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

Inclusion Criteria:

1. Age 18-75 years old, no gender limitation;
2. Pathologically confirmed gastric or gastroesophageal junction adenocarcinoma with cTNM stage II/III，T≥3, N ≥0, M=0；
3. Expected survival of ≥ 3 months;
4. The tumor specimens were PD-L1 positive (CPS ≥ 1)；
5. There is a measurable lesion with the possibility of radical R0 resection after evaluation by doctors；
6. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1;
7. 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 the first dose of study treatment and throughout the study;
2. Patients with positive HER-2；
3. Patients with gastrointestinal obstruction or active bleeding in the gastrointestinal tract, as well as perforation and dysphagia;
4. Patients with severe heart, lung, liver, kidney, endocrine, hematopoietic system or psychiatric diseases were considered not suitable for the study group;
5. Human immunodeficiency virus (HIV) infection or known acquired immune deficiency syndrome (AIDS) or autoimmune disease or immunosuppressant use；
6. There are patients who may increase the risk of participating in the study and study medication, or other severe, acute and chronic diseases, and are not suitable for participating in the clinical study according to the judgment of the investigator.