This study is researching an experimental drug called mibavademab. The study is focused on patients with a condition called monogenic obesity. Monogenic obesity is caused by a change in the leptin gene that keeps it from working properly. This causes the body to not be able to feel full or control feelings of hunger.

The aim of the study is to see how well mibavademab controls the body weight and how safe it is.

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

• How much mibavademab is in the blood at different times
• Whether the body makes proteins called antibodies against mibavademab (which could stop mibavademab from working as well or could lead to side effects)
• What side effects may happen from taking mibavademab

Key Inclusion Criteria:

1. Has documented medical history of biallelic loss of function variants of the LEP gene prior to the screening visit
2. Has class ≥2 obesity at screening and at baseline, as defined in the protocol

Key Exclusion Criteria:

1. Unwilling or unable to provide, or have the treating physician provide, documented historical weight for at least 6 months prior to screening
2. History of bariatric surgery within approximately the past 12 months of study screening
3. History of weight loss of ≥5% of body weight in approximately the past 3 months of study screening
4. History of genetic causes of obesity other than/in addition to biallelic loss of function variants of the LEP gene
5. History of schizophrenia, bipolar disorder, or other mental illness that, in the opinion of the investigator, might pose a safety risk to participation in a clinical study of an investigational drug
6. Any suicidal ideation of type 4 or 5 on the Columbia Suicide Severity Rating Scale (C-SSRS) during screening or baseline, or any lifetime history of a suicide attempt, or any lifetime history of suicidal behavior, including ideation
7. Treatment with medications for weight loss or medications with known side effects of weight loss within the past approximately 3 months of study screening
8. Participants currently being treated with metreleptin, or a history of prior treatment with metreleptin as defined in the protocol

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