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Introduction Endomyocardial biopsy (EMB)-based traditional microscopy remains the gold standard for the detection of cardiac allograft rejection, despite its limitation of inherent subjectivity leading to inter-reader variability. Alternative techniques now exist to surveil for allograft injury and classify rejection. Donor-derived cell-free DNA (dd-cfDNA) testing is now a validated blood-based assay used to surveil for allograft injury. The molecular microscope diagnostic system (MMDx) utilizes intragraft rejection-associated transcripts (RATs) to classify allograft rejection and identify injury. The use of dd-cfDNA and MMDx together provides objective molecular insight into allograft injury and rejection. The aim of this study was to measure the diagnostic agreement between dd-cfDNA and MMDx and assess the relationship between dd-cfDNA and MMDx-derived RATs which may provide further insight into the pathophysiology of allograft rejection and injury. Methods: This is a retrospective observational study of 186 endomyocardial biopsy (EMB) evaluated with traditional microscopy and MMDx. All samples were paired with dd-cfDNA from peripheral blood prior to EMB (up to 1 month). Diagnostic agreement between traditional microscopy, MMDx, and dd-cfDNA (threshold of 0.20%) were compared for assessment of allograft injury. In addition, the relationship between dd-cfDNA and individual RAT expression levels from MMDx was evaluated. Results MMDx characterized allograft tissue as no rejection (NR) (64.5%), antibody-mediated rejection (ABMR) (25.8%), T-cell-mediated rejection (TCMR) (4.8%), and mixed ABMR/ TCMR (4.8%). For the diagnosis of any type of rejection (TCMR, ABMR, and mixed rejection), there was substantial agreement between MMDx and dd-cfDNA (74.7% agreement). All transcript clusters (group of gene sets designated by MMDx) and individual transcripts considered abnormal from MMDx had significantly elevated dd-cfDNA. In addition, a positive correlation between dd-cfDNA levels and certain MMDx-derived RATs was observed. Tissue transcript clusters correlated with dd-cfDNA scores, including DSAST, GRIT, HT1, QCMAT and S4. For individual transcripts, tissue ROBO4 was significantly correlated with dd-cfDNA in both non-rejection and rejection as assessed by MMDx. Conclusion: Collectively, we have shown substantial diagnostic agreement between dd-cfDNA and MMDx. Furthermore, based on the findings presented, we postulate a common pathway between the release of dd-cfDNA and ROBO4 (a vascular endothelial-specific gene that stabilizes the vasculature) in the setting of AMR, which may provide a mechanistic rationale for observed elevations in dd-cfDNA in AMR, compared to ACR.

Introduction: Non-invasive quantification of donor-derived cell-free DNA (dd-cfDNA) has recently been shown to correlate with endomyocardial biopsy (EMB) for diagnosis of allograft rejection in heart transplant (HTx) patients. Hepatitis C virus-positive (HCV+) donor hearts are being more utilized with comparable survival outcomes. Hypothesis: The aim of this study is to evaluate the utility of dd-cfDNA monitoring in different types of rejections in recipients of HCV+ donor hearts. Methods: We performed a retrospective review of recipients of HCV+ donor hearts between 2018-2022 with paired dd-cfDNA/GEP and EMB results. The levels of dd-cfDNA/GEP were compared in different rejection types and no rejection for patients using non-parametric comparison. CMR ISHLT ≥ Grade 2R and AMR ≥ Grade 1 from histology were considered as allograft rejection. Results: There were 17 patients who underwent heart transplant from HCV+ donor heart. There was a total of 89 paired samples with dd-cfDNA and EMB. The reason for the biopsy was mostly for routine surveillance (N=68, 76.4%). There was a total of 1 case (1.1%) of grade 2 CMR and 16 cases of pAMR (18%; 10 cases of grade 1, 6 cases of grade 2). Levels of dd-cfDNA were elevated in cases of AMR when compared to no rejection (Median: 0.24% vs. 0.12%, respectively, P<0.001; Figure 1A). There were 57 samples (78%) with dd-cfDNA reference values of <0.12%. In patients with no rejection, dd-cfDNA levels were all below 0.25%. The AUC for elevation of dd-cfDNA and allograft rejection was 0.85 [95% C.I.: 0.72-0.97; P<0.001; Figure 1B]. Conclusions: Non-invasive quantitation of dd-cfDNA levels is elevated in allograft rejection as assessed by traditional microscopy from EMB. There was no false-positive rate of dd-cfDNA in allograft rejection at a threshold of 0.25%. Further studies are indicated to study whether dd-cfDNA levels transiently increase only in the setting of allograft rejection or active hepatitis C viremia at the time of biopsy.

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