The purpose of this study is to characterize the safety of QLS32015 injection and to determine the recommended Phase 2 dose (RP2D) and to further evaluate the efficacy and safety of QLS32015 injection in participants with relapsed or refractory multiple myeloma at the recommended Phase 2 dose.

Multiple myeloma (MM) is a malignant disease with abnormal proliferation of clonal plasma cell, which is often accompanied by multiple osteolytic damage, hypercalcemia, anemia, and kidney damage. QLS32015 is a humanized immunoglobulin gamma-1 (IgG1) type bispecific antibody targeting G protein-coupled receptor family C group 5-member D (GPRC5D) and cluster of differentiation 3 (CD3). The study consists 3 periods: screening phase, treatment phase and a post-treatment follow-up phase. The study will evaluate safety, tolerability, pharmacokinetics and preliminary antitumor activity of QLS32015 administered to participants with relapsed or refractory multiple myeloma. Total duration of study is up to 2 years.

Inclusion Criteria:

• Age ≥18 years old, regardless of gender.
• Subjects should be willing and able to comply with the study schedule and protocols.
• Documented initial diagnosis of multiple myeloma according to International Myeloma Working Group (IMWG) diagnostic criteria.
• Must have measurable disease as defined by the following: Serum M-protein greater than or equal to 1 g/dL; OR Urine M-protein greater than or equal to 200 mg/24 hours; OR Serum free light chain (FLC) assay; involved FLC level greater than or equal to 10 mg/dL provided the serum FLC ratio is abnormal.

Exclusion Criteria:

• Known hypersensitivity to any of the ingredients of this product.
• Diagnosis of active plasma cell leukemia or systemic light chain amyloidosis.
• Has any active severe mental illness, medical illness, or other symptoms/conditions that may affect treatment, compliance, or the ability to provide informed consent, as determined by the investigator.