Gain-of-function ADAMTS13 variants that are resistant to autoantibodies against ADAMTS13 in patients with acquired thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TIP) is primarily caused by immunoglobulin G (lgG) autoantibodies against A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats, 13 (ADAMTS13). Nearly all adult idiopathic TIP patients harbor lgGs, which bind the spacer domain of ADAMTS13, a region critical for recognition and proteolysis of von Willebrand factor (VWF). We hypothesize that a modification of an exosite in the spacer domain may generate ADAMTS13 variants with reduced autoantibody binding while preserving or enhancing specific activity. Site-directed mutagenesis was used to generate a series of ADAMTS13 variants, and their functional properties were assessed. Of 24 novel ADAMTS13 variants, 2 (ie, M4, R660K/F592Y/R568KIY661 F and MS, R660K/F592Y/R568KIY661 FN665F) exhibited increased specific activity approximately 4- to 5-fold and approximately 10-to 12-fold cleaving a peptide VWF73 substrate and multimeric VWF, respectively. More interestingly, the gain-of-function ADAMTS13 variants were more resistant to inhibition by anti-ADAMTS13 autoantibodies from patients with acquired idiopathic TIP because of reduced binding by anti-ADAMTS13 lgGs. These results shed more light on the critical role of the exosite in the spacer domain in substrate recognition. Our findings also help understand the pathogenesis of acquired autoimmune TIP. The autoantibody-resistant ADAMTS13 variants may be further developed as a novel therapeutic for acquired TIP with inhibitors. (Blood. 2012;119(16): 3836-3843) [ABSTRACT FROM AUTHOR]