The goal of this clinical trial is to test CD19-7×19 CAR-T cells combined with Tislelizumab in refractory and relapsed diffuse large B lymphoma. The main question[s] it aims to answer are:

question 1：What is the safety of CD19-7×19 CAR-T cells combined with Tislelizumab in the treatment of relapsed or refractory diffuse large B-cell lymphoma.

question 2：What is the efficacy of CD19-7×19 CAR-T cells combined with Tislelizumab in the treatment of relapsed or refractory diffuse large B-cell lymphoma.

Participants will be asked to receive clinical evaluation before CAR-T, including physical examination, blood routine test, biochemical test, imaging test, etc.Peripheral blood lymphocytes will be collected for preparation of CAR-T cells after enrollment. Pretreatment chemotherapy with fludarabine and cyclophosphamide will be used before CAR-T infusion. On the 31st day after CAR-T infusion, Tislelizumab 200mg was given once every 21 days for 6 cycles. Participants will be required to report concomitant medication and adverse events, and their disease was evaluated throughout the study.

Inclusion Criteria:

1. Age ≥ 18, upper limit 75, male or female;
2. ECOG score 0-3;
3. Histologically confirmed diffuse large B-cell lymphoma (DLBCL) [diagnostic criteria according to WHO 2008];
4. CD19 positive (immunohistochemistry or flow cytometry).
5. DLBCL refractory or relapse is defined as: complete remission is not achieved after 2-line treatment; let What disease progress occurs during treatment, or the disease stability time is equal to or less than 6 months; Or autologous hematopoietic stem Disease progression or recurrence within 12 months after cell transplantation;
6. Previous treatment for patients with diffuse large B cell lymphoma must include rituximab (CD20 monoclonal antibody) and anthracyclines;
7. At least one measurable lesion is required, and any lymph node lesion with a length greater than 1.5cm or extranodal lesion is required If any length diameter is greater than 1.0 cm, the lesions on PET-CT scan have uptake (SUV is larger than liver blood pool);
8. Absolute value of peripheral blood neutrophils ≥ 1000/ μ l. Platelets ≥ 45000/ μ l
9. Heart, liver and kidney functions: creatinine < 1.5mg/dL; ALT/AST Less than 2.5 times of normal upper limit; Total bilirubin < 1.5mg/dL; Cardiac ejection fraction (EF) ≥ 50%;
10. Have sufficient understanding and voluntarily sign the informed consent form;
11. People with fertility must be willing to use contraceptive methods;
12. According to the judgment of the researcher, the expected survival period is at least 4 months;
13. Willing to follow the visit schedule, administration plan, laboratory inspection and other test steps.

Exclusion Criteria:

1. Have a history of other tumors;
2. Autologous hematopoietic stem cell transplantation was performed within 6 weeks;
3. Any target CAR-T treatment was performed within 3 months before this CAR-T treatment;
4. Previously used any commercially available PD-1 monoclonal antibody;
5. Cytotoxic drugs, glucocorticoids and other targeted drugs were received within 2 weeks before cell collection;
6. Active autoimmune diseases;
7. Uncontrollable active bacterial and fungal infections;
8. HIV infection and syphilis infection; Active hepatitis B or hepatitis C: hepatitis B: HBV-DNA ≥ 1000 IU/mL; Hepatitis C: HCV RNA is positive and liver function is abnormal.
9. Known central nervous system lymphoma.