A Study to Evaluate the Safety and Efficacy of SCTC21C in Combination With Bortezomib, Lenalidomide and Dexamethasone in Patients With Newly Diagnosed Multiple Myeloma Not Eligible for Transplant

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.