This clinical trial is focused on studying a condition known as Systemic Light Chain Amyloidosis, which is a disease where abnormal proteins build up in organs and tissues, causing them to not work properly. The study is testing a new treatment called Linvoseltamab, which is being evaluated for its safety and effectiveness in patients whose disease has returned or has not responded to previous treatments. The purpose of the study is to determine the best dose of Linvoseltamab and to see how well it works in achieving a complete response in the blood, which means the disease is no longer detectable.

Participants in the study will receive Linvoseltamab as a solution for infusion, which means it will be administered directly into the bloodstream through a vein. The study will be conducted in two phases. In the first phase, the focus will be on assessing the safety and tolerability of Linvoseltamab, while the second phase will evaluate its effectiveness in treating the disease. Some participants may receive a placebo, which is a substance with no active medication, to compare the effects of Linvoseltamab. Throughout the study, participants will be closely monitored for any side effects or changes in their condition.

The study aims to gather information on how Linvoseltamab affects the disease and its progression, as well as any potential side effects. This information will help determine if Linvoseltamab can be a safe and effective treatment option for people with relapsed or refractory Systemic Light Chain Amyloidosis. The trial is expected to continue for several years to ensure comprehensive data collection and analysis.