The purpose of this study is to understand the effects of long-term treatment with inebilizumab on circulating levels of immunoglobulins, B-cell counts, and other safety measures, and to further monitor repletion of immunoglobins and B-cell counts in participants with NMOSD who discontinue treatment. The objectives include:

1. To establish the nadir in circulating immunoglobulins (Ig) during chronic treatment with inebilizumab and ascertain the time needed to ensure restoration of pre-treatment baseline serum levels of IgG and IgM after discontinuation of treatment
2. To characterize B-cell counts throughout treatment with inebilizumab and after discontinuation until repletion of Immunoglobulin (Ig levels)
3. To assess long-term safety of inebilizumab
4. To assess other long-term effects of inebilizumab

This study aims to enroll 30 participants who either participated in the open-label period (OLP) of the N-MOmentum study (CD-IA-MEDI-551-1155; NCT02200770), a global registrational study that determined the safety and efficacy of inebilizumab for treatment of NMOSD, or who are newly initiating inebilizumab treatment at the discretion of their physician at participating sites.

Acquired from Horizon in 2024.

Inclusion Criteria:

1. Age 18 years or above, and able to provide written informed consent and any locally required authorization (e.g., Health Insurance Portability and Accountability Act [HIPAA] in the United States of America (USA), European Union [EU] Data Privacy Directive in the EU) obtained from the subject/legal representative prior to performing any protocol-related procedures, including screening evaluations.
2. Have completed at least 2 years in the open-label period of the N-MOmentum study or are newly initiating inebilizumab treatment at a participating site.
3. Females of childbearing potential who are sexually active with a nonsterilized male partner must use a highly effective method of contraception as outlined in the protocol (subjects in the Czech Republic only must use 1 additional method of contraception) from screening, and must agree to continue using such precautions for 6 months after treatment with inebilizumab; cessation of contraception after this point should be discussed with a responsible physician.
4. Nonsterilized males who are sexually active with a female partner of childbearing potential must use a male condom plus spermicide (subjects in the Czech Republic only must use 1 additional method of contraception) from Day 1 for 3 months after receipt of last treatment with inebilizumab.
5. Sterilized males, without the appropriate post-vasectomy documentation on the absence of sperm in the ejaculate, who are sexually active with a female partner of childbearing potential must use a condom and spermicide from Day 1 for 3 months after receipt of the last treatment with inebilizumab.

Exclusion Criteria:

1. Have any condition that would place the participant at unacceptable risk of complications, interfere with evaluation of inebilizumab or confound the interpretation of participant safety or study results.
2. Received rituximab or any other B-cell depleting agent after exit from N-MOmentum study, or within the last 12 months prior to screening for non N-MOmentum participants.
3. Known history of allergy or reaction to any component of inebilizumab formulation or history of anaphylaxis following any biologic therapy
4. Have a severe clinically significant infection, including active chronic infection such as hepatitis B
5. Have active or untreated latent tuberculosis
6. Have a history of progressive multifocal leukoencephalopathy (PML)
7. Is severely immunocompromised state
8. Have active malignancies

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.