Characteristics associated with elevated dd-cfDNA in pediatric heart transplant recipients without rejection by biopsy

Purpose We sought to evaluate the performance of donor-derived cell-free DNA (dd-cfDNA) thresholds and characteristics associated with elevated dd-cfDNA in pediatric heart transplant recipients without rejection by biopsy. Methods Pediatric heart transplant patients with paired endomyocardial biopsy (EMB) and dd-cfDNA (AlloSure) samples from a single center between 12/2022-1/2025 were retrospectively reviewed. Rejection was defined as acute cellular rejection >1A (ACR 1990 ISHLT) or pAMR >0. (While all three are 2004 ISHLT Grade 1R, we considered 1A negative and 1B and 2 positive.) Performance characteristics of elevated dd-cfDNA thresholds for rejection were examined. In patients without rejection, associations of demographic, hemodynamic, laboratory, and imaging characteristics with elevated dd-cfDNA were evaluated. Results There were 118 patients (median age at transplant of 7.4y) with 308 paired EMB and dd-cfDNA assessments. Dd-cfDNA threshold ≥0.2% yielded sensitivity of 74.1% and specificity of 58.7% to predict rejection (AUC 0.74). In the 227 assessments in 100 patients without any rejection; elevated dd-cfDNA was strongly associated with donor specific antibodies (DSA, 55.7% vs. 16.3%, p<0.0001; DSA median peak MFI 9,455 vs. 2,401, p=0.003). Of these assessments with coronary angiography, those with elevated dd-cfDNA had a higher proportion of having cardiac allograft vasculopathy compared to those without (17/50 [34.0%] vs. 15/73 [20.5%], p=0.09). Conclusion In patients without rejection, dd-cfDNA is highly correlated with DSA. With elevated dd-cfDNA, possible biopsy-negative rejection and other forms of graft injury must be considered. The clinical significance and management of elevated dd-cfDNA, especially without histopathologic rejection, warrant further study.