• Previously untreated participants with CD20-positive LBCL

• Ability to provide tumor tissue

• International prognostic index (IPI) score 2-5

• Eastern cooperative oncology group (ECOG) performance status of 0, 1, or 2

• At least one bi-dimensionally measurable lesion, defined as \> 1.5 cm in its longest dimension as measured by CT or MRI

• Left ventricular ejection fraction (LVEF) \>/=50% on cardiac multiple-gated acquisition (MUGA) scan or cardiac echocardiogram (ECHO)

• Adequate hematologic function

• Negative HIV test at screening with exceptions as defined by the protocol

• Negative SARS-CoV-2 antigen or PCR test