Inclusion Criteria:

1. Willingness to participate in the trial and provision of signed informed consent.
2. Patients diagnosed with B-lymphocyte or plasma cell-derived malignancies as per the 2017 revised WHO criteria, including acute B-lymphoblastic leukemia (B-ALL), and mature B-cell lymphomas such as diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), marginal zone lymphoma (MZL), small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL), mantle cell lymphoma (MCL), multiple myeloma (MM), etc.
3. Refractory or recurrent B-lymphocyte or plasma cell-derived malignancies, defined as failure to achieve complete remission after standard treatment, or relapse during follow-up after achieving remission with first-line or salvage therapy.
4. Patients with B-cell acute lymphoblastic leukemia (ALL) who have achieved hematologic remission but have persistent minimal residual disease (MRD).
5. According to the revised International Working Group (IWG) criteria, relapsed/refractory lymphoma patients must have at least one measurable lesion with a longest diameter ≥1.5 cm.
6. 18 Years and older, regardless of gender.
7. An expected survival of ≥12 weeks.
8. Serum total bilirubin level < twice the upper limit of normal, serum creatinine level < upper limit of normal, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) < three times the upper limit of normal.
9. Absolute neutrophil count ≥0.5×10⁹/L, platelets ≥20×10⁹/L; for B-lymphocyte malignancies with definitive bone marrow involvement, no requirements for neutrophil and platelet counts.
10. ECOG performance status of 0 - 2.
11. Left ventricular ejection fraction (LVEF) ≥50% and no pericardial effusion.
12. At least 2 weeks have passed since the last treatment (radiotherapy, chemotherapy, monoclonal antibody therapy, or other treatments).

Exclusion Criteria:

1. Known allergies, hypersensitivity, intolerance, or contraindications to CD19/BCMA allogenic CAR-T or any components of the trial drugs (including fludarabine, cyclophosphamide, and rituximab), or a history of severe allergic reactions.

2. Recurrence after allogeneic hematopoietic stem cell transplantation with active graft - versus - host disease (GVHD) requiring steroid or immunosuppressive therapy.

3. Severe active infection.

4. Acquired or congenital immunodeficiency.

5. New York Heart Association (NYHA) Class Ⅲ or Ⅳ heart failure.

6. History of epilepsy or other central nervous system diseases.

7. Lymphoma with extranodal involvement of the brain, lungs, or gastrointestinal tract.

8. Other primary cancers, except:

   1. Non-melanoma skin cancer (e.g., basal cell carcinoma) cured by resection.
   2. Carcinoma in situ (e.g., cervical, bladder, or breast cancer) cured.

9. Systemic high-dose steroids within 2 weeks before treatment.

10. Pregnant, breastfeeding, or plans to become pregnant within 6 months.

11. Participation in another clinical trial within the past month.

12. Any situation the investigator deems may raise risks or interfere with trial results.