A Study of Nipocalimab Administered to Adults With Generalized Myasthenia Gravis

Myasthenia gravis (MG) is a rare, heterogeneous, neuromuscular disease characterized by fluctuating, fatigable muscle weakness. MG is caused by pathogenic autoantibodies that impair cholinergic transmission in the postsynaptic membrane at the neuromuscular junction and impair or prevent muscle contraction. Nipocalimab (also referred to as JNJ-80202135 or M281) is a fully human, aglycosylated immunoglobulin (Ig)G1 monoclonal antibody (mAb) designed to selectively bind, saturate, and block the IgG binding site on the endogenous neonatal Fc receptor (FcRn). This study will consist of a screening phase (up to 4 weeks), treatment phase (a 24-week double-blind placebo-controlled phase, and an open-label extension [OLE] phase [up to 2 years]) and a follow-up safety visit (up to 8 weeks after last infusion of study intervention). Efficacy evaluations will include assessments such as Myasthenia Gravis - Activities of Daily Living (MG-ADL) score. Safety evaluations (such as adverse events, physical examination, vital signs, electrocardiogram [ECG], and clinical laboratory tests) will be performed. The overall duration of study will be up to 4 years and 8 months.

Inclusion Criteria:

• Diagnosis of myasthenia gravis (MG) with generalized muscle weakness meeting the clinical criteria for generalized myasthenia gravis (gMG) as defined by the Myasthenia Gravis Foundation of America (MGFA) Clinical Classification Class II a/b, III a/b, or IVa/b at screening
• Myasthenia Gravis - Activities of Daily Living (MG-ADL) score of greater than or equal to (>=) 6 at screening and baseline
• Has sufficient venous access to allow drug administration by infusion and blood sampling as per the protocol
• A woman of childbearing potential must have a negative highly sensitive serum (beta-human chorionic gonadotropin [beta-hCG]) at screening and a negative urine pregnancy test at Day 1 prior to administration of study intervention
• A male participant must agree not to donate sperm for the purpose of reproduction during the study and for a minimum 90 days after receiving the last administration of study intervention

Exclusion Criteria:

• Has any confirmed or suspected clinical immunodeficiency syndrome not related to treatment of his/her gMG, or has a family history of congenital or hereditary immunodeficiency unless confirmed absent in the participant
• Has MGFA Class I disease or presence of MG crisis (MGFA Class V) at screening, history of MG crisis within 1 month of screening, or fixed weakness (and/or 'burnt out' MG)
• Has had a thymectomy within 12 months prior to screening, or thymectomy is planned during the study
• Has known allergies, hypersensitivity, or intolerance to nipocalimab or its excipients
• Has experienced myocardial infarction, unstable ischemic heart disease, or stroke within 12 weeks of screening