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:

• Age 6 months to < 18 years at the time of signing Informed Consent for Cohort A Part 1 and Cohort B of the study, and age 6 months to < 30 years old at the time ofsigning Informed Consent for Cohort A Part 2 of the study

• Histologically re-confirmed diagnosis, via tissue biopsy, or bone marrow aspirate,pleural effusion, or ascites, prior to study entry of aggressive mature B-NHL thatexpresses 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 offirst R/R disease for Cohort A and second or greater R/R disease for Cohort B

• Refractory or relapsed disease (i.e., prior treatment was ineffective orintolerable) following first-line standard-of-care chemoimmunotherapy for Cohort Aand following at least two prior systemic chemoimmunotherapy regimens and who haveexhausted all available established therapies for Cohort B

• Measurable disease, defined as: At least one bi-dimensionally measurable nodallesion, defined as > 1.5 cm in its longest dimension, or at least one bidimensionally measurable extranodal lesion, defined as > 1.0 cm in its longestdimension; or percentage of bone marrow involvement with lymphoma cells defined bycytomorphological analysis of bone marrow aspirates

• Adequate performance status, as assessed according to the Lansky or KarnofskyPerformance Status scales: Participants < 16 years old: Lansky Performance Status ≥ 50%; Participants ≥ 16 years old: Karnofsky Performance Status ≥ 50%

• Adequate bone marrow, liver, and renal function

• Negative test results for acute or chronic hepatitis B virus (HBV), hepatitis Cvirus (HCV)

• Negative HIV test at screening, with the following exception: Individuals with apositive HIV test at screening are eligible provided they are stable onanti-retroviral therapy for at least 4 weeks, have a CD4 count ≥200/uL, have anundetectable viral load, and have not had a history of opportunistic infectionattributable to AIDS within the last 12 months

• Negative SARS-CoV-2 antigen or PCR test within 7 days prior to enrollment

• Participants and/or caregivers who are willing and able to complete clinical outcomeassessments throughout the study using either paper or interviewer methods

Exclusion Criteria:

• Isolated CNS disease of mature B-NHL without systemic involvement, and primary CNSlymphoma

• Receipt of glofitamab prior to study enrollment

• Ongoing adverse events from prior anti-cancer therapy that were not resolved toGrade ≤ 1 (exceptions: alopecia, Grade 2 peripheral neuropathy)

• Grade ≥ 3 adverse events, with the exception of Grade 3 endocrinopathy managed withreplacement therapy

• Participants with active infections which are not resolved prior to Day 1 of Cycle 1

• Prior solid organ transplantation

• Known or suspected history of hemophagocytic lymphohistiocytosis (HLH), or chronicactive Epstein-Barr viral infection (CAEBV)

• Active autoimmune disease requiring treatment

• History of severe allergic or anaphylactic reactions to monoclonal antibody therapy (or recombinant antibody-related fusion proteins) or known sensitivity or allergy tomurine products, except if the participant was able to safely receive it afterinitial administration (consider consultation with Medical Monitor)

• History of confirmed progressive multifocal leukoencephalopathy

• Current or past history of uncontrolled non-malignant CNS disease, such as stroke,epilepsy, CNS vasculitis, or neurodegenerative disease

• Evidence of significant and uncontrolled concomitant diseases that could affectcompliance with the protocol or interpretation of results

• Major surgery or significant traumatic injury < 28 days prior to the obinutuzumabpretreatment infusion (excluding biopsies) or anticipation of the need for majorsurgery during study treatment

• Administration of a live, attenuated vaccine within 4 weeks before the start ofstudy treatment (obinutuzumab pretreatment) or at any time during the studytreatment period and within 12 months after end of study treatment

• Participants with any other diseases, metabolic dysfunction, physical examinationfinding, or clinical laboratory finding giving reasonable suspicion of a disease orcondition that would contraindicate the use of an investigational drug