Primary Objectives:To investigate the safety and tolerability of HBM 9161 in patients with attack of NMOSD in China

This is an open-label, dose exploration study.The investigational drug is HBM9161 injection, and the indication is NMOSD.

HBM9161(HL161BKN) is a human monoclonal antibody. HBM9161 targets the neonatal Fc receptor (FcRn) . By blocking the FcRn IgG-Fc binding site and accelerating the degradation of IgG, it can significantly reduce the total IgG level in blood (including pathological IgG).The serum aquaporin 4 antibody (AQP4-IgG) associated with NMOSD is a pathological IgG, so the combination of standard of care which is intravenous methylprednisolone (ivMP) with HBM9161 is expected to rapidly reduce AQP4-IgG levels.

Two dose groups (340 mg and 680 mg) were planned, and each dose group plans to enroll approximately 6 subjects. All subjects are weekly administered the HBM9161 by subcutaneous injection for a period of 4 weeks, together with standard of care which is of intravenous methylprednisolone (ivMP) by subcutaneous for a period of 4 weeks. The study will investigate the safety, and tolerability, pharmacodynamics and efficacy of HBM 9161 in patients with attack of NMOSD in China.

Inclusion Criteria:

1. In visit 1, Male or female aged ≥ 18 years.

2. Patient with NMOSD as defined by 2015 NMOSD diagnostic criteria by IPND (International Panel for NMO Diagnosis).

3. Core clinical manifestations characterized by new acute optic neuritis and/or transverse myelitis. A clinical event is defined as an episode of inflammation in the spinal cord and/or optic nerve leading to neurologic deficits which can be identified by physical examination and not attributable to another disease process.

4. The EDSS score should be ≥ 2.5 and ≤7.5 at visit 1.

5. AQP4-IgG is positive at visit 1 or had AQP4-IgG positive medical records before visit 1.

6. Be able to recognize English letters.

7. Patients should be on stable treatment of the following medications before screening (if anyone had a stable treatment ):

   • Immunosuppressant or immunomodulatory drugs (for example, azathioprine, cyclophosphamide, mycophenolate mofetil, tacrolimus, methotrexate and so on) must be stable for at least 8 weeks before screening and keep stable during study

     • Corticosteroids

   • At screening, the treatment dose must be stable for at least 1 month. • If patients accepted plasmapheresis or IVIg treatment, the last treatment dose/procedure must be finished at least 4 weeks ago before screening

Exclusion Criteria:

1. No acute optic neuritis and/or transverse myelitis symptoms or signs.
2. Severe NMOSD which may require plasmapheresis or intravenous immunoglobulin (IVIG) treatment, in opinion of investigator, very soon.
3. Have received plasmapheresis or IVIG treatment, the last treatment dose/procedure is less than 4 weeks before visit 1.
4. Have known autoimmune diseases other than NMOSD that would interfere with efficacy assessment or participation in this study (such as uncontrolled thyroid disease or severe rheumatoid arthritis), or have any comorbid diseases which would interfere with the efficacy evaluation of HBM9161 on NMOSD.
5. Have received rituximab or other anti-CD20 drugs treatment within 6 months before visit 1.
6. Have been used any monoclonal antibodies or research drugs for immunomodulatory effects within 3 months before visit 1 or within 5 half-life periods of the drug.
7. Females who are pregnant or lactating.
8. Patients who can't tolerate or have contraindication to high dose intravenous methylprednisolone per Investigator's opinion.
9. Have active infection at screening, or recent serious infection (i.e., requiring intravenous antimicrobial therapy or hospitalization) within 8 weeks before screening; history of or existing infection of human immunodeficiency virus(HIV), hepatitis C virus (HCV), or Mycobacterium tuberculosis. Patients must have negative test results for HCV antibody, HIV 1 and HIV 2 antibodies, and a mycobacterium tuberculosis test (test method to be determined) at visit 1.
10. Patients have positive test result for HBsAg; or HBsAg negative meanwhile HBcAb positive and HBV-DNA level>2000IU/mL.
11. Serum total IgG <700mg/dL at visit 1.
12. Absolute neutrophil count <1500个/mm3 at visit 1 and/or visit 2
13. Patients with acute liver function impairment (e.g., hepatitis) or severe liver cirrhosis (Child-Pugh Score, Class C)
14. Any malignant tumor.