This is a phase II study to determine the safety and efficacy of tislelizumab when given in combination with nab-paclitaxel as treatment for patients with high-risk non-muscle-invasive bladder cancer (HR NMIBC) which is not completely resectable. Patients will receive treatment with tislelizumab in combination with nab-paclitaxel every 3 weeks for 4 treatment cycles over 12 weeks followed by transurethral resection biopsy.

Inclusion Criteria:

1. Willing and able to provide written informed consent;

2. Ability to comply with the protocol;

3. Age ≥ 18 years;

4. High-risk non-muscle-invasive urothelial carcinoma or high-risk non-muscle-invasive urothelial carcinoma as the main pathological component > 50%, difined as following:

   a. T1 b. High-grade Ta c.Carcinoma in situ(CIS);

5. Multi-point biopsy of bladder shows there are more than 2 section and over 3 points of pathological specimens are diagnosed as above, meanwhile, the tumor has to be diagnosed as not completely resectable by at least 2 senior urologist;

6. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2;

7. Agreed to provide tissue examination samples (for detection of PD-L1 expression, tumor mutation load, IHC, detection of DNA and RNA, etc;)

8. Organ function level must meet the following requirements:

   • Hematological indexes: neutrophil count >= 1.5x10^9/L, platelet count >= 80x10^9/L, hemoglobin >= 6.0 g/dl (can be maintained by blood transfusion);
   • Liver function: total bilirubin <=1.5 ULN, alanine aminotransferase and aspartate aminotransferase <=2.5 ULN;

9. The subjects volunteered to join the study, signed informed consent, and had good compliance with follow-up;

Exclusion Criteria:

1. Receive live attenuated vaccine within 4 weeks before treatment or during the study period;

2. Active, known or suspected autoimmune diseases;

3. History of primary immunodeficiency;

4. Known history of allogeneic organ transplantation and allogeneic hematopoietic stem cell transplantation;

5. Pregnant or lactating female patients;

6. Untreated acute or chronic active hepatitis B or hepatitis C infection. Under the condition of monitoring the virus copy number of patients receiving antiviral treatment, doctors can judge whether they are in line with the patients' individual conditions;

7. Prior use of immunosuppressive drugs within 4 weeks prior to the start of treatment, excluding nasal and inhaled corticosteroids or physiological doses of systemic steroids (i.e. not more than 10 mg / day prednisolone or other corticosteroids with the same physiological dose);

8. Known or suspected allergy to tislelizumab and albumin paclitaxel;

9. Have a clear history of active tuberculosis;

10. Received PD-1 / PD-L1 / CTLA-4 antibody or other immunotherapy in the past;

11. Participating in other clinical researchers;

12. Men with reproductive capacity or women who are likely to become pregnant do not take reliable contraceptive measures;

13. Uncontrolled concurrent diseases, including but not limited to:

    • HIV infected (HIV antibody positive);
    • Severe infection in active stage or poorly controlled;
    • Evidence of serious or uncontrollable systemic diseases (such as severe mental, neurological, epilepsy or dementia, unstable or uncompensated respiratory, cardiovascular, liver or kidney diseases, uncontrolled hypertension [i.e. hypertension greater than or equal to CTCAE grade 2 after drug treatment]);
    • Patients with active bleeding or new thrombotic disease