RNA Expression Analysis of Antibody Mediated Rejection after Heart Transplant with or without Donor Specific Antibodies

Abstract

Antibody mediated rejection (AMR) is an increasingly studied cause of graft failure after heart transplantation. AMR diagnostic criteria previously required serum donor specific antibodies (DSA). However, the most recent criteria only requires pathological findings independent of DSA. This classification defined a subset of patients with AMR without known antibodies. To investigate this complication, we performed RNA sequencing using endomyocardial biopsy samples taken at the time of pathology confirmed AMR in the presence and absence of DSA. We evaluated the transcriptome profile of the paraffin-embedded endomyocardial biopsy specimens of 30 representative heart transplant recipients. Patients were categorized as having no evidence of AMR (controls), immunohistochemical findings of AMR (pAMR1i) in the presence of DSA (1i+D), pAMR1i in the absence of DSA (1i-D), histopathological findings of AMR (pAMR1h) in the presence of DSA (1h+D), pAMR1h in the absence of DSA (1h-D) or presence of both immunohistochemical and histopathological findings of AMR (pAMR2) in the presence of DSA. A total of 5 patients were analyzed per group. All were matched for previous mechanical circulatory support and time from transplant to biopsy. There was no differential RNA expression between patients with no AMR and those in the 1i-D group. There was also no differential expression between patients in the 1h+D and pAMR2 groups. The largest difference was seen between the no AMR and 1i+D groups and the no AMR and pAMR2 groups. In addition, there was RNA expression differences between patients with immunohistochemical evidence of AMR compared to those with histopathological findings, suggesting distinct mechanisms. These studies demonstrate that RNA expression profiling can be performed on endomyocardial biopsy tissue preserved in paraffin from the time of a rejection episode and that different expression patterns are observed dependent on the criteria used to diagnose AMR. In particular, AMR in the presence of DSA showed a different RNA expression profile than AMR without DSAs. The RNA expression associated with histological markers of AMR also appeared different than that associated with immunological markers. Overall, our findings suggest the existence of different subtypes of AMR that may rely on distinct mechanisms of injury.