Inclusion Criteria:
1. Sign the written informed consent;
2. Aged ≥ 18 and ≤ 70 years old;
3. Confirmed recurrent and metastatic triple negative breast cancer by imaging and pathology (ER negative (IHC ER positive percentage \< 1%), PR negative (IHC PR positive percentage \< 1%), HER2 negative (IHC -/+or IHC++but FISH/CISH -)), at least one measurable focus meeting the RECIST v1.1 standard;
4. Untreated local recurrence of unresectable TNBC or untreated distant metastasis of TNBC
5. Must be able to swallow tablets;
6. Clarify the positive status of PD-L1 expression and CPS score ≥ 1
7. ECOG score: 0 to 1;
8. Expected survival period ≥ 12 weeks;
9. The results of patient's blood tests are as follows (excluding the use of any blood components and cell growth factors during screening):
* Absolute neutrophil count ≥ 1.5 × 109/L;
* Platelets ≥ 100 × 109/L;
* Hemoglobin ≥ 9g/dL;
* Serum albumin ≥ 3g/dL;
* Thyroid stimulating hormone (TSH) ≤ ULN (if abnormal, T3 and T4 levels should be examined simultaneously. If T3 and T4 levels are normal, they can be included in the group);
* Bilirubin ≤ 1.0 times ULN (Gilbert's syndrome or liver metastasis subject total bilirubin ≤ 1.5 times ULN);
* ALT and AST ≤ 1.5 times ULN (liver metastasis subjects ≤ 3 times ULN);
* AKP ≤ 2.5 times ULN;
* Renal function within 7 days before the first administration: serum creatinine ≤ 1.5 times ULN or creatinine clearance rate ≥ 60mL/min (using the standard Cockcroft Gault formula, see Appendix 3);
10. Female subjects of childbearing potential must have a negative serum pregnancy test within 7 days before the first dose and must be willing to use very efficient barrier methods of contraception for the course of the study through 6 months after the last dose of study treatment.
11. Left ventricular ejection fraction ≥ 50%
Exclusion Criteria:
1. Received other interventional clinical trials within 28 days before the first dose;
2. Failure to recover from adverse reactions of previous treatment
3. Neurological disorders of grade ≥ 2
4. Untreated active brain metastases or meningeal metastases
5. Previously received nab-paclitaxel neoadjuvant therapy or adjuvant therapy and experienced local recurrence or distant metastasis within 12 months;
6. Has experienced severe allergic reactions to other monoclonal antibodies;
7. Received other anti-tumor treatments within 28 days before the first administration;
8. Suffering from hypertension and unable to achieve good control with antihypertensive medication (systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg);
9. Received antibody or T cell co stimulatory therapy such as PD-1, PD-L1, PD-L2, CTLA-4, Tim3, LAG3, etc;
10. Special genetic diseases (including rare galactose intolerance, primary lactase deficiency, or glucose galactose malabsorption);
11. Active autoimmune disease or history of autoimmune disease (such as but not limited to: autoimmune hepatitis, interstitial pneumonia, uveitis, enteritis, hepatitis, pituitary inflammation, vasculitis, nephritis, hyperthyroidism, hypothyroidism; subjects with vitiligo or complete remission of childhood asthma without any intervention in adulthood may be included; subjects with asthma requiring medical intervention with bronchodilators may not be included);
12. Heart diseases, such as:
* NYHA grade 2 or above heart failure
* Unstable angina pectoris
* Have experienced a myocardial infarction within the past year
* Clinically significant supraventricular or ventricular arrhythmias require treatment or intervention；
13. Urine protein level is ≥++, or the 24-hour urine protein level is ≥ 1.0 g;
14. Known genetic or acquired bleeding and thrombophilia tendencies (such as hemophilia patients, coagulation dysfunction, thrombocytopenia, splenomegaly, etc.);
15. Have a history of tuberculosis;
16. Active period of HBV or HCV, and other active infectious diseases;
17. Had or is currently experiencing qualitative pneumonia or requires steroid treatment for pneumonia;
18. Congenital or acquired immune dysfunction (such as HIV infected individuals);
19. Received or about to receive a live vaccine within 4 weeks prior to the study or possibly during the study period;
20. Allergic or contraindicated to the experimental drug.
