Patient description: The patient is a 16-year-old girl recently diagnosed with myasthenia gravis, class IIa. She complains of diplopia and weakness affecting in her upper extremities. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She is on acetylcholinesterase inhibitor treatment combined with immunosuppressants. But she still has some symptoms. She does not smoke or use illicit drugs. She is not sexually active, and her menses are regular. Her physical exam and lab studies are 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): 18.0-999.0,  Myasthaenia Gravis years and older, with life expectancy of greater than 1 year MG of class II to IVa inclusive Acetylcholine receptor (AChR) or muscle specific kinase (MuSK) antibody positive Stable dose (defined as no dose changes) not exceeding the maximum doses given in Section 5.6.1 of the following therapy(ies) prior to screening: Cholinesterase inhibitor(pyridostigmine or equivalent) for at least 2 weeks prior to screening and no immunosuppressants; Cholinesterase inhibitor (pyridostigmine or equivalent) for at least 2 weeks prior to screening and/or only one of the following: prednisone (up to 40 mg/day or equivalent) for at least 1 month prior to screening; azathioprine for at least 6 months prior to screening; mycophenolate for at least 6 months prior to screening, or cyclosporine for at least 3 months prior to screening; or Cholinesterase inhibitor (pyridostigmine or equivalent) for at least 2 weeks prior to screening and/or prednisone (up to 20 mg/day or equivalent) for at least 1 month prior to screening and only one of the following: azathioprine for at least 6 months prior to screening, mycophenolate for at least 6 months prior to screening, or cyclosporine for at least 3 months prior to screening Quantitative Myasthenia Gravis (QMG) score of 8 or greater, with at least 4 points derived from signs other than ocular A female subject is eligible to participate if she is: Of non-childbearing potential; Of childbearing potential and NOT pregnant or nursing, has a negative serum pregnancy test at screening, and agrees to one of the following: Complete abstinence from penile-vaginal intercourse, when this is the female's preferred and usual lifestyle, for the period from consent into the study until 16 weeks after the last dose of investigational product; or Consistent and correct use of one of the following acceptable methods of birth control for the period from consent into the study until 16 weeks after the last dose of investigational product: Oral contraceptives (either combined or progesterone only), Injectable progesterone, Implants of etonogestrel or levonorgestrel, Estrogenic vaginal ring, Percutaneous contraceptive patches, Intrauterine device (IUD) or intrauterine system (IUS) with a documented failure rate of less than 1% per year, Male partner sterilization (vasectomy with documentation of azoospermia) prior to the female subject's entry into the study; this male must be the sole partner for the subject, Double barrier method: condom and an occlusive cap (diaphragm or cervical/vault caps) with a vaginal spermicidal agent (foam/gel/film/cream/suppository) Capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form Single QTc less than 450 msec; or QTc less than 480 msec in subjects with Bundle Branch Block AST and ALT less than 2xULN; alkaline phosphatase and bilirubin less or = to 1.5xULN (isolated bilirubin greater than 1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin less than 35%)  Participated in a clinical trial and has received an investigational product within 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer) prior to screening or planning to take any investigational drug for the planned duration of study participation (6 months after the last dose of study drug) Presence or previous history of thymoma Thymectomy within 12 months Clinically significant (in the opinion of investigator) abnormal laboratory values Pregnant females as determined by positive (serum) hCG test at screening or prior to dosing, or lactating females or planning to become pregnant within 16 weeks after last dose of investigational product History of sensitivity to any of the study medications, or components thereof or a history of drug or other allergy that, in the opinion of the investigator or GSK Medical Monitor, contraindicates their participation May require (in the opinion of investigator) treatment with IVIg and/or plasmapheresis during the 24 week treatment period Have received IVIg and/or plasmapheresis within 90 days prior to screening Have received any other biopharmaceutical agent (except IVIg as described in #8) in the 364 days prior to screening Have received treatment with any B cell targeted therapy (e.g., rituximab, belimumab), at any time