Therapeutic Cancer Vaccine (AST-301, pNGVL3-hICD) in Gastric Cancer

The purpose of this early proof-of-concept study to evaluate the safety and immunologic efficacy of AST-301 in gastric cancer patients with HER2 expression (including both HER2 low expression and overexpression) who have completed the standard adjuvant treatment (including those who discontinued the standard adjuvant treatment due to intolerance). Participants will be randomized 1:1 to either Arm 1 (Q3W, 3 cycles), or Arm 2 (Q3W, 6 cycles) of the study. Safety Monitoring Committee (SMC) will oversee safety of study at 25% (6 participants), 50% (12 participants), and 75% (18 participants) of participants receive at least 1 dose of AST-301 and survival follow up will be performed to determine disease-free survival (DFS).