This study is for people with multiple myeloma, a type of blood cancer. It looks at a treatment called **bb2121** to see if it's safe and works well for folks whose cancer has come back or didn't respond to treatment, called relapsed and refractory multiple myeloma (RRMM). There are different groups (called cohorts) in the study based on past treatments. Some groups will also try another medicine called **talquetamab**. The study will take place in various centers and will involve about 264 people.

Participants need to be at least 18 years old and have had specific treatments before joining. They shouldn’t have serious health issues or be pregnant. People who've used certain medicines or had major surgeries recently might not join. The study will include checking the safety and effectiveness of the treatment.

• The study involves multiple visits and different treatments based on past cancer responses.
• Participants may receive different treatments depending on their group.
• Eligibility includes having had specific treatments and being in good health.