A Study of TAK-079 in Adults With Persistent/Chronic Primary Immune Thrombocytopenia

Inclusion Criteria: 1. Diagnosed with ITP that has persisted for ≥3 months, diagnosed in accordance to The American Society of Hematology 2011 Evidence-based Practice Guideline for Immune Thrombocytopenia or the International Consensus Report on The Investigation and Management of Primary Immune Thrombocytopenia as locally applicable. 2. Has a mean platelet count of \<30,000/μL (and individually ≤35,000/μL) on at least 2 measurements at least 1 week apart during screening. 3. Diagnosis of ITP supported by a prior response to an ITP therapy (other than a thrombopoietin receptor agonists \[TPO-RA\]) that achieved a platelet count of ≥50,000/μL. 4. If receiving standard background treatment for ITP, treatment should be stable in dose and frequency for at least 4 weeks before dosing. 1. Permitted standard background treatments may include: 1 oral corticosteroid; ±1 immunosuppressant from the following list: azathioprine, danazol, dapsone, cyclosporine, mycophenolate mofetil, mycophenolate sodium; ±1 TPO-RA (romiplostim, eltrombopag, avatrombopag); ±fostamatinib. Corticosteroids, including dexamethasone, must be given as oral, daily or every-other-day therapy as opposed to pulse therapy. 2. The dose of any permitted standard background therapy must be expected to remain stable through the study, unless dose reduction is required because of toxicities. Exclusion Criteria: 1. Use of anticoagulants or any drug with antiplatelet effect (such as aspirin) within 3 weeks before screening. 2. Has a history of any thrombotic or embolic event within 12 months before screening. 3. Has a history of splenectomy within 3 months before screening. 4. Use of intravenous immunoglobulin (IVIg), subcutaneous immunoglobulin or anti-D immunoglobulin treatment within 4 weeks of screening, or an expectation that any therapy besides the participant's standard background therapies may be used for treatment of thrombocytopenia (e.g., a rescue therapy) between screening and dosing. 5. Diagnosed with chronic obstructive pulmonary disease (COPD) or asthma, and a prebronchodilatory forced expiratory volume in 1 second (FEV1) \<50% of predicted normal. 6. Use of rituximab or any monoclonal antibody (mAb) for immunomodulation within 4 months before first dosing. Note: Participants with prior exposure to rituximab must have cluster of differentiation (CD) 19 counts within the normal range at screening. 7. Use of immunosuppressants (such as cyclophosphamide, vincristine) other than permitted oral immunosuppressants within 6 months before first dosing. 8. Has been diagnosed with myelodysplastic syndrome. 9. Has received a live vaccine within 4 weeks before screening or has any live vaccine planned during the study. 10 Has had an opportunistic infection ≤12 weeks before initial study dosing or is currently undergoing treatment for a chronic opportunistic infection, such as tuberculosis (TB), pneumocystis pneumonia, cytomegalovirus, herpes simplex virus, herpes zoster, or atypical mycobacteria.