Identification of Heart Transplant Rejection Subtypes With Circulating MicroRNAs.

BACKGROUND: Circulating microRNAs are promising biomarkers of acute cellular rejection (ACR) and antibody-mediated rejection (AMR) in heart transplantation. The study objective was to assess the characteristics and diagnostic performance of previously identified microRNAs and clinical rejection scores (CRS) in distinct blood samples obtained at the time of an endomyocardial biopsy (EMB). METHODS: In the 5-center, prospective, longitudinal cohort study, GRAfT (Genomic Research Alliance for Transplantation), microRNA sequencing was performed on blood samples. The previously identified microRNAs associated with ACR (n=12) and AMR (n=17) were used to fit a logistic regression model to the current cohort, and the scores were scaled from 0 to 100. Diagnostic performance of ACR and AMR microRNA panels was assessed by the area under the receiver-operating characteristic curve. An adjusted Cox proportional hazard model evaluated the effect of CRS on long-term outcomes. RESULTS: In 173 heart transplant recipients (29% female sex, 41% Black race, median follow-up 374 days after transplant), 922 blood samples were sequenced, 720 paired with EMB. Among 14 episodes of ACR, the median ACR CRS was 78 compared with 42 without ACR, P<0.001. Among 25 episodes of AMR, median AMR CRS was 75 compared with 53 without AMR, P<0.001. The area under the receiver-operating characteristics curve for the CRS was 0.93 for ACR and 0.92 for AMR. Using a CRS threshold of 65, the ACR CRS had 79% sensitivity, 97% specificity, and 100% negative predictive value; the AMR CRS had 84% sensitivity, 86% specificity, and 99% negative predictive value. The ACR and AMR CRS were both <65 in 589 (82%) of the tests. After adjustment, a 10-point increase in CRS was associated with ≥42% increase in hazard of the composite outcome: subsequent ACR or AMR by EMB, allograft dysfunction, or death (ACR hazard ratio, 1.42 [95% CI, 1.20-1.69]; P<0.001; AMR hazard ratio, 1.45 [95% CI, 1.14-1.86]; P=0.003). CONCLUSIONS: Circulating microRNAs reliably identified ACR and AMR on EMB. An elevated microRNA CRS was associated with an increased risk of subsequent rejection, allograft dysfunction, or death. This biomarker, with further validation, can serve as a noninvasive test to screen and diagnose ACR and AMR without the need for an EMB. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02423070.