This study is researching an experimental drug called linvoseltamab (called "study drug"). The study is focused on participants with newly diagnosed multiple myeloma (NDMM) who are eligible for high dose chemotherapy with autologous stem cell transplantation (transplant-eligible) or ineligible for autologous stem cell transplantation (transplant-ineligible).

The aim of this clinical trial is to study the safety, tolerability (how the body reacts to the drug), and effectiveness (tumor shrinkage) of linvoseltamab in study participants with NDMM as a first step in determining if the study drug has a role in the treatment of NDMM.

This study consists of 2 phases:

• In Phase 1 Parts A and B, the study drug will be given to participants to study the side effects of the study drug and to establish the regimen (initial doses and full dose) of the study drug to be given to participants in Phase 2.
• In Phase 1 Part C, the study drug will be given to participants to study the side effects when using different initial doses of the study drug.
• In Phase 2, the study drug will be given to more participants to continue to assess the side effects of the study drug and to evaluate the activity of the study drug to shrink the tumor (multiple myeloma) in participants with NDMM.

The study is looking at several research questions, including:

• What side effects may happen from taking linvoseltamab?
• What the right dosing regimen is for linvoseltamab?
• How many participants treated with linvoseltamab have improvement of their disease and for how long?
• The effects of linvoseltamab study treatment before and after transplant
• How much linvoseltamab is in the blood at different times?
• Whether the body makes antibodies against linvoseltamab (which could make the drug less effective or could lead to side effects).

Key Inclusion Criteria:

1. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2
2. Confirmed diagnosis of symptomatic Multiple Myeloma (MM) by International Myeloma Working Group (IMWG) diagnosis criteria, as described in the protocol
3. Response-evaluable myeloma, according to the 2016 IMWG response criteria, as defined in the protocol
4. No prior therapy for MM, with the exception of prior emergent or palliative radiation and up to 1 month of single-agent corticosteroids, with washout periods as per the protocol
5. Participants must have evidence of adequate bone marrow reserves and hepatic, renal and cardiac function as defined in the protocol
6. Participants must be age <70 and have adequate hepatic, renal, pulmonary and cardiac function to be considered transplant-eligible. The specific thresholds for adequate organ function are as per institutional guidance.

Key Exclusion Criteria:

1. Receiving any concurrent investigational agent with known or suspected activity against MM, or agents targeting the A proliferation-inducing ligand (APRIL)/ Transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI)/BCMA axis
2. Known Central Nervous System (CNS) involvement with MM, known or suspected Progressive Multifocal Leukoencephalopathy (PML), a history of neurocognitive conditions, or CNS movement disorder, or history of seizure within 12 months prior to study enrollment
3. Rapidly progressive symptomatic disease, (e.g. progressing renal failure or hypercalcemia not responsive to standard medical interventions), in urgent need of treatment with chemotherapy
4. Diagnosis of non-secretory MM, active plasma cell leukemia primary light-chain (AL) amyloidosis, Waldenström macroglobulinemia (lymphoplasmacytic lymphoma), or known POEMS syndrome (Plasma cell dyscrasia with polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal protein, and Skin changes)

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