A Phase 2, Multicenter, Randomized, Placebo-Controlled, Double-blind Study in Patients With Acquired Thrombotic Thrombocytopenic Purpura (aTTP) to Evaluate the Pharmacokinetics, Safety and Efficacy of rADAMTS-13 (SHP655) Administered in Addition to Standard Of Care (SoC) Treatment

• Participant or legally authorized representative voluntarily signs informed consent. For participants unable to provide consent, a fully recognized medical proxy may be used according to local laws.

• Participant is 18 to 75 years old at the time of screening.

• Participant has been diagnosed with primary or secondary autoimmune acquired thrombotic thrombocytopenic purpura (aTTP) based on the following criteria:

• a) Thrombocytopenia \[drop in platelet count \>=50% or platelet count \<100,000/microlitre (μL)\] i) No more than 3 participants per arm may be enrolled with a screening platelet count \>= 50,000/μL.

• b) Microangiopathic hemolytic anemia \[elevation of lactate dehydrogenase (LDH) \>2-fold or by presence or increase of schistocytes in peripheral blood smear\].

• Willingness to fully comply with study procedures and requirements, and intention to initiate plasma exchange (PEX). Participants may be provisionally entered into the trial and undergo randomization pending the results of the ADAMTS-13 activity, anti-ADAMTS-13 antibody, and genetic testing for congenital thrombotic thrombocytopenic purpura (cTTP).

• If female of childbearing potential, participant presents with a negative pregnancy test and agrees to employ adequate birth control measures for the duration of the study. Sexually active males must use an accepted and effective method of contraception during the treatment and until a minimum of 16 days after the last dose administered.