Inhibitors of ADAMTS13: a potential factor in the cause of thrombotic microangiopathy in a renal allograft recipient

BACKGROUND: Thrombotic microangiopathy (TMA) is a well-known complication after renal allograft transplantation. In most cases, calcineurin inhibitor is believed to play a role in the development of this disorder. Recent studies have shown that a deficiency in the activity of the von Willebrand factor-cleaving metalloprotease ADAMTS13 causes thrombotic thrombocytopenic purpura. A similar mechanism occurring in patients who develop TMA after renal transplantation has not been described. METHODS: Analysis of plasma samples from a patient who developed TMA after receiving a cadaveric renal allograft revealed undetectable ADAMTS13 activity and the presence of its inhibitors. RESULTS: Discontinuation of cyclosporine and daily plasma exchange increased the ADAMTS13 activity, which was followed by resolution of the microangiopathic hemolysis and improvement of the graft function. At 3-month follow-up, the ADAMTS13 activity remained in the normal range and no inhibitors were detected. CONCLUSIONS: This is the first case to demonstrate a correlation between the presence of ADAMTS13 inhibitors and transplant-associated TMA. Autoimmune inhibitors of ADAMTS13 should be considered in patients with transplant-associated thrombotic microangiopathy. The role of calcineurin inhibitor in the formation of autoantibodies to ADAMTS13 remains to be explored.