A Single-center Exploratory Clinical Study to Evaluate the Safety, Tolerability, and Efficacy of a BCMA-targeted Universal LCAR-BCX Cells in Patients With Relapsed/Refractory Multiple Myeloma

In this study, LCAR-BCX CAR+ cells will be evaluated at 5 dose levels including 0.25 × 10\^6 cells/kg, 0.5 × 10\^6 cells/kg, 1.0 × 10\^6 cells/kg, 2.0 × 10\^6 cells/kg, and 4.0 × 10\^6 cells/kg, with 0.25 × 10\^6 cells/kg as the starting dose, to determine RP2D for LCAR-BCX cell therapy