Inclusion Criteria:
• Has histologically-confirmed diagnosis of non-muscle invasive (T1, high grade Ta and/or CIS) transitional cell carcinoma (TCC) of the bladder

• Has been treated with one adequate course of BCG induction therapy for the treatment of HR NMIBC

• Following adequate BCG induction therapy, must have persistent or recurrent HR NMIBC

• Has undergone cystoscopy/ transurethral resection of bladder tumor (TURBT) to remove all resectable disease

• Has provided tissue for biomarker analysis

• Has Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

• Has adequate organ function

• Male participants must agree to use approved contraception during the treatment period and for at least 120 days after the last dose of study treatment and refrain from donating sperm during this period

• Female participants who are not pregnant, not breastfeeding, and either not a woman of child bearing potential (WOCBP) or are a WOCBP who agrees to use approved contraception during the treatment period and for at least 120 days after the last dose of study treatment

Exclusion Criteria:
• Has persistent T1 disease following an induction course of BCG

• Has muscle invasive (i.e., T2, T3, T4), locally advanced non-resectable or metastatic UC

• Has concurrent extra-vesical (i.e., urethra, ureter, renal pelvis) non-muscle invasive TCC of the urothelium, concurrent upper tract involvement, or invasive prostatic TCC including T1 or greater disease, or ductal invasion

• WOCBP who has a positive urine pregnancy test within 72 hours prior to randomization

• Has received prior therapy with anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another co-inhibitory T-cell receptor

• Has received prior systemic anti-cancer therapy including investigational agents within 4 weeks of start of study treatment

• Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks of start of study treatment

• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy or any other form of immunosuppressive therapy within 7 days of start of study treatment

• Has a known additional malignancy that is progressing or requires active treatment within the past 3 years

• Has an active autoimmune disease that has required systemic treatment in past 2 years

• Has a history of (non-infectious) pneumonitis that required steroids or has current pneumonitis

• Has one or more of the following contraindications to BCG: prior BCG sepsis or systemic infection, total bladder incontinence, or an adverse experience to a previous BCG instillation that resulted in treatment discontinuation and precludes retreating with BCG

• Has an active infection requiring systemic therapy

• Has a known history of human immunodeficiency virus (HIV) infection

• Has a known history of Hepatitis B or known active Hepatitis C virus infection

• Has evidence of active tuberculosis

• Is pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit through 120 days after the last dose of trial treatment