Inclusion Criteria:
* Primary ITP if aged ⩾18 years;
* With an average of two platelet counts ⩾1 day apart of \<30×10\^9/L during screening and no single platelet count \>35×10\^9/L within 2 weeks before study treatment;
* Patients who have previously received at least one first-line standard therapy for ITP (corticosteroid and/or intravenous immunoglobulin) with unsustained efficacy, relapse, intolerance to standard therapy, or insufficient response.
Exclusion Criteria:
* Pregnant or lactating women, and who were possibly pregnant, planning to become pregnant, or who had partners planning to become pregnant;
* With active malignancy or a history of malignant tumor;
* Having experienced severe bacterial, viral, fungal or parasitic infection within the past 4 weeks;
* With a history of symptomatic herpes zoster infection within 12 weeks prior to screening;
* Active or chronic HBV, HCV or HIV infection;
* Evidence of active tuberculosis; or previous evidence of active tuberculosis without appropriate and documented treatment; or household contact with patients with active tuberculosis without appropriate and documented tuberculosis prophylaxis;
* Receipt of live vaccines within the past 12 weeks, or planned live vaccination during the study period;
* Prior ATRA therapy;
* History of solid organ transplant or planned surgery;
* Myelodysplastic syndrome, aplastic anemia or myelofibrosis;
* Patients with other diseases were undergoing treatment with immunosuppressants;
* Clinically significant thromboembolic events within the past 24 weeks, or ongoing anticoagulant treatment, who are deemed ineligible for the study by the investigator;
* History or presence of myocardial infarction, unstable ischemic heart disease, stroke, or NYHA Class IV heart failure;
* History or presence of cardiovascular, respiratory, hepatic, gastrointestinal, endocrine, neurological, neuropsychiatric or any other severe and/or unstable diseases that, in the opinion of the investigator, may pose an unacceptable risk with the investigational product or interfere with the interpretation of study data;
* AST \> 2 times the upper limit of normal (ULN), ALT \> 2×ULN, TBIL ≥ 1.5×ULN;
* WBC \< 2500/µL, neutrophil count \< 1200/µL, lymphocyte count \< 750/µL, hemoglobin \< 9 g/dL;
* eGFR \< 50 mL/min/1.73m²;
* Other patients deemed unsuitable for enrollment in this study by the investigator.
