Introduction: Donor-derived cell-free DNA (dd-cfDNA) emerged as a candidate biomarker for detecting graft injury, particularly from antibody-mediated rejection, and is currently proposed to complement donor-specific antibodies (DSAs) as an alloimmune-mediated injury surveillance method. We sought to investigate the impact of an initial increase of dd-cfDNA level on subsequent decline in graft function.

Materials: The study included all kidney transplant (KT) recipients that underwent dd-cfDNA testing as part of their clinical care between September 2017 and December 2019 at our center. Only patients with a follow-up of at least 12 months were included in this analysis. An elevated dd-cfDNA was defined as a level over 0.5%.

Results: Of the 171 KT recipients tested for dd-cfDNA, 49 were followed for at least 12 months since initial testing. The study cohort had an initial serum creatinine and eGFR of 1.64 ± 0.58 mg/dl and 48 ± 21 ml/min/1.73m2, respectively. Overall, the absolute and percentual decline of eGFR were -0.12 ml/min/month (IQR, -0.43 to 0.56) and -4.26% (IQR, -20.5% to 17%), with 26.5% and 10.2% of patients having an eGFR decline of more than 15% and 30%, respectively. Fifteen patients (30.6%) had an elevated dd-cfDNA (over 0.5%) and had a similar baseline allograft function compared to those without an elevated dd-cfDNA level. After a median follow-up period of 15.3 months (IQR:13.6-19), patients with elevated dd-cfDNA had a faster decline of eGFR [absolute eGFR decline, -0.21 ml/min/month (IQR, -0.36 to 0.22); percentual GFR decline, -8.7% (IQR, -25% to 4.4%)], compared to those without elevated dd-cfDNA [absolute eGFR decline, +0.03 ml/min/month (IQR, -0.5 to 0.6); percentual GFR decline, +1.14% (IQR, -14% to 28%)](p=0.09)(Figure 1). Similarly, there was a tendency for a higher percentage of patients with elevated dd-cfDNA for a decline of eGFR greater than 15% (33.3% vs. 23.5%, p=0.5) or 30% (13.3% vs. 8.8%, p=0.6), respectively. In addition, patients with DSAs and an elevated dd-cfDNA showed a greater percentual eGFR decline (-9.1±16.5%), compared to those with DSAs and normal dd-cfDNA (+3.3±21.1%), or to those without DSAs and normal dd-cfDNA (+2.3±18.05%). In multivariable logistic regression analysis, an elevated dd-cfDNA level was independently associated with the subsequent percentual decline of eGFR (OR, 0.96; 95%CI, 0.93 to 1.00; p=0.05).

Conclusion: We have shown that despite initial stable allograft function, a higher dd-cfDNA level associates with subsequent decline of eGFR. Thus, the initial identification of subclinical graft injury could associate with long-term graft outcomes, expanding the clinical utility of dd-cfDNA.