This study is researching the experimental drugs called pozelimab and cemdisiran, and cemdisiran monotherapy. The study is focused on patients with generalized Myasthenia Gravis (gMG). Myasthenia gravis is a disease that causes weakness and fatigue in muscles in the body because the nerves and muscles are not communicating properly.

The aim of the study is to see how effective pozelimab and cemdisiran are when used in combination and when pozelimab and cemdisiran are used alone for patients with gMG.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drugs
• How the study drugs work inside the body
• How much of the study drugs are in the blood at different times
• Whether the body makes antibodies against pozelimab and cemdisiran (which could make the drugs less effective or could lead to side effects)

DBTP- Double Blind Treatment Period (24 weeks) ETP - Extension Treatment Period (28 weeks) OLTP- Open Label Treatment Period (68 weeks) FUP-Off treatment Follow Up Period (52 weeks)

Key Inclusion Criteria:

1. Male or female participants ≥18 years of age at screening (or ≥ legal age of adulthood based on local regulations, whichever is older)
2. Participant with documented diagnosis of Myasthenia Gravis (MG) based on medical history and supported by previous evaluations as described in the protocol
3. 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.
4. Myasthenia Gravis Foundation of America (MGFA) Clinical Classification Class II to IVa at screening
5. 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
6. Currently receiving an acetylcholinesterase inhibitor or documented reason for not using acetylcholinesterase inhibitor therapy per investigator
7. Currently receiving an Immunosuppressive Therapy (IST) for MG, or documented reason why the participant is not taking an IST per investigator
8. If currently receiving an IST, not anticipated to have IST dosage changed before randomization or during Double-Blind Treatment Period (DBTP).
9. 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

Key Exclusion Criteria:

1. Patients 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
2. History of thymectomy within 12 months prior to screening or planned during the study
3. 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
4. Myasthenic crisis or MGFA Class V within 1 month of screening
5. 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
6. Known contraindication to meningococcal vaccines (group ACWY conjugate and group B vaccines) as described in the protocol
7. 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
8. 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
9. History of Human Immunodeficiency Virus (HIV) infection or a positive test at screening per local requirements

NOTE: Other protocol-defined Inclusion/ Exclusion Criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry),
• the legal authority to share the data, and
• ensured the ability to protect participant privacy.

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf