This is a Phase Ib, open-label,single-arm, clinical study, aiming to investigate the safety, tolerability and pharmacokinetics of ZKAB001 (a fully human monoclonal antibody targeting the Programmed Death - Ligand 1 (PD-L1) membrane receptor ) combined with capecitabine as adjuvant chemotherapy for patients with biliary tract cancers after radical resection.After completing 8 courses of combined treatment ,ZKAB001 was continued to be administered separately once 3 weeks for a total of 16 cycles or 1 year.

This study includes two phases,the first phase is the dose exploration, 6 subjects were first included at the initial dose to confirm the dose safety. If the toxicity is not tolerated, the dose of the chemotherapeutic agent will be reduced depending on the toxicity(including hematological toxicity and non-hematological toxicity) for further exploration. If it can be tolerated, the recommended dose is determined and expanded on this dose. the second phase is the dose expansion, 4 subjects will be enrolled to further observe the safety and efficacy. The DLT(Dose limited toxicity) observation period is set as the first course of treatment(3 weeks). The end point is that the patient has been taking the drug for 16 cycles or 1 year, or the patient dies or develops intolerable toxicity or confirmed disease recurrence or distant metastasis or withdrawal of informed consent.

Inclusion Criteria:

1. both men and women, age ≥ 18 years old；
2. A histopathological or cytological diagnosis of gallbladder cancer and extrahepatic cholangiocarcinoma after radical resection
3. Postoperative pathological stage is T2-4 or N1 R0/R1 resection；
4. No more than 12 weeks from radical resection；
5. Eastern Cooperative Oncology Group(ECOG) performance status score 0-1;
6. Estimated life expectancy >6 months;
7. Biliary drainage is in good condition, no current infection ;
8. Have not received radiotherapy, chemotherapy, or immunotherapy for the primary tumor;
9. The function of important organs meets the following requirements:

(1) Blood routine test: absolute neutrophil count (ANC) ≥ 1.5×109/L, platelets ≥ 100×109/L, hemoglobin ≥100g/L; (2) Biochemical tests : ALT, AST ≤ 2.5×ULN; ALB≥ 35g/L;total bilirubin ≤3×ULN; serum creatinine ≤ 1.5×ULN, creatinine clearance rate ≥50 mL/min(Crockcroft-Gault formula); 10.Subjects voluntarily joined the study, signed an informed consent form, had good compliance, and cooperated with the follow-up.

Exclusion Criteria:

1. Local recurrence or distant metastasis (including ascites or malignant pleural effusion);
2. Severe cardiovascular disease, such as New York Heart Association (New York Heart Association, NYHA standard) heart failure above grade 2, unstable angina, unstable arrhythmia, or color photos of the heart suggest LVEF (left ventricular ejection fraction) )<50%;
3. Known allergy or hypersensitivity to monoclonal antibodies or fluorouracil drugs or their analogues;
4. Subjects with known, active or suspicious autoimmune diseases, who are in a stable state and do not require systemic immunosuppressive therapy can be included in the group;
5. Subjects were treated with immunosuppressants or systemic or absorbable topical corticosteroids within 2 weeks before the first study to achieve immunosuppressive purposes (>10mg/day prednisone or equivalent dose) ;
6. Suffered from other active malignancies within 5 years before the first administration of the study drug. Cured localized tumors, such as skin basal cell carcinoma, skin squamous cell carcinoma, superficial bladder cancer, prostate carcinoma in situ, cervical carcinoma in situ, breast carcinoma in situ, etc. can be included in the group;
7. Active viral hepatitis (such as hepatitis B, hepatitis C, unless antiviral treatment is given and the HBV or HCV viral load is below the minimum detection limit can be considered for inclusion), HIV positive or a known history of acquired immunodeficiency syndrome ；
8. Any active infection that requires systemic anti-infective treatment occurs within 14 days before the first medication;
9. Have active tuberculosis in the past 1 year, regardless of treatment;
10. Live attenuated vaccines have been used within 28 days before screening;
11. Subjects who have previously received allogeneic bone marrow transplantation or solid organ transplantation;
12. Have received any other experimental drug treatment within 28 days before signing the ICF;
13. People who have difficulty swallowing or have known drug absorption disorders;
14. Women who are pregnant or breastfeeding;
15. Subjects of childbearing age who refuse to use effective contraceptive measures;
16. Situations that other researchers think are not suitable for inclusion. -