This is a Phase I/II and multicenter study designed to evaluate the efficacy and safety of 4SCAR-T cells in participants with locally advanced or metastatic urothelial bladder cancer (UBC) who have no further treatment available.

Inclusion Criteria:

1. Histologically or cytologically documented locally advanced or metastatic UBC (including renal pelvis, ureters, urinary bladder, and urethra)
2. Representative tumor specimens as specified by the protocol
3. Adequate hematologic and end organ function
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
5. Life expectancy greater than or equal to (>/=) 12 weeks
6. Measurable disease, as defined by RECIST v1.1

Exclusion Criteria:

1. Any approved anti-cancer therapy within 3 weeks prior to initiation of study treatment
2. Treatment with any other investigational agent or participation in another clinical trial with therapeutic intent within 28 days prior to enrollment
3. Active or untreated central nervous system (CNS) metastases as determined by computed tomography (CT) or magnetic resonance imaging (MRI) evaluation during screening and prior radiographic assessments
4. Leptomeningeal disease
5. Malignancies other than UBC within 5 years prior to Cycle 1, Day 1
6. Pregnant and lactating women
7. Significant cardiovascular disease
8. Severe infections within 4 weeks prior to infusion
9. Major surgical procedure other than for diagnosis within 4 weeks
10. History of severe allergic, anaphylactic, or other hypersensitivity reactions to chimeric or humanized antibodies or fusion proteins; known hypersensitivity or allergy to biopharmaceuticals produced in Chinese hamster ovary cells or any component of the atezolizumab formulation
11. History of autoimmune disease
12. Prior allogeneic stem cell or solid organ transplant
13. History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, idiopathic pneumonitis, or evidence of active pneumonitis on screening chest CT scan
14. Positive test for human immunodeficiency virus (HIV) and/or active hepatitis B or hepatitis C or tuberculosis