A Study of MBS314 in Participants With Relapsed/Refractory Multiple Myeloma.

Inclusion criteria

• Able and willing to provide written informed consent and to comply with the study protocol;
• ≥18 years of age;
• Documented diagnosis of multiple myeloma according to 2014 IMWG diagnostic criteria.
• Phase Ⅰb/Ⅱ: At least one measurable disease: Serum monoclonal paraprotein (M-protein) ≥5 g/L or Urine M-protein ≥200 mg/24 hours or Serum immunoglobulin free-light chains (FLCs) ≥100 mg/L and abnormal kappa/lambda FLC ratio (<0.26 or >1.65)
• Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
• Life expectancy ≥3 months.
• Adequate hematologic, hepatic, and renal function.

Exclusion criteria

• Known active central nervous system (CNS) involvement or exhibits clinical signs of meningeal involvement of multiple myeloma.
• Participants with known active infection within 14 days prior to the first MBS314.
• Infection with human immunodeficiency virus (HIV), hepatitis B or hepatitis C (including HBsAg, HBcAb positive with abnormal hepatitis B virus DNA or hepatitis C virus RNA).
• Previously received anti-myeloma treatment within the specified time frame prior to the first administration.
• Live, attenuated vaccines within 28 days prior to the first infusion of MBS314, or expected to receive live, attenuated vaccines during the study period.
• Major surgery within 28 days prior to the first infusion of MBS314, or expected to undergo major surgery during the study treatment.
• Participants with a history of autoimmune diseases.
• Known severe allergic reactions to other antibodies, or known allergies or hypersensitivity to any components of MBS314.