A Study Evaluating Different Immunotherapies (LAG-3 and PD-1 With or Without TIGIT, Compared to PD-L1 Alone) in Participants With Untreated Locally Advanced Metastatic Urothelial Cancer

Inclusion Criteria:

1. Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2
2. Histologically or cytologically documented locally advanced or metastatic transitional cell carcinoma (TCC) of the urothelium. Participants with squamous, sarcomatoid, micropapillary, and glandular variant histologies are eligible for inclusion in the study, provided that a urothelial component is present in the tumor specimen. Participants with other variant histologies or pure variant histologies are not eligible for inclusion in this study
3. Ineligible ("unfit") to receive platinum-based chemotherapy
4. No prior chemotherapy for inoperable locally advanced or metastatic or recurrent urothelial carcinoma (UC)
5. Measurable disease; at least one measurable lesion as defined by response evaluation criteria in solid tumors, version 1.1 (RECIST v1.1)
6. Availability of a representative leftover tumor specimen that is suitable for determination of PD-L1 status as assessed by a central laboratory
7. Adequate hematologic and end organ function
8. Negative for hepatitis B and hepatitis C virus (HCV)
9. Adequate cardiovascular function

Exclusion Criteria:

1. Pregnancy or breastfeeding
2. GFR <15 mL/min/1.73 m2
3. Symptomatic, untreated, or actively progressing central nervous system (CNS) metastases
4. History of leptomeningeal disease
5. Uncontrolled tumor-related pain
6. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures
7. Uncontrolled or symptomatic hypercalcemia
8. Active or history of autoimmune disease or immune deficiency
9. History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan
10. Active tuberculosis (TB) or acute Epstein-Barr virus (EBV)
11. Significant cardiovascular/cerebrovascular disease within 3 months prior to initiation of study treatment
12. Major surgical procedure, other than for diagnosis, within 4 weeks prior to initiation of study treatment, or anticipation of need for a major surgical procedure during the study
13. History of another primary malignancy other than urothelial carcinoma within 2 years prior to initiation of study treatment, with the exception of malignancies with a negligible risk of metastasis or death
14. Severe infection within 4 weeks prior to initiation of study treatment
15. Treatment with therapeutic oral or intravenous antibiotics within 2 weeks prior to initiation of study treatment. Participants receiving prophylactic antibiotics (e.g., to prevent a urinary tract infection or chronic obstructive pulmonary disease [COPD] exacerbation), or who are receiving oral antibiotics to treat a urinary tract infection are eligible for the study
16. Prior allogeneic stem cell or solid organ transplantation
17. Treatment with a live, attenuated vaccine within 4 weeks prior to initiation of study treatment, or anticipation of need for such a vaccine during treatment or within 5 months after the final dose of atezolizumab, 4 months after the final dose of tobemstomig, or 90 days after the final dose of tiragolumab
18. Current treatment with anti-viral therapy for HBV
19. Treatment with any approved anti-cancer therapy, including chemotherapy or hormonal therapy, within 3 weeks prior to initiation of study treatment
20. Treatment with investigational therapy within 4 weeks or 5 drug-elimination half-lives (whichever is longer) prior to initiation of study treatment
21. Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including anti-TIGIT and anti-LAG3 therapeutic antibodies or pathways targeting agents
22. Treatment with systemic immunostimulatory agents within 4 weeks or 5 drug-elimination half-lives prior to initiation of study treatment
23. Treatment with systemic immunosuppressive medication within 2 weeks prior to initiation of study treatment, or anticipation of need for systemic immunosuppressive medication during study treatment
24. History of severe allergic anaphylactic reactions to chimeric or humanized antibodies or fusion proteins