Combining donor-derived cell-free DNA and donor specific antibody testing as non-invasive biomarkers for rejection in kidney transplantation.

Donor specific anti-HLA antibodies (DSA) and donor-derived cell-free DNA (dd-cfDNA) have lead to substantial progress in the non-invasive monitoring of the renal allograft by being able to detect or rule out subclinical rejection and guide immunosuppressive changes. In this study we sought to analyze the clinical, de novo DSA (dnDSA) and histological determinants of dd-cfDNA levels. The study included a cohort of stable renal function kidney transplant (KT) recipients who underwent anti-HLA dnDSA and dd-cfDNA testing between September 2017-December 2019. Statistical models were constructed to detect association with predictors of dd-cfDNA levels and other clinical characteristics. 171 renal allograft recipients were tested for dd-cfDNA and dnDSA at a median 1.06 years posttransplant (IQR: 0.37-4.63). Median dd-cfDNA was 0.25% (IQR: 0.19-0.51), 18.7% of patients having a dd-cfDNA ≥ 1%. In a multivariate linear regression model the presence of dnDSA MFI ≥ 2500 was the best independent determinant of dd-cfDNA level (p < 0.001). Among patients tested, 54 had concurrent dd-cfDNA determination at the time of an allograft biopsy. dd-cfDNA had an AUC of 0.82 (95% CI 0.69-0.91; p < 0.001) and of 0.96 (95% CI 0.87-0.99) to discriminate any rejection and ABMR, respectively. After multivariate adjustment, the models that included ABMR (R = 0.82, R = 0.67, p < 0.001), or ptc (R = 0.79, R = 0.63, p < 0.001) showed the best correlation with dd-cfDNA level. We are confirming a strong association of dd-cfDNA with dnDSA and underlying alloimmune-mediated injury in renal allograft recipients in a cohort of patients with unsuspecting clinical characteristics for rejection and excellent allograft function. Our findings support the need for noninvasive biomarker surveillance in KT recipients and we propose that dd-cfDNA may complement dnDSA screening.