The purpose of the study is to compare the efficacy of QLS4131(SC) in combination with QL2109, with or without pomalidomide or lenalidomide, and QLS4131 (SC) in combination with QL2109, and QLS4131 (SC) in combination with Pomalidomide, and QLS4131(SC) in combination with QL2109 and Lenalidomide.

Inclusion Criteria:

- Diagnosis of multiple myeloma confirmed according to the 2016 International Myeloma Working Group (IMWG) diagnostic criteria, or diagnosis of plasma cell leukemia and primary light-chain amyloidosis confirmed in accordance with relevant guidelines.;

For patients with multiple myeloma and plasma cell leukemia, measurable disease at screening is defined as meeting any one of the following:

• Serum M-protein ≥0.5 g/dL (5 g/L);
• Urine M-protein ≥200 mg/24 hours;
• Serum immunoglobulin free light chain ≥10 mg/dL (100 mg/L) with an abnormal serum immunoglobulin κ/λ free light chain ratio.

For patients with light-chain amyloidosis:Measurable disease is defined as Involved serum free light chain ≥ 50 mg/L with an abnormal light chain ratio,ordifference between involved and uninvolved serum free light chains (dFLC) ≥ 50 mg/L.

Exclusion Criteria:

• History of Grade 3 or higher cytokine release syndrome (CRS) associated with any T-cell redirecting therapy (e.g., CD3-redirecting technologies or CAR-T cell therapy);

• Patients who received any of the following prior anti-tumor therapies before the first dose of investigational productt:

  1. Previous treatment with BCMA/GPRC5D/CD3-targeted therapy;

  2. Received any anti-tumor therapy within 4 weeks prior to the first dose, except for the following circumstances:

     • Cytotoxic therapy or small-molecule targeted therapy within 2 weeks or 5 half-lives, If the half-life is unknown, the washout period shall be 2 weeks (whichever is longer);
     • Immunomodulatory drug therapy within 7 days
     • Genetically modified adoptive cell therapy within 3 months.;
     • Traditional Chinese medicine with anti-tumor indications within 14 days.;
     • Radiotherapy within 14 days

• Prior intolerance to Pomalidomide (applies to treatment cohorts containing Pomalidomide);

• Prior intolerance to Lenalidomide (applies to treatment cohorts containing Lenalidomide);

• Prior intolerance to QL2109 (applies to treatment cohorts containing QL2109).