To Evaluate the Efficacy of CT041 in Sequential Treatment After First-line Treatment of Advanced Gastric/Esophagogastric Junction Adenocarcinoma

Inclusion Criteria: Individuals must meet all of the following criteria to be eligible for participation in this trial: 1. Voluntarily participate in this trial; Fully understand and be informed of this trial and sign the informed consent form; Willing to follow and able to complete all trial procedures; 2. Age 18-75 years (inclusive), male or female; 3. Pathologically confirmed unresectable locally advanced or metastatic advanced gastric/esophagogastric junction (G/GEJ) adenocarcinoma; 4. Immunohistochemical (IHC) staining of tumor tissue sample is CLDN18.2 positive, defined as staining intensity ≥ 2 + in at least 40% of tumor cells; 5. Completed 12 weeks of first-line therapy according to clinical guidance, without disease progression as assessed by the investigator: Permitted treatment regimens include: fluoropyrimidine + platinum (± taxane) regimen chemotherapy, with or without immunotherapy or zolbetuximab. Other treatment regimens may be allowed to be included after discussion between the investigator and medical monitor of the collaborator; For the treatment regimen of every 2 weeks, 6 cycles should be completed, and for the treatment regimen of every 3 weeks, 4 cycles should be completed; According to the investigator's assessment and decision, participants without disease progression after at least 6 weeks of first-line treatment can undergo apheresis after meeting other eligibility criteria; 6. Eastern Cooperative Oncology Group (ECOG) performance status 0-1 (within 7 days prior to apheresis); 7. Adequate venous access for apheresis and no other contraindications for apheresis. 8. Laboratory test results within 7 days prior to apheresis should meet the following criteria (a repeat test within one week is allowed, if still not meeting the criteria, it will be considered a screening failure): 1. Blood routine (without transfusion, platelet transfusion, colony-stimulating factor, platelet growth factor and other supportive treatment within 7 days before test, except recombinant human erythropoietin): absolute neutrophil count (ANC) ≥ 1.5×109/L, lymphocyte (LY) ≥ 0.5×109/L, platelet (PLT) ≥ 75×109/L, hemoglobin (Hb) ≥ 9.0 g/dL. The results of blood routine test within 24 hours before apheresis should also meet the above criteria. 2. Blood chemistry: endogenous creatinine clearance ≥ 50 mL/min (Cockcroft-Gault formula), alanine aminotransferase (ALT) ≤ 2.5×upper limit of normal (ULN), aspartate aminotransferase (AST) ≤ 2.5×ULN, total bilirubin ≤ 2×ULN; serum amylase ≤ 2.0×ULN; alkaline phosphatase ≤ 2.5×ULN; AST, ALT and alkaline phosphatase ≤ 5 × ULN if there is bone metastasis or liver metastasis; 3. Prothrombin time (PT) prolongation ≤ 4 seconds. 9. Female participants of childbearing potential (WOCBP) must have a negative serum pregnancy test at screening and be willing to use highly effective and reliable contraception (\< 1% failure rate per year) for at least 12 months after receiving trial treatment and egg donation is absolutely prohibited during this period. 10. Male participants who are sexually active with a female of childbearing potential, who have not had a vasectomy, must agree to practice abstinence or use highly effective and reliable contraception (failure rate \< 1% per year) for at least 12 months after receiving trial treatment and sperm donation is prohibited during this period. Exclusion Criteria: Participants who meet any of the following criteria will be excluded from this trial: 1. Presence of a known tumor tissue with high HER2 expression; 2. Presence of gastrointestinal bleeding/perforation/obstruction or significant risk with these, including but not limited to anastomotic recurrence involving the full thickness of gastric wall, deep large ulcer, unstable/active ulcer, history of gastrointestinal bleeding/perforation/obstruction within 3 months (excluding those with surgical resection of the lesion leading to such event); 3. Participants who have previously received any anti-tumor therapy other than the first-line treatment regimen for G/GEJ adenocarcinoma allowed in this trial (see Item 5 of the inclusion criteria), including any other systemic anti-tumor drugs, any radiotherapy or interventional therapy, etc.; 4. Systemic anti-tumor treatment for G/GEJ adenocarcinoma within 21 days (or within 5 half-lives of the drug, whichever is shorter) prior to apheresis; 5. Major surgery (excluding cataract surgery and other surgery requiring local anesthesia) or significant traumatic injury within 4 weeks prior to apheresis and has not adequately recovered from toxicity and/or complications; 6. Previously received any genetic engineering modified cell therapy (such as CAR-T cells, TCR-T cells, etc.); 7. Toxicities from previous treatment that have not recovered to Common Terminology Criteria for Adverse Events (CTCAE) v5.0 ≤ Grade 1, excluding alopecia, pigmentation, peripheral neuropathy, other events that, at the discretion of the investigator, do not affect the tolerability of the participant to the trial intervention, and laboratory abnormalities allowed in this trial. Note: Participants with non-clinically significant Grade 2 AE may be allowed to be included in the trial after discussion with medical monitor of the collaborator; 8. Positive serology for human immunodeficiency virus (HIV), Treponema pallidum, or hepatitis C virus (HCV). Participants with positive HCV antibody but negative HCV RNA can be enrolled; 9. Any active infection, including but not limited to active tuberculosis infection, active HBV infection (including hepatitis B surface antigen \[HBsAg\] positive, or hepatitis B core antibody \[HBcAb\] positive with HBV DNA above the lower limit of the trial center lab), and infection with other pathogens requiring systemic treatment. Participants receiving prophylactic anti-infective therapy may be enrolled at the discretion of the investigator; 10. Participants with clinically significant thyroid dysfunction or severe comp