Neuromyelitis Optica Spectrum Disorder (NMOSD) is a severe inflammatory disease of the central nervous system characterized by relapsing optic neuritis and longitudinal extensive transverse myelitis. The specific autoantibody against aquaporin 4 (AQP4-ab) has been suggested to contribute to the pathogenesis of the disease. Peripheral blood plasma cells are a major source of AQP4-ab. Previous studies have observed increased IL-6 levels in serum and cerebrospinal fluid of patients with NMOSD, particularly during relapses. Exogenous interleukin (IL)-6 promotes the survival of plasma cells and their production of AQP4-ab in vitro. And blockade of IL-6 receptor signaling by an anti-IL-6 receptor antibody reduces the survival of plasma cells in vitro. Tocilizumab (ACTEMRA®), a humanized monoclonal antibody against the IL-6 receptor, has shown beneficial clinical effects in some patients with NMOSD when concomitant immunosuppressive medications were administered. However, the long-lasting biological effects of preceding immunotherapies such as rituximab might overlap with the subsequent tocilizumab therapy. To reduce the side effects of concomitant treatments to large extent and verify the beneficial effects of tocilizumab, we evaluate the safety and efficacy of tocilizumab as monotherapy in patients with NMOSD.

The purpose of this study is to determine if the drug tocilizumab as monotherapy contributes to reduce the average relapsing rate (ARR) and improve neurological disability in NMOSD patients, who still have experienced relapses when common immunosuppressive medications including rituximab had been used.

The primary (most important) objectives of this study are to determine: Whether bortezomib reduces relapse frequency in patients with relapsing NMO. The number of attacks during the one year treatment period will be compared to the number of attacks that occurred prior to initiation of tocilizumab treatment.

The secondary objectives are to determine:

The safety profile of tocilizumab in patients with NMO and whether tocilizumab improves walking, visual function and quality of life as measured by a variety of established disability scales.

Inclusion Criteria:

1. Diagnosis of NMOSD, as defined by 2015 criteria.
2. NMOSD patients with at least one attack requiring rescue therapy in the last year or two attacks requiring rescue therapy in the last 2 years.
3. Provision of written informed consent to participate in the study.
4. Peripheral blood B cell count must be normal (5-20% of total lymphocytes) in subjects before administration of tocilizumab.
5. EDSS <= 7.5 (8 in special circumstances).

Exclusion Criteria:

1. Current evidence or known history of clinically significant infection (HSV, VZV, CMV, EBV, HIV, Hepatitis viruses, Syphilis, etc)
2. Pregnant, breastfeeding, or child-bearing potential during the course of the study
3. Patients will not participate in any other clinical therapeutic study or will not have participated in any other experimental treatment study within 30 days of screening
4. Participation in another interventional trial within the last 3 months
5. Heart or kidney insufficiency
6. Tumor disease currently or within last 5 years
7. Clinically relevant liver, kidney or bone marrow function disorder
8. Receipt of rituximab or any experimental B-cell depleting agent within 6 months prior screening and B-cells below the lower limit of normal.
9. Receipt of IVIG within 1 month prior to randomization.
10. Receipt of any other concomitant immunosuppressive therapies including corticosteroids, azathioprine, mycophenolate mofetil.