This study is looking at two ways to help patients with multiple myeloma after they have received a special treatment called idecabtagene vicleucel, which involves modifying a patient's own T-cells to fight cancer. One group will receive iberdomide, a medicine that may boost the immune system, while the other group will be monitored without additional medicine. Researchers hope to find out if iberdomide helps keep the cancer under control for longer than just monitoring. Key Points:

• Participants will be divided into two groups: one taking iberdomide and the other under observation.
• Regular clinic visits and tests, including blood samples and scans, are required.
• Participants will be followed for up to four years after the study treatment ends.

Participants must meet certain health criteria, including having stable disease after initial CAR-T therapy and not having any severe side effects from previous treatments. Both men and women must use effective birth control due to possible risks to unborn babies. The study aims to ensure safety and collect useful data on how iberdomide may improve outcomes for patients with multiple myeloma.