Patient description: The patient is a 35-year-old woman with myasthenia gravis, class IIa. She complains of diplopia and fatigue and weakness that affects mainly her upper limbs. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She takes pyridostigmine 60 mg three times a day. But she still has some symptoms that interfere with her job. She is a research coordinator and has 3 children. Her 70-year-old father has hypertension. She does not smoke or use illicit drugs. She drinks alcohol occasionally at social events. Her physical exam and lab studies were not remarkable for any other abnormalities. BP: 110/75 Hgb: 11 g/dl WBC: 8000 /mm3 Plt: 300000 /ml Creatinine: 0.5 mg/dl BUN: 10 mg/dl Beta hcg: negative for pregnancy

Clinical trial eligibility criteria: eligible ages (years): 18.0-85.0,  Myasthenia Gravis, Generalized Diagnosis of MG class IIa to IVa inclusive (Myasthenia Gravis Foundation of America Clinical Classification). 2. Quantitative Myasthenia Gravis (QMG) score of 10 or greater. If the QMG score is < 15 no more than 4 points may be derived from items 1 or 2 (ocular motility disturbance and ptosis). 3. Documented history of acetylcholine receptor (AChR) or Muscle Specific Kinase (MuSK) antibody positive. 4. Only one immunosuppressant or immunomodulatory drug at a stable dose is allowed during the study (i) azathioprine and mycophenolate mofetil must be stable for at least 4 months prior to randomization (ii) cyclosporine must be stable for at least 3 months prior to randomization. 5. If the patient is on oral corticosteroids, methotrexate or tacrolimus at screening, the dose must be stable for at least 1 month prior to randomization. 6. If the patient is on cholinesterase inhibitors at screening, the dose must be stable for at least 2 weeks prior to randomization. 7. Women of child-bearing potential, defined as all women physiologically capable of becoming pregnant, may be included in the study if they are using highly effective methods of contraception during the study and for 12 weeks after study treatment  MGFA grade I, IVb, or V disease. 2. Documented presence of unresected thymoma. 3. Patients having undergone thymectomy or thymo thymectomy (resection of thymoma) within 6 months of screening. 4. Patients having received any of the following treatments prior to randomization: 1. IVIg or plasma exchange within 8 weeks; 2. oral or IV cyclosphosphamide treatment within 3 months; 3. IV corticosteroid bolus (dose higher than 1 mg/kg) within 3 months; 4. belimumab within 6 months. For patients who received belimumab earlier, B cell count should be within normal range; 5. rituximab within 12 months. For patients who received rituximab earlier, B cell count should be within normal range; 6. any other biologic or an investigational drug within 1 month or five times thehalf-life, whichever is longer. 7. Live vaccines within 4 weeks of study drug infusion. 5. Patients who are at significant risk for TE as judged by the investigator or have any one of the following: 1. History of either thrombosis or 3 or more spontaneous abortions with or without the presence of anti-cardiolipin autoantibodies; 2. Presence of prolonged partial thromboplastin time (PTT)