Myasthenia gravis is an autoimmune condition that causes muscle weakness. Autoimmune means the body makes antibodies that attack its own cells and tissues. These types of antibodies are also known as autoantibodies. People with generalized myasthenia gravis have a weakness in many muscles.

TAK-079 is a medicine to help people with generalized myasthenia gravis.

The main aim of this study is to check if people with generalized myasthenia gravis have side effects from 2 doses of TAK-079. Other aims are to learn if TAK-079 improves their clinical condition and lowers their autoantibody levels.

At the first visit, the study doctor will check if each person can take part. For those who can take part, participants will continue with their standard medicines for this condition during the study. Each participant will have a check-up by the study doctor.

Then, the participants will have 1 of 3 treatments:

• A low dose of TAK-079.
• A high dose of TAK-079.
• A placebo. In this study, a placebo looks like TAK-079 but does not have any medicine in it.

Participants will not know which treatment they received, nor will their study doctors. This is to help make sure the results are more reliable.

For each treatment, participants will receive injections just under the skin, once a week for 8 weeks. The study doctors will check for side effects from the study treatments. The study doctors can stop or delay the injections in each participant if needed.

Then, the study doctors will continue to check for side effects for up to 24 weeks after treatment. They will also check the clinical condition of the participants, including their autoantibody levels.

Myasthenia gravis (MG) is an autoimmune disorder in which autoantibodies, such as those targeting the nicotinic acetylcholine receptor (AChR) or muscle specific kinase (MuSK), interfere with neuromuscular transmission, resulting in fatigue and weakness.

The drug being tested in this study is called TAK-079. TAK-079 is being tested to treat people who have generalized myasthenia gravis.

Main Inclusion Criteria:

1. Diagnosis of Myasthenia Gravis (MG) supported by a positive serologic test for anti-AChR or anti-MuSK antibodies at screening.
2. Myasthenia Gravis Foundation of America (MGFA) clinical classification II to IV at screening.
3. Myasthenia Gravis Activities of Daily Living (MG-ADL) total score of 6 or greater at screening, with at least 4 points attributed to nonocular items.
4. If receiving immunosuppressive drugs (ie, mycophenolate mofetil, methotrexate, cyclosporine, tacrolimus, cyclophosphamide), therapy must be ongoing for at least 6 months, with stable dosing ongoing for at least 3 months before screening. Participants receiving azathioprine must be on a stable dose for at least 6 months before screening.
5. If receiving oral corticosteroids, therapy must be ongoing for at least 3 months, with a stable dose at least 1 month before screening. Corticosteroids, including dexamethasone, must be given as oral, daily or every-other-day therapy, as opposed to pulse therapy.
6. If receiving cholinesterase inhibitors, therapy with a stable dose is required at least 2 weeks before screening.
7. The doses of concomitant standard background therapy must be expected to remain stable throughout the study unless dose reduction is required due to toxicities. Allowed background therapy is defined as no more than a cholinesterase inhibitor ± corticosteroid ± 1 steroid-sparing immunosuppressive drug (limited to azathioprine, mycophenolate mofetil, methotrexate, cyclosporine, tacrolimus, or cyclophosphamide). Participants must be on at least one allowed background medication.

Main Exclusion Criteria:

1. Presence of a thymoma (previous history of a fully encapsulated thymoma removed ≥ 12 months before screening is allowed) or history of invasive thymic malignancy unless deemed cured by adequate treatment with no evidence of recurrence for ≥ 5 years before screening.

2. History of thymectomy within 12 months before screening.

3. MGFA class I or V.

4. Received intravenous immunoglobulin (IVIg), subcutaneous immunoglobulin (SCIg), or plasmapheresis/plasma exchange within 4 weeks before screening, or an expectation that any therapy besides the participants standard background therapies may be used for treatment of MG (eg, a rescue therapy) between screening and dosing.

5. Chronic obstructive pulmonary disease (COPD) or asthma with a pre-bronchodilatory forced expiratory volume in 1 second (FEV1) <50% of predicted normal.

   Note: FEV1 testing is required for participants suspected of having COPD or asthma.

6. Received rituximab, belimumab, eculizumab, or any monoclonal antibody for immunomodulation within 6 months before first dosing. Participants with prior exposure to rituximab must have CD19 counts within the normal range at screening.

7. Known autoimmune disease other than MG that could interfere with the course and conduct of the study.

8. Received a live vaccine within 4 weeks before screening or has any live vaccination planned during the study.

9. Opportunistic infection ≤12 weeks before initial study dosing or currently receiving treatment for a chronic opportunistic infection, such as tuberculosis (TB), pneumocystis pneumonia, cytomegalovirus, herpes simplex virus, herpes zoster, or atypical mycobacteria. A mild, localized herpes simplex infection within 12 weeks of study dosing is allowed, as long as the lesion has resolved without systemic therapy prior to Day 1.

Takeda provides access to the de-identified individual participant data (IPD) for eligible studies to aid qualified researchers in addressing legitimate scientific objectives (Takeda's data sharing commitment is available on https://clinicaltrials.takeda.com/takedas-commitment?commitment=5). These IPDs will be provided in a secure research environment following approval of a data sharing request, and under the terms of a data sharing agreement.

IPD from eligible studies will be shared with qualified researchers according to the criteria and process described on https://vivli.org/ourmember/takeda/. For approved requests, the researchers will be provided access to anonymized data (to respect patient privacy in line with applicable laws and regulations) and with information necessary to address the research objectives under the terms of a data sharing agreement.