A Phase III Study of TACI-antibody Fusion Protein Injection (RC18) in Subjects With Neuromyelitis Optica Spectrum Disorders

Inclusion Criteria: * Meet the 2015 international consensus diagnostic criteria for Neuromyelitis Optica Spectrum Disorders and astrocyte water channel aquaporin-4 (AQP4) antibody positivity. * EDSS 0-7.5 * Clinical evidence of at least 2 relapses within the first two years of randomization and/ or 1 relapse within the first one year of randomization * Consent to use effective contraception during the study period (women of childbearing age) * Voluntarily signed informed consent Exclusion Criteria: * Abnormal laboratory parameters need to be excluded, including but not limited to: * Currently suffering from active hepatitis or serious liver disease and medical history * Patients were treated with rituximab or other monoclonal antibodies within 6 months prior to randomization . * Any concomitant disease other than neuromyelitis optica（NMO）/ neuromyelitis optica Spectrum disorders（NMOSD）that required treatment with lucocorticoid. * pregnant , lactating women and men or women who have birth plans during the research; * Have a history of allergic reaction to contrast agent for parenteral administration and human biological medicines. * Receipt of intravenous immune globulin （ IVIG） within 28 days prior to randomization. * Receipt of any of the following prior to randomization: Azathioprine,Cyclosporin, Methotrexate Mitoxantrone,Cyclophosphamide,Tocilizumab,Tacrolimus,Mycophenolate,and Patients discontinued more than 5 times the half-life of the drug before they could get into the group .If the patients taking leflunomide and teriflunomide,they should need to take colestyramine for elution. * Have participated in any clinical trial in the first 28 days of the initial screening or 5 times half-life period of the study compound (taking shorter time ). * The patients have severe psychiatric symptoms and are not compatible with clinical studies * Malignant tumor patients ; * patients experienced any of the following events within 12 weeks before screening : myocardial infarction, unstable ischemic heart disease, stroke, or New York Heart Association class IV heart failure * Patients can't accept magnetic resonance imaging inspection during the trial. * Infection with herpes zoster or HIV virus at the screening; * The anti-hepatitis C virus （anti-HCV） of patients show positive; * Investigator considers candidates not appropriating for the study.