Routine C4d immunohistochemistry in cardiac allografts: Long-term outcomes

Abstract

In the past decade, C4d has emerged as a potential marker for antibody-mediated rejection (AMR); however, evidence on its use as a prognostic tool has been controversial. Although the International Society for Heart and Lung Transplantation guideline recommends early routine surveillance of C4d in heart transplantation, there is no consensus on its value in the pathologic assessment of AMR. Herein we present a correlation analysis of C4d immunoreactivity in endomyocardial biopsies with clinical cardiac dysfunction, cellular rejection, human leukocyte antigen (HLA) status, cardiac allograft vasculopathy (CAV) and death. A total of 5,840 endomyocardial biopsies from 296 heart transplant recipients (January 2004 to December 2014) were stained prospectively for C4d. Strong, diffuse endothelial staining was considered positive. All patients had at least 1 year of follow-up. Positive C4d staining was present in 53 biopsies from 28 patients. Sixteen of 28 patients had clinically significant cardiac dysfunction at the time of positive biopsy. In C4d-positive patients, the mean panel-reactive antibody (PRA) level was 33%. Ten patients demonstrated a first C4d positivity within the first year post-transplant, whereas 18 patients had C4d positivity after 1 year post-transplant. At autopsy, all 11 C4d-positive patients examined demonstrated cardiac allograft vasculopathy (CAV) as the underlying cause of death. In contrast, only 2 of 8 (25%) C4d-negative patients had CAV at autopsy. In the surviving cohort, there was an angiographic diagnosis of higher-than-moderate CAV in 10 patients (3.8%). C4d-positive patients contributed to 67% of the overall institutional mortality in heart transplant recipients. Late C4d positivity (>1 year post-transplant) demonstrated an even higher risk for developing CAV and poor prognosis than early C4d positivity (within 1 year). In the C4d-negative group with postmortem examination, 75% (6 of 8) deaths were due to non-cardiac causes. Our findings show a positive association of C4d with CAV and death. We identified a prognostic role for C4d in heart transplantation warranting routine long-term detection of this marker in the pathologic evaluation of cardiac AMR.