Inclusion criteria:

1. Age ≥ 18, male or female;
2. Subject must have had documented MM;
3. At screening phase, subject must have measurable disease;
4. Subject is in a state of progressive disease (PD);
5. Subject must have life expectancy of no less than 6 months;
6. Subject must have an ECOG (Eastern Cooperative Oncology Group) performance status score of 0~2;

Exclusion criteria:

1. Subject has received anti-CD38 monoclonal antibody treatment previously;
2. Subject has received CAR-T cell therapy previously;
3. Subject has previously received allogenic stem cell transplant, or subject has received autologous stem cell transplant within 3 months before administration of the study agent;
4. Primary refractory multiple myeloma (subject failed to generate any minimal response or any degree of response to any therapy);
5. Subject has received anti-myeloma treatment (radiotherapy is excluded) within 4 weeks or 5 PK half-lives of the treatment, whichever longer, before the first study agent administration.