This study is a Phase Ib/II clinical study. It includes two stages: Phase Ib and Phase II. In the Phase Ib stage, the primary objective is to evaluate the safety and tolerability of SYS6006 in combination with Enlonstobart Injection in participants with advanced solid tumors, and to provide a basis for dose selection in later clinical studies. The primary objective of the Phase II stage is to assess efficacy and safety of SYS6006 in combination with Enlonstobart Injection in participants with advanced solid tumors.

Inclusion Criteria:

• 1. Able to understand and voluntarily sign the written informed consent form (ICF);
• 2. Male or female subjects aged over 18 years old (inclusive).
• 3. Patients with solid tumor who have unresectable locally advanced or metastatic disease;
• 4. At least one measurable lesion, as defined by RECIST 1.1 criteria;
• 5. ECOG performance status of 0-2;
• 6. Expected survival ≥ 3 months;
• 7. Adequate function of major organs and bone marrow;
• 8. Women or man of childbearing potential must use highly effective contraception.

Exclusion Criteria:

• 1. Patients with metastases to meninges; with spinal cord compression; symptomatic and unstable brain metastasis;
• 2. Patients with a history of autoimmune diseases;
• 3. Presence of active infection (e.g., subjects are receiving anti-infection therapy);
• 4. Severe or uncontrolled cardiovascular disorder requiring treatment;
• 5. Women who are pregnant or breastfeeding.