The purpose of this study is to evaluate if the addition of SCTC21C to bortezomib, lenalidomide and dexamethasone (VRd) in patients with newly diagnosed multiple myeloma not eligible for transplant will prolong progression-free survival (PFS) and/or improve overall minimal residual disease (MRD) negativity rate compared with VRd alone.

This study comprises two phases: Part 1 is the safety run in, while Part 2 is a randomized, controlled, open-label, multicenter study. Both parts are divided into three stages: the screening period (up to 28 days before first dose/randomization), the treatment period (from Cycle 1 [28 days] Day 1 and continues until disease progression or unacceptable toxicity), and the follow-up period (Postintervention). Safety endpoints include treatment-emergent adverse events , treatment-related adverse events, serious adverse events, clinical laboratory tests, vital signs, physical examinations, electrocardiograms , etc. Efficacy endpoints include objective response rate (ORR), progression-free survival (PFS), and minimal residual disease (MRD) negativity rate.

Inclusion Criteria:

• Newly diagnosed multiple myeloma (IMWG criteria) not eligible for transplant.
• Evidence of measurable disease.
• With adequate organ function and hematological parameters.
• Contraception，and during the study period and for 5 months after the last dose, all subjects must not donate reproductive cells.

Exclusion Criteria:

• Other hematologic malignancies.
• Subjects with confirmed or suspected central nervous system infiltration or meningeal involvement.
• Uncontrolled infection.
• Subjects with conditions that may affect safety or efficacy assessments include, but are not limited to, cardiovascular, respiratory, endocrine/metabolic, immune system, hepatic, gastrointestinal (such as gastrointestinal bleeding, perforation, ulcers, etc.), and malignant neoplasms, and are deemed clinically significant by the investigator.
• Subjects who have undergone major surgery or experienced significant trauma within 4 weeks prior to the first use of the investigational drug, or who require elective surgery during the trial period.
• Received a live or attenuated vaccine within 30 days prior to the first dose; Female subjects who are currently breastfeeding.
• Subjects with mental disorders or poor compliance, or other circumstances deemed unsuitable for participation in this study by other investigators.