A Study of Mezagitamab in Adults With Chronic Primary Immune Thrombocytopenia

Primary immune thrombocytopenia (ITP) is a condition where the immune system mistakenly destroys platelets, which are cells that help stop bleeding. This leads to a low number of platelets, making it easier to bruise or bleed. The main aim of this study is to learn whether mezagitamab, when given just under the skin (subcutaneously \[SC\]), is effective in keeping the platelet count of adults with ITP stable when compared to a placebo. A placebo looks like medicine but doesn't have any active ingredients in it. The participants will be treated with mezagitamab for up to 6 months. During the study, participants will visit their study clinic several times. Participants who complete the TAK-079-3002 study or do not have any response to study treatment by week 16 (according to study criteria) will be given the opportunity to participate in a continuation study to receive open label mezagitamab (if they are eligible and the site is able to open the continuation study).