Dose-Escalation Study of BFCR4350A in Participants With Relapsed or Refractory Multiple Myeloma (R/R MM)

Inclusion Criteria:

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

- Life expectancy of at least 12 weeks

- Participants must have relapsed or refractory (R/R) multiple myeloma (MM) for which no
established therapy for MM is appropriate and available or be intolerant to those
established therapies

- Adverse events from prior anti-cancer therapy resolved to Grade < or = 1, except any
grade alopecia and/or peripheral sensory or motor neuropathy which must have resolved
to Grade < or = 2

- Measurable disease defined by laboratory test results

- Female participants of childbearing age must agree to remain abstinent or use reliable
contraceptive methods during the treatment period, and at least 3 months after last
dose of study drug

- Male participants must agree to refrain from donating sperm, to abstain or use a
condom during the treatment period, and at least 60 days after last dose of study drug

Exclusion Criteria:

- Inability to comply with protocol-mandated hospitalization and activities restrictions

- Pregnant, lactating, or planning to become pregnant during the study and up to 3
months after last dose of study drug

- Prior use of any monoclonal antibody, radioimmunoconjugate, or antibody-drug conjugate
within 4 weeks before first infusion

- Prior treatment with systemic immunotherapeutic agents within 12 weeks or 5 half-lives
of the drug, whichever is shorter, before first infusion

- Treatment-related, immune-mediated adverse events associated with prior
immunotherapeutic agents

- Treatment with radiotherapy, any chemotherapeutic agent, or treatment with any other
anti-cancer agent (investigational or otherwise) within 4 weeks or 5 half-lives of the
drug, whichever is shorter, prior to first BFCR4350A infusion

- Autologous stem cell transplantation (SCT) within 100 days prior to first infusion

- Prior allogeneic SCT or solid organ transplantation

- Primary or secondary plasma cell leukemia

- History of autoimmune disease or of confirmed progressive multifocal
leukoencephalopathy

- History of severe allergic or anaphylactic reactions to monoclonal antibody therapy
(or recombinant antibody-related fusion proteins)

- Patients with known history of amyloidosis (e.g., positive Congo Red stain or
equivalent in tissue biopsy)

- Patients with lesions in proximity of vital organs that may develop sudden
decompensation/deterioration in the setting of a tumor flare

- History of other malignancy that could affect compliance with the protocol or
interpretation of results

- Current or past history of central nervous system (CNS) disease, or CNS involvement by
MM

- Significant cardiovascular disease or active pulmonary disease that may limit a
patient's ability to adequately respond to a CRS event

- Known active bacterial, viral, fungal, mycobacterial, parasitic, or other infection
(excluding fungal infections of nail beds) at study enrollment, or any major episode
of infection requiring treatment with IV antibiotics within 4 weeks prior to first
infusion

- Known or suspected chronic active Epstein-Barr virus (EBV) infection, acute or chronic
hepatitis C virus (HCV) infection

- Positive serologic or polymerase chain reaction (PCR) test results for acute or
chronic hepatitis B virus (HBV) infection

- Recent major surgery within 4 weeks prior to first infusion

- Human Immunodeficiency Virus (HIV) positive

- History of illicit drug or alcohol abuse within 12 months prior to screening

- Any medical condition or laboratory test abnormality that precludes the participant's
safe participation in and completion of the study, or which could affect compliance
with the protocol or interpretation of results