This study is testing a new treatment, bb2121, for people with multiple myeloma (MM), a type of blood cancer that affects white blood cells. The study has different groups (called cohorts) for people whose cancer has returned after treatment or who didn't respond well to initial treatments. It includes people who have had a special procedure called autologous stem cell transplantation (ASCT), where their own stem cells are used to help fight the cancer. The study will see how well bb2121 works and its safety. About 264 people will join, with separate groups for different treatment histories.

Key Points:

• This is a Phase 2 study, meaning it's testing safety and how well the treatment works.
• Participants must be over 18 and meet specific health criteria related to MM.
• Participants cannot join if they have certain health conditions or recent treatments.

Those interested should discuss with their doctor to see if they meet the criteria and understand the risks and benefits of joining the study.