1. Patients of both genders, ≤18 y.

2. Patient has a newly diagnosed HLH.

3. The diagnosis of HLH must meet HLH-2004 diagnostic criteria.²¹ 

4. Presence of active HLH at enrollment.

5. Patient has no prior HLH therapy.

6. Patients who had received corticosteroid treatment (prednisone acetate at the dose of ≥2 mg/kg per day or equivalent) for ≥3 d without achieving disease improvement or ≥7 d without achieving partial response with intermittent fever were eligible to participate.

7. Signed an informed consent form before participating in the study.

1. Patients with known active malignancy or rheumatologic disorder.

2. Patients with active mycobacteria, histoplasma capsulatumparasitic, leishmania, fungal infection, or other uncontrolled infection.

3. Patient has severe CNS involvement presenting with obvious brain MRI abnormalities or neurological dysfunctions, including convulsions, disturbance of consciousness, and paralysis.

4. Patient has severe organ dysfunction, including serious renal dysfunction (creatinine clearance <15 mL/min or glomerular filtration rate <15 mL/min), liver failure with a Model for End-stage Liver Disease (MELD) score >20, cardiorespiratory failure requiring any extracorporeal life support.

5. Patient has active gastrointestinal bleeding.

6. History of severe allergic, anaphylactic, or other hypersensitivity reactions to chemicals.