Study of Inebilizumab in Pediatric Subjects With Neuromyelitis Optica Spectrum Disorder

Inclusion Criteria

• Male or female participants, minimum body weight of 15 kg, age 2 to \< 18 years at the time of screening.
• Positive serum anti-AQP4-IgG result at screening and diagnosed with NMOSD according to the criteria of Wingerchuk et al, 2015.
• Documented history of one or more NMOSD acute relapses within the last year, or 2 or more NMOSD acute relapses within 2 years prior to screening.

Exclusion Criteria

• Any condition that, in the opinion of the Investigator, would interfere with the evaluation or administration of the Investigational Product or interpretation of participant safety or study results.
• Concurrent/previous enrollment in another clinical study involving an investigational treatment within 4 weeks or 5 published half-lives of the investigational treatment, whichever is the longer, prior to Day 1.
• Evidence of significant hepatic, renal, or metabolic dysfunction or significant hematological abnormality (one repeat test may be conducted to confirm results within the same screening period).
• B-cell counts \< one-half of the lower limit of normal (LLN) for age according to the central laboratory.
• Receipt of the following at any time prior to Day 1:

• Alemtuzumab
• Total lymphoid irradiation
• Bone marrow transplant
• T-cell vaccination therapy
• Receipt of rituximab or any experimental B-cell depleting agent within 6 months prior to screening unless B-cell counts have returned to ≥ one-half the LLN.
• Receipt of intravenous immunoglobulin (IVIG) within one month prior to Day 1.
• Receipt of any of the following within 2 months prior to Day 1:

• Cyclosporine
• Methotrexate
• Mitoxantrone
• Cyclophosphamide
• Tocilizumab
• Satralizumab
• Eculizumab
• Receipt of natalizumab (Tysabri®) within 6 months prior to Day 1.
• Severe drug allergic history or anaphylaxis to 2 or more food products or medicine (including known sensitivity to acetaminophen/paracetamol, diphenhydramine or equivalent antihistamine, and methylprednisolone or equivalent glucocorticoid).
• Diagnosed with a concurrent autoimmune disease that is uncontrolled (unless approved by the medical monitor).
• Recent receipt of live/attenuated vaccine or blood transfusion.

Receipt of any of the following

• Any live or attenuated vaccine within 4 weeks prior to Day 1 (administration of killed vaccines and nucleoside-modified mRNA-based vaccines is acceptable; the Sponsor recommends that Investigators ensure all participants are up to date on required vaccinations prior to study entry).
• Bacillus Calmette Guérin vaccine within one year of screening.
• Blood transfusion within 4 weeks prior to screening or during screening.

• Clinically significant serious active or chronic viral, bacterial, or fungal infection that requires treatment with anti-infectives, hospitalization, or, in the Investigator's opinion, represents an additional risk to the participant, within 2 months prior to Day 1.
• Known history of congenital or acquired immunodeficiency (e.g., due to human immunodeficiency virus [HIV] infection, splenectomy, immunosuppression-related or idiopathic T-cell deficiencies) that predisposes the participant to infection.
• Positive test for chronic hepatitis B infection at screening, defined as either:

a. Positive hepatitis B surface antigen (HBsAg), or b. Positive hepatitis B core (HBc) antibody (anti-HBc) plus negative hepatitis B surface (HBs) antibody (anti-HBs).

• Positive test for hepatitis C virus antibody.
• Negative test for varicella zoster virus (VZV)-IgG.
• History of cancer, apart from squamous cell or basal cell carcinoma of the skin treated with documented success of curative therapy > 3 months prior to Day 1.
• History of active or latent tuberculosis (TB), or a positive QuantiFERON®-TB Gold test at screening, unless treatment for TB was completed per local guidelines. Participants with latent TB or a positive QuantiFERON®-TB Gold test who are actively on anti-TB treatment can enroll if they have completed at least one month of anti-TB treatment and intend to complete the full course of anti-TB treatment. Participants with an indeterminate QuantiFERON®-TB Gold test result can enroll if a repeat QuantiFERON®-TB Gold test is negative or a tuberculin skin test is negative.
• For participants who may undergo MRI scans:

• Unable to undergo an MRI scan (e.g., hypersensitivity to Gd-containing MRI contrast agents, implanted pacemakers, defibrillators, or other metallic objects on or inside the body that limit performing MRI scans), or
• Unable to tolerate or comply with the MRI procedure.