• Age 6-17 years old (including both ends), male and female;

• Patients aged 6-11 years (including values at both ends) were diagnosed with chronic ITP, and patients aged 12-17 years (including values at both ends) were diagnosed with persistent or chronic ITP, with platelet counts less than 20×109/L;

• Patients did not respond to glucocorticoid therapy or relapsed. Previous ITP treatment may include, but is not limited to, glucocorticoids, immunomodulators (IVIG), azathioprine, danazole, cyclophosphamide and immunomodulators.

• Treatment for ITP (including but not limited to glucocorticoids, recombinant human thrombopoietin, TPO agonist (TPO-RA), azathioprine, danazole, cyclosporin A, mycophenate) must be completed or dose stabilized before enrollment, and therapeutic dose should not be increased after enrollment (e.g. The glucocorticoid dose should be stable for ≥14 days and the immunosuppressant dose should be stable for \> 3 months before the first administration of the study drug. TPO drugs should be stopped \> 1 month, TPO-RA drugs should be stopped \> 1 month).

• No infectious fever (including but not limited to lung infection) in the past 1 month.

• Laboratory examination of coagulation function should show that the prothrombin time (PT) and activated partial thrombin time (aPTT) values did not exceed 20% of the normal laboratory value range; No history of abnormal coagulation except for ITP.

• WBC count, neutrophil absolute value and hemoglobin should be within the normal range of laboratory values. No other abnormality except for ITP. Other exceptions except the following:

‣ If the anemia is clearly caused by excessive blood loss associated with ITP.

⁃ If the increase in WBC count/neutrophil absolute value was clearly due to steroid therapy.

• Understand the study procedure and voluntarily sign the informed consent.

‣ For subjects aged 6-7 (including both ends), parents/guardians understand the study procedure and voluntarily sign the informed consent in person, and subjects are encouraged to participate in the informed process and voluntarily sign the informed consent in person;

⁃ For subjects aged 8-16 (including both ends), parents/guardians and subjects themselves should understand the study procedure and voluntarily sign the informed consent in person;

⁃ For the minor subjects \> 16 years old, if the subjects rely on their own income as the main source of living, they are regarded as persons with full capacity for civil conduct and can independently carry out legal acts. The subjects can sign informed consent on the premise that they understand the research procedures and are willing to do so;

⁃ For minor subjects \> 16 years old, if the subjects do not rely on their own income as the main source of living, they cannot be regarded as persons with full capacity for civil conduct and cannot independently carry out legal acts. Parents/guardians and subjects should understand the study procedures and voluntarily sign the informed consent in person.