A Study of Bortezomib, Lenalidomide and Dexamethasone (VRd)-Based Regimen Followed by BCMA CAR-T Therapy in Transplant-Ineligible Patients With Primary Plasma Cell Leukemia

Inclusion Criteria: 1. Age ≥ 18 years and ≤ 75 years. 2. Participants with documented primary plasma cell leukemia according to IMWG diagnostic criteria (circulating plasma cells ≥5%, determined by morphology on peripheral blood smear; or absolute value of peripheral blood tumorigenic plasma cells exceeds 2×10\^9/L). 3. Measurable disease, at screening as defined by any of the following: Serum monoclonal paraprotein (M-protein) level ≥1.0 g/dL or urine M-protein level ≥200 mg/24 hours; or Light chain MM without measurable disease in serum or urine: serum Ig free-light chain (FLC) ≥10 mg/dL and abnormal serum Ig kappa lambda FLC ratio. 4. Not considered for high-dose chemotherapy with Autologous Stem Cell Transplant (ASCT) due to: Ineligible due to advanced age (≥65); or Ineligible evaluated by researchers; or Eastern Cooperative Oncology Group Performance Status grade of 3 or 4; or Repeated hematopoietic stem cell mobilization failure； or Deferral of high-dose chemotherapy with ASCT as initial treatment. 5. Bone marrow sample is confirmed as BCMA-positive by flow cytometry or pathological examination. 6. All screening blood biochemistry: tests should be performed according to the protocol and within 14 days before enrollment. Screening laboratory values must meet the following criteria: a.TBIL\<2 x upper limit of normal (ULN) (\<3 x ULN in patients with Gilbert's syndrome); b.AST and ALT \<3 x ULN.; c. Creatinine clearance ≥ 30mL/min (calculated using Cockroft-Gault formula). 7. Routine blood tests (performed within 7 days, no RBC transfusion, no G-CSF/GM-CSF/platelet agonists, no drug correction within 14 days before screening, no PLT transfusion within 7 days) : WBC ≥ 1.5 x 109/L, ANC ≥ 1.0 x 109/L, Hb ≥ 70 g/L PLT ≥ 75 x 109/L (if BMPC \< 50%) or PLT ≥ 50 x 109/L (if BMPC ≥ 50%). 8. Patients must be able to take prophylactic anticoagulant therapy as recommended by the study. 9. The woman is not breastfeeding, is not pregnant and agrees not to be pregnant during the study period and for the following 12 months. Male patients agreed that their spouse would not become pregnant during the study period and for 12 months thereafter. Exclusion Criteria: 1. Documented active amyloidosis. 2. Documented with central nervous system (CNS) invasion. 3. Prior exposure to any BCMA-targeted therapy or CAR-T therapy. 4. Patients with peripheral neuropathy greater than grade 2 or peripheral neuropathy greater than grade 2 with pain at baseline, regardless of whether they were currently receiving medical therapy. 5. Known intolerance, hypersensitivity, or contraindication to glucocorticoids, bortezomib, lenalidomide, and BCMA-CART cellular products. 6. Seropositive for human immunodeficiency virus (HIV) 7. Hepatitis B infection 8. Hepatitis C infection 9. Life expectancy of \<6 months 10. Women who are pregnant or breastfeeding 11. Any active gastrointestinal dysfunction that affects the patient's ability to swallow tablets, or any active gastrointestinal dysfunction that may affect the absorption of the studied treatment medication 12. Subjects had major surgery within 2 weeks before randomization (for example, general anesthesia), or is not fully recovered from the surgery, or surgery is arranged during study period. 13. Received live attenuated vaccine within 4 weeks prior to study treatment. 14. According to the researcher's judgment, any condition including but not limited to serious mental illness, medical illness, or other symptoms/conditions that may affect study treatment, compliance, or the capability of providing informed consent. 15. Necessary medication or supportive therapy is contraindicated with study treatment. 16. Any diseases or complications that may interfere with the study. 17. Patients are not willing to or cannot comply with study scheme.