This study is a multicenter, open-label, dose-escalation/dose-expansion clinical Phase I trial designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy profile of SHR-9539 Injection in patients with multiple myeloma.

Inclusion Criteria:

1. Age ≥ 18 years on day of signing the Informed Consent Form;
2. Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Status Scale；
3. Documented initial diagnosis of multiple myeloma according to IMWG diagnostic criteria ；
4. Have a life expectancy of at least 3 months；
5. Male and female subjects with fertility must agree to use efficient contraceptive measures with their partners within 3 months after the last administration of the test drug from the time of signing the informed consent form, and have no fertility plan and avoid donating sperm / eggs. The pregnancy test during the screening period must be negative.

Exclusion Criteria:

1. Central nervous system (CNS) involvement of MM；
2. Diagnosis of amyloidosis, plasma cell leukemia, Wahl's macroglobulinemia, or POEMS syndrome;
3. Prior Grade 3 or higher CRS (Per ASTCT standards) related to any T cell redirection (eg, CD-3 redirection technology or CAR-T cell therapy).
4. Have other factors that may force the termination of the study, e.g., non-compliance with the protocol, other serious illnesses (including psychiatric illnesses) that require comorbid treatment, serious laboratory abnormalities, associated family or social factors, which would affect the safety of the subjects or the collection of data and samples, as determined by the investigator.