Study of Brexucabtagene Autoleucel in Adults With Rare B-cell Malignancies

Key Inclusion Criteria: All Substudies: * Presence of toxicities due to prior therapy must be stable and recovered to Grade 1 or lower. * Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1 * Adequate hematologic and end-organ function. * Individuals of childbearing potential who engage in heterosexual intercourse must agree to use specified method(s) of contraception. Substudy B: * Confirmed diagnosis of chronic lymphocytic leukemia (CLL) based on International Workshop on Chronic Lymphocytic Leukemia (IWCLL) 2018 criteria with histologically confirmed Richter transformation (RT) to a diffuse large B-cell lymphoma (DLBCL) subtype. * Relapsed or refractory disease after 1 line of therapy, defined as at least 1 of the following: * Refractory disease, defined as progressive disease or stable disease as best response to first-line therapy. * Relapsed disease, defined as complete remission to first-line therapy followed by biopsy-proven disease relapse. * At least 1 measurable lesion based on the Lugano Classification. Lesions that have been previously irradiated will be considered measurable only if progression has been documented following completion of radiation therapy. Substudy C: * Histologically confirmed mature B-cell non-Hodgkin lymphoma (NHL) Burkitt lymphoma/leukemia. * Relapsed or refractory disease after first-line chemoimmunotherapy, defined as 1 of the following: * Refractory disease, defined as progressive disease or stable d…