A Pilot Study of Efgartigimod for Immune-mediated Thrombotic Thrombocytopenic Purpura (iTTP)

Inclusion Criteria: 1. Subject must provide a signed informed consent form 2. Subject is 18 years or older at the time of screening 3. Subject has a prior history of iTTP as defined by the presence of ADAMTS13 activity \< 10% with ADAMTS13 antibodies or inhibitor, thrombocytopenia (platelet count \< 100) and microangiopathic hemolytic anemia (defined by the presence of schistocytes on blood smear) 4. Subject is in clinical remission from iTTP (normal platelet count) for at least 90 days 5. Subject has ADAMTS13 activity \< 70% and \> 30% on 2 separate occasions separate by at least 7 days 6. Subject is at least 6 months from last dose of rituximab or other intravenous immunosuppression 7. If taking other oral immunosuppressants, no change in dose for at least 60 days 8. Female subjects of childbearing potential must present with a negative pregnancy test and agree to employ highly effective birth control measures for duration of study. Sexually active male subjects must agree to use an effective method of contraception for the duration of the study Exclusion Criteria: 1. Subject has been diagnosed with cTTP 2. Subject has been exposed to another investigational product within 30 days prior to enrollment or is scheduled to participate in another clinical study involving investigational product or investigational device during the course of the study 3. Subject is unable to understand the nature, scope, and possible consequences of the study. 4. Subject is pregnant or lactating 5. Subject has a known life-threatening hypersensitivity reaction to efgartigimod