Correlation between acute cellular rejection detected with cryobiopsy and elevated dd-cfDNA in lung transplant recipients.

Introduction: Donor-derived cell-free DNA (dd-cfDNA) may be a promising biomarker for detecting acute cellular rejection (ACR) in lung transplant recipients (LTR) without the need for invasive transbronchial biopsies. We aimed to validate a clinical plasma dd-cfDNA assay for the detection of ACR, as determined by cryobiopsy, and to assess its clinical utility. Methods: In this prospective cohort, dd-cfDNA fraction was measured using a novel single-nucleotide polymorphism-based assay in LTR undergoing surveillance bronchoscopy with cryobiopsies 2, 4, 6, and 12 months after transplantation (and when indicated). Performance characteristics were calculated for LTR without ACR and LTR with ACR (defined as ACR based on pathological assessment of the cryobiopsies ≥A1). Results: The incidence of ACR (A1 (N = 2), grade A2 (N = 3), grade A3 (N = 1), and no grade A4 or antibody-mediated rejection) was 14% in 43 samples of 39 LTR. The median dd-cfDNA fraction was similar for the stable cohort and the cohort with ACR (median 0.41% [0.15% to 0.72%] vs. 0.56% [0.10% to 3.07%], p = 0.630). The area under the receiver operator characteristic curve for ACR was 59.3% (95% CI 38.3% to 80.3%). Using a ≥1% dd-cfDNA fraction threshold (≥0.5% for single lung transplantations), the negative predictive value for ACR was 87.9% (95% CI 74.1% to 97.6%), and the positive predictive value was 20.0% (95% CI 8.0% to 32.0%). In the sensitivity analysis, altering the ACR category (≥A1 vs. ≥A2) or the dd-cfDNA threshold >0.85% did not produce significant changes in the outcomes. Conclusions: The incidence of ACR (≥A1 or ≥A2) did not appear to be closely associated with the fraction of dd-cfDNA. More research with a larger sample size and long-term follow-up is needed to evaluate the association between dd-cfDNA and ACR incidence detected by cryobiopsy.