This study is for adults with a type of cancer called large B-cell lymphoma (LBCL). LBCL is a cancer of the lymphatic system, which helps fight infection. Participants must have finished their first treatment and have little cancer left, detected by a special test. The study compares a new treatment, called cema-cel (a type of cell therapy), to just watching without specific treatment. The study has two parts. In Part A, participants are randomly chosen to either get the treatment or be observed. In Part B, the best way from Part A is used. Participants must be adults, have good health, and not have other serious illnesses or past treatments that might affect the study.

• Study involves regular visits and tests to monitor health and progress.
• Participants may receive a new cell therapy treatment or be observed without treatment.
• Risks include typical side effects from cancer treatments and the new therapy.