This study is for people with a new diagnosis of multiple myeloma, a type of blood cancer, who have had an autologous stem cell transplant (a treatment where your own stem cells are used to replace damaged bone marrow). The study compares different maintenance therapies, which are treatments given to help keep cancer from coming back. The treatments tested are teclistamab (an experimental drug that helps the immune system fight cancer) with lenalidomide (a drug that slows cancer growth), teclistamab alone, and lenalidomide alone.

Participants must have received only one prior treatment and show no signs of cancer progression. They must not have previous treatments like BCMA-directed therapy or have stopped lenalidomide due to side effects. They should also meet certain health criteria and not have received certain vaccines recently.

• The study is open-label, meaning both doctors and participants know which treatment is being given.
• Participants will be randomly placed in one of the treatment groups.
• The study will occur at multiple centers, so travel may be required.