Inclusion Criteria:

1. Men and women 18 years or older with diagnosis of NMO/NMOSD
2. Confirmation of NMO/NMOSD status:
   1. AQP4-IgG sero-positive NMO/NMOSD with at least one attack requiring rescue therapy in the last year or two attacks requiring rescue therapy in the last 2 years
   2. AQP4-IgG sero-negative NMO with at least one attack requiring rescue therapy in the last year or two attacks requiring rescue therapy in the last 2 years
3. Able and willing to give written informed consent and comply with the requirements of the study protocol.
4. EDSS <= 7.5 (8 in special circumstances)
5. Men and women of reproductive potential must agree to use a highly effective method of birth control from screening to 6 months after final dose of the investigational product.

Exclusion Criteria:

1. Lactating and pregnant females
2. Treatment with any investigational agent within 4 weeks of screening
3. Known history of a severe allergy or reaction to any component of the investigational product formulation or history of anaphylaxis following any biologic therapy.
4. Known active severe bacterial, viral, or other infection or any major episode of infection requiring hospitalization.
5. History of alcohol, drug, or chemical abuse, or a recent history of such abuse < 1 year prior to randomization
6. Receipt of the following at any time prior to randomization:
   1. Alemtuzumab
   2. Total lymphoid irradiation
   3. Bone marrow transplant
   4. T-cell vaccination therapy
7. Receipt of rituximab or any experimental B-cell depleting agent within 6 months prior screening and B-cells below the lower limit of normal.
8. Receipt of IVIG within 1 month prior to randomization.
9. Receipt of any of the following within 3 months prior to randomization:
   1. Natalizumab (Tysabri®)b.
   2. Cyclosporin
   3. Methotrexate
   4. Mitoxantrone
   5. Cyclophosphamide
   6. Tocilizumab
   7. Eculizumab
10. History of Hepatitis B and/or Hepatitis C (Hep B/C at screening)
11. Known history of a primary immunodeficiency (congenital or acquired) or an underlying condition such as human immunodeficiency virus (HIV) infection
12. History of malignancies, apart from squamous cell or basal cell carcinoma of the skin treated with documented success of curative therapy > 3 months prior to randomization
13. Any concomitant disease other than NMO/NMOSD that required treatment with oral or intravenous steroids at doses over 20 mg a day for over 21 days