• Relapsed/refractory multiple myeloma.

• Confirmed by immunohistochemistry (IHC) or flow cytometry of bone marrow samples: plasma cell membrane expression of BCMA is positive (≥30%); no requirement for CD19 positivity rate. All sites must centrally submit bone marrow or plasmacytoma biopsy specimens to the lead site's pathology department or bone marrow/liquid specimens to KingMed Diagnostics (third-party laboratory) for BCMA expression verification.

• Relapsed/refractory patients must meet the following criteria:

• No response or disease progression after 3 cycles of bortezomib (proteasome inhibitor) or lenalidomide therapy No response or disease progression after 3 cycles of prior treatment regimen Interval between last treatment and disease progression \>30 days No current indication for hematopoietic stem cell transplantation (HSCT), or patient refusal of HSCT

• Definition of disease progression follows the 2021 International Myeloma Working Group (IMWG) criteria, meeting at least one of the following:

• Serum M protein ≥ 5 g/L Urine M protein ≥ 200 mg/24 h If serum free light chain (FLC) ratio is abnormal, patient FLC level ≥ 100 mg/L Biopsy-confirmed evaluable plasmacytoma Increased myeloplasmacytic percentage ≥25% (absolute increase ≥10%) Myeloplasm cells constitute ≥30% of total bone marrow cells

• Expected survival \>12 weeks;

• Disease status is evaluable and meets at least one of the following:

• Serum M-protein ≥10 g/L, 24-hour urine M-protein ≥ 200 mg, Serum FLC ≥ 50 mg/L, Plasmacytoma evaluable by imaging or laboratory testing, Bone marrow plasma cell percentage ≥ 30%

• Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1;

• Sufficient venous access for apheresis or venipuncture, with no other contraindications to blood cell separation;

• white blood cell (WBC) ≥ 1.5 × 10⁹/L; platelet (PLT) ≥ 45 × 10⁹/L.

• Serum creatinine ≤ 1.5 times the upper limit of normal (ULN).

⁃ Alanine Aminotransferase (ALT) ≤ 2.5 ULN, Aspartate Aminotransferase (AST) ≤ 2.5 ULN.

‣ All laboratory values within the above ranges must be achieved without ongoing supportive therapy.