A Clinical Study to Evaluate the Safety and Preliminary Efficacy of QI-019B in Patients With Relapsed/Refractory Multiple Myeloma.

Inclusion Criteria: * 1\. Age ≥ 18 years, any gender; * 2\. Diagnosed with multiple myeloma (MM) according to IMWG diagnostic criteria; * 3\. Have received at least 2 lines of anti-MM treatment, with at least one full treatment cycle per line, and experienced disease progression during the most recent anti-myeloma treatment or within 12 months after it, confirmed by available clinical evidence; or deemed by the investigator to be refractory to both immunomodulatory agents and proteasome inhibitors, with disease progression during the most recent anti-myeloma treatment or within 2 months after it (according to IMWG diagnostic criteria); * 4\. Disease must be measurable at screening, meeting one or more of the following criteria: * Serum M protein level ≥ 0.5 g/dL; * Or urine M protein level ≥ 200 mg/24h; * Or involved serum free light chain ≥ 10 mg/dL with abnormal serum free light chain κ/λ ratio; * 5\. ECOG performance status 0-2, with an expected survival of ≥ 3 months; * 6\. Bone marrow function test results (from screening or within 2 months prior) meet the following requirements: * Hemoglobin ≥ 6 g/dL (no red blood cell transfusion within 1 week before screening), recombinant human erythropoietin allowed; for patients meeting the ≥ 6 g/dL hemoglobin requirement at screening, red blood cell transfusions are allowed to maintain hemoglobin ≥ 6 g/dL; * Absolute neutrophil count (ANC) ≥ 600/μL (no use of granulocyte colony-stimulating factor (G-CSF) within 1 week…