Inclusion Criteria:
1. Voluntarily participate in this study and sign the informed consent form.
2. Age range: 18 - 75 years old. Gender is not restricted.
3. Histologically confirmed large B-cell lymphoma, including: diffuse large B-cell lymphoma (DLBCL), primary mediastinal large B-cell lymphoma (PMBCL), transformed follicular lymphoma (tFL), and mantle cell lymphoma (MCL).
4. CD19-positive (as determined by immunohistochemistry or flow cytometry; based on the most recent tumor biopsy results).
5. Definition of relapsed/refractory: Failure to achieve complete remission (CR) after at least two lines of therapy (which must include a CD20 monoclonal antibody and an anthracycline); or disease progression during any course of treatment; or relapse/progression within 12 months after autologous hematopoietic stem cell transplantation.
6. At least one measurable lesion: any lymph node lesion with a longest dimension \>1.5 cm, or any extranodal lesion with a longest dimension \>1.0 cm, and the lesion shows uptake on PET-CT (SUV greater than the hepatic pool).
7. Absolute neutrophil count in peripheral blood ≥ 1,000/μL; platelet count ≥ 45,000/μL.
8. Cardiac, hepatic, and renal function: creatinine \< 1.5 mg/dL; ALT/AST ≤ 2.5 times the upper limit of normal; total bilirubin \< 1.5 mg/dL; ejection fraction ≥ 50%.
9. Possess sufficient cognitive capacity to voluntarily sign the informed consent form.
10. Participants of reproductive potential must be willing to use effective contraception (from the time of signing the informed consent form until 12 months after CAR-T infusion).
11. The investigator estimates a life expectancy of at least 4 months.
12. Willing to comply with the schedule of visits, dosing regimen, laboratory tests, and other trial procedures.
Exclusion Criteria:
1. History of other malignant tumors (excluding cured basal cell carcinoma, cervical carcinoma in situ, papillary thyroid carcinoma, etc.).
2. Autologous hematopoietic stem cell transplantation within the past 6 weeks.
3. Any targeted CAR-T therapy within 3 months prior to this CAR-T treatment.
4. Patients who have previously received PD-1 monoclonal antibodies must have a washout period of ≥3 months before enrollment.
5. Received cytotoxic drugs, glucocorticoids (except for prednisone-equivalent doses of ≤10 mg/day), or other targeted therapies within 2 weeks prior to cell collection.
6. Active autoimmune diseases (e.g., systemic lupus erythematosus, inflammatory bowel disease, etc.).
7. Uncontrolled active bacterial, fungal, or viral infections.
8. HIV infection, syphilis; active hepatitis B or C: Hepatitis B: HBsAg-positive and HBV-DNA ≥ 1,000 IU/mL; Hepatitis C: HCV RNA-positive and abnormal liver function.
9. Known central nervous system lymphoma (confirmed by brain MRI or CT and cerebrospinal fluid examination).
