Pfizer: C6001001

Inclusion Criteria: 1. 18 years of age or older (or the minimum age of consent per local regulations) 2. Histological diagnosis of high-risk, non-muscle invasive urothelial carcinoma of the bladder defined according to the WHO grading system as carcinoma in situ (CIS), with or without concurrent T1/Ta papillary disease. Note: High-grade T1/Ta papillary disease, in the absence of CIS, may be eligible for certain cohorts in Part 2 and 3 3. BCG unresponsive and BCG-exposed cohorts should have persistent or recurrent disease after receiving at least 5 out of 6 doses of the BCG induction therapy. 4. Have refused or are ineligible or not appropriate for radical cystectomy 5. Tissue Requirement: Available tumor tissue within the last 6 months. On-treatment tumor biopsy is optional, unless mandated based on emerging data, or participating in the Biomarker Cohort, or for disease assessment 6. ECOG PS 0 or 1

Exclusion Criteria: 1. Concomitant anti-cancer therapy for Non-Muscle Invasive Bladder Cancer (NMIBC); and prior radiation therapy to the bladder are not allowed 2. Renal or hepatic impairment; and hematologic abnormalities as defined in the protocol 3. Participants with active, uncontrolled infection as specified in the protocol