A Study to Test How Safe Pozelimab and Cemdisiran Combination Therapy and Cemdisiran Alone Are and How Well They Work in Adult Patients With Generalized Myasthenia Gravis

Prior treatment

• Participants with antibody profile that is only positive for Muscle-Specific tyrosine Kinase (MuSK) (MuSK positivity is based on a documented prior history of positive serologic test for antibodies to MuSK or a positive result during screening
• History of thymectomy within 12 months prior to screening or planned during the study
• Not meeting meningococcal vaccination requirements and, at a minimum, documentation of quadrivalent meningococcal vaccination within 5 years prior to randomization and serotype B vaccine (when available) within 3 years prior to randomization as described in the protocol
• Known contraindication to meningococcal vaccines (group ACWY conjugate and group B vaccines) as described in the protocol

Other illness

• History of malignant thymoma (patients with stage 1 may be enrolled), or history of cancer within the past 5 years, except for adequately treated basal cell skin cancer, squamous cell skin cancer, or in situ cervical cancer
• Participants who require antibiotics for meningococcal prophylaxis and have a contraindication, warning, or precaution precluding the use of penicillin class and penicillin-alternative antibiotics planned to be used for prophylaxis, or a history of intolerance leading to the discontinuation of these antibiotics
• Positive hepatitis B surface antigen or hepatitis C virus Ribonucleic Acid (RNA) during screening. NOTE: Cases with unclear interpretation should be discussed with the medical monitor
• History of Human Immunodeficiency Virus (HIV) infection or a positive test at screening per local requirements
  • NOTE: Other protocol-defined Inclusion/ Exclusion Criteria apply

Other

• Myasthenic crisis or MGFA Class V within 1 month of screening

• Male or female participants ≥18 years of age at screening (or ≥ legal age of adulthood based on local regulations, whichever is older)
• Participant with documented diagnosis of Myasthenia Gravis (MG) based on medical history and supported by previous evaluations as described in the protocol
• Documented prior history of positive serologic test or a positive result during screening of Anti-acetylcholine Receptor (AChR) antibodies or anti-Lipoprotein Receptor-related Protein 4 (LRP4) antibodies
• Myasthenia Gravis Foundation of America (MGFA) Clinical Classification Class II to IVa at screening
• Myasthenia Gravis-Activities of Daily Living (MG-ADL) score ≥6 at screening. Ocular items should not contribute more than 50% of MG-ADL total score as described in the protocol
• Currently receiving an acetylcholinesterase inhibitor or documented reason for not using acetylcholinesterase inhibitor therapy per investigator
• Currently receiving an Immunosuppressive Therapy (IST) for MG, or documented reason why the participant is not taking an IST per investigator
• If currently receiving an IST, not anticipated to have IST dosage changed before randomization or during Double-Blind Treatment Period (DBTP)
• Willing and able to comply with clinic visits and study-related procedures, including completion of the primary series of the meningococcal vaccinations required per protocol
• For the optional PK sub-study: Must have a Body Mass Index (BMI) ≥ 18.5 kg/m\^2 and ≤ 30 kg/m\^2 at screening