A Double-masked, Placebo-controlled Study With Open Label Period to Evaluate MEDI-551 in Neuromyelitis Optica and Neuromyelitis Optica Spectrum Disorders

MEDI-551 is a genetically engineered humanized monoclonal antibody that binds to the B cell
specific surface antigen CD19 resulting in the depletion of B cells. CD19 positive (CD19+)
B-lineage plasmablasts are responsible for the production of autoantibodies against the AQP4
channel protein.

The main objective of this study is to determine whether MEDI-551 compare to placebo
decreases the risk of an attack in subjects with NMO/NMOSD.

This is a multicenter, multinational, randomized, double-masked, placebo controlled study
with an open-label extension period to evaluate the efficacy and safety of intravenous (IV)
MEDI-551 in adult subjects with NMO/NMOSD.

After a screening period, eligible subjects will enter a randomized-controlled period (RCP)
of maximum 197 days where they will be randomized in a 3:1 ratio to receive either IV
MEDI-551 or placebo. NMO/NMOSD attacks will be evaluated by the investigator and confirmed
against the attack criteria by an independent Adjudication Committee (AC). Subjects for whom
the attack was confirmed by the AC will be given the option to enroll into an open label
period (OLP) with MEDI-551 treatment. Subjects who complete the RCP without experiencing an
attack will be given the option to enroll into an OLP with MEDI-551 treatment. The OLP will
continue for a minimum of 1 year and a maximum of 3 years after the last subject enter the
OLP.

All subjects who discontinue from the RCP or the OLP will continue in a Safety Follow-up for
a total of 12 months from last dose to evaluate the long-term safety of the investigational
product.

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