A Trial of Mosunetuzumab (BTCT4465A) as Consolidation Therapy in Participants With Diffuse Large B-Cell Lymphoma Following First-Line Immunochemotherapy and as Therapy in Participants With Previously Untreated Diffuse Large B-Cell Lymphoma Who Are Unable to Tolerate Full-Dose Chemotherapy

Inclusion Criteria for All Cohorts

- At least one bi-dimensionally measurable nodal lesion, defined as > 1.5 cm in its
longest dimension, or one bi-dimensionally measurable extranodal lesion, defined as >
1.0 cm in its longest diameter

- Adequate hematologic function

- Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1, or 2

Inclusion Criteria Specific to Cohort A

Participants in Cohort A must also meet the following criteria for study entry:

- Histologically confirmed DLBCL according to World Health Organization (WHO) 2016
expected to express the cluster of differentiation-20 (CD20) antigen

- Best response of PR to prior systemic chemotherapy at the end of induction treatment
in accordance with Lugano 2014 Response Criteria

Inclusion Criteria Specific to Cohort B

Participants in Cohort B must also meet the following criteria for study entry:

- Previously untreated, histologically confirmed, DLBCL according to WHO 2016
classification

Exclusion Criteria for All Cohorts

Participants who meet any of the following criteria will be excluded from study entry:

- Transformed lymphoma

- Prior treatment with mosunetuzumab

- Prior stem cell transplant (autologous and allogeneic)

- History of confirmed progressive multifocal leukoencephalopathy (PML)

- Known or suspected chronic active Epstein Barr virus (CAEBV), hepatitis B, hepatitis C
(HCV), or Human Immunodeficiency Virus (HIV)

- Prior solid organ transplantation

- Current or past history of central nervous system (CNS) disease, such as stroke,
epilepsy, CNS vasculitis, or neurodegenerative disease

- Clinically significant history of liver disease

- Prior treatment with radiotherapy within 2 weeks prior to Cycle 1, Day 1 (C1D1)

- Significant cardiovascular disease

Exclusion Criteria Specific to Cohort A

Participants in Cohort A who meet the following criteria will be excluded from study entry:

- Prior treatment with chemotherapy, immunotherapy, or biologic therapy 4 weeks prior to
C1D1

Exclusion Criterion Specific to Cohort B

Participants in Cohort B who meet the following criterion will be excluded from study
entry:

- Prior treatment for DLBCL with chemotherapy, immunotherapy, and biologic therapy