Donor-derived cell-free DNA (dd-cfDNA) is a potential biomarker of acute cellular rejection (ACR) in organ transplant recipients. We determined plasma levels of dd-cfDNA in heart transplant recipients with a biopsy-confirmed rejection, and compared them to levels of dd-cfDNA in non-rejecting heart transplant recipients.
In total, 151 plasma samples from 63 patients (pts) from the CARGO II multicenter trial were included in this study. For 132 samples, a biopsy was performed and graded by up to 4 independent pathologists. 28 samples assigned a biopsy grade of 2R or 3R, by at least 2 pathologists, were classified as rejection (R). 27 samples assigned a biopsy grade of 0R, by 4 pathologists, were classified as non-rejection (NR). Samples from up to two prior visits leading up to R and NR events constituted the remaining 96 samples. Circulating cfDNA purified from plasma was sequenced to quantify levels of dd-cfDNA. Using RNA extracted from mononuclear cells, AlloMap® score was determined. Standard statistical measures of correlation and significance were used.
dd-cfDNA levels were significantly higher (P=0.017) in pts undergoing biopsy-confirmed rejection (R, mean 1.7%) compared to stable pts (NR, mean 0.99%). An ROC curve yielded the AUC of 0.68 (95% CI 0.56-0.80). The mean AlloMap® score in these samples was 24.3 for NR and 28.3 for R, (P=0.007). As for the dd-cfDNA results, the AUC for the Allomap® score of these samples was 0.68 (95% CI 0.56-0.80). However, levels of dd-cfDNA and AlloMap® score were not significantly correlated, suggesting that each may provide complementary information. The two results were scaled to equivalent ranges and additively combined per sample. The resulting combined score differentiated R from NR (P<0.0001) with an AUC of 0.78 (95% CI 0.67-0.87). We analyzed 16 cases with biopsy-confirmed ACR and 2 serial samples preceding the rejection event, and found that in 10 cases the levels of dd-cfDNA were elevated in preceding samples as early as 25 days prior to rejection event.
dd-cfDNA is a useful biomarker of heart-transplant rejection. This non-invasive test may aid in the long-term monitoring of allograft health and identification of patients with ACR. Used in combination with AlloMap®, the utility of the dd-cfDNA test is further increased. (Study sponsored by CareDx, Inc.)
© 2015 Published by Elsevier Inc.