This study was conducted to evaluate an synergistic effect and immune response of the combination of AST-301 and HER2-ADC in HER2-expressed gastric cancer xenograft model….It was showed that adding AST-301 to LCB01 or Kadcyla inhibited a tumor growth based on TGI rate at days 25; AST-301 combining with LCB01 vs LCB01 mono (52% vs 43%), AST-301 combining with Kadcyla vs Kadcyla mono (43% vs 34%). It was also observed or that myeloid-derived suppressor cells (MDSCs) elevation was inhibited in tumor site in the combination groups of all ADCs with AST-301 compared to control group....With combining AST-301 and HER2 ADCs, it was demonstrated that antitumor effects were likely synergistic in athymic mouse model.