A Study to Evaluate the Pharmacokinetics, Pharmacodynamics, Safety and Tolerability of Inebilizumab in Children With Generalized Myasthenia Gravis (gMG)

Prior treatment

• Thymectomy within 12 months prior to baseline (Day 1) visit or planned thymectomy during the duration of the treatment period.
• Unresected thymoma- Participants with benign thymoma resected \> 12 months prior to screening may enroll.
• Receipt of any biologic B-cell-depleting therapy (eg, rituximab, ocrelizumab, obinutuzumab, ofatumumab, inebilizumab) or any experimental B-cell-depleting agent in the 6 months prior to screening.
• Receipt of any other monoclonal antibody (mAb) or large molecule biologic, including but not limited to FcRn inhibitors, anti-TNF mAbs, anti-janus kinase (JAK) Stat mAbs, and complement inhibitors within 6 months prior to screening.
• Receipt of the following medications or treatments at any time prior to enrollment: alemtuzumab, total lymphoid irradiation, bone marrow transplant, T-cell vaccination therapy, natalizumab.
• Receipt of intravenous immunoglobulin (IVIg) or subcutaneous immunoglobulin (SCIg) within 4 weeks prior to enrollment.

Other illness

• History of recurrent significant infections.
• Known immunodeficiency disorder, including current infection or positive test for human immunodeficiency virus (HIV).
• Positive test for chronic hepatitis B infection at screening.
• History of untreated hepatitis C infection, or positive antibody test for hepatitis C virus (HCV).
• Active tuberculosis (TB); latent TB with no documented history of adequate treatment per local standard of care; or a positive QuantiFERON®-TB test at screening, unless treatment for TB was completed per local guidelines.
• History of progressive multifocal leukoencephalopathy.
• Participants diagnosed with congenital myasthenic syndromes.

Other

• Employees of the Sponsor, contract research organization (CRO), site staff, and their family members.
• Participants who are pregnant or breastfeeding or planning to get pregnant.

• Participant's legally authorized representative has provided informed consent when the participant is legally too young to provide informed consent and the participant has provided written assent based on local regulations and/or guidelines before any study-specific activities/procedures being initiated.
• Age ≥ 2 to \< 18 years of age on the day of enrollment.
• Diagnosis of gMG defined as:
  • Positive serologic test for anti-acetylcholine receptor (AChR) or anti-muscle-specific tyrosine kinase (MuSK) antibody (Ab) titers as confirmed at screening (1 retest allowed), and
  • At least 1 of the following:
  • History of abnormal neuromuscular transmission test results demonstrated by single-fiber electromyography or repetitive nerve stimulation; or
  • History of positive anticholinesterase test (eg, edrophonium chloride test); or
  • Participant demonstrated improvement in gMG signs on oral cholinesterase inhibitors, as assessed by the treating physician; or
  • Clinical syndrome consistent with a diagnosis of gMG, and not otherwise explained by another condition.
• Myasthenia Gravis Foundation of America Clinical Classification Class II, III, or IV at the time of screening.
• Participants must be on:
  • Corticosteroids only, with no dose increase within 4 weeks prior to screening, or
  • One allowed non-steroidal immunosuppressive therapies (IST), (azathioprine, mycophenolate mofetil, or mycophenolic acid) with continuous use for at least 6 months prior to screening and no dose increase within 4 months prior to screening, or
  • Combination of (1) corticosteroids with no dose increase within 4 weeks prior to screening and (2) one allowed non-steroidal IST with continuous use for at least 6 months prior to screening and no dose increase within 4 months prior to screening.
  • Note:
  • The maximum allowed dose of prednisone at the time of enrollment will be 40 mg/day or 80 mg every other day, or equivalent corticosteroid dose.
  • Tacrolimus is allowed in Japan only, with continued use for ≥ 6 months prior to screening and no dose increase within 4 months prior to screening.
• Participants may enter the study on a stable dose of acetylcholinesterase inhibitors (pyridostigmine dose). The acetylcholinesterase inhibitor dose must have been stable for at least 2 weeks prior to enrollment.
• Vital signs and laboratory parameters within the normal ranges at screening, or, if outside normal ranges, deemed not clinically significant by the investigator.