This study is researching an investigational drug called linvoseltamab ("study drug") in participants at high risk of developing Multiple Myeloma (MM), a group commonly labeled as High-Risk Smoldering Multiple Myeloma (HR-SMM).

The aim of the study is to understand the safety and tolerability (how the body reacts to linvoseltamab) as well as the effectiveness (how well linvoseltamab eliminates plasma cells and prevents the development of MM) of the study drug. There are 2 parts to the study.

• In Part 1, linvoseltamab will be given to a small number of participants to study the early side effects (safety) of the study drug and make sure the treatment is acceptable.
• In Part 2, linvoseltamab will be given to more participants to further assess the side effects of the study drug and to evaluate the ability of linvoseltamab to treat HR-SMM and prevent progression to MM.

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

• How many participants treated with linvoseltamab (study drug) have improvement of their HR-SMM?
• What side effects may happen from taking the study drug?
• How much study drug is in the blood at different times?
• Whether the body makes antibodies against the study drug (which could make linvoseltamab less effective or could lead to side effects)

Key Inclusion Criteria:

1. High-risk SMM diagnosis within 5 years of study enrollment, as described in the protocol
2. Eastern Cooperative Oncology Group (ECOG) performance status ≤1
3. Adequate hematologic and hepatic function, as described in the protocol
4. Estimated glomerular filtration rate ≥30 mL/min/1.73 m^2

Key Exclusion Criteria:

1. Evidence of myeloma defining events *SLiM CRAB, as described in the protocol

   *SLiM (greater than or equal to Sixty percent clonal plasma cells in the bone marrow, involved/uninvolved free Light chain ratio of ≥100 with the involved free light chain (FLC) being ≥100 mg/L, MRI with >1 focal lesion) CRAB (hyperCalcemia, Renal insufficiency, Anemia, or lytic Bone lesions)

2. Diagnosis of systemic light chain amyloidosis, Waldenström macroglobulinemia (lymphoplasmacytic lymphoma), soft tissue plasmacytoma, or symptomatic multiple myeloma

3. Clinically significant cardiac or vascular disease within 3 months of study enrollment, as described in the protocol

4. Any infection requiring hospitalization or treatment with intravenous anti-infectives within 28 days of first dose of study drug

5. Uncontrolled Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV), or Hepatitis C Virus (HCV) infection; or other uncontrolled infection or unexplained signs of infection, as described in the protocol

6. History of severe allergic reaction attributed to compounds with a similar chemical or biologic composition as the study drug or excipient

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