• The patient understands and voluntarily signs the informed consent, and is expected to complete the follow-up examination and treatment of the study procedure.

• Age 18 to 75 years old, gender is not limited.

• Diagnosed with multiple myeloma according to IMWG diagnostic criteria.

• Have received third-line or above treatment.

• Have measurable lesions at screening period, defined as any of the following : (1) serum monoclonal immunoglobulin (M-protein) level ≥1.0 g/dL. (2) urine M protein level ≥200 mg/ 24h. (3) Light chain multiple myeloma diagnosed with no measurable lesion in serum or urine: serum immunoglobulin free light chain is ≥10 mg/dL and serum immunoglobulin κ/γ free light chain ratio is abnormal.

• The patient has recovered from the toxicity of the previous treatment, that is, the CTCAE toxicity grade is less than 2 (unless the abnormality is related to the tumor or is in a stable state as judged by the investigator, which has little effect on safety or efficacy).

• Eastern cooperative oncology group (ECOG) score is 0-2, and survival is expected to be greater than 3 months.

• Has proper organ function: (1) Alanine aminotransferase (ALT) ≤3 times the upper limit of normal (ULN). (2) Aspartate aminotransferase (AST) ≤3 times ULN. (3) Total bilirubin ≤1.5 ULN. (4) Serum creatinine ≤1.5 ULN, or creatinine clearance ≥60 mL/min. (5) Indoor oxygen saturation ≥92%. (6) Left ventricular ejection fraction (LVEF) ≥45%, echocardiography confirmed no pericardial effusion, no ECG findings with clinical sense. (6) There was no clinically significant pleural effusion.

• The venous access required for collection can be established, and there are no contraindications to leukocyte collection.