Inclusion Criteria:

• Subjects must satisfy the following criteria to be enrolled in the study:
  • Subject is ≥ 18 years of age at the time of signing the informed consent form (ICF).
  • Subject has documented diagnosis of MM and measurable disease
  • Subject has received at least 2 but no greater than 4 prior MM regimens.
  • Subject has received prior treatment with DARA, a proteasome inhibitor and an immunomodulatory compound-containing regimen for at least 2 consecutive cycles.
  • Subject must be refractory to the last treatment regimen. Refractory is defined as documented progressive disease during or within 60 days (measured from the last dose of any drug within the regimen) of completing treatment with the last anti-myeloma regimen before study entry.
  • Subject achieved a response (minimal response [MR] or better) to at least 1 prior treatment regimen.
  • Subject has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
  • Recovery to Grade 1 or baseline of any non-hematologic toxicities due to prior treatments, excluding alopecia and Grade 2 peripheral neuropathy.

Exclusion Criteria:

• Subject has nonsecretory multiple myeloma (MM). 
• Subject has inadequate pulmonary function defined as oxygen saturation (SaO2) < 92% on room air. 
• Subject has prior history of malignancies, other than MM, unless the subject has been free of the disease for ≥ 5 years. 
• Subject has active or history of plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS syndrome or amyloidosis. 
• Subject with known central nervous system (CNS) involvement with myeloma. 
• Subject has clinical evidence of pulmonary leukostasis and disseminated intravascular coagulation. 
• Subject has known chronic obstructive pulmonary disease (COPD) with a forced expiratory volume in 1 second (FEV1) 50% of predicted normal. 
• Subject has a history or presence of clinically relevant CNS pathology. 
• Subject was treated with DARA in combination with POM with or without dex (DP±d) as part of their most recent anti-myeloma treatment regimen, cannot receive DPd as bridging therapy but may receive DVd or IRd as bridging as per Investigator's discretion if randomized to Treatment Arm A. 
• Subject was treated with DP±d as part of their most recent anti-myeloma treatment regimen, cannot receive DPd if randomized to Treatment Arm B but may receive DVd or IRd as per Investigator's discretion. 
• Subject was treated with DARA in combination with BTZ with or without dex (DV±d) as part of their most recent anti-myeloma treatment regimen, cannot receive DVd as bridging therapy but may receive DPd or IRd as bridging as per Investigator's discretion if randomized to Treatment Arm A. 
• Subject was treated with DV±d as part of their most recent anti-myeloma treatment regimen, cannot receive DVd if randomized to Treatment Arm B but may receive DPd or IRd as per Investigator's discretion. 
• Subject was treated with IXA in combination with LEN with or without dex (IR±d) as part of their most recent anti-myeloma treatment regimen, cannot receive IRd as bridging therapy but may receive DPd or DVd as bridging as per Investigator's discretion if randomized to Treatment Arm A.