This clinical trial is for adult participants who have a diagnosis of immune-mediated thrombotic thrombocytopenic purpura (iTTP).
   
The purpose of this study is to find out if an investigational study drug called TAK-755 is effective in treating iTTP with and without the current standard-of-care (SoC) treatment, which is daily plasma exchange (PEX). The purpose is also to find out how safe TAK-755 is, what are the side effects that might be related to it, and how often do they occur.
   
TAK-755 is an investigational drug, which means it has not been approved by the U.S. Food and Drug Administration (FDA) and other regulatory authorities for iTTP.
   
TAK-755 will be administered as infusions (delivered through a needle into a vein). Each infusion will take about 5 minutes. Participants will be assigned randomly (like flipping a coin) to one of two groups receiving either approximately 40 units per kilogram (40 IU/kg) twice a day OR approximately 80 units per kilogram (80 IU/kg) twice a day of TAK-755 during the acute phase of their study participation. If the platelet and LDH levels have normalized and the participant has achieved clinical response, the participant will receive approximately 80 units per kilogram (80 IU/kg) of TAK-755 3 times a week for 1 week and then twice a week for 2 weeks.

Participants will be in the study for approximately 8 to 12 weeks.