Neutralization of inhibitory antibodies and restoration of therapeutic ADAMTS-13 activity levels in inhibitor-treated rats by the use of defined doses of recombinant ADAMTS-13.
BACKGROUND
Acquired thrombotic thrombocytopenic purpura (TTP) is caused by an autoantibody-mediated deficiency of the von Willebrand factor-cleaving protease ADAMTS-13. Acute episodes of the disease are treated with a combination of immunosuppression and repeated cycles of plasma exchange to remove anti-ADAMTS-13 autoantibodies and, at the same time, replenish functional ADAMTS-13. Although this is often effective, the mortality rate has remained between 10% and 20%, highlighting the need for safer treatment options.


OBJECTIVE
We previously showed that, in vitro, human recombinant ADAMTS-13 (rADAMTS-13) is able to override neutralizing antibodies and restore ADAMTS-13 activity in plasma from patients with acquired TTP. In the present study, we assessed the in vivo feasibility of this strategy by using a rat model.


METHODS
Wild-type rats were adjusted to an ADAMTS-13 inhibitor (inhibitor) titer of ~ 10 BU mL(-1) with goat anti-ADAMTS-13 IgG, and treated with increasing doses of rADAMTS-13. Blood samples were drawn and analyzed for ADAMTS-13-specific parameters, including FRETS-VWF73 activity, inhibitor, and ADAMTS-13-specific immune complexes (ICs). The pharmacokinetics of ADAMTS-13 activity and inhibitors were evaluated.


RESULTS
Administration of inhibitor titer-adjusted doses of rADAMTS-13 to inhibitor-treated rats predictably restored activity. Inhibitors were readily neutralized through formation of ADAMTS-13-specific ICs, which were cleared at a higher rate than the free inhibitor. Surplus protease was enzymatically active in plasma, and showed similar pharmacokinetics to ADAMTS-13 in not inhibitor-treated rats.


CONCLUSIONS
Defined doses of rADAMTS-13 neutralized circulating anti-ADAMTS-13 antibodies and enabled reconstitution of ADAMTS-13 activity in plasma in our model, indicating that the protease may be a promising candidate for further exploration in treating acute episodes of acquired TTP.
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
B
B
Plaimauer
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
A
A
Schiviz
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
S
S
Kaufmann
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
W
W
Höllriegl
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
H
H
Rottensteiner
Baxalta Innovations GmbH, DC-Tower Vienna, Vienna, Austria.
F
F
Scheiflinger
D051722:ADAM Proteins / Q000097:blood / Q000172:deficiency / Q000276:immunology / Q000627:therapeutic use*; D000071120:ADAMTS13 Protein; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood* / Q000276:immunology / Q000633:toxicity; D000936:Antigen-Antibody Complex / Q000097:blood; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D006041:Goats / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology / Q000633:toxicity; D008297:Male; D011499:Protein Processing, Post-Translational; D011697:Purpura, Thrombotic Thrombocytopenic / Q000276:immunology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000276:immunology / Q000627:therapeutic use; D014841:von Willebrand Factor / Q000378:metabolism
D057134:Antibodies, Neutralizing; D000936:Antigen-Antibody Complex; D001323:Autoantibodies; D007074:Immunoglobulin G; D011994:Recombinant Proteins; D014841:von Willebrand Factor; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human
ADAMTS-13 protein, human; animal model; immune complex; thrombosis; thrombotic thrombocytopenic purpura, acquired