This project aims to evaluate the efficacy and safety of oral taurine supplementation combined with PD-1 inhibitor (sintilimab) and chemotherapy in inducing systemic CD8+ T cell responses and achieving improved gastric cancer patient outcomes than with sintilimab and chemotherapy alone.

Inclusion Criteria:

1. Age 18 or older, no gender limitation;
2. Pathologically confirmed gastric cancer or adenocarcinoma of the gastroesophageal junction, local lesions cannot be radically resected or metastatic gastric cancer;
3. Expected survival of ≥ 3 months;
4. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1;
5. At least one measurable lesion outside the stomach (RECIST 1.1);
6. Patients informed about the purpose and course of the study and provided a written consent to participate.

Exclusion Criteria:

1. Use of taurine agent within 1 month prior to randomization on this study;
2. Patients received prior systemic therapy for gastric cancer;
3. Patients with operable gastric cancer;
4. Patients with positive HER-2 and willing to receive herceptin treatment;
5. Patients with gastrointestinal obstruction or active bleeding in the gastrointestinal tract, as well as perforation and dysphagia;
6. Patients with active autoimmune disease that has required systemic treatment in past 2 years;
7. Patients diagnosed as immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy;
8. Patients with severe heart, lung, liver, kidney, endocrine, hematopoietic system or psychiatric diseases were considered not suitable for the study group;
9. Patients with other medical conditions that interfere with the trial and are deemed unsuitable for inclusion in the trial by the investigator;
10. Other conditions that the investigator thinks are not suitable to participate in this clinical trial.