Capable of giving signed informed consent Subjects aged 18 to 75 years (inclusive) at Screening (signing the ICF). Expected survival period is >12 weeks. Diagnosis of MM according to the IMWG criteria (2016 version). One of the following criteria must be met: If immunoglobulin (Ig)G type MM, then serum M protein >10 g/L; if IgA, IgD, IgE or IgM type MM, then serum M protein >5 g/L Urine M protein level >200 mg/24 hour If light chain type MM, then serum free light chain (sFLC) >100 mg/L and K/λ FLC ratio is abnormal. Extramedullary lesions (>1 cm for diameter of the short axis). For Phase I (dose-escalation) - Subjects who had received at least 3 prior lines of therapy, had previous exposure to BCMA-Ag+ therapies, and were refractory to the last line of therapy. For Phase I (dose-expansion) and Phase II: Subjects with previous exposure to BCMA directed therapies including BCMA bispecific antibody (e.g., teclistamab), BCMA antibody directed conjugate (such as BLENREP), and BCMA-CAR-T (such as CARVYKT1TM) Subjects with adequate hematologic, renal, hepatic, pulmonary and cardiac function. Subject and partners willing to take and or use effective contraceptive measures until 2 years post IMP infusion.

Pregnant or breastfeeding. Seropositive for history of human immunodeficiency virus Active Hepatitis B infection and or Hepatitis C infection Known active or prior history of CNS involvement History of autoimmune diseases (such as Crohn's disease, rheumatoid arthritis, systemic lupus erythematosus) caused damage to terminal organs or required systemic application of immunosuppressive or other drugs in the past 2 years Presence of uncontrolled active infection Subjects who received autologous hematopoietic stem cell transplantation (ASCT) within 8 weeks of Screening Visit or who plan to undergo ASCT during the study. Subjects who received allogeneic stem cell therapy. Any condition that in the opinion of the Investigator, would interfere with evaluation of the IMP. Received Bendamustine treatment 1 year prior to Screening Visit.