This phase I/II trial tests the safety, side effects, best dose, and effectiveness of iberdomide in combination with belantamab mafodotin and dexamethasone in treating patients with multiple myeloma (MM) that has come back after a period of improvement (relapsed) or that does not respond to treatment (refractory). Multiple myeloma is a cancer that affects white blood cells called plasma cells, which are made in the bone marrow and are part of the immune system. Multiple myeloma cells have a protein on their surface called B-cell maturation antigen (BCMA) that allows the cancer cells to survive and grow. Immunotherapy with iberdomide, may induce changes in body's immune system and may interfere with the ability of cancer cells to grow and spread. Belantamab mafodotin has been designed to attach to the BCMA protein, which may cause the myeloma cell to become damaged and die. Dexamethasone is in a class of medications called corticosteroids. It is used to reduce inflammation and lower the body's immune response to help lessen the side effects of chemotherapy drugs. Iberdomide plus belantamab mafodotin may help slow or stop the growth of cancer in patients with multiple myeloma.

This study is designed to evaluate the safety and efficacy of nonconforming idecabtagene vicleucel (ide-cel) in participants with multiple myeloma per the approved prescribing information. This is an expanded access protocol (EAP) to be conducted at Risk Evaluation and Mitigation Strategies (REMS) qualified sites approved for commercial administration of idecabtagene vicleucel and where the EAP is authorized to be conducted for use of nonconforming idecabtagene vicleucel.

Non-conforming idecabtagene vicluecel is idecabtagene vicleucel that does not meet commercial release specifications but may be acceptable for use as an investigational product in the Expanded Access Protocol setting.

The purpose of this expanded access program (EAP) is to provide ciltacabtagene autoleucel (cilta-cel) that does not meet the commercial release specifications of CARVYKTI and is not available via the local health care system in the country where the treatment is requested.