RecruitingPhase 1Biological interventionBC001 in Combination with Sintilimab and XELOX in the Treatment of HER-2 Negative Advanced or Metastatic Gastric Cancer or Gastroesophageal Junction Adenocarcinoma.The goal of this clinical trial is to learn the efficaty and safety of BC001 in combination with Sintilimab and XELOX in treating patients with advanced or metastatic GC/GEJ. Participants will: Be administered with BC001, Sintilimab and Oxaliplatin once every three weeks for up to 24 months or until disease progression as per RECIST 1.1 or withdrawal from this study. Take Capecitabine once daily in the first two weeks of each three-week treatment cycle for up to 24 months or until disease progression as per RECIST 1.1 or withdrawal from this study.