Key Inclusion Criteria:

1. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
2. Life expectancy ≥ 6 months.
3. Subject must have receive at least 3 prior lines of treatment which include a proteasome inhibitor (e.g., bortezomib), an immunomodulator (e.g., lenalidomide), and an anti-CD38 antibody (e.g., daratumumab).
4. Subject must have one or more measurable disease as the following measurements:

1) Serum M protein level ≥0.5g/dL. 2) Urine M protein level≥ 200 mg/24h. 3) Serum immunoglobulin free light chain ≥10 mg/dL and abnormal serum immunoglobulin kappa lambda free light chain ratio.

5. Subjects must show appropriate organ and marrow function.

Key Exclusion Criteria:

1. Subject has received anti-GPRC5D treatment previously.
2. Subject has previously received allogenic stem cell transplant, or subject has received autologous stem cell transplant within 3 months before administration of the IMP.
3. Primary refractory multiple myeloma (subject failed to generate any minimal response or any degree of response to any therapy).

4. Subject has received anti myeloma treatment (radiotherapy is excluded) within 2 weeks or 5 PK half-lives of the treatment, whichever longer, before the first study agent administration.

5. Subject is exhibiting clinical signs of central nervous system (CNS) involvement of MM.

6. Subject with known chronic obstructive pulmonary disease (COPD). 7. Subjects who have severe cardiovascular disease,