Background: Donor-derived cell-free DNA (dd-cfDNA) shows good diagnostic performance for the detection of antibody-mediated rejection (AMR) in kidney transplant recipients (KTR). However, the clinical benefits of dd-cfDNA monitoring need to be established. Early diagnosis of AMR at potentially reversible stages may be increasingly important due to emerging treatment options for AMR. We hypothesized that monitoring dd-cfDNA in KTR with de novo donor-specific anti-HLA antibodies (dnDSA) and performing kidney biopsy in case of increased dd-cfDNA may reduce time to AMR diagnosis in comparison with clinical indication biopsy. Methods: In this diagnostic, single-center, open-label, randomized clinical trial, we assigned 40 KTR with prevalent dnDSA and estimated glomerular filtration rate ≥20 mL/min/1.73 m2, but without previous biopsy-proven AMR, to either dd-cfDNA-guided biopsy (intervention group) or clinician-guided biopsy (control group) over a 12-month period. In both groups, dd-cfDNA was assessed at inclusion and 1, 3, 6, 9 and 12 months. In the intervention group, dd-cfDNA >50 copies/mL indicated a biopsy. Biopsies for clinical indication could be performed at any point during the study period in both groups. A protocol biopsy was scheduled after 12 months for patients without dd-cfDNA-guided biopsy or clinical indication biopsy until study completion. The primary endpoint was time from study inclusion to diagnosis of active or chronic active AMR. Results: Thirty-nine of 40 patients had functioning grafts at study completion. From these, 26 patients underwent biopsy, 13 in each group. AMR was diagnosed earlier in the intervention group than in the control group [median 2.8 months, interquartile range (IQR) 1.7–5.3 vs median 14.5 months, IQR 13.3–16.7, P = .003]. Longitudinal dd-cfDNA monitoring had 77% positive predictive value and 85% negative predictive value for AMR. Conclusions: Dd-cfDNA-guided biopsy in KTR with prevalent dnDSA can reduce the time to AMR diagnosis and hereby expedite therapy initiation. Trial registration: ClinicalTrials.gov, NCT04897438.

Background: De novo donor-specific HLA antibodies (dnDSA) are key factors in the diagnosis of antibody-mediated rejection (ABMR) and related to graft loss.Methods: This retrospective study was designed to evaluate the natural course of dnDSA in graft function and kidney allograft survival and to assess the impact of mean fluorescence intensity (MFI) evolution as detected by annual Luminex^® screening. All 400 kidney transplant recipients with 731 dnDSA against the last graft (01/03/2000-31/05/2021) were included.Results: During 8.3 years of follow-up, ABMR occurred in 24.8% and graft loss in 33.3% of the cases, especially in patients with class I and II dnDSA, and those with multiple dnDSA. We observed frequent changes in MFI with 5-year allograft survivals post-dnDSA of 74.0% in patients with MFI reduction ≥ 50%, 62.4% with fluctuating MFI (MFI reduction ≥ 50% and doubling), and 52.7% with doubling MFI (log-rank p < 0.001). Interestingly, dnDSA in 168 (24.3%) cases became negative at some point during follow-up, and 38/400 (9.5%) patients became stable negative, which was associated with better graft survival. Multivariable analysis revealed the importance of MFI evolution and rejection, while class and number of dnDSA were not contributors in this model.Conclusion: In summary, we provide an in-depth analysis of the natural course of dnDSA after kidney transplantation, first evidence for the impact of MFI evolution on graft outcomes, and describe a relevant number of patients with a stable disappearance of dnDSA, related to better allograft survival.

Immunosuppression withdrawal after graft failure seems to favor sensitization. A high percentage of calculated panel-reactive antibody (cPRA) and the development of de novo donor specific antibodies (dnDSA) indicate human leukocyte antigen (HLA) sensitization and may hinder the option of retransplantation. There are no established protocols on the immunosuppressive treatment that should be maintained after transplant failure. A retrospective analysis including 77 patients who lost their first renal graft between 1 January 2006–31 December 2015 was performed. Two sera were selected per patient, one immediately prior to graft loss and another one after graft failure. cPRA was calculated by Single Antigen in all patients. It was possible to analyze the development of dnDSA in 73 patients. By multivariate logistic regression analysis, the absence of calcineurin inhibitor (CNI) at 6 months after graft failure was related to cPRA > 75% (OR 4.8, CI 95% 1.5–15.0, p = 0.006). The absence of calcineurin inhibitor (CNI) at 6 months after graft loss was significantly associated with dnDSA development (OR 23.2, CI 95% 5.3–100.6, p < 0.001). Our results suggest that the absence of CNI at the sixth month after graft loss is a risk factor for sensitization. Therefore, maintenance of an immunosuppressive regimen based on CNI after transplant failure should be considered when a new transplant is planned, since it seems to prevent HLA allosensitization.

Kidney transplantation implies a significant improvement in patient survival. Nevertheless, early mortality after transplant remains high. Growth differentiation factor 15 (GDF-15) is a novel biomarker under study as a mortality predictor in multiple scenarios. The aim of this study is to assess the utility of GDF-15 to predict survival in kidney transplant candidates. For this purpose, 395 kidney transplant recipients with pretransplant stored serum samples were included. The median GDF-15 was 5331.3 (50.49–16242.3) pg/mL. After a mean of 90.6 ± 41.5 months of follow-up, 82 (20.8%) patients died. Patients with higher GDF-15 levels (high risk tertile) had a doubled risk of mortality after adjustment by clinical characteristics (p = 0.009). After adjustment by EPTS (Estimated Post Transplant Survival score) the association remained significant for medium hazards ratios (HR) 3.24 95%CI (1.2–8.8), p = 0.021 and high risk tertiles HR 4.3 95%CI (1.65–11.54), p = 0.003. GDF-15 improved the prognostic accuracy of EPTS at 1-year (ΔAUC = 0.09, p = 0.039) and 3-year mortality (ΔAUC = 0.11, p = 0.036). Our study suggests an independent association between higher GDF-15 levels and mortality after kidney transplant, adding accuracy to the EPTS score, an established risk prediction model currently used in kidney transplant candidates.

De novo donor-specific antibodies (dnDSA) may cause antibody-mediated rejection and graft dysfunction. Little is known about the clinical course after first detection of dnDSA during screening in asymptomatic patients. We aimed to assess the value of estimated glomerular filtration rate-eGFR and proteinuria to predict graft failure in patients with dnDSA and their potential utility as surrogate endpoints. All 400 kidney transplant recipients with dnDSA at our center (01/03/2000–31/05/2021) were included in this retrospective study. The dates of graft loss, rejection, doubling creatinine, ≥30% eGFR decline, proteinuria ≥ 500 mg/g and ≥ 1000 mg/g were registered from first dnDSA appearance. During 8.3 years of follow-up, graft failure occurred in 33.3% of patients. Baseline eGFR and proteinuria correlated with 5-year-graft loss (AUC-ROC 0.75 and 0.80, p < 0.001). Creatinine doubled after a median of 2.8 years (1.5–5.0) from dnDSA, and the time from doubling creatinine to graft failure was 1.0 years (0.4–2.9). Analyzing eGFR reduction ≥ 30% as surrogate endpoint (148/400), the time from dnDSA to this event was 2.0 years (0.6–4.2), with a positive predictive value (PPV) of 45.9% to predict graft loss, which occurred after 2.0 years (0.8–3.2). The median time from proteinuria ≥ 500 mg/g and ≥ 1000 mg/g to graft failure was identical-1.8 years, with PPV of 43.8% and 49.0%. Composite endpoints did not improve PPV. Multivariable analysis showed that rejection was the most important independent risk factor for all renal endpoints and graft loss. Renal function, proteinuria and rejection are strongly associated with graft failure in patients with dnDSA and may serve as surrogate endpoints.