Are Two Tests Better Than One? Combining Donor Derived Cell-Free DNA and Gene Expression Profiling for Non-Invasive Surveillance after Heart Transplantation

Abstract

Endomyocardial biopsy (EMBx) is the gold standard for acute cellular rejection (ACR) after heart transplantation (HTx). However, the limitations of EMBx has led to the adoption of non-invasive rejection surveillance. With the commercial introduction of gene-expression profiling (GEP) and more recently, donor-derived cell-free DNA (cfDNA), the predictive ability of cfDNA and its utility in combination with GEP are not well known. Retrospective study of data from Allosure cfDNA and AlloMap GEP assays (CareDx). We collected cfDNA results from the D-OAR Registry as well as cfDNA and GEP from clinical testing, then evaluated the combination of these results with EMBx results to derive test sensitivity (SN), specificity (SP), positive predictive (PPV) and negative predictive values (NPV) for cfDNA using a threshold of 0.2%. We also assessed the utility of both non-invasive assays in combination. We included 168 patients (total 422 samples) with 67 patients from the initial D-OAR cohort. This cohort was predominantly male (72%) and Caucasian (60%) with a median (IQR) 316 (238 - 484) days from transplant to cfDNA test. We found a SN of 0.78, SP 0.75, PPV 0.30 and NPV of 0.96 to detect ACR. Among patients who had EMBx, GEP and cfDNA, 70% had concordant cfDNA and GEP results (Fig 1A). Of those with a positive cfDNA but negative GEP, none had significant (<2R) rejection. In our cohort after both assays were available, there were 101 patients who had surveillance 237 times with both tests. In 85% (n=201) both tests were below threshold and, of these, 97% had no biopsy (Fig 1B). When monitoring patients with both cfDNA and GEP, the most common result was that both were below threshold. When the results were discordant and a biopsy was performed, no treatable ACR was observed. The use of combination non-invasive testing may allow for safe and complementary information for rejection surveillance after HTx.