Safety and Efficacy Study of QL0911 to Treat Immune Thrombocytopenia (ITP) in Pediatric Patients

Inclusion Criteria: 1. Age ≥ 1 years old and \< 18 years old. 2. Diagnosed primary ITP for at least 12 months; 3. Had received at least one first-line ITP treatment with no response or recurrence after treatment; 4. Had a platelet count \<30×10\^9/L within 48 hours before the first dose; 5. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2; 6. Patients of child-bearing potential must agree to use effective contraception during the study and for 3 months following the last dose of study treatment. Exclusion Criteria: 1. Had a history of bone marrow stem cell abnormalities or myelodysplastic syndrome other than ITP-specific changes. 2. Underwent splenectomy within 12 weeks before the first dose; 3. Had received ITP treatments (including rescue treatment) within 2 weeks before the first dose; 4. Had received romiplostim (Nplate®) or eltrombopag (Revolade®), rhTPO or other agents that stimulate TPO receptors (also known as c-Mpl)within 4 weeks before the first dose; 5. Had received antibody-based therapies within 14 weeks before the first dose. 6. Patients with concurrent or past malignant disease. 7. Serum creatinine or total bilirubin \>1.5\*ULN) alanine transaminase (ALT) or aspartate transaminase (AST) \>3\* ULN. 8. Had received antibody-based therapies within 14 weeks before the first dose. 9. Had prothrombin time (PT) or prothrombin time-international normalized ratio (PT-INR) or activated partial thromboplastin time (APTT) exceeded 20% of the reference range of normal values.