A Study Evaluating Safety, Tolerability, and Clinical Activity of Forimtamig-Based Treatment Combinations in Participants With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1

• Life expectancy of at least 12 weeks

• Documented diagnosis of MM according to the IMWG diagnostic criteria

• Evidence of progressive disease based on Investigator's determination of response byIMWG criteria on or after last dosing regimen

• Measurable disease

• AEs from prior anti-cancer therapy resolved to Grade ≤ 1,

• Adequate organ functions

Exclusion Criteria:

• Pregnant or breastfeeding or intending to become pregnant during the study or within 3 months after the last dose of study drug

• Plasma cell leukemia with circulating plasma cell count ≥ 5% or >500/microliter (µL)

• Participants with known amyloidosis

• Participants with myelodysplastic syndrome

• Prior treatment with monoclonal antibody (mAb) and antibody-drug conjugate within 4weeks or 5 half-lives of the drug, whichever is shorter

• Prior anti-cancer therapy (chemotherapy, small molecule/tyrosine kinase inhibitors,radiotherapy) within 14 days prior to first forimtamig administration

• Prior solid organ transplantation

• Active auto-immune disease or flare within 6 months prior to start of studytreatment

• Known or suspected chronic active Epstein-Barr virus (EBV) infection

• Hepatitis B virus (HBV) infection

• Acute or chronic hepatitis C virus (HCV) infection

• Known history of HIV seropositivity

• Live vaccine(s) within one month prior to start of the treatment

• Participants not fully vaccinated for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as per local recommendations

• Previous refractoriness to carfilzomib

• Participants who discontinued prior carfilzomib treatment due to treatment-relatedtoxicity

• Participants with known liver cirrhosis

• Participants eligible for allogeneic stem cell transplantation (SCT) or autologousSCT at the time of enrollment for Study BP43437 are excluded