Inclusion Criteria:

1. Be informed and voluntarily sign the Informed Consent Form (ICF).
2. Age ≥18 years old.
3. Diagnosed with multiple myeloma according to IMWG diagnostic criteria.
4. Developed CRS (grade ≥1) and/or ICANS (grade ≥1) after CAR-T treatment.

Exclusion Criteria:

1. Creatinine clearance <30 mL/min.
2. Platelet count <75,000/μL, absolute neutrophil count <1,000/μL, or hemoglobin <60 g/L at screening.
3. ALT or AST >3× ULN, or bilirubin >2× ULN.
4. Known severe cardiac conditions, including NYHA class III/IV heart failure, uncontrolled angina, arrhythmia, or hypertension, myocardial infarction within 6 months, or other uncontrolled/severe cardiovascular diseases, including prior cerebrovascular events with residual deficits.
5. Severe comorbidities, including active infections, known active HBV/HCV, HIV infection, uncontrolled diabetes, or serious conditions like chronic restrictive lung disease or cirrhosis.
6. Known intolerance to Siltuximab.
7. Known central nervous system (CNS) involement.