A Proof-of-Concept Trial to Study the Safety and Activity of Linvoseltamab in Adult Participants With Smoldering Multiple Myeloma at High Risk of Developing Multiple Myeloma

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)