An Open-Label Phase lB/II Study of Glofitamab and Atezolizumab or Polatuzumab Vedotin in Adult Patients With Relapsed/Refractory B-Cell Non-Hodgkin's Lymphoma

Main Inclusion Criteria

* Histologically-confirmed hematologic malignancy that is expected to express CD20 (Relapsed after or refractory to respond to at least one prior treatment regimen; no available treatment options that are expected to prolong survival or patients refusing chemotherapy or autologous stem cell transplant (SCT))
* Dose-escalation: Grades 1-3b relapsed or refractory (R/R) follicular lymphoma (FL) or marginal zone lymphoma (MZL) (nodal; extra-nodal; or splenic), diffuse large B-cell lymphoma (DLBCL), primary mediastinal large B-cell lymphoma (PMBCL), high-grade B-cell lymphoma (HGBCL) with MYC and BCL2 and/or BCL6 rearrangements (double-hit lymphoma), HGBCL not otherwise specified (NOS), DLBCL arising from FL (transformed FL)
* Dose-expansion: R/R LBCL, including DLBCL NOS, DLBCL arising from FL (transformed FL), PMBCL, HGBCL with MYC and BCL2 and/or BCL6 rearrangements (i.e., double-hit and triple-hit lymphomas), and HGBCL NOS
* At least one measurable target lesion
* Fresh pre-treatment biopsy, but if this cannot be taken, a previous archived biopsy from metastatic lesion can be taken as replacement if it is not older than 6 months and not confounded by major events (progression, treatment)
* Eastern Cooperative Oncology Group (ECOG) performance status of 0-2
* Adequate organ function (liver, hematological, renal)
* Negative test results for hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV)

Inclusion Criteria Specific to Imaging Substudy

* At least two measurable target lesions
* Able to provide two fresh tumor biopsies (baseline and on-treatment)

Main Exclusion Criteria

* Participants with Chronic Lymphocytic Leukemia (CLL), acute lymphoblastic leukemia (ALL), lymphoblastic lymphoma, Richter's transformation, CD20-positive ALL, Burkitt lymphoma, or lymphoplasmacytic lymphoma
* Current \> Grade 1 peripheral neuropathy (only for participants being treated in the polatuzumab vedotin arm)
* Patients with known active infection, or reactivation of a latent infection within 4 weeks prior to Obinutuzumab (Gpt) infusion
* Patient with history of confirmed progressive multifocal leukoencephalopathy (PML)
* History of leptomeningeal disease
* Current or past history of central nervous system (CNS) lymphoma
* Current or past history of CNS disease
* Major surgery or significant traumatic injury \</=28 days prior to Gpt infusion
* Significant cardiovascular disease or significant pulmonary disease
* Active or history of autoimmune disease or immune deficiency (with exceptions, e.g. hypothyroidism and Diabetes mellitus Type 1)
* History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g. bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan
* Treatment with any other standard anti-cancer radiotherapy / chemotherapy including investigational therapy within 4 weeks prior to Gpt infusion
* Prior solid organ transplantation
* Prior allogenic stem cell transplant (SCT)
* Autologous SCT within 100 days prior to Gpt infusion
* Documented refractoriness to an obinutuzumab-monotherapy regimen
* Prior treatment with anti-cancer/lymphoma therapies and systemic immunotherapeutic/immunostimulating agents within 4 weeks or 5 half-lives of the drug, whichever is shorter, prior to Gpt infusion
* Any history of immune related \>/= Grade 3 adverse events (AE) with the exception of endocrinopathy managed with replacement therapy
* Ongoing corticosteroid use \>25 milligrams/day of prednisone or equivalent within 4 weeks prior to and during study treatment
* Treatment with systemic immunosuppressive medication
* Administration of a live, attenuated vaccine within 4 weeks prior to Gpt infusion or anticipation that such a live attenuated vaccine will be required during the study or within 5 months after last dose of study treatment

Exclusion Criteria Specific to Imaging Substudy

* Circulating lymphoma cells, defined by out of range (high) absolute lymphocyte count and/or the presence of abnormal/malignant cells in the peripheral blood differential signifying circulating lymphoma cell
* Participants who have had splenectomy or functional asplenia that could compromise protocol objectives