Nanobody-based Biepitope CAR-T Cells Targeting BCMA in the Treatment of R/RMM

Inclusion Criteria: * Patient or his or her legal guardian voluntarily participates in and signs an informed consent form. * Aged ≥ 18 years and ≤ 75 years. * Diagnosed as Multiple Myeloma (MM) according to the international standard for multiple myeloma (IMWG 2014). * Diagnosed as relapsed/refractory disease or primary refractory disease; relapse is defined as disease progression within 60 days of the most recent treatment with three or more lines of therapy with different mechanisms of action; refractory is defined as failure to achieve MR or above efficacy with prior treatment and disease progression with recent treatment, or disease progression within 60 days of treatment. * Flow cytometry or immunohistochemistry showed positive BCMA expression in myeloma cells. * Have not been treated with antibody-based drugs within 2 weeks prior to cell therapy. * ECOG score 0-2 points. * HGB≥70g/L，PLT≥30×10\^9/L. * Liver, kidney and cardiopulmonary functions meet the following requirements: 1. Serum creatinine ≤ 1.5× ULN or creatinine clearance (Cockcroft-Gault) \>30 ml/min； 2. Left ventricular ejection fraction (LVEF) ≥50%, 3. Baseline peripheral oxygen saturation \> 90%; 4. Total bilirubin ≤ 1.5×ULN; ALT and AST ≤2.5×ULN. Exclusion Criteria: * Previous diagnosis and treatment of other malignancies within 3 years; * Presence of one of the following cardiac criteria: atrial fibrillation; Myocardial infarction within the last 12 months; Prolonged QT syndrome or secondary QT prolongation, as judged by the investigator. Echocardiogram LVSF \<30% or LVEF \<50%; Clinically significant pericardial effusion; Cardiac insufficiency NYHA (New York Heart Association) III or IV (absence of this symptom confirmed by echocardiography within 12 months of treatment); * Patients with active GVHD; * Patients with a history of severe pulmonary impairment disease; * Combined with other malignant tumors in the advanced stage; * Co-infection with severe or persistent infection that cannot be effectively controlled; * Combined with severe autoimmune disease or congenital immunodeficiency; * Active hepatitis (hepatitis B virus deoxyribonucleic acid \[HBV-DNA ≥ 500 IU/ml and abnormal liver function\] or hepatitis C antibody \[HCV-Ab\] positive, HCV-RNA above the lower limit of detection of the analytical method and abnormal liver function); * Human immunodeficiency virus (HIV) infection or syphilis infection; * Patients with a history of severe allergy to biological products (including antibiotics); * Patients with central nervous system disorders such as uncontrolled epilepsy, cerebrovascular ischemia/hemorrhage, dementia, cerebellar disease, etc; * Pregnant or Lactating Women; Patients and his or her spouses have a fertility plan within 12 months after CAR-T cell infusion; * Other conditions considered inappropriate by the researcher.