Inclusion Criteria:  Participants >= 1 and < 18 years old at time of primary diagnosis with Burkitt's or Burkitt-like lymphoma/leukemia, diffuse large B-cell lymphoma (DLBCL), or other aggressive mature (CD20+) B-cell lymphomas. Participants up to 25 years of age with Burkitt's or Burkitt-like lymphoma/leukemia are also eligible. Disease pathologically confirmed (tumor tissue) by local testing.  Relapsed or primary refractory disease meeting any of the following criteria:  Progressive disease at any time during second-line chemoimmunotherapy (CIT). Best response of stable disease (SD) after a minimum of 2 cycles of second-line CIT. Best response of partial response (PR) after a minimum of 3 cycles of second-line CIT. Complete Response (CR) after a minimum of 3 cycles of second-line CIT therapy but unfit or ineligible for consolidation with cell therapy. Not in CR and unable to initiate or tolerate (i.e., must discontinue) second-line CIT. Have received cell therapy (allogeneic or autologous transplant or chimeric antigen receptor T-cell (CAR-T) therapy) as consolidation but have not obtained or maintained a CR. Recovery from toxic effects of prior chemoimmunotherapy. Performance status by Lansky (< 16 years old at evaluation) or Karnofsky (>= 16 years old at evaluation) score >= 50 or ECOG score <= 2 . Adequate bone marrow, hepatic, and renal function.  Exclusion Criteria:  Known central nervous system (CNS) involvement by lymphoma at screening as confirmed by screening magnetic resonance imaging (MRI)/computed tomography (CT)/positron emission tomography (PET) brain scans (participants with evidence of CNS disease only in the cerebrospinal fluid (CSF) will be eligible). Other malignancy requiring therapy. Currently receiving anti-cancer therapy, including chemotherapy (excluding intrathecal therapy), radiotherapy, small molecules, monoclonal antibodies, cell therapy, or other investigational agents.