Inclusion Criteria:

• Voluntarily signed the informaed consent from.
• Age ≥ 18 and ≤ 80 years.
• Pathologically/histologically confirmed diagnosis of adenocarcinoma of the stomach or gastroesophageal junction, referred to collectively as STAD, or pancreatic adenocarcinoma (PAAD).
• Must have CLDN18.2-positive tumor expression as determined by the CLDN18.2 IHC assay.
• Pathologically/histologically confirmed diagnosis of STAD, or PAAD who have failed or been intolerant of prior lines of systemic therapy.
• Estimated life expectancy > 12 weeks.
• At least 1 measurable lesion per RECIST 1.1.
• ECOG performance status of 0 or 1.
• Sufficient venous access for leukapheresis collection and no other contraindications to leukapheresis.
• Patients should meet the following without intensive supporting therapy:
  • Complete blood count (CBC) results (without transfusion and growth factor support): WBC count ≥ 2.0 × 109/L, absolute neutrophil count (ANC) ≥ 1.0 × 109/L, lymphocytes (LY) ≥ 0.4 × 109/L, platelets (PLT) ≥ 80 × 109/L, hemoglobin (Hb) ≥ 9.0 g/dL.
  • Blood biochemistry: creatinine clearance ≥ 50 mL/min (Cockcroft –Gault formula), alanine aminotransferase (ALT) ≤ 2.5 × ULN), aspartate aminotransferase (AST) ≤ 2.5 × ULN, total bilirubin ≤ 1.5 × ULN; Gilbert’s syndrome, total bilirubin ≤ 2.5 × ULN, AST < 5 × ULN, ALT < 5 × ULN; if bone and liver metastasis occur and alkaline phosphatase (ALP) < 2.5 × ULN, AST < 5 × ULN, ALT < 5 × ULN.
  • PT < ULN + 4 seconds.
• Women of childbearing age must undergo a serum pregnancy test with negative results before screening and infusion and be willing to use effective and reliable method of contraception.
• Men must be willing to use effective and reliable method of contraception for at least 6 months after T-cell infusion.

Exclusion Criteria:

• Pregnant or lactating women
• HIV, active hepatitis C virus (HCV), or active hepatitis B virus (HBV) infusion
• Any uncontrolled active infection
• AEs from previous treatment that have not recovered
• Patients who have clinically significant thyroid dysfunction
• Patients allergic to any drugs of the preconditioning regimen, tocilizumab, dimethyl sulfoxide (DMSO), or CT041 CAR-CLDN18.2 T-cell
• Patients who have received prior cellular therapy such as (CAR T, TCR, tumor-infiltrating lymphocytes) or organ transplantation; Untreated central nervous system (CNS) metastatic disease, leptomeningeal disease, or cord compression
• Patients with heavy tumor burdens:
  • Patients with a tumor lesion > 4 cm identified as measurable per RECIST1.1.
  • Centric or wide-spreading metastatic lung lesion(s) that have involved more than 5% of thoracic tissues (each individual lesion does not need to be measurable per RECIST1.1).
• Unstable/active ulcer or digestive tract bleeding or recent digestive surgery that may have increased risk of bleeding
• Patients who have a history of esophageal or gastric resection with increased risk of bleeding or perforation
• Patients requiring anticoagulant therapy such as warfarin or heparin
• Patients requiring long-term antiplatelet therapy
• Use of prednisone or other equivalent within 14 days before leukapheresis or preconditioning
• Anticancer treatment within approximately 2 weeks prior to leukapheresis or approximately 3 weeks before preconditioning
• Major surgery less than 1 week prior to leukapheresis or 3 weeks prior to preconditioning
• Patients who have any of the following cardiac conditions:
  • New York Heart Association (NYHA) Stage III or IV congestive heart failure (CHF).
  • Myocardial infarction or coronary artery bypass graft within 6 months prior to enrollment.
  • History of clinically significant ventricular arrhythmia or unexplained syncope, not believed to be vasovagal in nature or due to dehydration.
  • History of severe non-ischemic cardiomyopathy.
  • Uncontrolled blood pressure as defined as systolic > 160 mmHg, diastolic > 100 mmHg within 3 months prior to enrollment.
  • Left ventricular ejection fraction (LVEF) < 45% as assessed by echocardiogram or multiple-gated acquisition (MUGA) scan.
  • Other conditions that the treating physicians believe may endanger the health of the patients by their participation in this clinical trial.
• Patients who have 1 of the following pulmonary conditions:
  • Forced expiratory volume in 1 second (FEV1) < 60%.
  • Active obstructive chronic pulmonary disease.
  • Oxygen dependence as defined by a blood oxygen saturation that can only be maintained above 92% by oxygen inhalation (finger oxygen detection method).
• Patients known to have active autoimmune diseases
• Patients with second malignancies in addition to STAD or PAAD
• Patients have significant neurologic disorders
• Patients are unable or unwilling to comply with the requirements of clinical trial.