Absolute versus Percent of Donor-Derived Cell-Free DNA to Detect Lung Transplantation Rejection

Abstract

<h3>Purpose</h3> Plasma donor-derived cell-free DNA (ddcfDNA) is a sensitive biomarker for acute rejection (AR). Percent ddcfDNA, expressed as percent of donor DNA to donor plus recipient cfDNA, is reliant on stable recipient cfDNA. However, lung transplant patients are predisposed to kidney and other end-organ injury, which changes recipient cfDNA. In this study, we assessed the test performance of absolute amount of ddcfDNA measured in copies per mL of plasma and %ddcfDNA for detecting lung transplant rejection. <h3>Methods</h3> Prospectively enrolled patients (n=56) were adjudicated for antibody-mediated rejection (AMR) and acute cellular rejection (ACR) using ISHLT consensus guidelines. <b>Measurement</b><i>:</i> Serially collected plasma samples (n=729) were assayed for %ddcfDNA by shotgun sequencing and for absolute ddcfDNA by digital droplet PCR using primers that target donor recipient single nucleotide polymorphisms. <b>Analysis:</b> We assessed the area under the receiver operator characteristics curve (AUROC) of %ddcfDNA and absolute ddcfDNA to detect AR, a composite endpoint of AMR and ACR. <h3>Results</h3> Over the median 19.6 months follow-up, there were 60 episodes of AR (AMR = 31, ACR = 29). ddcfDNA levels, measured as absolute or as %, were highest after transplant surgery and decayed to baseline levels of 74.7 (IQR = 45.7-116.9) Copies/mL or 0.34% (IQR = 0.21%-0.82%), respectively. Levels increased with AR compared to controls for %ddcfDNA (1.17% vs. 0.34%, <i>p = <0.</i>0001) and absolute ddcfDNA (232 versus 74 copies/mL, <i>p = 0.</i>0014). %ddcfDNA showed an AUROC of 0.73 to detect AR, higher than the AUROC of 0.66 for absolute ddcfDNA (<b>Fig.1A</b>). In select patients with increased recipient cfDNA (<b>Fig.1B</b>), absolute ddcfDNA was better to detect AR than %ddcfDNA. <h3>Conclusion</h3> %ddcfDNA performed better than absolute ddcfDNA quantitation to detect AR. However, absolute ddcfDNA detects AR better when concurrent recipient tissue injury occurs. A combination of these strategies may provide the optimal method to diagnose acute rejection.