy subjects. The graft-derived cfDNA proportion is significantly higher in subjects with biopsy-confirmed rejection compared to stable subjects. There was a median cfDNA proportion difference of 10-fold in CARGO and 5-fold in CARGOII subjects greater than 55 days post transplant when cfDNA from plasma drawn at the time of rejection was compared to plasma from stable subjects. In kidney transplant subjects greater than 55 days post transplant, the median cfDNA level from the graft was 3-fold higher in the plasma from subjects with biopsy-confirmed rejection as compared to stable subjects. Conclusion: Graft-derived cfDNA is a useful biomarker of heart and kidney transplant rejection. This non-invasive test may aid in the identification of patients with acute cellular rejection and may be applicable to monitoring other organ transplants. DISCLOSURE:Woodward, R.: Employee, XDx. Grskovic, M.: Employee, XDx. Dedrick, R.: Employee, XDx.