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

Key Inclusion Criteria: * Underwent a curative surgery with standard lymph node dissection (confirmed with no residual tumor, R0 resection) and have completed standard adjuvant treatment * Has stages II or III according to the 8th edition of the American Joint Committee on Cancer (AJCC) * HER2 low expression and HER2 overexpression diagnosed according to the 2016 College of American Pathologists (CAP)/American Society for Clinical Pathology (ASCP)/American Society of Clinical Oncology (ASCO) guidelines * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 * Demonstrates adequate organ function. Key Exclusion Criteria: * Has a history of hypersensitivity or other contraindications to rhuGM-CSF * Has a history of other malignancies ≤5 years prior to first administration of Investigational Product (IP) except for adequately treated non-melanoma skin cancer or epithelial carcinoma without evidence of disease. * Has received systemic immunosuppressants or were treated with systemic immunosuppressants ≤4 weeks prior to the first administration of Investigational Product (IP). * Has a history of autoimmune disease or inflammatory disease * Has active infection including tuberculosis, hepatitis B, hepatitis C or human immunodeficiency virus (HIV) infection * Is pregnant or breastfeeding or expecting to conceive children