Advanced Gastric and Pancreatic Cancer

The goal of this clinical trial is to learn if CBG131 works to treat advanced gastric cancer or pancreatic cancer in adults whose tumors are CLDN18.2-positive. It will also learn about the safety of CBG131 and find the best dose to use. The main questions it aims to answer are: Is CBG131 safe, and what medical problems do participants have when receiving it? Does CBG131 shrink tumors in participants with CLDN18.2-positive cancers? How long do the CAR-T cells stay and work in the body? Researchers will test different doses of CBG131 to see which dose is safest and most effective. This is an early-stage trial, so there is no placebo group-everyone who joins will receive the actual treatment. Participants will: Have their blood cells collected through a procedure called leukapheresis (so the CAR-T cells can be made). Receive chemotherapy for 3 days to prepare their body for the CAR-T cells Get a single infusion of CBG131 CAR-T cells through an IV. Visit the clinic frequently for the first month, then regularly for 2 years for checkups, blood tests, and tumor assessments. Keep track of their symptoms and any side effects they experience.