Inclusion Criteria: 1. Age ≥ 18 years. 2. Signed written informed consent prior to any study procedure. 3. Subject has a diagnosis of multiple myeloma with relapsed and/or refractory disease. Subjects must have documented progressive disease on or within 12 months of completing treatment with the last anti-myeloma treatment regimen, except for subjects with cellular therapy (eg, CAR T-cell therapy) as their last treatment, who may enroll beyond 12 months. 4. Subjects must have received at least 3 prior anti-myeloma treatment regimens (note: induction with or without HSCT and with or without maintenance therapy is considered one regimen), including: - Autologous stem cell transplant - A regimen that included an immunomodulatory agent (eg, thalidomide, lenalidomide, pomalidomide) and a proteasome inhibitor (eg, bortezomib, carfilzomib, ixazomib), either alone or combination - Anti-CD38 (eg, daratumumab), either alone or combination 5. Measurable disease 6. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 7. Adequate organ function Exclusion Criteria: 1. Known active or history of central nervous system (CNS) involvement of MM 2. Active or history of plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, skin changes) syndrome, or clinically significant amyloidosis 3. Uncontrolled or active infection 4. Active autoimmune disease requiring immunosuppressive therapy 5. History or presence of clinically significant CNS pathology such as seizure disorder, aphasia, stroke, severe brain injuries, dementia, Parkinson's disease, cerebellar disease, organic brain syndrome, or psychosis