Clinical Study of the Safety and Efficacy of BCMA CAR-NK

The goal of this clinical trial is to study of the Safety and Efficacy of Chimeric Antigen Receptor NK Cell Injection Targeting BCMA (BCMA CAR-NK) in Patients with Relapsed/Refractory Multiple Myeloma Primary Endpoints: To evaluate the safety and tolerability of patients with relapsed/refractory multiple myeloma (RR/MM) after BCMA CAR-NK infusion. To determine the maximum tolerated dose (MTD) and/or subsequent recommended dose (RD) of BCMA CAR-NK in patients with RR/MM. Secondary Endpoints: To preliminarily evaluate the effectiveness of BCMA CAR-NK in patients with RR/MM. To preliminarily evaluate the pharmacokinetic parameters of BCMA CAR-NK cells in patients with RR/MM. To preliminarily evaluate BCMA CAR-NK cell survival in subjects blood in relation to efficacy, adverse events and relevant biomarker levels. To preliminarily evaluate the relationship between donors and subjects KIR-Ligand mismatch and safety \& efficacy. To preliminarily evaluate the impact of the degree of HLA genotype matching between donors and subjects on the survival of BCMA CAR-NK cells in the subjects blood. Subjects are enrolled and treated with lymphocyte clearance chemotherapy (including pre-clearance evaluation), pre-infusion evaluation and BCMA CAR-NK cells infusion and enter the follow-up period after the end of the DLT observation period.