RecruitingPhase 2ProcedureEpcoritamab Compared to Observation for Treating B-cell Lymphoma Patients Not in Complete Remission After CD19-directed CAR-T TherapyThis phase II trial compares epcoritamab to standard practice (observation) for the treatment of patients with B-cell lymphomas who are not in complete remission after treatment with CD19-directed chimeric antigen receptor T-cell (CAR-T) therapy. Epcoritamab is a bispecific antibody. It works by simultaneously attaching to a molecule called CD20 on cancerous B-cells and a molecule called CD3 on effector T-cells, which are a type of immune cell. When epcoritamab binds to CD20 and CD3, it brings the two cells together and activates the T-cells to kill the cancerous B-cells. Epcoritamab may increase a patient's chances of achieving complete remission after CD19-directed CAR-T therapy, compared to standard observation.