∙ Cohorts A and B

• High-grade (HG) NMIBC (HG Ta, CIS, and/or T1) of urothelial histology that is unresponsive to adequate BCG therapy.

• Stage, grade, and histology must be confirmed by the MSK Department of Pathology

• Subjects with tumors of mixed urothelial/non-urothelial histology may be included, but urothelial carcinoma must be the predominant histology; subjects with predominant or exclusively non-urothelial histology are excluded

• In those subjects with CIS, the CIS must be present on the tumor sample from the most recent cystoscopy/TURBT

• In this context, adequate BCG therapy is defined as at least one of the following:

• At least five of six doses of an initial induction course plus at least two of three doses of maintenance therapy

• At least five of six doses of an initial induction course plus at least two of six doses of a second induction course

• Disease unresponsive to adequate BCG therapy is defined as the following. Suspected recurrence from suspicious cytology or cystoscopy, and later confirmed via TURBT, is acceptable:

• Persistent or recurrent CIS alone or with recurrent Ta/T1 disease (noninvasive papillary disease/tumor invades the subepithelial connective tissue) within 12 months of completion of adequate BCG therapy

• Recurrent HG Ta/T1 disease within 6 months of completion of adequate BCG therapy

• HG T1 disease at the first evaluation following an induction BCG course

∙ Cohort C:

• Bladder cancer of any stage that has a predominant urothelial histology.

• Stage, grade, and histology must be confirmed by the MSK Department of Pathology

• Subjects with tumors of mixed urothelial/non-urothelial histology may be included, but urothelial carcinoma must be the predominant histology; subjects with predominant or exclusively non-urothelial histology are excluded

∙ Cohort A and B Only:

• In subjects with papillary tumors (Ta and T1), a complete TURBT must have been performed.

∙ This is characterized by:

• Attainment of a visually complete resection of all papillary tumors (Ta and T1)

• Residual CIS not amenable to complete transurethral resection is acceptable

• Receipt of restaging transurethral resection for any tumor with invasion into the lamina propria (HG T1) as part of standard care, with documented presence of uninvolved detrusor muscle.

• Most recent cystoscopy/TURBT must have been performed within 6 months of the first dose of trial treatment.

• Absence of urothelial carcinoma involving the upper urinary tract (documented by radiological imaging or ureteroscopy).

• Have elected not to undergo or are considered ineligible for radical cystectomy, as determined by the treating surgeon. Reasons for ineligibility or refusal of radical cystectomy should be discussed with the subject as part of the informed consent process.

• Ineligibility factors for radical cystectomy may include, but are not limited to:

• Cardiovascular disease (e.g., recent acute coronary syndrome, arrhythmia, heart failure)

• Chronic obstructive pulmonary disease that would preclude a safe surgical procedure, as determined by the treating surgeon

• Poor performance status

• Prior major abdominal and pelvic surgery that would preclude a safe surgical procedure, as determined by the treating surgeon

∙ Cohort C Only:

• Are willing to undergo a standard of care examination under anesthesia or cystoscopy within four weeks of scheduled radical cystetomy.

• In subjects previously treated with pembrolizumab for BCG-unresponsive NMIBC that are found to have disease persistence, the disease persistence must have been confirmed no earlier than 12 weeks after initiation of pembrolizumab; subjects previously treated with pembrolizumab that are found to have disease recurrence or progression from HG Ta and/or CIS to T1 disease prior to 12 weeks after initiation of pembrolizumab may be included after discussion with the Principal Investigator.

• Patients who have received prior cisplatin-based neoadjuvant chemotherapy may be included in the study

• Age ≥18 years on day of signing informed consent.

• Eastern Cooperative Oncology Group (ECOG) performance status ≤2 / Karnofsky performance status ≥60%, as assessed within 28 days prior to treatment initiation.

• Required values for screening laboratory tests, performed within 28 days prior to treatment initiation:

∙ Absolute neutrophil count (ANC) ≥1000/mm3

• Platelets \>75,000/mm3 without

• Hemoglobin \>8 g/dL

• Creatinine clearance \>40 mL/min for the dose-escalation phases, \>25 mL/min for the dose expansion phases (estimated GFR can also be used in place of creatinine clearance)

• AST/ALT ≤3 times the institutional upper limit of normal (ULN)

• Total bilirubin ≤1.5 times the institutional ULN

‣ Female subjects of childbearing potential must have a negative serum pregnancy test within 72 hours prior to receiving the first dose of study treatment.

⁃ Female subjects will be considered of non-reproductive potential if any of the following:

⁃ Postmenopausal \[defined as at least 12 months with no menses without an alternative medical cause; in women \<45 years of age a high follicle stimulating hormone (FSH) level in the post-menopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. In the absence of 12 months of amenorrhea, a single FSH measurement is insufficient.

⁃ Have had a hysterectomy and/or bilateral oophorectomy, bilateral salpingectomy, or bilateral tubal ligation/occlusion, at least 6 weeks prior to screening

⁃ Has a congenital or acquired condition that prevents childbearing

⁃ Male and female subjects of childbearing potential must agree, if participating in sexual activity that could lead to pregnancy, to use of an adequate method of contraception from the day of study medication initiation (or 14 days prior to the initiation of study medication for oral contraception) throughout the study period up to 120 days after the last dose of trial therapy. Subjects should be informed that taking the study medication(s) may involve unknown risks to the fetus (unborn baby) if pregnancy were to occur during the study.

∙ Male subjects will be considered of non-reproductive potential if they have azoospermia (whether due to vasectomy or an underlying medical condition). Female subjects will be considered of non-reproductive potential if as described above. Acceptable methods of contraception:

• Single method (one of the following is acceptable): intrauterine device, vasectomy of a female subject's male partner, or contraceptive rod implanted into the skin

• Combination method (requires use of two of the following): diaphragm with spermicide (cannot be used in conjunction with cervical cap/spermicide), cervical cap with spermicide (nulliparous women only), contraceptive sponge (nulliparous women only), male condom or female condom (cannot be used together), or hormonal contraceptive \[oral contraceptive pill (estrogen/progestin pill or progestin-only pill), contraceptive skin patch, vaginal contraceptive ring, or subcutaneous contraceptive injection

• Male subjects must agree not to donate sperm during and after the study

• Able to comply with the treatment schedule as determined by the participant and the licensed practitioner.