A Study to Investigate the Safety, Tolerability, Efficacy, Pharmacokinetics, and Immunogenicity of TAK-079 Administered Subcutaneously as a Single Agent in Participants With Relapsed/Refractory (r/r) Multiple Myeloma (MM)

Inclusion Criteria

• Eastern Cooperative Oncology Group (ECOG) performance status of =0.5 g/dL (>=5 gram per liter [g/L]).
• Urine M-protein >=200 mg/24 hours.
• In participants without measurable M-protein in serum protein electrophoresis (SPEP) or urine protein electrophoresis (UPEP), a serum FLC assay result with involved FLC level >=10 mg/dL (>=100 milligram per liter [mg/L]), provided serum FLC ratio is abnormal.
• Prior therapy should meet all the following criteria:

Participants in the dose Escalation Cohort (escalation phase) and participants in the dose Confirmation Cohort;

• Should be previously treated with at least a proteasome inhibitor (PI), an immunomodulatory drug (IMiD), and a steroid. Note: Participants who have had a previous autologous stem cell transplant will have additionally been exposed to an alkylating agent; however, participant who have not had a previous autologous stem cell transplant may not have been exposed to an alkylating agent per standard practice.
• Should be refractory or intolerant to at least 1 PI and at least 1 IMiD.
• Should either have received >= 3 prior lines of therapy or should have received at least 2 prior lines of therapy if one of those lines included a combination of PI and IMiD.
• In phase 1, previous exposure to an anti-CD38 agent, as a single agent or in combination, is allowed but is not required. (Participants in the dose Escalation Cohort).
• In phase 1 dose Confirmation Cohort, cohorts of participants that are refractory at any time to at least 1 anti-CD38 agent or who are anti-CD38 naïve will be enrolled.

Participants in the Combination Cohort (TAK-079 added to PomDex cohort only):

• Have undergone prior therapy with >=2 prior anti-myeloma therapies (line of therapy defined below).
• Has either relapsed or relapsed and refractory disease. Should have progressed on or within 60 days of completing the last anti-myeloma therapy (refractory defined below).
• In the phase 2a portion of the study, up to 2 cohorts of participants with RRMM may be enrolled: 1 that is refractory to at least 1 anti-CD38 monoclonal antibody (mAb) therapy at any time during treatment and 1 that is naïve to daratumumab.

Note:

o Refractory is defined as at least a 25% increase in M-protein (response of stable disease during prior therapy) or PD during treatment or within 60 days after last dose of prior therapy.

Exclusion Criteria

• Sensory or motor neuropathy of National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) Grade >=3.
• Have received allogeneic stem cell transplant.
• Have received anti-CD38 antibody therapy and do not fulfill a 180-day washout period before receiving TAK-079.
• Not recovered from adverse reactions to prior myeloma treatment or procedures (chemotherapy, immunotherapy, radiation therapy) to NCI CTCAE Grade <=1 or baseline, excluding alopecia.
• Clinical signs of central nervous system (CNS) involvement of MM.
• Active chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection, active HIV, or cytomegalovirus (CMV) infection.
• POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin changes) syndrome, monoclonal gammopathy of unknown significance, smoldering myeloma, solitary plasmacytoma, amyloidosis, Waldenström macroglobulinemia, or IgM myeloma.
• Positive Coombs tests at screening.
• For participants in the Combination Cohort (TAK-079-PomDex) only: participant has previously received pomalidomide or has hypersensitivity to thalidomide or lenalidomide.