Fatal accelerated rejection with a prominent natural killer cell infiltrate in a heart transplant recipient with peripartum cardiomyopathy

Accelerated rejection is uncommon after cardiac transplantation. The mechanism is hypothesized to be mediated by cytotoxic T cells and anti-HLA antibodies resulting from a memory response to the donor allograft in sensitized patients. A role for Natural Killer (NK) cell in cellular rejection has also been suggested. We report a case of fulminant accelerated rejection in a heart transplant recipient, with a history of peripartum cardiomyopathy (PPMC). The patient had no pre-transplant donor specific antibody and flow cytometric T and B cell crossmatches were negative. Autopsy revealed left ventricular subendocardial and intramyocardial hemorrhage with diffuse lymphocytic infiltrates and myocyte damage (Grade 3R rejection). Immunohistochemistry revealed a large proportion (50-70%) of mature CD16 + NK cells with cytotoxic potential in the interstitium and the intra capillary compartments. This case highlights the need for evaluating the potential role of NK cells in accelerated rejection in heart transplant recipients.