A Study of IBI3003 in Subjects With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: * Subjects in Parts 1(dose escalation) \& 2 (dose expansion) must satisfy all of the following criteria to be enrolled into the study: 1. Age ≥18 years. For Part 1, age ≥18 years and ≤75 years. 2. Documented initial diagnosis of multiple myeloma according to IMWG diagnostic criteria. Multiple myeloma is defined as clonal bone marrow plasma cells ≥10% or biopsy-proven bony or extramedullary plasmacytoma and any one or more of the following myeloma-defining events in protocol 3. Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1 4. Life expectancy ≥3 months. 5. Subjects with the ability to understand and give written informed consent for participation in this trial, including all evaluations and procedures as specified by this protocol. Exclusion Criteria: 1. Known active CNS involvement or exhibits clinical signs of meningeal involvement of multiple myeloma. 2. Have amyloidosis, plasma cell leukemia, Waldenstrom macroglobulinemia, POEMS syndrome, or solitary plasmacytoma, or smoldering MM as defined by the International Myeloma Working Group(IMWG) criteria. 3. Spinal cord compression that results in limited self-care occurs within 6 months prior to informed consent, or is expected to occur in the near future. 4. History of primary immunodeficiency. 5. Current or previous other malignancy within 3 years of study entry, except cured basal or squamous cell skin cancer, superficial bladder cancer, prostate intraepithelial neoplasm, carcinoma in situ of the cervix, or other noninvasive or indolent malignancy.