Absolute quantification of donor-derived cell-free DNA as a marker of rejection and graft injury in kidney transplantation: Results from a prospective observational study.

Donor-derived cell-free DNA (dd-cfDNA) is a noninvasive biomarker for comprehensive monitoring of allograft injury and rejection in kidney transplantation (KTx). dd-cfDNA quantification of copies/mL plasma (dd-cfDNA[cp/mL]) was compared to dd-cfDNA fraction (dd-cfDNA[%]) at prespecified visits in 189 patients over 1 year post KTx. In patients (N = 15, n = 22 samples) with biopsy-proven rejection (BPR), median dd-cfDNA(cp/mL) was 3.3-fold and median dd-cfDNA(%) 2.0-fold higher (82 cp/mL; 0.57%, respectively) than medians in Stable Phase patients (N = 83, n = 408) without rejection (25 cp/mL; 0.29%). Results for acute tubular necrosis (ATN) were not significantly different from those with biopsy-proven rejection (BPR). dd-cfDNA identified unnecessary biopsies triggered by a rise in plasma creatinine. Receiver operating characteristic (ROC) analysis showed superior performance (P = .02) of measuring dd-cfDNA(cp/mL) (AUC = 0.83) compared to dd-cfDNA(%) (area under the curve [AUC] = 0.73). Diagnostic odds ratios were 7.31 for dd-cfDNA(cp/mL), and 6.02 for dd-cfDNA(%) at thresholds of 52 cp/mL and 0.43%, respectively. Plasma creatinine showed a low correlation (r = 0.37) with dd-cfDNA(cp/mL). In a patient subset (N = 24) there was a significantly higher rate of patients with elevated dd-cfDNA(cp/mL) with lower tacrolimus levels (<8 µg/L) compared to the group with higher tacrolimus concentrations (P = .0036) suggesting that dd-cfDNA may detect inadequate immunosuppression resulting in subclinical graft damage. Absolute dd-cfDNA(cp/mL) allowed for better discrimination than dd-cfDNA(%) of KTx patients with BPR and is useful to avoid unnecessary biopsies.

Association between pharmacodynamic biomarkers and clinical events in the early phase after kidney transplantation: a single-center pilot study.

INTRODUCTION: Strategies based on monitoring pharmacodynamic effects are increasingly evaluated to individualize immunosuppressive therapy. In the present investigation, both drug-specific and general pharmacodynamic biomarkers were assessed and their association with clinical events early after kidney transplantation was examined. METHODS: Thirty-five de novo kidney transplant patients receiving basiliximab, enteric-coated mycophenolate sodium (2×720 mg/day), steroids, and tacrolimus (target: 6-8 µg/L) were included. Blood was drawn on days 7(±1) and 21(±2) after transplantation. Mononuclear leucocytes were isolated and the following parameters were investigated: inosine monophosphate dehydrogenase activity (high-performance liquid chromatography-diode array detection), cell proliferation (bromodeoxyuridine test), and CD marker cell surface expression (CD25, CD71, CD26) on stimulated (phytohemagglutinin 2.5 µg/10(6) cells) and nonstimulated CD3 cells. Acute rejection, gastrointestinal adverse effects, leucopenia, and infections were monitored over 3 months. RESULTS: There was no association between clinical events and inosine monophosphate dehydrogenase activity apart from patients with diarrhea showing a significantly higher inosine monophosphate dehydrogenase activity 2 hours after the enteric-coated mycophenolate sodium dose (P<0.05). Cell proliferation was significantly reduced in patients with leucopenia (P<0.05). CD71 expression was less inducible in patients with infections (P<0.05). A lower CD26 expression on non stimulated CD3 cells predicted freedom from rejection (Day 7; negative predictive value 100%). No associations were found between CD25 expression and events. CONCLUSIONS: A potential benefit of pharmacodynamic monitoring to optimize immunosuppressive combination therapy has been demonstrated. In particular, CD26 and CD71 may be promising biomarkers to assess adequate immunosuppression in the early phase after kidney transplantation. The results of this pilot study require verification in further trials with more patients and events as well as with different graft types.