Assessment of dd-cfDNA Levels in Clinically Stable Lung Allograft Recipients Beyond the Initial 2 y Posttransplant

Background. Donor-derived cell-free DNA (dd-cfDNA) is a useful biomarker for the diagnosis of acute allograft injury within the first 1 to 2 y after lung transplant, but its utility for diagnosing chronic lung allograft dysfunction (CLAD) has not yet been studied. Understanding baseline dd-cfDNA kinetics beyond the initial 2 y posttransplant is a necessary first step in determining the utility of dd-cfDNA as a CLAD biomarker. We seek to establish baseline dd-cfDNA% levels in clinically stable lung allograft recipients who are > 2 y posttransplant. Methods. We performed a prospective, single-center, observational study to identify plasma dd-cfDNA levels in clinically stable lung allograft recipients > 2 y posttransplant. Results. Fiftyone subjects were enrolled and >= 3 baseline dd-cfDNA measurements were acquired during a median of 252 d. The median baseline percent dd-cfDNA level in our cohort was 0.45% (interquartile range [IQR], 0.26-0.69). There were statistically significant differences in dd-cfDNA based on posttransplant duration (<= 5 y posttransplant median 0.41% [IQR, 0.21-0.64] versus > 5 y posttransplant median 0.50% [IQR, 0.33-0.76]; P < 0.02). However, the clinical significance of this small change in dd-cfDNA is uncertain because this magnitude of change is within the biologic test variation of 73%. Conclusions. This study is the first to define levels of dd-cfDNA in clinically stable patients who are > 2 y post-lung transplant. These findings lay the groundwork for the study of dd-cfDNA as a possible biomarker for CLAD.