A Vaccine (Ad5.F35-hGCC-PADRE) for the Treatment of Gastrointestinal Adenocarcinoma

PRIMARY OBJECTIVES: 1. Evaluate the safety and tolerability of sequential Ad5.F35-hGCC-PADRE vaccine administration, delivered intramuscularly (IM) at three dose levels (1011, 1012, and 5x1012 vp) four weeks apart in subjects with high-risk colorectal, pancreatic, gastric, esophageal, or small bowel adenocarcinomas with no evidence of disease after surgery and standard therapy. 2. For Cohort 2B, evaluate the safety and tolerability of single Ad5.F35-hGCC-PADRE vaccine at 1012 dose level in MRD+ colon cancer patients with no evidence of radiographic disease 3. Evaluate the cellular (T-cell) responses to Ad5.F35-hGCCPADRE at three different dose levels (1011, 1012, and 5x1012 vp) administered intramuscularly (IM) as three sequential doses four weeks apart in subjects with high-risk colorectal, pancreatic, gastric, esophageal, or small bowel adenocarcinomas with no evidence of disease after surgery and standard therapy. 4. For cohort 2B, evaluate the cellular (T-cell) responses to Ad5.F35-hGCC-PADRE vaccine at 1012 dose administered IM as one dose in subjects with MRD+ colon cancer with no evidence of radiographic disease after surgery and standard therapy. EXPLORATORY OBJECTIVES: * Evaluate the humoral (antibody) responses to Ad5.F35- hGCC-PADRE at three different dose levels (1011, 1012, and 5x1012 vp) administered IM as three sequential doses four weeks apart in subjects with high-risk colorectal, pancreatic, gastric, esophageal, or small bowel adenocarcinomas with no evidence of disease after surgery and standard therapy * Evaluate the association of neutralizing antibodies to Ad5 with immunologic response * Evaluate the correlation of the immune response to the GCC protein expression in tumors to assess immune tolerance * Evaluate disease-free survival (DFS) * Evaluate overall survival (OS), where feasible * Evaluate the circulatory tumor DNA (ctDNA) status and correlation with clinical recurrence, where feasible * Evaluate the ctDNA dynamics after single dose of 1012 Ad5.F35-hGCC-PADRE vaccine in an expansion cohort of ctDNA+ colon cancer patients