Efficacy and Safety of Sintilimab Combined With Nab-paclitaxel and Tegio (aTS) as First-line Treatment of Unresectable Locally Advanced, Recurrent or Metastatic Adenocarcinoma of Gastric and Gastroesophageal Junction，a Phase II Clinical Study

The goal of this clinical trial is to find better protocal for adenocarcinoma of the gastric and gastroesophageal juncion. The main question is aim to answer is: 1\. The efficacy and safety of PD-1 monoclonal antibody (Sintilimab) combined with nab-paclitaxel and S-1 in the first-line treatment of advanced gastric and gastroesophageal junction adenocarcinoma. Participants will be given PD-1 monoclonal antibody, nab-paclitaxel and tegio.