A Study to Evaluate Glofitamab Monotherapy and Glofitamab + Chemoimmunotherapy in Pediatric and Young Adult Participants With Relapsed/Refractory Mature B-Cell Non-Hodgkin Lymphoma

Inclusion Criteria:

1. Age 6 months to < 18 years at the time of signing Informed Consent for Part 1 and Cohort B of the study, and age 6 months to ≤ 30 years old at the time of signing Informed Consent for Part 2 of the study
2. Histologically re-confirmed diagnosis, via tissue biopsy, or bone marrow aspirate, pleural effusion, or ascites, prior to study entry of aggressive mature B-NHL that expresses CD20 (reconfirmed by IHC or flow cytometry if IHC is not possible), including BL, BAL (mature B-cell leukemia FAB L3), DLBCL, and PMBCL, at the time of first R/R disease for Cohort A and second or greater R/R disease for Cohort B
3. Refractory or relapsed disease (i.e., prior treatment was ineffective or intolerable) following first-line standard-of-care chemoimmunotherapy for Cohort A and following at least two prior systemic chemoimmunotherapy regimens and who have exhausted all available established therapies for Cohort B
4. Measurable disease, defined as: At least one bi-dimensionally measurable nodal lesion, defined as > 1.5 cm in its longest dimension, or at least one bi dimensionally measurable extranodal lesion, defined as > 1.0 cm in its longest dimension; or percentage of bone marrow involvement with lymphoma cells defined by cytomorphological analysis of bone marrow aspirates
5. Adequate performance status, as assessed according to the Lansky or Karnofsky Performance Status scales: Participants < 16 years old: Lansky Performance Status ≥ 50%; Participants ≥ 16 years old: Karnofsky Performance Status ≥ 50%
6. Adequate bone marrow, liver, and renal function
7. Negative test results for acute or chronic hepatitis B virus (HBV), hepatitis C virus (HCV)
8. Negative HIV test at screening, with the following exception: Individuals with a positive HIV test at screening are eligible provided they are stable on anti-retroviral therapy for at least 4 weeks, have a CD4 count ≥200/uL, have an undetectable viral load, and have not had a history of opportunistic infection attributable to AIDS within the last 12 months
9. Negative SARS-CoV-2 antigen or PCR test within 7 days prior to enrollment
10. Participants and/or caregivers who are willing and able to complete clinical outcome assessments throughout the study using either paper or interviewer methods

Exclusion Criteria:

1. Isolated CNS disease of mature B-NHL without systemic involvement, and primary CNS lymphoma
2. Receipt of glofitamab prior to study enrollment
3. Ongoing adverse events from prior anti-cancer therapy that were not resolved to Grade ≤ 1 (exceptions: alopecia, Grade 2 peripheral neuropathy)
4. Grade ≥ 3 adverse events, with the exception of Grade 3 endocrinopathy managed with replacement therapy
5. Participants with active infections which are not resolved prior to Day 1 of Cycle 1
6. Prior solid organ transplantation
7. Known or suspected history of hemophagocytic lymphohistiocytosis (HLH), or chronic active Epstein-Barr viral infection (CAEBV)
8. Active autoimmune disease requiring treatment
9. History of severe allergic or anaphylactic reactions to monoclonal antibody therapy (or recombinant antibody-related fusion proteins) or known sensitivity or allergy to murine products, except if the participant was able to safely receive it after initial administration (consider consultation with Medical Monitor)
10. History of confirmed progressive multifocal leukoencephalopathy
11. Current or past history of uncontrolled non-malignant CNS disease, such as stroke, epilepsy, CNS vasculitis, or neurodegenerative disease
12. Evidence of significant and uncontrolled concomitant diseases that could affect compliance with the protocol or interpretation of results
13. Major surgery or significant traumatic injury < 28 days prior to the obinutuzumab pretreatment infusion (excluding biopsies) or anticipation of the need for major surgery during study treatment
14. Administration of a live, attenuated vaccine within 4 weeks before the start of study treatment (obinutuzumab pretreatment) or at any time during the study treatment period and within 12 months after end of study treatment
15. Participants with any other diseases, metabolic dysfunction, physical examination finding, or clinical laboratory finding giving reasonable suspicion of a disease or condition that would contraindicate the use of an investigational drug