Recombinant ADAMTS13 for Immune Thrombotic Thrombocytopenic Purpura

Abstract

In patients with immune thrombotic thrombocytopenic purpura (iTTP), autoantibodies against the metalloprotease ADAMTS13 lead to catastrophic microvascular thrombosis. However, the potential benefits of recombinant human ADAMTS13 (rADAMTS13) in patients with iTTP remain unknown. Here, we report the clinical use of rADAMTS13, which resulted in the rapid suppression of disease activity and complete recovery in a critically ill patient whose condition had proved to be refractory to all available treatments. We also show that rADAMTS13 causes immune complex formation, which saturates the autoantibody and may promote its clearance. Our data support the role of rADAMTS13 as a novel adjunctive therapy in patients with iTTP.

Figure 1.. Clinical Features of Severe Refractory iTTP.

Panel A shows the peripheral smear taken on day 0 (50X magnification) after application of a computerized algorithm for the automated detection of schistocytes (blue shaded cells). The patient’s heart rate trend (Panel B) and subcostal view on a transthoracic echocardiogram performed on day 14 (Panel C) reflect progressive pericardial tamponade, including a large circumferential pericardial effusion (red arrow) and evidence of right ventricular diastolic inversion (red arrowhead). The patient’s heart rate declined immediately following pericardiocentesis (Panel B, blue arrow). Pathologic examination of the pericardium is depicted in Panel D. At 40X magnification (left), there is fibrin on the surface of the pericardium (arrowheads). At 200X magnification (right), the fibrin (asterisks) is being organized by mononuclear cells (arrows).

Figure 2.. Laboratory Parameters Before and After Administration of Recombinant ADAMTS13.

Panels A through F depict the trajectories of key laboratory values for this patient in relation to the noted clinical events. The vertical red arrows and marks denote initiation of rADAMTS13 treatment at 80 IU/kg intravenously every 12 hours. Blue lines and shaded areas represent the corresponding mean ± 95% CI values for 102 consecutive iTTP patients in the Harvard TMA Research Collaborative dataset. The patient received daily plasma exchange treatments throughout the period shown. Panel G shows the gross appearance of the patient’s plasma pheresate at the conclusion of daily plasma exchange treatments on days 12–26. The purple arrow marks the administration of caplacizumab, while the red arrow denotes the initiation of rADAMTS13. Abbreviations: PLT, platelet count; RBC, red blood cell count; LDH, lactate dehydrogenase; MCV, mean corpuscular volume; WBC, white blood cell count.

Figure 3.. Characterization of Recombinant ADAMTS13 Function in vivo.

Panel A shows serial half-life modeling for rADAMTS13 over 14 non-consecutive days using fitted one-phase exponential decay curves based on ADAMTS13 activity levels measured at 0, 1, 4, 8, and 12 hours after administration (left) as well as the computed ADAMTS13 activity half-life by treatment day (right). The red line and data point represent the first dose, while the blue line and data point represent the 41st dose. The dotted line in the left panel represents 10% ADAMTS13 activity level, the diagnostic cutoff for severe deficiency. The results of simple linear regression analysis are shown in the right panel. Panel B depicts serial ADAMTS13 activity measurements between days 0 and 30. The vertical red arrow and mark denote initiation of intravenous rADAMTS13 treatment. Similarly, ADAMTS13 autoantibody was measured serially via two independent methods (Panel C), including titer in Bethesda-like units (BU) evaluated by FRETS-VWF73 assay (blue) and plasma anti-ADAMTS13 antibody concentration, measured by sandwich ELISA (black). The gray bar denotes periods during which rADAMTS13 (80 IU/kg) was dosed every 12 hours, while the black bar represents dosing every 24 hours. Immunoblotting of patient plasma for ADAMTS13 at 3 timepoints relative to the first dose of rADAMTS13 is shown Panel D alongside normal pooled plasma (NPP) and purified rADAMTS13 in buffer. Corresponding levels of ADAMTS13 antigen (assessed by densitometry) and activity (assessed by FRETS-VWF73 assay) are noted below the image. Assessments of total ADAMTS13 antigen and autoantibody-bound plasma ADAMTS13 levels are shown in Panel E. Sandwich ELISA assays were performed on patient plasma at the indicated times after rADAMTS13 administration to detect total plasma ADAMTS13 (red) and autoantibody-bound ADAMTS13 in the form of circulating immune complexes (CIC) (black). ADAMTS13 CIC concentration is expressed in arbitrary units (AU), while total plasma ADAMTS13 is expressed in ng/ml. Time 0 samples were drawn immediately after daily plasma exchange treatment and prior to administration of rADAMTS13. Data represents the mean (± SD) of four consecutive dosing cycles. The horizontal red dotted line represents the mean baseline plasma ADAMTS13 antigen level at time 0 (225.9 ng/ml).