NL80681.078.22

Treatment tested

• Imlifidase

  Antibodies hydrolytic enzyme

Inclusion: - 1. Signed lnformed Consent obtained before any study-related procedures. 2. Willingness and ability to comply with the protocol. 3. Male or female aged 􀀪18 years at the time of screening. 4. NMOSD diagnosed according to the Wingerchuck criteria[4] with a positive anti-AQP4 lgG serum test using a cell-based assay at presentation or in medical history. 5. Onset of weakness or loss of visual acuity due to the exacerbation of NMOSD is not more than 14 days prior to administration of imlifidase. 6. Exacerbation of myelitis is associated with an increase in functional system motor score of at least 1 point, and requires at least bilateral assistance to walk; exacerbation of uni­or bilateral optie neuritis is associated with an increase in functional system visual score of at least 1 point, and results in a visual acuity of 20/60 to 20/99 (0.33-0.21) or worse. 7. Acute steroid treatment is indicated. 8. Incident cases or prevalent cases treated with maintenance/ prophylactic therapies including azathioprine, mycophenolate mofetil/mycophenol acid, and rituximab, or no maintenance treatment. 9. Negative serological screening test for hepatitis B surface antigen, hepatitis C antibody, or human immunodeficiency virus. 10. Wamen of child-bearing potential willing or able to use at least one highly effective contraceptive method from the day of treatment until at least 6 months after the dose of imlifidase if not abstinent. In the context of this study, an effective method is defined as those which result in low failure rate (i.e. less than 1 % per year) when used consistently and correctly 11. Men willing to use double-barrier contraception from the day of treatment until at least 2 months after the dose of imlifidase if not abstinent. Exclusion: - 1. Previous treatment with imlifidase 2. Subjects who are already on plasma exchange. 3. lntravenous immunoglobulin (IVlg) treatment S28 days prior to administration of imlifidase 4. Wamen of child-bearing potential unwilling or unable to use at least one highly effective contraceptive method from the screening visit until at least 180 days following imlifidase dosing. 5. Signs or symptoms suggestive of Thrombotic Thrombocytopenic Purpura (TTP). 6. Hypersensitivity to IVlg or to any of the excipients. 7. Subject known to have a severe concurrent disease, e.g. malignancy, severe cardiovascular disease and severe chronic obstructive pulmonary disease. 8. Any condition that in the opinion of the investigator could increase the subject's risk by participating in the study or confound the outcome of the study. 9. Known mental incapacity or language barriers precluding adequate understanding of the lnformed Consent information and the study activities. 10. Subjects with clinical signs of ongoing infectious diseases that requires treatment. 11. Subjects with active SARS-CoV-2 (COVID-19) infection as shown by PCR 12. Subjects should not have received other investigational drugs within 5 half-lives prior to imlifidase dosing.

To analyse the proportion of participants with a depletion of circulating pathogenie anti-AQP4 lgG antibodies below detection limit as measured with a cell-based assay in the timeframe within 6 hours after treatment with imlifidase in participants presenting with severe optie neuritis and/or myelitis.