Safety and Tolerability of BION-1301 in Adults With Relapsed or Refractory Multiple Myeloma (MM)

Key Inclusion Criteria: Individuals eligible to participate in this study must meet the following key criteria and additional criteria as specified in the protocol: 1. Male or female, aged ≥ 18 years 2. Confirmed diagnosis of MM per IMWG criteria 3. Measurable disease as defined by one or more of the following: * Serum M-protein ≥ 0.5 g/dL * Urine M-protein ≥ 200 mg/24 hours * Serum Free Light Chain (FLC) assay: involved FLC level ≥ 10 mg/dL provided serum FLC ratio is abnormal * In cases where SPEP is unreliable, serum quantitative immunoglobulin (qIgA) ≥ 750 mg/dL (0.75 g/dL) is acceptable 4. Relapsed or refractory (Rajkumar, 2011) to 3 or more different prior lines of therapy for MM, including immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs), chemotherapies, or monoclonal antibodies, and not a candidate for, or intolerant to established therapy known to provide clinical benefit. 5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 - 1 6. Adequate organ and marrow function at Screening, as defined by the study protocol. Key Exclusion Criteria: 1. Monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma, Waldenstrom's macroglobulinemia, or IgM myeloma 2. Active plasma cell leukemia (˃ 2.0 × 109/L circulating plasma cells by standard differential) 3. POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes) 4. Prior treatment directed to B-cell Activating Factor (BAFF; BLyS), B-cell Maturation Antigen (BCMA;TNFSF17) or Transmembrane Activator and CAML interactor (TACI; TNFSF13B), including antibodies or BCMA- or TACI-directed Chimeric Antigen Receptor (CAR)-T cell therapy