Donor-derived cell-free DNA kinetics in the first year post-transplant in patients without acute cellular rejection

Background Donor-derived cell-free DNA (dd-cfDNA) appears to be an excellent biomarker for acute cellular rejection (ACR) in heart transplant (HT) recipients. However, a significant rise in the immediate post-transplant phase probably related to direct myocardial damage during harvesting-implantation process has been described, and could potentially affect the biomarker’s performance in the first post-HT month. We sought to describe the biomarker’s kinetics in the first year post-HT in patients without ACR. Methods Prospective, multicentre study performed between 2019 and 2022. All patients underwent surveillance endomyocardial biopsy (EMB) at 7 pre-specified time points in the first post-HT year (0.5, 1, 2, 3, 4, 6 and 12 months). Dd-cfDNA levels were determined prior to each EMB, using Next Generation Sequencing technology. Results A total of 1006 pairs of EMB-dd-cfDNA from 206 patients were available for analysis (mean age 54 ±12 years, 74% male). Of these, 44 (4.3%) had clinically relevant rejection, defined as ACR grade ≥2, and 962 (95.7%) did not (562 0R and 400 1R). 15 samples that had pAMR≥1 were excluded from this analysis. We divided the 947 samples with ACR 0-1 into three subgroups, according to the time of blood sampling: at 15 days (time point 1), at 30 days (time point 2) and 2 to 12 months post-HT (time point 3). Samples with 0R that were drawn at 15 and 30 days showed significantly higher levels of dd-cfDNA than those drawn between the second month and first year post-transplant (p <0.001) (Figure 1A). When we included patients with 1R, a similar trend was observed (p <0.001) (Figure 1B). Median dd-cfDNA levels for 0R and for 0-1R at the three time points are shown in Figure 2. Conclusions Dd-cfDNA levels in patients without clinically relevant rejection are significantly higher in the first month post-transplant. Further studies are needed in order to determine if a different cut-off point for ACR during the first post-HT month is useful for ACR diagnosis.Donor-derived cell-free DNA kineticsDd-cfDNA values at three time points