This study is a open, multi-center phase II clinical study to explore the efficacy, safety and pharmacokinetic/pharmacodynamic characteristics of SI-B001+SI-B003 combined with platinum-based chemotherapy as first-line treatment in patients with recurrent or metastatic head and neck squamous cell carcinoma.

Inclusion Criteria:

1. Sign the informed consent form voluntarily and follow the protocol requirements;
2. Gender is not limited;
3. Age ≥18 years old and ≤75 years old;
4. Expected survival time ≥3 months;
5. Patients with recurrent or metastatic head and neck squamous cell carcinoma;
6. Consent to provide tumor tissue samples or fresh tissue samples archived from the primary or metastatic lesions within 2 years;
7. At least one measurable lesion meeting the RECIST v1.1 definition was required;
8. Physical status score: ECOG ≤1;
9. The toxicity of previous antineoplastic therapy has returned to ≤ grade 1 as defined by NCI-CTCAE v5.0;
10. No severe cardiac dysfunction, left ventricular ejection fraction ≥50%;
11. No blood transfusion or colony-stimulating factor was allowed within 14 days before the first use of the study drug, and the organ function level must meet the requirements;
12. Coagulation function: international normalized ratio (INR) ≤1.5, and activated partial thromboplastin time (APTT) ≤1.5×ULN;
13. Urinary protein ≤1+ or ≤1000mg/24h;
14. Fertile female subjects, or male subjects with fertile partners, must use highly effective contraception from 7 days before the first dose until 24 weeks after the dose. Female subjects of childbearing potential had to have a negative serum pregnancy test within 7 days before the first dose.

Exclusion Criteria:

1. Squamous cell carcinoma of the nasopharynx, salivary gland, paranasal sinus, skin or of unknown primary site;
2. Patients with any of the following conditions were not eligible for the study: a) suitable and willing for local treatment; b) received systemic therapy, excluding treatment for locally advanced disease as part of multimodal therapy;
3. Patients with active central nervous system metastasis;
4. Who had participated in any other clinical trial within 4 weeks before the study dose;
5. Received radiotherapy within 4 weeks before the first dose of study drug;
6. Use of traditional Chinese medicine with anti-tumor indications within 2 weeks;
7. Had undergone major surgery within 4 weeks before the first dose;
8. Systemic corticosteroids or immunosuppressive agents were required within 2 weeks before study dosing;
9. Pulmonary disease was defined as ≥ grade 3 according to NCI-CTCAE v5.0; Patients with existing or a history of interstitial lung disease (ILD);
10. Have active infection requiring intravenous anti-infective therapy;
11. Had received immunotherapy and had grade ≥3 irAE or grade ≥2 immune-related myocarditis;
12. Received live attenuated vaccine within 4 weeks before the first dose of study drug;
13. Had taken an immunomodulatory drug within 14 days before the first dose of study drug;
14. Patients at risk for active autoimmune disease or with a history of autoimmune disease;
15. Other malignant tumors within 5 years before the first administration;
16. Human immunodeficiency virus antibody positive, active tuberculosis, active hepatitis B virus infection or hepatitis C virus infection;
17. Poorly controlled hypertension;
18. Patients with poor blood glucose control before the first dose;
19. Had a history of severe cardiovascular and cerebrovascular diseases;
20. Previous history of allogeneic stem cell, bone marrow or organ transplantation;
21. Patients with massive or symptomatic effusions or poorly controlled effusions;
22. Patients with a history of allergy to recombinant humanized antibodies or to any of the excipients of SI-B001 or SI-B003;
23. Had severe infusion reactions to antibody therapy in the past;
24. Had autologous or allogeneic stem cell transplantation;
25. Pregnant or lactating women;
26. The investigator did not consider it appropriate to apply other criteria for participation in the trial.