Assess the safety and efficacy of 9MW2821 in patients with high-risk non-muscle-invasive bladder cancer (NMIBC) who have previously failed to intravesical therapy. Provide a new treatment option for patients with NMIBC recurrence, reduce the risk of tumor recurrence, decrease the rate of radical bladder surgery, and enhance the quality of life for patients.

Inclusion Criteria:

• Age≥18 years old before signing the informed consent.
• Subjects must have previously failed to at least one kind of intravesical therapy, including but not limited to BCG, gemcitabine, etc.
• Subjects refuse or are intolerant to BCG therapy.
• Subjects must have completed a standard TURBT surgery within 6 weeks before the first dose of the study drug and have no evidence of residual tumors in the surgical field.
• Tumor tissue samples from TURBT must be provided (≥5 slides), along with relevant pathological reports.
• Histological and pathological diagnosis of urothelial carcinoma (with a major component >50%) , with the confirmation of no-muscle invasion.
• Subjects must be categorized as high-risk NMIBC
• Subjects refuse or are intolerant to radical cystectomy.
• Clinical non-metastatic bladder cancer (N0, M0) determined by CT scan.
• Adequate function of heart, bone marrow, liver, and kidney.
• ECOG 0-1
• Subjects must be willing to take highly effective contraception during the study and 180 days after the last dose of 9MW2821 (a negative serum pregnancy test result within ≤7 days before enrollment for the female).

Exclusion Criteria:

• History of muscle invasive or metastatic bladder cancer.
• History of other malignancies within 3 years.
• Other systemic anti-cancer therapies within 3 weeks before the first dose of the study drug.
• Surgery (such as TURBT) or radiotherapy for bladder lesions within 2 weeks before the first dose.
• Hypersensitivity reactions to certain components of 9MW2821 or similar drugs.
• Persistence of adverse reactions caused by prior anti-tumor therapy before the first dose, does not recover to grade 1 and below, according to NCI-CTCAE v5.0.
• Active systemic infections that require treatments within 7 days before the first dose.
• Severe cardiovascular diseases within 6 months before the first dose.
• History of allogeneic hematopoietic stem cell transplantation or organ transplantation.
• History of autoimmune diseases.
• Serum virology tests: positive results for HBsAg or HBcAb, with positive HBV-DNA copies (≥500IU/mL); positive HCV-Ab results, with positive HCV-RNA results; positive HIV-Ab results.
• Prior treatment with drugs targeted Nectin-4 or MMAE-conjugated ADC.