Clinical Study to Evaluate the Safety and Efficacy of IM21 CAR-T Cells in the Treatment of Elderly Patients With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: 1. Patients with relapsed or refractory multiple myeloma who had received at least second line regular treatment failure; 2. Age ≥60 years old; 3. The expected survival time is more than 3 months; 4. ECOG score is 0-2; 5. Those who voluntarily participate in the study and sign the informed consent; 6. Hemoglobin (Hb)≥80g/L; Absolute count of neutrophils (ANC) \>1×10\^9/L Total platelet count (PLT)≥35×10\^9/L; 7. left ventricular ejection fraction \> 45%. Exclusion Criteria: 1. High-risk viscera-involved patients: the tumor invaded the gastrointestinal tract, lung, pericardium and one of the great vessels; 2. Those who have graft versus host disease and need to use immunosuppressive agents; 3. Use of systemic steroids in combination within 5 days prior to the blood collection period (except for recent or current use of inhaled steroids); 4. Active hepatitis B or C virus, HIV or other untreated active infected persons; 5. Any circumstance that, in the opinion of the investigator, may increase the risk to the subject or interfere with test results; 6. Patients who use chemotherapy or radiotherapy within 3 days before the blood collection stage.