Dose Escalation Study of Talquetamab in Participants With Relapsed or Refractory Multiple Myeloma

64407564MMY1001: A Phase 1/2, First-in-Human, Open-Label, Dose Escalation Study of Talquetamab, a Humanized GPRC5D x CD3 Bispecific Antibody, in Subjects With Relapsed or Refractory Multiple Myeloma

The purpose of this study is to characterize the safety of Talquetamab and to determine the recommended Phase 2 dose(s) (RP2Ds) and dosing schedule assessed to be safe for Talquetamab (Part 1 [Dose Escalation]) and to further characterize the safety of Talquetamab at the recommended Phase 2 dose(s) (RP2Ds) (Part 2 [Dose Expansion]).

Inclusion Criteria:

• Documented initial diagnosis of multiple myeloma according to International Myeloma Working Group (IMWG) diagnostic criteria
• Part 1: Participants with measurable multiple myeloma who have progressed on, or could not tolerate, all available established therapies. Part 2: Participants with multiple myeloma measurable by central laboratory assessment who have progressed on, or could not tolerate, all available established therapies; Serum monoclonal paraprotein (M-protein) level greater than or equal to (>=) 1.0 gram per deciliter (g/dL) or urine M-protein level >=200 milligram per 24 hours (mg/24 h) or light chain multiple myeloma without measurable disease in the serum or the urine: serum immunoglobulin free light chain (FLC) >= 10 mg/dL and abnormal serum immunoglobulin kappa lambda FLC ratio; If central laboratory assessments are not available, relevant local laboratory measurements must exceed the minimum required level by at least 25%
• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1
• Women of childbearing potential must have a negative pregnancy test at screening and prior to the first dose of study drug using a highly sensitive pregnancy test either serum (Beta human chorionic gonadotropin [beta-hCG]) or urine
• Sign an informed consent form (ICF) indicating that he or she understands the purpose of and procedures required for the study, and is willing to and able participate in the study. Consent is to be obtained prior to the initiation of any study-related tests or procedures that are not part of standard-of-care for the participant's disease

Exclusion Criteria:

• Participants who received or plan to receive any live, attenuated vaccine within 4 weeks prior to the first dose, during treatment, or within 4 weeks of the last dose of Talquetamab. Non-live or non-replicating vaccines approved or authorized for emergency use (example, coronavirus disease [COVID]-19) by local health authorities are allowed
• Toxicities from previous anticancer therapies should have resolved to baseline levels or to Grade 1 or less except for alopecia or peripheral neuropathy
• Received a cumulative dose of corticosteroids equivalent to greater than or equal to ( >=) 140 milligram (mg) of prednisone within the 14-day period before the first dose of study drug (does not include pretreatment medication)
• An allogenic stem cell transplant within 6 months before first dose of study drug. Participants who received an allogeneic transplant must be off all immunosuppressive medications for 6 weeks without signs of graft-versus-host disease (GVHD); and/or an autologous stem cell transplant less than or equal to (<=) 12 weeks before first dose of study drug
• Documented history of central nervous system (CNS) involvement or exhibits clinical signs of meningeal involvement of multiple myeloma. If either is suspected, whole body magnetic resonance imaging (MRI) and lumbar cytology are required