A Dose Escalating Study of CD19/CD22/BCMA CAR-T Therapy in Relapsed/ Refractory Multiple Myeloma

Inclusion Criteria: * Participants must meet all of the following criteria in order to be enrolled: 1. Understand and voluntarily sign an informed consent form (ICF) before conducting any research related evaluations/procedures; 2. Age range: 18-75 years old; 3. Expected survival period is not less than 12 weeks; 4. ECOG score ≤ 2 points; 5. The bone marrow flow cytometry results showed positive BCMA antigen (including weak positive, moderate positive, and strong positive); 6. According to the IMWG criteria, a diagnosis of multiple myeloma with measurable lesions must meet at least one of the following criteria: 1. Serum M protein (SPEP) ≥ 5g/L 2. 24-hour urinary M-protein excretion rate ≥ 0.2g (200mg) 3. Serum free light chain (sFLC) ≥ 100 mg/L and abnormal free light chain ratio 4. The ratio of primitive plasma cells to immature plasma cells in bone marrow cytology examination is greater than 5%, or the flow cytometry detection of monoclonal plasma cells is greater than 5% 7. Those who have received treatment with at least three different mechanisms of action (including anti-CD38 monoclonal antibodies, protease inhibitors, immunosuppressants, etc.) but have failed, and have experienced relapse (within 12 months), difficulty in treatment, or intolerance to the last line treatment regimen, including primary difficulty in treatment (subjects who have not achieved minimal remission \[MR\] or developed disease progression \[PD\] during treatment) or secondary difficulty in treatment (subjects who develop disease progression within 60 days after completion of treatment); 8. There is no significant abnormality in lung function, and the oxygen saturation is greater than 92% in the absence of oxygen inhalation; 9. The blood biochemistry test results meet the following criteria: 1. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 x upper limit of normal (ULN) 2. Total bilirubin ≤ 1.5 × ULN 3. 24-hour serum creatinine clearance rate ≥ 30 mL/min 4. Lipase and amylase ≤ 2 × ULN 10. The blood routine test meets the following criteria: 1. Lymphocyte count\>0.5 × 10 \^ 9/L 2. Neutrophil count ≥ 1.0 × 10 \^ 9/L 3. Hemoglobin ≥ 60g/L 4. Platelets ≥ 40 × 10 \^ 9/L 11. Men with fertility and women of childbearing age must agree to use effective contraceptive measures from the signing of the informed consent form until 2 years after the use of the study drug. Women of childbearing age include premenopausal women and women within 2 years after menopause. The blood pregnancy test for women of childbearing age must be negative during screening. Exclusion Criteria: * Any of the following situations cannot be selected as a subject: 1. Asymptomatic (smoking type) multiple myeloma; 2. Multiple myeloma with only extramedullary lesions present; 3. Plasma cell leukemia; 4. Merge amyloidosis; 5. Central nervous system (CNS) metastasis, leptomeningeal disease, or metastatic central compression; 6. Pregnancy or lactation period; 7. Individuals who are HBsAg positive or HBcAb positive, unless HBV-DNA is less than 100 IU/ml or below the minimum detectable value; Individuals who are positive for hepatitis C virus (HCV) antibodies and HCV-RNA; Individuals who are HIV antibody positive; Individuals who are positive for syphilis specific antibodies and have a positive TRUST (toluidine red unheated serum test) test; Individuals who test positive for Cytomegalovirus (CMV) DNA; 8. Cardiovascular diseases with clinical significance, including any of the following: 1. QT interval (QTcF) after heart rate correction:\>470 milliseconds; 2. New York Heart Association Grade II and above heart failure; 3. Left ventricular ejection fraction (LVEF) ≤ 50%; 4. Poorly controlled hypertension (systolic blood pressure ≥ 150 mm Hg and/or diastolic blood pressure ≥ 95 mm Hg) 5. Arrhythmias that have clinical significance or require antiarrhythmic treatment (such as persistent ventricular tachycardia, ventricular fibrillation, apical torsion tachycardia, and complete left bundle branch block); 9. Has experienced unstable angina or acute myocardial infarction within the 6 months prior to signing the ICF; 10. Previously received any anti-CD45 or anti-CD3 treatment; 11. Individuals who are allergic to any of the components of the drugs used in this study, including but not limited to Qing Lin drugs (cyclophosphamide, fludarabine), etc; 12. Received any investigational drug or systemic anti-tumor treatment within 4 weeks (or 5 half lives of the drug, whichever the researcher deems more appropriate) prior to single collection; 13. History of other primary malignant tumors within 5 years prior to treatment, except for the following situations: 1. Fully treat cured cervical carcinoma in situ; 2. Localized basal cell carcinoma or squamous cell carcinoma of the skin; 14. Any uncontrolled active infection within 4 weeks prior to single collection requires parenteral antibiotics, antiviral or antifungal treatment; 15. Individuals with a history of active pulmonary tuberculosis infection within one year prior to single sampling (excluding subjects with a history of active pulmonary tuberculosis infection more than one year ago who, according to the researcher's judgment, currently have no evidence of active pulmonary tuberculosis); 16. Accompanying or having a history of interstitial lung disease or interstitial pneumonia; 17. Subjects who receive autologous hematopoietic stem cell transplantation (ASCT) within 8 weeks of signing the ICF, or who plan to undergo ASCT during the study period; 18. Subjects who have received allogeneic stem cell therapy in the past; The researchers believe that complications or other conditions in the subjects may affect their compliance with the protocol or make them unsuitable to participate in this study.